Mireille Chinain

Clémence M Gatti

Hélène Martin-Yken

Mélanie Roué

H Taiana

Ciguatera poisoning: an increasing burden for Pacific islands communities in light of climate change?

), i.e., in

Introduction

Harmful algal blooms (HABs) are natural phenomena that have apparently expanded worldwide in recent decades [START_REF] Van Dolah | Marine algal toxins: origins, health effects, and their increased occurrence[END_REF][START_REF] Geohab | Global ecology and oceanography of harmful algal blooms -Science plan[END_REF][START_REF] Hallegraeff | Ocean climate change, phytoplankton community responses, and harmful algal blooms: a formidable predictive challenge[END_REF]. They can cause damage to the environment, alter marine food webs and threaten seafood safety and human health [START_REF] Erdner | Centers for oceans and human health: a unified approach to the challenge of harmful algal blooms[END_REF][START_REF] Berdalet | Marine harmful algal blooms, human health and wellbeing: challenges and opportunities in the 21 st century[END_REF][START_REF] Sanseverino | Algal bloom and its economic impact[END_REF], thus causing significant socioeconomic problems most notably among world populations that rely heavily on marine resources for their subsistence [START_REF] Bell | Planning the use of fish for food security in the Pacific[END_REF]. It is suggested that this observed HAB increase is linked to both anthropogenic influences on the biosphere and naturally occurring environmental changes such as climate change (Hallegraeff, 1993, and references therein;[START_REF] Anderson | Harmful algal blooms and eutrophication: examining linkages from selected coastal regions of the United States[END_REF][START_REF] Gobler | Ocean warming since 1982 has expanded the niche of toxic algal blooms in the North Atlantic and North Pacific Oceans[END_REF], and that current projections of water temperature warming will eventually result in even greater problems due to HABs in the future (Marques et al., 2010, and references therein).

Among the many algal toxins that can find their way through marine food webs to human consumers where they cause various poisoning illnesses, are ciguatoxins (CTXs), potent neurotoxins produced by dinoflagellates in the genera Gambierdiscus and Fukuyoa. Ciguatoxins are responsible for Ciguatera Poisoning (CP), a disease resulting from the consumption of poisonous coral-reef finfish and marine invertebrates [START_REF] Anderson | The continuing enigma of ciguatera[END_REF][START_REF] Lehane | Ciguatera: recent advances but the risk remains[END_REF]Darius et al., 2018b). With an estimated occurrence of 10,000 to 50,000 cases per year [START_REF] Friedman | Ciguatera fish poisoning: treatment, prevention and management[END_REF], CP is regarded as the most prevalent noninfectious seafood-borne disease worldwide. This poisonous syndrome is particularly well known to communities of the Pacific Island Countries and Territories (PICTs) where the highest incidence rates (IRs) in the world are consistently reported since the 1970s [START_REF] Bagnis | Epidemiology of ciguatera in French Polynesia from 1960 to 1984[END_REF]Chateau-Degat et al., 2007a;[START_REF] Friedman | Ciguatera fish poisoning: treatment, prevention and management[END_REF][START_REF] Rongo | Ciguatera poisoning in Rarotonga, southern Cook Islands[END_REF][START_REF] Skinner | Ciguatera fish poisoning in the Pacific Islands (1998 to 2008)[END_REF][START_REF] Chinain | Ciguatera poisoning in French Polynesia: insights into the novel trends of an ancient disease[END_REF]. This has prompted extensive studies in various Pacific ciguatera hotspots to assess the genetic diversity and distribution of the causative algal organisms [START_REF] Chinain | Intraspecific variation in the dinoflagellate Gambierdiscus toxicus (Dinophyceae). I. Isozyme analysis[END_REF][START_REF] Rhodes | Toxic dinoflagellates (Dinophyceae) from Rarotonga, Cook Islands[END_REF][START_REF] Murray | Molecular phylogenetics and morphology of Gambierdiscus yasumotoi from tropical eastern Australia[END_REF][START_REF] Xu | Distribution, abundance and diversity of Gambierdiscus spp. from a ciguatera-endemic area in Marakei, Republic of Kiribati[END_REF]Rhodes et al., 2017b;[START_REF] Smith | Molecular identification of Gambierdiscus and Fukuyoa (Dinophyceae) from environmental samples[END_REF]Darius et al., 2018b;[START_REF] Larsson | Toxicology of Gambierdiscus spp. (Dinophyceae) from tropical and temperate Australian waters[END_REF][START_REF] Rhodes | Ciguatera fish poisoning: the risk from an Aotearoa/New Zealand perspective[END_REF], the marine species at risk [START_REF] Halstead | Poisonous and venomous marine animals of the world[END_REF][START_REF] Kodama | Variations in symptomatology of ciguatera poisoning[END_REF][START_REF] Legrand | La ciguatera: un phénomène d'écotoxicologie des récifs coralliens[END_REF][START_REF] Rongo | Ciguatera poisoning in Rarotonga, southern Cook Islands[END_REF][START_REF] Laurent | Ciguatera shellfish poisoning (CSP): a new ecotoxicological phenomenon from cyanobacteria to humans via giant clams[END_REF][START_REF] Mak | Pacific ciguatoxins in food web components of coral reef systems in the Republic of Kiribati[END_REF]Darius et al., 2018a;Darius et al., 2018b), the suite of toxins involved [START_REF] Yasumoto | Toxins produced by benthic dinoflagellates[END_REF][START_REF] Murata | Structures and configurations of ciguatoxin from the moray eel Gymnothorax javanicus and its likely precursor from the dinoflagellate Gambierdiscus toxicus[END_REF][START_REF] Holmes | Purification and characterisation of large and small maitotoxins from cultured Gambierdiscus toxicus[END_REF][START_REF] Yasumoto | Structural elucidation of ciguatoxin congeners by fast-atom bombardment tandem mass spectroscopy[END_REF][START_REF] Satake | Marine polyether compounds[END_REF]Chinain et al., 2010a;[START_REF] Rhodes | Production of ciguatoxin and maitotoxin by strains of Gambierdiscus australes, G. pacificus and G. polynesiensis (Dinophyceae) isolated from Rarotonga, Cook Islands[END_REF][START_REF] Munday | Ciguatoxins and maitotoxins in extracts of sixteen Gambierdiscus isolates and one Fukuyoa isolate from the South Pacific and their toxicity to mice by intraperitoneal and oral administration[END_REF][START_REF] Larsson | Toxicology of Gambierdiscus spp. (Dinophyceae) from tropical and temperate Australian waters[END_REF][START_REF] Longo | Intraspecific variability in the toxin production and toxin profiles of in vitro cultures of Gambierdiscus polynesiensis (Dinophyceae) from French Polynesia[END_REF], the socioeconomic impacts on local communities' well-being [START_REF] Lewis | Ciguatera -Implications for nutrition and marine resource development in the Pacific Islands[END_REF][START_REF] Lewis | Socioeconomic impacts and management ciguatera in the Pacific[END_REF][START_REF] Lewis | Ciguatera: ecological, clinical, and socioeconomic perspectives[END_REF][START_REF] Rongo | Socioeconomic consequences of ciguatera poisoning in Rarotonga, southern Cook Islands[END_REF][START_REF] Morin | Ciguatera fish poisoning: incidence, health costs and risk perception on Moorea Island (Society archipelago, French Polynesia)[END_REF][START_REF] Friedman | An updated review of ciguatera fish poisoning: clinical, epidemiological, environmental, and public health management[END_REF], etc. But, despite significant advances in the understanding of this complex ecotoxicological phenomenon, CP outbreaks are still difficult to predict and the prevalence of this disease dangerously high in PICTs.

The present paper will deal with several ciguatera-related issues specific to PICTs and neighboring countries in the Oceania region. A first section describes the genetic heterogeneity and chemodiversity of Gambierdiscus and Fukuyoa species occurring in thearea and how climate change is likely to influence CP risk locally as illustrated by the recent expansion of ciguatera to previously unaffected areas. A second section presents the epidemiology of CP in the region and the survey networks currently in place which have allowed identification of novel vectors of ciguatera among marine invertebrates highly prized by local populations. A further section deals with ciguatera perception among Pacific islands communities and the various adaptive strategies and traditional practices developed to cope with this poisoning risk. The fourth and last section addresses the issue of the implementation of monitoring capabilities and risk management programs in PICTs, by highlighting the potential interest and applicability of several monitoring and detection tools particularly well adapted to the context of Pacific islands, and the importance of outreach and communication strategies to modify high risk-taking behaviors among local communities. A concluding section outlines some of the issues that remain to be addressed for increased food safety among the island communities of the Pacific region.

2 Ciguatera poisoning in the context of climate change 2.1 The Oceania region, a "biodiversity hotspot" for Gambierdiscus species 2.1.1 Geographical distribution of Gambierdiscus/Fukuyoa species in the Oceania region Among the major locales presently regarded as CP-endemic areas, the Oceania region is likely the area where the diversity and geographic distribution of Gambierdiscus and Fukuyoa species are best documented. Today, this region continues to be the site of extensive sampling efforts. As a result, five of the eight newly described Gambierdiscus species since 2016 originated from various South Pacific locales, i.e., G. cheloniae (Smith et al., 2016), G. honu (Rhodes et al., 2017a), G. lapillus [START_REF] Kretzschmar | Characterization of Gambierdiscus lapillus sp. nov. (Gonyaulacales, Dinophyceae): a new toxic dinoflagellate from the Great Barrier Reef (Australia)[END_REF], G. lewisii and G. holmesii (Kretzschmar et al., 2019a), and it is highly likely that additional species will be characterized in the near future, as the genus Gambierdiscus is also comprised of four unidentified clades that are genetically distinct and may constitute new undescribed species [START_REF] Litaker | Taxonomy of Gambierdiscus including four new species, Gambierdiscus caribaeus, Gambierdiscus carolinianus, Gambierdiscus carpenteri and Gambierdiscus ruetzleri (Gonyaulacales, Dinophyceae)[END_REF][START_REF] Nishimura | Genetic diversity and distribution of the ciguatera causing dinoflagellate Gambierdiscus spp. (Dinophyceae) in coastal areas of Japan[END_REF][START_REF] Xu | Distribution, abundance and diversity of Gambierdiscus spp. from a ciguatera-endemic area in Marakei, Republic of Kiribati[END_REF][START_REF] Dai | Taxonomic assignment of the benthic toxigenic dinoflagellate Gambierdiscus sp. type 6 as Gambierdiscus balechii (Dinophyceae), including its distribution and ciguatoxicity[END_REF]. Currently 15 Gambierdiscus/Fukuyoa spp. out of the 21 published species are known in the South Pacific, the six species not yet reported in this region being G. carolinianus, G. excentricus, G. jejuensis, G. silvae, F. rutzleri and F. yasumotoi. Table 1 and Figure 1 provide an updated summary of the current distribution of Gambierdiscus and Fukuyoa species in the Pacific region.

Tab. 1 Fig. 1 From Figure 1, it is clear that several island groups in the Pacific such as Hawaii, French Polynesia, the Cook Islands, the Kingdom of Tonga, the Republic of Kiribati and the Kermadec Islands could represent "biodiversity hotspots" of Gambierdiscus with the report of at least five distinct species in each of these island groups (Tab. 1 and references therein): of note, up to six Gambierdiscus species were found to co-exist within a single sampling location of Rikitea Bay on Mangareva Island, a long-standing ciguatera hotspot in the Gambier archipelago (French Polynesia) [START_REF] Chinain | Update on ciguatera research in French Polynesia[END_REF]. Similarly, eight species are currently known in Australia from tropical Queensland to the more temperate waters of New South Wales.

This increase in species number has raised concerns about the future trends of ciguatera in this CP-prone region, as it is believed that the global distribution of CP will dramatically increase in the coming years in the context of climate change and global warming [START_REF] Hales | Ciguatera (fish poisoning), El Nino, and Pacific sea surface temperatures[END_REF][START_REF] Villareal | Petroleum production platforms as sites for the expansion of ciguatera in the northwestern Gulf of Mexico[END_REF][START_REF] Llewellyn | Revisiting the association between sea surface temperature and the epidemiology of fish poisoning in the South Pacific: reassessing the link between ciguatera and climate change[END_REF]. Indeed, average annual increases in sea water temperatures have been reported for both south-eastern Australia and for New Zealand's coastal waters (New South Wales Government; Ministry for the Environment (Manatū Mō Te Taiao), 2016), consistent with occurrence reports of both Fukuyoa and Gambierdiscus in the sub-tropical northern region of New Zealand and Kermadec Islands (Rhodes et al., 2017b;Rhodes et al., 2017c;[START_REF] Rhodes | A checklist of the benthic and epiphytic marine dinoflagellates of New Zealand, including Rangitāhua/Kermadec Islands. New Zeal[END_REF][START_REF] Rhodes | Ciguatera fish poisoning: the risk from an Aotearoa/New Zealand perspective[END_REF], and in the more temperate waters of New South Wales, Australia [START_REF] Kohli | High abundance of the potentially maitotoxic dinoflagellate Gambierdiscus carpenteri in temperate waters of New South Wales, Australia[END_REF][START_REF] Larsson | Toxicology of Gambierdiscus spp. (Dinophyceae) from tropical and temperate Australian waters[END_REF][START_REF] Larsson | Toxicological characterization of Fukuyoa paulensis (Dinophyceae) from temperate Australia[END_REF]. It has been suggested that blooms of G. carpenteri populations stretching as far as 37°S, south of Sidney (New South Wales) may be explained by currents bringing cells from tropical Queensland to the warming New South Wales waters [START_REF] Kohli | Occurrence of the ciguatera fish poisoning causing dinoflagelle Gambierdiscus in temperate waters of New South Wales, Australia[END_REF][START_REF] Kohli | High abundance of the potentially maitotoxic dinoflagellate Gambierdiscus carpenteri in temperate waters of New South Wales, Australia[END_REF]. It should be noted that recent observations indicate that Gambierdiscus and/or Fukuyoa spp. are also presently established in other temperatelike areas globally, including Korea [START_REF] Jeong | First report of the epiphytic dinoflagellate Gambierdiscus caribaeus in the temperate waters of Jeju Island, Korea: morphology and molecular characterization[END_REF][START_REF] Jang | Gambierdiscus jejuensis sp. nov., an epiphytic dinoflagellate from the waters of Jeju Island, Korea, effect of temperature on the growth, and its global distribution[END_REF], Japan [START_REF] Nishimura | Quantitative PCR assay for detection and enumeration of ciguatera-causing dinoflagellate Gambierdiscus spp. (Gonyaulacales) in coastal areas of Japan[END_REF], the northern Gulf of Mexico [START_REF] Tester | Gambierdiscus (Dinophyceae) species diversity in the Flower Garden Banks National Marine Sanctuary, Northern Gulf of Mexico, USA[END_REF], and the Mediterranean Sea [START_REF] Aligizaki | Morphological identification of two tropical dinoflagellates of the genera Gambierdiscus and Sinophysis in the Mediterranean Sea[END_REF][START_REF] Tudó | First report of Gambierdiscus in the Western Mediterranean Sea (Balearic Islands)[END_REF]. In particular, G. australes is among the few species that appear to have the widest latitudinal ranges from 40.00°N to 35.25°S [START_REF] Tester | Climate change and harmful benthic microalgae[END_REF]. But whether this current expansion of the geographic range of Gambierdiscus/Fukuyoa spp. in South Pacific areas may lead to increasing risk of CP outbreaks locally is still a matter of current debate: e.g., there is no concurrent report of human health impacts in northern New-Zealand, yet [START_REF] Rhodes | Ciguatera fish poisoning: the risk from an Aotearoa/New Zealand perspective[END_REF], while in New South Wales, there has been an apparent increase in CP from both imported fish and Spanish mackerel (Scomberomorus commerson) caught in the region's coastal waters [START_REF] Farrell | Management of ciguatoxin risk in eastern Australia[END_REF][START_REF] Seger | National ciguatera research strategy: reducing the incidence of ciguatera in Australia through improved risk management[END_REF].

Chemodiversity in Gambierdiscus/Fukuyoa species from the Oceania region

Tab. 2

Gambierdiscus is also known to produce several other cyclic polyether compounds, which were characterized from Pacific strains for the majority of them. MTX1, for instance, was first isolated from a French Polynesian strain identified as G. toxicus (potential misidentification) [START_REF] Murata | Structure of maitotoxin[END_REF], and further detected in numerous G. australes strains from the Cook Islands and the Kermadec Islands by means of LC-MS/MS (Rhodes et al., 2014;[START_REF] Kohli | Polyketide synthesis genes associated with toxin production in two species of Gambierdiscus (Dinophyceae)[END_REF][START_REF] Smith | A new Gambierdiscus species (Dinophyceae) from Rarotonga, Cook Islands: Gambierdiscus cheloniae sp[END_REF][START_REF] Munday | Ciguatoxins and maitotoxins in extracts of sixteen Gambierdiscus isolates and one Fukuyoa isolate from the South Pacific and their toxicity to mice by intraperitoneal and oral administration[END_REF]Rhodes et al., 2017b;

Influence of environmental factors

It is well known that reports of CP events/outbreaks are significantly underestimated because of failure to recognize its symptoms [START_REF] Friedman | An updated review of ciguatera fish poisoning: clinical, epidemiological, environmental, and public health management[END_REF], limited collection of epidemiological data on a global level [START_REF] Goater | Critical issues in the development of health information systems in supporting environmental health: a case study of ciguatera[END_REF], and even a generalized reticence to report ciguatera in endemic regions (e.g., within island communities) since many patients tend to rely on traditional medicine for treatment [START_REF] Bourdy | Traditional remedies used in the Western Pacific for the treatment of ciguatera poisoning[END_REF][START_REF] Kumar-Roiné | A review of traditional remedies of ciguatera fish poisoning in the Pacific[END_REF]. Moreover, the lack of standardization in data collection methodologies and timelines makes it difficult to compare incidence data across regions. Thereby, it is difficult to conclude whether there has been a global increase in CP incidents frequency over the past decades, and even more difficult to link such observations to climate change impacts.

Many laboratory studies have investigated Gambierdiscus/Fukuyoa spp. growth responses and toxin production under varying environmental factors [START_REF] Parsons | Gambierdiscus and Ostreopsis: reassessment of the state of knowledge of their taxonomy, geography, ecophysiology, and toxicology[END_REF]Chinain et al., 2020, for reviews and references therein). Temperature and pH are some of the environmental drivers most representative of climate change, e.g., global ocean warming and acidification [START_REF] Orr | Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms[END_REF]Intergovernmental Panel on Climate Change (IPCC), 2007;[START_REF] Meehl | Global climate projections[END_REF][START_REF] Brown | Projected sea surface temperature changes in the equatorial Pacific relative to the Warm Pool edge[END_REF][START_REF] Nurse | Projected SST trends across the Caribbean Sea based on PRECIS downscaling of ECHAM4, under the SRES A2 and B2 scenarios[END_REF]. The effects of temperature changes are, by far, the best documented in the literature. However, it should be mentioned that many of the previous studies were conducted at a time when Gambierdiscus taxonomy was unresolved, so the extent to which, e.g., growth responses may vary across the multiple species now known in Gambierdiscus and Fukuyoa genera remains to be clarified. To date, growth data for the following species/phylotypes: G. australes, G. belizeanus, G. caribaeus, G. carolinianus, G. carpenteri, G. jejuensis (formerly known as Gambierdiscus sp. type 2), G. pacificus, G. polynesiensis, G. scabrosus, G. silvae, F. ruetzleri, and Gambierdiscus spp. types 3, 4 and 5 can be found in the literature (Chinain et al., 2010a;[START_REF] Kibler | Growth of eight Gambierdiscus (Dinophyceae) species: effects of temperature, salinity and irradiance[END_REF][START_REF] Yoshimatsu | Effects of temperature, salinity and their interaction on growth of Japanese Gambierdiscus spp. (Dinophyceae)[END_REF][START_REF] Tawong | Temperature and salinity effects and toxicity of Gambierdiscus caribaeus (Dinophyceae) from Thailand[END_REF][START_REF] Xu | Influence of environmental variables on Gambierdiscus spp. (Dinophyceae) growth and distribution[END_REF][START_REF] Jang | Gambierdiscus jejuensis sp. nov., an epiphytic dinoflagellate from the waters of Jeju Island, Korea, effect of temperature on the growth, and its global distribution[END_REF][START_REF] Vacarizas | Taxonomy and toxin production of Gambierdiscus carpenteri (Dinophyceae) in a tropical marine ecosystem: the first record from the Philippines[END_REF], and results confirm that differences in both tolerance and optimum growth ranges exist not only across species but strains as well [START_REF] Vacarizas | Taxonomy and toxin production of Gambierdiscus carpenteri (Dinophyceae) in a tropical marine ecosystem: the first record from the Philippines[END_REF]. Based on sea surface temperature projections over the coming century, a substantial shift in both the distribution and abundance of ciguatera dinoflagellates is to be expected [START_REF] Parsons | A simple model capable of simulating the population dynamics of Gambierdiscus, the benthic dinoflagellate responsible for ciguatera fish poisoning[END_REF][START_REF] Kibler | Effects of ocean warming on growth and distribution of dinoflagellates associated with ciguatera fish poisoning in the Caribbean[END_REF], with some species becoming dominant whereas others will become less prevalent. In the long-term, however, temperatures may get too warm according to [START_REF] Llewellyn | Revisiting the association between sea surface temperature and the epidemiology of fish poisoning in the South Pacific: reassessing the link between ciguatera and climate change[END_REF], thereby hindering Gambierdiscus/Fukuyoa growth and resulting in a lower risk of ciguatera. In any case, as outlined by [START_REF] Tester | Climate change and harmful benthic microalgae[END_REF]: "as surface waters warm, range extension (of harmful benthic microalgae) of several degrees of latitude are anticipated, but only where speciesspecific habitat requirements can be met (e.g., temperature, suitable substrate, low turbulence, light, salinity, pH)".

There are very few published data about the influence of pH on the growth and/or toxicity of ciguatera-related organisms. Actually, only one laboratory study has examined the linked effects of pH, temperature and salinity on the cell viability of the marine diatom Phaeodactylum tricornutum and has found that low pH combined with high temperature and salinity showed adverse effects on cultures of P. tricornutum [START_REF] Bautista-Chamizo | Will temperature and salinity changes exacerbate the effects of seawater acidification on the marine microalga Phaeodactylum tricornutum?[END_REF]. Concerning the ciguatera-causing dinoflagellates, recent studies on G. polynesiensis suggest lower growth rates but increased ciguatoxicity in cultured strains at low pH values (Chinain, unpublished results), which is in marked contrast with data obtained for strains of G. balechii and Gambierdiscus sp. type 5 which showed a growth suppression at elevated pH, and reduced ciguatoxicity at decreasing pH values (Chan, personal comm.).

Numerous field observations linking climate change to CP outbreaks in the tropical Pacific can be found in the literature: cyclical weather patterns such as El Niño, associated with unusual warming of Pacific Ocean waters, have resulted in spikes of ciguatera cases in the Republic of Kiribati, Western Samoa, the State of Tuvalu and the Cook Islands [START_REF] Hales | Ciguatera (fish poisoning), El Nino, and Pacific sea surface temperatures[END_REF], consistent with observations by [START_REF] Gingold | Ciguatera fish poisoning and climate change : analysis of national poison center data in the United States, 2001-2011[END_REF] who found an association between CP incidence and warmer sea surface temperatures in the Caribbean basin. A general consensus is that the massive colonization of dead corals by macroalgae provides more substrate for the settlement of epiphytic Gambierdiscus/Fukuyoa spp. populations [START_REF] Lewis | Disease and development: ciguatera fish poisoning[END_REF][START_REF] Litaker | Global distribution of ciguatera causing dinoflagellates in the genus Gambierdiscus[END_REF], as first hypothesized by [START_REF] Randall | A review of ciguatera, tropical fish poisoning, with a tentative explanation of its cause[END_REF]. This may explain why reef disturbances or degradations linked to extreme climatic events (e.g., hurricanes, heavy rains, coral bleaching) or human activities (e.g., dredging and filling, constructions, military activities) frequently precede ciguatoxic events [START_REF] Bagnis | Ciguatera fish poisoning: an objective witness of the coral reef stress[END_REF][START_REF] Ruff | Ciguatera in the Pacific: a link with military activities[END_REF][START_REF] Lehane | Ciguatera: recent advances but the risk remains[END_REF]. In the Cook Islands and French Polynesia, for instance, CP outbreaks were associated with both cyclone activity and infestations of crown-of-thorns starfish (Acanthaster planci) [START_REF] Bagnis | Correlation between ciguateric fish and damage to the reefs in the Gambier Islands (French Poynesia)[END_REF][START_REF] Rongo | The effects of natural disturbances, reef state, and herbivorous fish densities on ciguatera poisoning in Rarotonga, southern Cook Islands[END_REF][START_REF] Morin | Ciguatera fish poisoning: incidence, health costs and risk perception on Moorea Island (Society archipelago, French Polynesia)[END_REF]. Similarly, while studying the fluctuations of G. toxicus populations in a ciguateric site in Tahiti Island (French Polynesia), Chinain et al. (1999b) found an increase in both the density and frequency of Gambierdiscus blooms following unusually high water temperatures, concomitant with a severe coral bleaching episode affecting large areas of the study site. Of note, Gambierdiscus spp. cell density peaked approximately 10 months after water temperature started to increase (Chinain et al., 1999b). Further, health impacts (peak number of CP cases) were recorded three months after these peak densities of Gambierdiscus [START_REF] Chateau-Degat | Seawater temperature, Gambierdiscus spp. variability and incidence of ciguatera poisoning in French Polynesia[END_REF], indicating that a time frame of approximately 13 months is required for increased cases of CP to be observed after climate-induced changes to sea water temperature. Such findings substantiate the idea that global warming as a result of climate change may increase the incidence of CP in the South Pacific. Additionally, climate change projections show that the intensity of hurricanes will also increase in the tropical Pacific [START_REF] Meehl | Global climate projections[END_REF].

Geographical expansion of ciguatera to novel areas: the case study of Rapa Island (Australes archipelago, French Polynesia)

Ciguatera-endemic regions classically overlay coral development areas between 35°N and 35°S, i.e., tropical and sub-tropical areas of the Caribbean Sea, and Pacific and Indian Oceans [START_REF] Parsons | Gambierdiscus and Ostreopsis: reassessment of the state of knowledge of their taxonomy, geography, ecophysiology, and toxicology[END_REF]. However, recent observations clearly highlight the current expansion of Gambierdiscus spp. and ciguatoxic fish to previously unaffected areas, most notably in temperate locales such as the west coast of Africa [START_REF] Bienfang | Ciguatera fish poisoning: a synopsis from ecology to toxicity[END_REF] and the eastern Atlantic Ocean (Canary Islands, Madeira, Selvagens Islands) where reports of CP endogenous cases are documented since 2004 [START_REF] Pérez-Arellano | Ciguatera fish poisoning, Canary Islands[END_REF][START_REF] Boada | Ciguatera fish poisoning on the West Africa Coast: an emerging risk in the Canary Islands (Spain)[END_REF][START_REF] Nuñez | Outbreak of ciguatera food poisoning by consumption of amberjack (Seriola spp.) in the Canary Islands, May 2012[END_REF]. These observations are consistent with the concurrent detection of toxigenic Gambierdiscus spp. in Macaronesian waters [START_REF] Fraga | Gambierdiscus excentricus sp. nov. (Dinophyceae), a benthic toxic dinoflagellate from the Canary Islands (NE Atlantic Ocean)[END_REF][START_REF] Fraga | Genus Gambierdiscus in the Canary Islands (NE Atlantic Ocean) with description of Gambierdiscus silvae sp. nov., a new potentially toxic epiphytic benthic dinolflagellate[END_REF]Pisapia et al., 2017a;Pisapia et al., 2017b;[START_REF] Rodríguez | Canary Islands (NE Atlantic) as a biodiversity 'hotspot' of Gambierdiscus: implications for future trends of ciguatera in the area[END_REF][START_REF] Reverté | Assessment of cytotoxicity in ten strains of Gambierdiscus australes from Macaronesian Islands by neuro-2a cellbased assays[END_REF], and the confirmation of CTX contamination in locally-sourced fish [START_REF] Pérez-Arellano | Ciguatera fish poisoning, Canary Islands[END_REF][START_REF] Otero | First toxin profile of ciguateric fish in Madeira arquipelago (Europe)[END_REF][START_REF] Caillaud | Towards the standardisation of the neuroblastoma (neuro-2a) cell-based assay for ciguatoxin-like toxicity detection in fish: application to fish caught in the Canary Islands[END_REF][START_REF] Bravo | Ciguatera, an emerging human poisoning in Europe[END_REF][START_REF] Costa | New insights into the occurrence and toxin profile of ciguatoxins in Selvagens Islands (Madeira, Portugal)[END_REF][START_REF] Estevez | An attempt to characterize the ciguatoxin profile in Seriola fasciata causing ciguatera fish poisoning in[END_REF][START_REF] Sanchez-Henao | Predictive score and probability of CTX-like toxicity in fish samples from the official control of ciguatera in the Canary Islands[END_REF][START_REF] Sanchez-Henao | Presence of CTXs in moray eels and dusky groupers in the marine environment of the Canary Islands[END_REF].

As previously mentioned, similar observations are also documented in the southern hemisphere, such as in New South Wales, Australia [START_REF] Farrell | Management of ciguatoxin risk in eastern Australia[END_REF][START_REF] Kohli | Qualitative and quantitative assessment of the presence of ciguatoxin, P-CTX-1B, in Spanish mackerel (Scomberomorus commerson) from waters in New South Wales (Australia)[END_REF][START_REF] Seger | National ciguatera research strategy: reducing the incidence of ciguatera in Australia through improved risk management[END_REF]. The case of Rapa Island (Australes archipelago, French Polynesia) is another emblematic example of the current extension of CP to temperate-like areas of the South Pacific. Rapa Island (27°38'S -144°20'W) was reputed free of ciguatera until 2008 when six isolated CP cases were first reported [START_REF] Pawlowiez | Evaluation of seafood toxicity in the Australes archipelago (French Polynesia) using the neuroblastoma cell-based assay[END_REF]. Further, from August 2009 to November 2010, a mass-poisoning outbreak involving 114 local residents (based on declared cases, but it is highly likely that half the population was affected) occurred following community fishing in the rahui zone, a widely used practice in many PICTs to protect local fishing resources. The unusual severity and magnitude of this outbreak resulted in two fatalities within a three months' period. Clinical records indicated symptoms typical of ciguatera in affected individuals, including cold allodynia, paresthesia and dysesthesia which were reported in 92%, 95% and 86% of affected patients, respectively, at the peak of the epidemic (Tab. 3). Moreover, three fish species were primarily involved in this mass-CP incident, namely Leptoscarus vaigiensis (seagrass parrotfish), Kyphosus cinerascens (highfin chub) and Seriola lalandi (king fish) which were responsible of nearly 90% of the reported cases between 2009 and 2010. Field investigations revealed the presence of toxic Gambierdiscus populations in several sampling locations around Rapa Island (Pawlowiez et al., 2013). Additionally, a random test survey of the toxic status of 250 herbivorous and carnivorous fish collected from the main fishing sites allowed confirmation of CTXs at concentrations well above the US Food and Drug Administration (FDA) advisory level (0.01 ppb) (US Food and Drug Administration (FDA), 2019) in >60% of the tested fish (Pawlowiez et al., 2013). Fortunately, the local population was highly reactive to educational and community outreach interventions, as illustrated by a five-fold reduction in CP cases between 2009 and 2012 (Fig. 2). Recent data (i.e., mean IR around 128 cases per 10,000 population over the past two years) indicate that ciguatera is still present in Rapa Island but increased awareness among the local population about this toxic threat has helped maintain a low prevalence as compared to the alarming IR peak of 1,758 cases per 10,000 population reported in 2009. A careful analysis of the clinical forms shows that these good results are clearly attributable to self-regulating behavior among the population towards avoidance of high-risk fish species and fishing area, as evidenced by a noticeable shift in the fish species implicated in CP cases over the ensuing years (Fig. 2). Of note, similar encouraging results following public outreach interventions have been previously obtained in Raivavae Island, another ciguatera hotspot in the Australes archipelago (Chinain et al., 2010b). Further investigations are currently underway in order to ascertain the link between this emerging poisoning incident in Rapa Island and global warming in the area (Chinain et al., in preparation).

Tab. 3 Fig. 2 3 Epidemiology of ciguatera poisoning in the Pacific 3.1 The Pacific, a region with the highest ciguatera poisoning incidence rates in the world Historically, the first description of ciguatera related syndromes in the South Pacific was provided in 1606 by Pedro Fernandes de Queirós (1565-1614) who reported a masspoisoning event among crew members following the consumption of a snapper in the Republic of Vanuatu. Later, in the 20 th century, some Pacific countries such as French Polynesia, New-Caledonia, the Territory of Wallis and Futuna Islands, the Republic of Marshall Islands and the Republic of Kiribati experienced a substantial number of CP outbreaks linked to military activities during and following the World War II (battles, naval ships activities, war material dumping, nuclear test, etc.) [START_REF] Ruff | Ciguatera in the Pacific: a link with military activities[END_REF][START_REF] Brunet | The follow-up of a possible risk of the ciguatera fish poisoning in Wallis and Futuna, Workshop on Ciguatera Fish Poisoning -RAS7026 Project[END_REF].

Based on the South Pacific Epidemiological and Health Information Service (SPEHIS) database (Australian Institute of Marine Science (AIMS), 2009), PICTs are among the nations with the highest IRs in the world as compared to other affected regions of the globe [START_REF] Lewis | Ciguatera -Parameters of a tropical health problem[END_REF]. This was particularly true during the last two decades of the XX's century. Of note, a survey conducted among Marshallese families in 1982, showed that 56% of them counted at least one family member with a previous CP in the past [START_REF] Lewis | Ciguatera -Parameters of a tropical health problem[END_REF]. In Hao Island (French Polynesia), 43% of the inhabitants were affected by CP, two years after the onset of military activities in the atoll [START_REF] Bagnis | Naissance et développement d'une flambée de ciguatera dans un atoll des Tuamotu[END_REF]. According to [START_REF] Skinner | Ciguatera fish poisoning in the Pacific Islands (1998 to 2008)[END_REF], it is estimated that ≈ 500,000 people from 17 PICTs where affected by CP over a period of 35 years, with 39,677 CP cases recorded between 1998 and2008. This corresponds to an annual IR of 194/100,000 people, and represents a 60% increase compared to the IR of 104/100,000 recorded for the period 1973-1983. Based on more recent data, the Republic of Fiji, French Polynesia, the Republic of Kiribati, Queensland (Australia), the Republic of the Marshall Islands, the Cook Islands, Hawaii and the Territory of Wallis and Futuna Islands (where CP was not considered as a concern until 2010), cumulated over 31,461 cases between 2000and 2016(Institut Louis Malardé (ILM), 2007-2018;[START_REF] Chateau-Degat | Epidemiological survey of ciguatera in French Polynesia[END_REF][START_REF] Skinner | Ciguatera fish poisoning in the Pacific Islands (1998 to 2008)[END_REF][START_REF] Capelle | Marshall Islands country report, Workshop on Ciguatera Fish Poisoning -RAS7026 Project[END_REF][START_REF] Skinner | Ciguatera fish poisoning in specific Pacific Island Countries, from 2009 to 2014[END_REF][START_REF] Iorangi | National health information bulletin 2016[END_REF]Disease Outbreak Control Division -State of Hawaii, 2019;[START_REF] Stafford | The epidemiology of ciguatera fish poisoning in Australia, Ciguatera Fish Poisoning Science Day -SafeFish[END_REF]. It should be noted that the toxic status in a given country/island may significantly vary from one year to another, as illustrated by the example of Rapa Island (French Polynesia) where IRs went from 1,230/100,000 in 2008 up to 17,580/100,000 people in 2009 (Institut Louis Malardé (ILM), 2007-2018). Likewise, since the 80's, IRs reported from several South Pacific countries such as the Republic of Kiribati, the State of Tuvalu, the Tokelau Islands and the Cook islands may sporadically exceed 1,000/100,000 people (Australian Institute of Marine Science (AIMS), 2009). This situation is all the more worrying since it is recognized that CP cases reported in the Pacific likely represent only 20% of the actual cases [START_REF] Skinner | Ciguatera fish poisoning in the Pacific Islands (1998 to 2008)[END_REF].

Over the past two decades, however, a significant decrease in data collection is observed in the Pacific due to a progressive decline in the documentation of CP incidents in the SPEHIS database by participating countries. To date, fragmented CP data exist for the Oceania region [START_REF] Goater | Critical issues in the development of health information systems in supporting environmental health: a case study of ciguatera[END_REF] with only four countries which currently have specific records of CP cases: (i) the Republic of Fiji, where CP is currently considered as a "high priority" by health authorities (http://www.health.gov.fj/); (ii) French Polynesia, where specific CP epidemiological surveillance tools and strategies are implemented since 2007 (see section 3.2); (iii) Hawaii (Hawaii State Department of Health, https://health.hawaii.gov/docd/disease_listing/ciguatera/); and (iv) Australia, where a "National Ciguatera Fish Poisoning Research Strategy" has been recently launched with the objective of reducing CP incidence through improved risk management [START_REF] Seger | National ciguatera research strategy: reducing the incidence of ciguatera in Australia through improved risk management[END_REF] The high IRs consistently reported in the Oceania region largely result from the strong reliance of local communities on marine resources [START_REF] Dalzell | Sustainability and management of reef fisheries in the Pacific Islands[END_REF][START_REF] Bell | Planning the use of fish for food security in the Pacific[END_REF]Chinain et al., 2010b;[START_REF] Chan | Spatial distribution of ciguateric fish in the Republic of Kiribati[END_REF][START_REF] Rongo | Ciguatera poisoning in Rarotonga, southern Cook Islands[END_REF][START_REF] Kronen | Socio-economic and fishery indicators to identify and monitor artisanal finfishing pressure in Pacific Island countries and territories[END_REF]. Indeed, in these developing countries, fish consumption rates are among the highest in the world due to limited range of crops and animal protein, with an average annual fish consumption rate between 10.2 -167 kg/capita/year in PICTs [START_REF] Bell | Planning the use of fish for food security in the Pacific[END_REF][START_REF] Rongo | Socioeconomic consequences of ciguatera poisoning in Rarotonga, southern Cook Islands[END_REF] vs. a global rate of 18.8 kg/capita/year in 2011, 25 kg/capita/year in Europe, and 7 kg/capita/year in the US (Food and Agricultural Organization of the United Nations (FAO), 2012). There is also a strong tradition of eating fresh fish in PICTs, with 30-90% of the fish caught by the household [START_REF] Bell | Planning the use of fish for food security in the Pacific[END_REF][START_REF] Kronen | Socio-economic and fishery indicators to identify and monitor artisanal finfishing pressure in Pacific Island countries and territories[END_REF][START_REF] Rongo | Socioeconomic consequences of ciguatera poisoning in Rarotonga, southern Cook Islands[END_REF]. But despite these alarming statistics, ciguatera is still largely ignored by most PICT national governments, mostly due to a lack of resources that are dedicated primarily to the control of non-communicable diseases which represent an unprecedented public health issue in the region.

Survey networks in the Pacific: the example of French Polynesia

French Polynesia (276,300 inhabitants), is composed of 121 high islands and atolls stretching from 134°W to 155°W and 8°S to 28°S (Institut de la Statistique de Polynésie française (ISPF), 2018). Although it has been suggested that the celebrated Polynesian voyages noted from AD 1000 to 1450 in eastern Polynesia may have been prompted by CP [START_REF] Rongo | Did ciguatera prompt the late Holocene Polynesian voyages of discovery?[END_REF], the earliest account of CP in French Polynesian dates back to the 18 th century and was provided by James Morrison, leading rate on board the HMS Bounty, while mooring in the Society archipelago [START_REF] Jaunez | Journal de James Morrison : second maître à bord de la « Bounty[END_REF]as cited in Chinain, 2017). Later, in the 19 th century, accounts of the presence of poisonous fish in the Tuamotu, the Gambier and the Marquesas archipelagoes were successively provided by the explorer Jacques-Antoine Moerenhout, Father Honoré Laval and Father Pierre, respectively [START_REF] Chinain | Ciguatéra: connaissances d'antan, connaissances modernes[END_REF]. French Polynesia is also the site of nearly five decades of research on ciguatera : following a major poisoning outbreak in Bora Bora Island in 1964 which resulted in three fatalities [START_REF] Bagnis | A propos de quelques cas d'intoxications par des mollusques du genre "bénitier" dans une île de la Société[END_REF], a dedicated ciguatera research unit was created in 1967 at the Institut Louis Malardé (ILM) to investigate the etiology of this enigmatic poisoning (www.ilm.pf). This initiative eventually led to the identification of the causative agent almost a decade later, the dinoflagellate Gambierdiscus toxicus, named after the Gambier Island where it was first described [START_REF] Yasumoto | Finding of a dinoflagellate as a likely culprit of ciguatera[END_REF][START_REF] Bagnis | Origins of ciguatera fish poisoning: a new dinoflagellate, Gambierdiscus toxicus Adachi and Fukuyo, definitively involved as a causal agent[END_REF].

In a recent survey conducted on Moorea Island (Society archipelago, French Polynesia), over 50% of households interviewed declared they consume fish six to seven times a week, with 76% of them having at least one member of the household actively involved in local reef fishing activity [START_REF] Rassweiler | Perceptions and responses of Pacific Island fishers to changing coral reefs[END_REF]. This heavy dependence on fish resources for subsistence explains why French Polynesian communities are so highly exposed to CP risk: between 1999 and 2005, CP was responsible for 96% of hospitalized cases registered under the codification T61: ''Toxic effect of noxious substances eaten as seafood'' (International Statistical Classification of Diseases and Related Health Problem (ICD-10) of the World Health Organization) [START_REF] Gatti | Severe seafood poisoning in French Polynesia: a retrospective analysis of 129 medical files[END_REF]. Since 2007, CP annual IRs have varied from 75 to 233 cases/100,000 people (i.e., 202 to 615 cases reported annually), but this number has sporadically reached 17,580/100,000 people in 2009 (Institut Louis Malardé (ILM), 2009). Moreover, no archipelago is spared from ciguatera, from the extreme north of the territory that is subject to a tropical climate, to the extreme south exposed to a subtropical climate. The general trend presently observed in French Polynesia as a whole points towards a stable annual IR, although rates can significantly differ between islands and, in a given island, from one year to another (www.ciguatera.pf).

Since 2007, a country-wide epidemiological surveillance program

Despite the high IRs recorded over the past decades in French Polynesia, CP is not a notifiable disease due mainly to the (too) high prevalence of this illness, the absence of a duly validated laboratory diagnosis for clinical cases and the lack of a clearly defined medical protocol for patient's management (Direction de la Santé de Polynésie française (DSP), 2019). The first CP epidemiological studies in French Polynesia date back to the 1960's [START_REF] Bagnis | A propos de quelques cas d'intoxications par des mollusques du genre "bénitier" dans une île de la Société[END_REF][START_REF] Bagnis | Clinical apsects of ciguatera (fish poisoning) in French Polynesia[END_REF][START_REF] Bagnis | Naissance et développement d'une flambée de ciguatera dans un atoll des Tuamotu[END_REF]. From then, epidemiological data were periodically updated through specific studies [START_REF] Bagnis | Epidemiology of ciguatera in French Polynesia from 1960 to 1984[END_REF]Chateau-Degat et al., 2007a) until 2007 when local health authorities agreed to set up a CP dedicated epidemiological surveillance program jointly managed by the Health Monitoring Office (Public Health Directorate of French Polynesia) and the Laboratory of Marine Biotoxins (LBM) of ILM. Initially, the aim of this program was to take advantage of the existing sentinel network of public health physicians to collect declaration forms filled in by each patient suspected of having CP. Over the years, this network progressively extended to the healthcare workers of the 61 public health medical facilities in French Polynesia (including outlying hospitals, medical centers, dispensaries and infirmaries), and even to some private practitioners. Information gathered on this one-page declaration form, which was updated twice since 2007, concern the patient's age, gender and island of residence, the context of the poisoning (date, fishing area, fish species), the symptoms, the number of previous CP, etc. (Fig. 3). Data collected through this country-wide surveillance program are centralized at LBM-ILM which produces an annual report widely disseminated through the Public Health Directorate website, medical newsletters/forum, social media, local media, etc. In addition, a dedicated email address was created to answer to the general public's questions about CP (veille.ciguatera@ilm.pf).

Fig. 3

Since reporting is made on a voluntary basis, CP prevalence is significantly underestimated throughout the country, especially as many patients tend to forgo medical treatment and/or rely on traditional medicine (see section 4.2.2). It is estimated that ciguatera figures in French Polynesia could quite possibly be at least doubled as, in more than half the reported cases, patients stated they had shared the toxic meal with others at table who had also gone ill but failed to report the poisoning [START_REF] Chinain | Update on ciguatera research in French Polynesia[END_REF]. This situation has prompted the implementation of a dedicated ciguatera website (www.ciguatera.pf) in 2014, in an effort to open up the notification program to private practitioners and the general public. The implementation of this community-based participatory reporting program has allowed the production of dynamic risk maps of French Polynesian lagoons, as well as a list of fish species involved in CP incidents in each reporting island. In an effort to increase community outreach, this website also provides a wealth of general information on ciguatera to web users. One main advantage of this IT-based surveillance program is that alerts about the toxic events as well as prevention messages can be issued quickly, since the majority of CP cases are generally notified within 72h after the poisoning incident.

In case of a major outbreak, the response mechanism to CP incidents currently in place in French Polynesia involves three main entities, each having specific mandates: (i) the Health Monitoring Office which issues CP outbreak alerts; (ii) the Hygiene and Public Health Department which sends requests for confirmatory analyses on suspect fish batches and takes all necessary measures to remove toxic fish from retail outlets; and (iii) the LBM-ILM, in charge of conducting confirmatory analyses on suspect fish samples, and field campaigns to investigate the etiology of mass-poisoning outbreaks in newly affected areas.

Contribution of herbivores and marine invertebrates to ciguatera poisoning incidents

According to [START_REF] Halstead | Poisonous and venomous marine animals of the world[END_REF], more than 400 fish species are considered to be potential vectors of CP. Historically, CP was thought of as a "carnivore problem" [START_REF] Lewis | Ciguatera: Australian perspectives on a global problem[END_REF][START_REF] Rongo | Ciguatera poisoning in Rarotonga, southern Cook Islands[END_REF], and in fact, Serranidae, Lutjanidae, Carangidae, Muraenidae, Lethrinidae, Sphyraenidae consistently account for the majority of outbreaks worldwide [START_REF] Quod | Ciguatera in Reunion Island (SW Indian Ocean): epidemiology and clinical patterns[END_REF][START_REF] Oshiro | Ciguatera incidence and fish toxicity in Okinawa, Japan[END_REF][START_REF] Caillaud | Towards the standardisation of the neuroblastoma (neuro-2a) cell-based assay for ciguatoxin-like toxicity detection in fish: application to fish caught in the Canary Islands[END_REF][START_REF] Tester | Gambierdiscus (Dinophyceae) species diversity in the Flower Garden Banks National Marine Sanctuary, Northern Gulf of Mexico, USA[END_REF]Chan, 2015b;[START_REF] Hossen | Contribution to the risk characterization of ciguatoxins: LOAEL estimated from eight ciguatera fish poisoning events in Guadeloupe (French West Indies)[END_REF][START_REF] Farrell | Management of ciguatoxin risk in eastern Australia[END_REF]. However, it is well established that the transfer of algal CTXs in the food web requires passage through herbivorous fish [START_REF] Lewis | Origin and transfer of toxins involved in ciguatera[END_REF]. This may explain why in CP-prone reef ecosystems, clear shifts in the types of reef fishes involved in CP were generally observed beginning with herbivores, then followed by carnivores years later [START_REF] Bagnis | Correlation between ciguateric fish and damage to the reefs in the Gambier Islands (French Poynesia)[END_REF][START_REF] Rongo | Ciguatera poisoning in Rarotonga, southern Cook Islands[END_REF].

(a) Herbivorous fish species are major contributors to ciguatera poisoning events in French Polynesia

Unlike what is observed in other CP endemic areas such as the Indian Ocean, the Caribbean and the eastern Atlantic Ocean where CP events rarely involve herbivorous species, in the Pacific, Scaridae, Acanthuridae and Kyphosidae are frequently reported in CP cases occurring in the Cook Islands [START_REF] Rongo | Ciguatera poisoning in Rarotonga, southern Cook Islands[END_REF] and French Polynesia [START_REF] Darius | Ciguatera risk assessment in two toxic sites of French Polynesia using the receptor-binding assay[END_REF]Chinain et al., 2010b;[START_REF] Pawlowiez | Evaluation of seafood toxicity in the Australes archipelago (French Polynesia) using the neuroblastoma cell-based assay[END_REF]. Of note, from 2008 to 2018, herbivorous species consistently ranked among the top 5 species most frequently involved in CP cases recorded annually in French Polynesia (www.ciguatera.pf), accounting for approximately 14 to 33.6% of cases. Table 4 compares the CTX contents found in herbivorous, omnivorous and carnivorous species (either fish or marine invertebrates) in three Pacific islands: Raivavae (Australes archipelago, French Polynesia), Nuku Hiva (Marquesas archipelago, French Polynesia) and Marakei (Republic of Kiribati). Results confirm that these three islands should be regarded as ciguatera hotspots as significant levels of CTXs were detected in all trophic levels of the food web (Tab. 4). Another important finding is that, in some cases, the amounts of CTXs found in herbivorous species can largely exceed those measured in carnivores, although the highest concentration, i.e., 81.84 ppb P-CTX1, was found in top apex predator such as Muraenidae (Tab. 4). When different tissues (e.g., flesh vs. liver) were compared for their toxicity in Mureanidae specimens, data showed the liver generally harbored higher toxin concentrations [START_REF] Chan | Spatial distribution of ciguateric fish in the Republic of Kiribati[END_REF][START_REF] Jiang | Proteomic analysis of hepatic tissue of ciguatoxin (CTX) contaminated coral reef fish Cephalopholis argus and moray eel Gymnothorax undulatus[END_REF] as reported elsewhere in the literature [START_REF] Arnett | Ciguatera fish poisoning: impact for the military health care provider[END_REF][START_REF] O'toole | Linking ciguatera poisoning to spatial ecology of fish: a novel approach to examining the distribution of biotoxin levels in the great barracuda by combining non-lethal blood sampling and biotelemetry[END_REF]Kohli et al., 2017;Clausing et al., 2018) (Tab. 4). Fortunately, these fish are rarely consumed by local populations due to their bad reputation.

Tab. 4

Based on detailed LC-MC/MS studies by Yogi et al. [START_REF] Yogi | Detailed LC-MS/MS analysis of ciguatoxins revealing distinct regional and species characteristics in fish and causative alga from the Pacific[END_REF][START_REF] Yogi | Determination of toxins involved in ciguatera fish poisoning in the Pacific by LC/MS[END_REF]), distinct regional differences and species-specific toxin profiles in fish may explain the regional variations observed in fish toxicity. Therefore, gaining insights into the CTX profiles of CP-prone fish species is useful to inform risk assessment and management programs. Studies conducted on three species frequently involved in CP incidents in French Polynesia, i.e., Chlorurus microrhinos (ex Scarus gibbus, steephead parrotfish), Lutjanus bohar (red snapper) and Gymnothorax javanicus (giant moray eel) confirmed the remarkable diversity encountered in the toxic profiles of fish from various trophic levels of the ciguatera food chain [START_REF] Murata | Structures of ciguatoxin and its congener[END_REF][START_REF] Legrand | Characterization of ciguatoxins from different fish species and wild Gambierdiscus toxicus[END_REF][START_REF] Murata | Structures and configurations of ciguatoxin from the moray eel Gymnothorax javanicus and its likely precursor from the dinoflagellate Gambierdiscus toxicus[END_REF][START_REF] Satake | Isolation and structures of new ciguatoxin analogs, 2,3-dihydroxy CTX3C and 51-hydroxyCTX3C, accumulated in tropical reef fish[END_REF] (Fig. 4), consistent with observations by [START_REF] Mak | Pacific ciguatoxins in food web components of coral reef systems in the Republic of Kiribati[END_REF] collected from various species representative of distinct trophic levels in the Republic of Kiribati.

Fig. 4 (b) Marine invertebrates as novel vectors of ciguatera poisoning in French Polynesia

Ciguatera classically results from the ingestion of tropical and subtropical coral reef fish. However, the epidemiological surveillance program in French Polynesia allowed to highlight that a variety of marine invertebrates, which also represent a valuable source of protein and revenue for Pacific islands communities, may occasionally be involved in CP-like incidents.

The first report concerns the giant clam Tridacna maxima which was implicated in a mass-poisoning event in 1964 in Bora Bora Island (Society archipelago) leading to three fatalities [START_REF] Bagnis | A propos de quelques cas d'intoxications par des mollusques du genre "bénitier" dans une île de la Société[END_REF]. Years later, from 2001 and onwards, similar incidents were again reported from French Polynesia, but also New Caledonia, the Republic of Vanuatu and the Cook Islands [START_REF] Laurent | Are cyanobacteria involved in ciguatera fish poisoning-like outbreaks in New Caledonia?[END_REF][START_REF] Rongo | Ciguatera poisoning in Rarotonga, southern Cook Islands[END_REF][START_REF] Laurent | Ciguatera shellfish poisoning (CSP): a new ecotoxicological phenomenon from cyanobacteria to humans via giant clams[END_REF]. Of note, besides the digestive and neurological manifestations typically evocative of a CP, patients displayed additional symptoms, such as the rapid onset of the disease, burning of mouth and tongue, and unusual severity of symptoms including paralysis in some patients which require their hospitalization [START_REF] Laurent | Ciguatera shellfish poisoning (CSP): a new ecotoxicological phenomenon from cyanobacteria to humans via giant clams[END_REF].

Additional poisoning cases following the ingestion of sea urchins, i.e., Tripneustes gratilla, have also been described in French Polynesia in 1958 [START_REF] Randall | A review of ciguatera, tropical fish poisoning, with a tentative explanation of its cause[END_REF] and in 2005 [START_REF] Pawlowiez | Evaluation of seafood toxicity in the Australes archipelago (French Polynesia) using the neuroblastoma cell-based assay[END_REF]. In this latter study, fractionation experiments of toxic extracts by high performance liquid chromatography (HPLC) bio-guided with CBA-N2a and rRBA suggested the presence of CTX-like compounds in sea urchins from Rurutu Island [START_REF] Pawlowiez | Evaluation of seafood toxicity in the Australes archipelago (French Polynesia) using the neuroblastoma cell-based assay[END_REF]. Toxic incidents following the ingestion of Tripneustes gratilla and Tectus niloticus (gastropod) were subsequently reported in 2014 and 2015 from Nuku Hiva Island (Marquesas archipelago) (Darius et al., 2018a;Darius et al., 2018b). Patients experienced both classic and atypical symptoms (Gatti et al., 2018b), as the one previously reported by [START_REF] Laurent | Ciguatera shellfish poisoning (CSP): a new ecotoxicological phenomenon from cyanobacteria to humans via giant clams[END_REF]. Coincidentally, the affected area in Nuku Hiva Island was also the one with high Gambierdiscus densities and high prevalence of toxic fish (Darius et al., 2018a;Darius et al., 2018b).

Detailed toxicological analysis using the CBA-N2a and LC-MS/MS were further performed on T. niloticus and T. gratilla toxic samples collected from Anaho Bay, a longstanding ciguatera hotspot from Nuku Hiva Island (https://www.ciguatera.pf/index.php/fr/nos-services/bilan-annuel). They allowed for the unambiguous detection of CTX compounds in these samples (Darius et al., 2018a;Darius et al., 2018b), at levels consistently above the guidance level of 0.01 ng of P-CTXs per gram of fish flesh (or 0.01 ppb) recommended by the European Union and US Food and Drug Administration (European Food Safety Authority (EFSA), 2010; US Food and Drug Administration (FDA), 2019). Based on LC-MS/MS data, at least five distinct CTX congeners could be detected (Darius et al., 2018a;Darius et al., 2018b), some of which are known to be primarily produced by G. polynesiensis in in vitro cultures (Chinain et al., 2010a;[START_REF] Longo | Intraspecific variability in the toxin production and toxin profiles of in vitro cultures of Gambierdiscus polynesiensis (Dinophyceae) from French Polynesia[END_REF] (Fig. 5). Interestingly, some of these compounds also corresponded to the CTXs mainly detected in giant clams (T. maxima) experimentally fed highly toxic cells of G. polynesiensis [START_REF] Roué | Evidence of the bioaccumulation of ciguatoxins in giant clams (Tridacna maxima) exposed to Gambierdiscus spp. cells[END_REF]Roué et al., 2018b). All these findings suggest that Gambierdiscus is the likely source of the CTX compounds naturally bio-accumulated in a variety of marine invertebrates.

Fig. 5

It should be noted that reports of sporadic emerging or re-emerging poisoning cases following the consumption of popular marine invertebrates not only concern French Polynesia. At a regional scale, T. maxima, Octopus cyanea (big blue octopus), Percnon spp. (nimble spray crab) and Dendropoma maxima (large worm shell) from the Cook Islands were reportedly implicated in CP incidents [START_REF] Rongo | Ciguatera poisoning in Rarotonga, southern Cook Islands[END_REF], as well as Panulirus penicillatus (lobsters) and octopus in the Republic of Kiribati [START_REF] Mak | Pacific ciguatoxins in food web components of coral reef systems in the Republic of Kiribati[END_REF].

Confirmatory analyses in fish remnants

CP is diagnosed clinically when characteristic symptoms follow the ingestion of ciguatera-prone marine products. However, one way of confirming the diagnosis of ciguatera is by testing food remnants for the presence of CTXs. As previously mentioned, the amount of CTXs considered to be harmful for human consumption is estimated at 0.01 ppb, taking into account a 10-fold safety margin (European Food Safety Authority (EFSA), 2010; US Food and Drug Administration (FDA), 2019).

Toxicological investigations aiming at linking the amount of CTXs found in toxic meal remnants to patients' clinical symptoms were conducted as part of the surveillance program currently in place in French Polynesia. Tab. 5 details the CTX contents measured by means of rRBA in fish remnants involved in CP cases in 15 French Polynesian patients. Results showed that CTXs varied from 0.38 to 8.38 ng P-CTX3C eqv.g -1 (or 0.16 to 3.51 ng P-CTX1B eqv.g -1 ), consistent with the risk value of 0.1 ng P-CTX1B eqv.g -1 of fish flesh proposed by Lewis [START_REF] Lewis | The changing face of ciguatera[END_REF]. Interestingly, the variety (number) of symptoms recorded does not seem to be linked to the CTX concentration in fish leftovers (Tab. 5). These findings are in good agreement with LC-MS/MS data obtained from fish implicated in local CP incidents in Australia, showing P-CTXs contents ranging from 0.02 to 14.9 ng P-CTX eqv.g -1 in fish [START_REF] Hamilton | Human fatality associated with Pacific ciguatoxin contaminated fish[END_REF][START_REF] Farrell | Clinical diagnosis and chemical confirmation of ciguatera fish poisoning in New South Wales, Australia[END_REF][START_REF] Farrell | Management of ciguatoxin risk in eastern Australia[END_REF][START_REF] Edwards | Four recent ciguatera fish poisoning incidents in New South Wales, Australia linked to imported fish[END_REF]. As in French Polynesia, these data exclusively concerned carnivorous species such as the Spanish mackerel (Scomberomorus commerson), redthroat emperor, purple rockcod, green jobfish grouper and sawtooth barracuda.

Tab. 5

The very high levels of CTXs found in fish from the Pacific raise the question of the potential effects of CTX accumulation in fish. CTXs are known to bind to both sodium channels isolated from mammalian (rat) and fish brains, therefore a high toxin load is likely to cause morphological changes and/or abnormal behavior in fish [START_REF] Lehane | Ciguatera: recent advances but the risk remains[END_REF][START_REF] Ledreux | Dynamics of ciguatoxins from Gambierdiscus polynesiensis in the benthic herbivore Mugil cephalus: trophic transfer implications[END_REF]Clausing et al., 2018, and references therein). Concentrations of CTXs well above 10 ng.g -1 have been detected in Pacific herbivorous species such as Scarus rubroviolaceus and Ctenochaetus striatus (i.e., 18.04 and 12.65 ng P-CTX3C eqv.g -1 ) as well as in omnivorous species such as Crenimugil crenilabis and Liza vaigiensis (i.e., 21.02 and 16.23 ng P-CTX3C eqv.g -1 , respectively) [START_REF] Darius | Ciguatera risk assessment in two toxic sites of French Polynesia using the receptor-binding assay[END_REF], with no apparent detrimental effects on their behavior and/or physiology. Similar observations exist for carnivores such as Cephalopholis argus and moray eels, with concentrations ranging from [10-24.4] ng P-CTX1B eqv.g -1 and [17.17-81.8] ng P-CTX1B eqv.g -1 , respectively [START_REF] Chan | Spatial distribution of ciguateric fish in the Republic of Kiribati[END_REF][START_REF] Bienfang | Ciguatoxicity in the main Hawaiian Islands: spatial and temporal variability in the introduced reef carnivore Cephalopholis argus[END_REF][START_REF] Jiang | Proteomic analysis of hepatic tissue of ciguatoxin (CTX) contaminated coral reef fish Cephalopholis argus and moray eel Gymnothorax undulatus[END_REF][START_REF] Mak | Pacific ciguatoxins in food web components of coral reef systems in the Republic of Kiribati[END_REF]. These data clearly suggest adaptations for resistance in fish or marine invertebrate species naturally exposed to CTXs in the wild [START_REF] Banner | Intoxication par le poisson: notes sur la ciguatera et son mode d'action et quelques suggestions thérapeutiques[END_REF][START_REF] Clausing | Experimental evidence of dietary ciguatoxin accumulation in an herbivorous coral reef fish[END_REF].

Socio-economic impacts and ciguatera perception in Pacific Island Countries and Territories

Evaluating the true socio-economic impacts of CP on the life of the 400 million people living in tropical and subtropical coastal regions [START_REF] Glaziou | The epidemiology of ciguatera fish poisoning[END_REF] proves extremely challenging due to its numerous sociological and cultural ramifications that go far beyond the public health aspects. For example, a survey conducted among Rarotonga communities (Cook Islands) showed that CP may interfere and disrupt the intergenerational transmission of traditional knowledge in affected communities, particularly with regard to fishing practices [START_REF] Rongo | Socioeconomic consequences of ciguatera poisoning in Rarotonga, southern Cook Islands[END_REF]. Too, the potential damage to trade, tourism and indirectly to health by poor nutrition and diet modification following ciguatera outbreaks are also often overlooked. For example, [START_REF] Rongo | Did ciguatera prompt the late Holocene Polynesian voyages of discovery?[END_REF] draw attention on the shift towards processed foods in the Cook Islands and the 1990s mass migration of Cook Islanders to New Zealand and Australia during CP events. On another plan, assessing the ciguatera perception among local populations in relation with adaptive strategies to avoid or limit their daily exposure to this toxic threat may also prove useful in promoting targeted prevention messages in the frame of risk management programs. As it stands, the secular cohabitation of Pacific islands communities with ciguatera often results in high risk-taking behaviors.

Socio-economic impacts of ciguatera poisoning, including dietary and cultural shifts

A remarkable effort to evaluate the worldwide economic impact of HABs has been undertaken in 2007 by [START_REF] Nau | Global economic cost of harmful algal blooms[END_REF] as a PhD project. Information compiled from 17 countries revealed a range of annual costs from USD $1,712,784 to USD $185,573,530. Recently, an extensive assessment of the global cost of algal bloom has been conducted, taking into account all aspects including human health impacts, commercial fishery impacts, tourism/recreation impacts, monitoring and management impacts [START_REF] Sanseverino | Algal bloom and its economic impact[END_REF]. Although the ciguatera issue was included in these two studies, it only represented a marginal part of the estimated costs.

On a local and punctual basis however, the cost of medical expenses linked to ciguatera outbreaks stricto sensu can be estimated. For example, in the French Polynesian island of Moorea, this cost has been estimated to USD $241,847 over the single time period of 2007-2013 [START_REF] Morin | Ciguatera fish poisoning: incidence, health costs and risk perception on Moorea Island (Society archipelago, French Polynesia)[END_REF]. In addition, the negative outcomes of CP on the populations of endemic area go way beyond the cost of intoxication cases medical treatment. Instead, CP consequences have huge economic and social impacts for PICTs. First, the threat of CP induces a loss of confidence of consumers towards fish and seafood which are a primary and high nutritional value food resource for these populations, but also their main protein source from a traditional point of view [START_REF] Dalzell | Sustainability and management of reef fisheries in the Pacific Islands[END_REF][START_REF] Bell | Planning the use of fish for food security in the Pacific[END_REF][START_REF] Kronen | Socio-economic and fishery indicators to identify and monitor artisanal finfishing pressure in Pacific Island countries and territories[END_REF]. It thus causes a progressive shift of the dietary patterns of locals towards less healthy products resulting in a strong reliance on imported and/or canned products, with the risk of increasing sugar and fat intake [START_REF] Lewis | Ciguatera: ecological, clinical, and socioeconomic perspectives[END_REF][START_REF] Dewailly | Fish consumption and health in French Polynesia[END_REF][START_REF] Counil | La transition alimentaire et sanitaire en Polynésie française -Faits saillants des résultats de l'étude menée en 2007 à Papeete et dans les îles Australes[END_REF][START_REF] Ferland | Glycemic index in relation to nutrient intake, body composition, and metabolic risk factors in French Polynesia[END_REF][START_REF] Rongo | Ciguatera poisoning in Rarotonga, southern Cook Islands[END_REF][START_REF] Gillett | Fisheries in the economies of Pacific Island Countries and Territories[END_REF][START_REF] Friedman | An updated review of ciguatera fish poisoning: clinical, epidemiological, environmental, and public health management[END_REF]. Socioeconomic consequences of CP have been carefully studied in 2011 on the example of Rarotonga, one of the southern Cook Islands [START_REF] Rongo | Ciguatera poisoning in Rarotonga, southern Cook Islands[END_REF]. The authors collected data on protein consumption preferences from 179 households and compared them with a previous similar study. They showed that consumption of fresh fish had been diminished by 50% between 1989 and 2006 due to CP events while alternative proteins (mostly imported meats) had increased. These authors also used a "cost savings-andavoidance" valuation technique to estimate the direct loss in marketable goods and services value which allowed them to evaluate the economic consequences of CP around NZD $750,000 per year and the approximate costs of dietary shifts to NZD $1 million per year. Hence on one hand the average cost of food rations increases as an indirect consequence of CP, and on the other hand this progressive dietary shift leads to the appearance of health issues such as diabetes, obesity, and cardiovascular troubles directly related to alimentary choices. The increased occurrence of these metabolic diseases in turn significantly raises the public health expenses [START_REF] Skinner | Ciguatera fish poisoning in the Pacific Islands (1998 to 2008)[END_REF]. Additional economic consequences include a decrease in productivity of the exposed populations, of local fishermen incomes as well as exportations opportunities [START_REF] Magnien | The dynamics of science, perception, and policy during the outbreak of Pfiesteria in the Chesapeake Bay[END_REF][START_REF] Bauer | The importance of human dimensions research in managing harmful algal blooms[END_REF][START_REF] Berdalet | Marine harmful algal blooms, human health and wellbeing: challenges and opportunities in the 21 st century[END_REF][START_REF] Gillett | Fisheries in the economies of Pacific Island Countries and Territories[END_REF]. In addition, these costs estimations neither include the expenses of chronic effects care nor the cost of diagnostic difficulties experienced in countries located in temperate areas by the returning tourists who contracted CP during their stay in PICTs. Finally, legal actions can be undertaken by affected consumers against restaurants and/or fish suppliers, a new kind of lawsuits which is expected to only increase in the coming years.

PICTs are already challenged with an array of environmental problems such as land degradation, coastal erosion, loss of terrestrial and marine biodiversity, contamination of freshwater resources due to urban, agricultural and industrial development and marine pollution and coral reef degradation [START_REF] Barnett | Dangerous climate change in the Pacific Islands: food production and food security[END_REF]. PICTs ecosystems are thus considered as extremely vulnerable to the effects of climate change. Given the critical role of fisheries in their food supply and economic development the potential consequences of climate change on food security is especially threatening for these communities [START_REF] Gillett | Fisheries in the economies of Pacific Island Countries and Territories[END_REF]. Indeed, the United Nations Food and Agriculture Organization (FAO) predicts ciguatera to become an increasing food safety threat due to climate change at a global scale (Food and Agricultural Organization of the United Nations (FAO), 2014). Should this prediction prove to be accurate, the economic and social burden of ciguatera will rise exponentially with both climate change and world trade globalization. Hence, a smart and thorough planning of the use of fish for food security in the Pacific regions should be conducted to avoid potentially dramatic lack of this essential resource before 2030 [START_REF] Bell | Planning the use of fish for food security in the Pacific[END_REF]. Collaboration between the governments of all concerned countries and territories is required to develop multiple solutions, such as increasing local access to tuna, develop aquaculture and diversify the fish supply. Concerning aquaculture, three regional organizations, i.e., the Pacific Community (SPC), the International Center for Living Aquatic resources Management (ICLARM) and the University of the South Pacific (USP) have recently committed to a "Regional Strategy for the Development of Aquaculture" which should help decision-making by convening regular meetings of island nations, stakeholders and other local organizations [START_REF] Adams | Current status of aquaculture in the Pacific Islands[END_REF]. However, long-term research and education programs are required to design and test economically and environmentally sustainable methods for expansion of aquaculture in the Pacific region.

Risk-taking behaviors vs. adaptive strategies among island communities

Based on data collected through the epidemiological surveillance program currently established in French Polynesia, approximately 52% of patients affected by CP in 2018 has actually experienced a previous CP at least once in their lifetime (over 10 to 20 times for some patients) (Institut Louis Malardé (ILM), [2007][2008][2009][2010][2011][2012][2013][2014][2015][2016][2017][2018]. This was particularly visible in communities living in the most remote islands of French Polynesia where food availability and diversity is more limited than in Tahiti and the main islands (Gatti et al., 2018a). These data are consistent with the results of a study conducted in 2005 in New Caledonia among 559 patients, which indicated that 37.8% already presented a history of CP [START_REF] Baumann | Prevalence, symptoms and chronicity of ciguatera in New Caledonia: results from an adult population survey conducted in Noumea during 2005[END_REF], as well as observations by [START_REF] Rongo | Ciguatera poisoning in Rarotonga, southern Cook Islands[END_REF] in the Cook Islands.

In some atolls of the Tuamotu archipelagoe, with limited food supply and high unemployment, the population has no other choice than to eat the product of their daily fishing, even if they are aware of a potential toxic hazard. In a recent questionnaire survey conducted in Takaroa, Raivavae and Mangareva Islands, 29% of informants with a previous history of CP declared they were fully aware they were taking a risk to get poisoned. Among the many reasons given for this high risk-taking behavior were: (i) they suspected the fish was toxic but deliberately consumed it to prevent other family members from poisoning themselves; (ii) the pleasure of eating the fish (even toxic) was more compelling than the "inconvenience" associated with CP (ILM, unpublished data). Another possible explanation for this somewhat fatalistic attitude may be the strong confidence local populations have towards a number of traditional remedies that are easily accessible to everyone (see section 4.2.2).

Adaptive strategies developed by local populations in French Polynesia to limit ciguatera poisoning risk

Toxic fish are not distinguishable from edible ones as CTXs do not seem to affect fish physiology and behavior, fish aspect (skin color variation), smell or taste [START_REF] Lehane | Ciguatera: recent advances but the risk remains[END_REF]. Of note, CTXs are present in fish in trace levels (nanograms) making their detection very challenging. Therefore, in the absence of field test kits readily available for local people and fishermen, local populations have no other way out but the use of ancestral folk tests to detect toxic individuals [START_REF] Lewis | Ciguatera -Implications for nutrition and marine resource development in the Pacific Islands[END_REF][START_REF] Alvarez | Ciguatera: clinical, epidemiological and anthropological aspects[END_REF].

One frequent way to struggle for life in many communities in PICTs was the oral transmission of folk knowledge from one generation to the next. Despite the risks of loss related to oral tradition, popular beliefs in PICTs have maintained the knowledge about several folk detection tests to avoid ciguatera [START_REF] Darius | Use of folk tests to detect ciguateric fish: a scientific evaluation of their effectiveness in Raivavae Island (Australes, French Polynesia)[END_REF]. To date, a wide range of tests are still largely used: e.g., feeding ants or flies with a small piece of fish; cooking fish with a silver coin or ring and looking for skin discoloration; watching for the physical aspect of the flesh [START_REF] Lewis | Ciguatera -Implications for nutrition and marine resource development in the Pacific Islands[END_REF][START_REF] Lewis | Disease and development: ciguatera fish poisoning[END_REF]Chinain et al., 2010b;[START_REF] Darius | Use of folk tests to detect ciguateric fish: a scientific evaluation of their effectiveness in Raivavae Island (Australes, French Polynesia)[END_REF]. The most widespread test, however, is a simple "folk bioassay" which consists in feeding a piece of fish (usually the liver) to a dog or a cat, and watch for signs of poisoning in the animal [START_REF] Lewis | Ciguatera -Implications for nutrition and marine resource development in the Pacific Islands[END_REF][START_REF] Lewis | Disease and development: ciguatera fish poisoning[END_REF][START_REF] Darius | Use of folk tests to detect ciguateric fish: a scientific evaluation of their effectiveness in Raivavae Island (Australes, French Polynesia)[END_REF]. If most of these tests are frequently mentioned in the literature, none of them have been scientifically evaluated for their effectiveness. For instance, the "folk bioassay" itself can hardly be evaluated even in laboratory conditions, for obvious ethical reasons [START_REF] Lewis | Ciguatera (fish poisoning) with special reference to cats[END_REF][START_REF] Dickey | Ciguatera: a public health perspective[END_REF].

A study aiming at evaluating the effectiveness of two traditional methods, namely the rigor mortis test (RMT) and the hemorrhagic test (HT), was conducted in Raivavae Island (Australes archipelago). Based on RMT and HT, flabby fish or the presence of hemorrhagic signs at the tail of the dead fish, respectively, are the signs that these individuals are toxic ones [START_REF] Darius | Use of folk tests to detect ciguateric fish: a scientific evaluation of their effectiveness in Raivavae Island (Australes, French Polynesia)[END_REF]. A total of 107 fish collected by spear-fishing at various fishing sites around the island were further subjected to the diagnosis of five local testers by means of these two tests, and the results compared with laboratory toxicity data obtained via the rRBA [START_REF] Darius | Use of folk tests to detect ciguateric fish: a scientific evaluation of their effectiveness in Raivavae Island (Australes, French Polynesia)[END_REF]. Results showed that the performance of RMT and HT varied from one tester to another, depending primarily on the tester's skillness and/or whether he had a long practice of the test. The best scores observed were 55% and 70% respectively for RMT and HT. The best agreement between testers was also obtained with HT. Moreover, results also suggested that the best way to limit the number of poisoning cases would be to perform the RMT and HT in parallel [START_REF] Darius | Use of folk tests to detect ciguateric fish: a scientific evaluation of their effectiveness in Raivavae Island (Australes, French Polynesia)[END_REF]. It was concluded that the use of these two traditional tests combined with a good knowledge of the risky fishing zones and fish species may help reduce CP in areas where CP is endemic. Another obvious advantage of these homemade tests is that they can be carried out on the fishing site itself at a lower cost, and therefore may constitute undeniable assets in terms of ciguatera risk management on a daily basis.

Complementary to these folk detection tests, local populations have also developed a number of adaptive strategies to avoid or limit the risk of contracting CP: e.g. reject risky fish species, avoid risky fishing areas, discard liver and head, preferentially eat fish specimens of smaller size for a given species, space out fish meals, etc. [START_REF] Lewis | Ciguatera -Implications for nutrition and marine resource development in the Pacific Islands[END_REF][START_REF] Lewis | Disease and development: ciguatera fish poisoning[END_REF]. However, the research progress achieved in the past decades have led to progressively reconsider several of the early paradigms or common assumptions in ciguatera, in particular those pertaining to factors likely to influence toxins concentration in fish. For example, studies aiming at examining the relationship between toxicity and fish size or weight exist for a limited number of species. While some authors concluded that biological characteristics such as size, weight or lipid content were not a good predictor of fish ciguatoxicity [START_REF] Pottier | Characterisation of multiple Caribbean ciguatoxins and congeners in individual specimens of horse-eye jack (Caranx latus) by highperformance liquid chromatography/mass spectrometry[END_REF][START_REF] Darius | Ciguatera risk assessment in two toxic sites of French Polynesia using the receptor-binding assay[END_REF][START_REF] Dierking | Ciguatera in the introduced fish Cephalopholis argus (Serranidae) in Hawaii and implications for fishery management[END_REF]Chinain et al., 2010b;[START_REF] Bienfang | Ciguatoxicity in the main Hawaiian Islands: spatial and temporal variability in the introduced reef carnivore Cephalopholis argus[END_REF][START_REF] Caillaud | Towards the standardisation of the neuroblastoma (neuro-2a) cell-based assay for ciguatoxin-like toxicity detection in fish: application to fish caught in the Canary Islands[END_REF][START_REF] Darius | Use of folk tests to detect ciguateric fish: a scientific evaluation of their effectiveness in Raivavae Island (Australes, French Polynesia)[END_REF][START_REF] Mak | Pacific ciguatoxins in food web components of coral reef systems in the Republic of Kiribati[END_REF][START_REF] Gaboriau | Ciguatera fish toxicity in French Polynesia : size does not always matter[END_REF][START_REF] Robertson | Invasive lionfish (Pterois volitans): a potential human health threat for ciguatera fish poisoning in tropical waters[END_REF][START_REF] Bravo | Ciguatera, an emerging human poisoning in Europe[END_REF][START_REF] Soliño | Prevalence of ciguatoxins in lionfish (Pterois spp.) from Guadeloupe, Saint Martin, and Saint Barthélmy Islands (Caribbean)[END_REF][START_REF] Kohli | Qualitative and quantitative assessment of the presence of ciguatoxin, P-CTX-1B, in Spanish mackerel (Scomberomorus commerson) from waters in New South Wales (Australia)[END_REF], others reached contradictory conclusions [START_REF] Oshiro | Ciguatera incidence and fish toxicity in Okinawa, Japan[END_REF][START_REF] Chan | Spatial distribution of ciguateric fish in the Republic of Kiribati[END_REF][START_REF] Wong | Ciguatera fish poisoning in Hong Kong: a 10-year perspective on the class of ciguatoxins[END_REF][START_REF] Ha | Identification of causative ciguatoxins in red snappers Lutjanus bohar implicated in ciguatera fish poisonings in Vietnam[END_REF][START_REF] Loeffler | Ciguatoxin prevalence in 4 commercial fish species along an oceanic exposure gradient in the US Virgin Islands[END_REF]. Such findings suggest that CTX concentration in fish tissues may be the result of more complex biological and physiological processes. Moreover, although size is very useful to describe the morphology of a fish, it does not provide accurate information on its age, its past growth trajectory and its physiological state, as some fish species will reach their maximum size at a very young age, while in other species the maximum size will be reached only after several years [START_REF] Nadon | Length-based assessment of coral reef fish populations in the main and Northwestern Hawaiian Islands[END_REF]. In this regard, an estimate of the real age of fish via the analysis of otoliths of fish appears much more relevant [START_REF] Campana | Otoliths, increments, and elements: keys to a comprehensive understanding of fish populations? Can[END_REF][START_REF] Vigliola | The back-calculation of fish growth from otoliths[END_REF] and could prove useful to inform fish toxicity predictive models. In conclusion, current management practices based on the simple avoidance of fish of certain sizes [START_REF] Clua | Prevalence and proposal for costeffective management of the ciguatera risk in the Noumea fish market, New Caledonia (South Pacific)[END_REF][START_REF] Sumner | Hazards affecting Australian seafood[END_REF]Sydney Fish Market, 2013;Chan, 2015b;Chan, 2015a;[START_REF] Sanchez-Henao | Predictive score and probability of CTX-like toxicity in fish samples from the official control of ciguatera in the Canary Islands[END_REF] do not seem of much use to the consumers to minimize CP risk, but may cause significant financial losses to the fishing industry instead.

Use of traditional remedies to treat ciguatera

Allopathic medicine has as yet failed to develop a truly effective and specific treatment for ciguatera and consists mainly of a symptom-based palliative approach [START_REF] Friedman | An updated review of ciguatera fish poisoning: clinical, epidemiological, environmental, and public health management[END_REF]. Alternatively, many South Pacific communities use traditional remedies to treat ciguatera, especially in remote locations where limited healthcare services are available. Ethnobotanical research conducted by the Institut de Recherche pour le Développement (IRD) among Pacific islands communities have identified nearly 100 plants of interest used in traditional medicine for ciguatera treatment or prevention [START_REF] Bourdy | Traditional remedies used in the Western Pacific for the treatment of ciguatera poisoning[END_REF][START_REF] Laurent | La gratte ou ciguatéra: ses remèdes traditionnels dans le Pacifique Sud[END_REF]. Roots, leaves, bark or fruits are prepared by decoction, infusion or maceration, in different proportions and to a proper dosage, based on "recipes" transmitted from one generation to the next [START_REF] Bourdy | Traditional remedies used in the Western Pacific for the treatment of ciguatera poisoning[END_REF][START_REF] Laurent | La gratte ou ciguatéra: ses remèdes traditionnels dans le Pacifique Sud[END_REF][START_REF] Kumar-Roiné | A review of traditional remedies of ciguatera fish poisoning in the Pacific[END_REF].

French Polynesia does not stand as an exception in the Pacific region as an important traditional healers community is established in this country, which can locally represents more than a dozen of healers for less than 600 inhabitants, as reported by [START_REF] Moretti | Médecine et pharmacopée végétale traditionnelles aux îles Marquises (Polynésie française)[END_REF] in Fatu Hiva island (Marquesas archipelago). Moreover, a survey conducted among 88 public healthcare professionals exercising in French Polynesia in 2018, revealed that 49% of them were keen to recommend the use of traditional medicine to CP patients, especially the one prepared from the leaves of Heliotropium foerterianum (or tāhinu in local language) [START_REF] Tranchet | Ciguatera fish poisoning: healthcare workers knowledge and practice assessment in an endemic region, 18 th International Conference on Harmful Algae[END_REF]. Of note, in certain locales of the Tuamotu archipelago where H. foerterianum is widely present and accessible to everyone, local residents have so much confidence in the effectiveness of this traditional remedy that they no longer fear CP episodes (ILM, 2019, unpublished data).

The potential presence of active molecules capable of counteracting the neurotoxic effects of CTXs was sought in the extracts of ≈ 20 plants using CBA-N2a (Boydron-Le Garrec et al., 2005;[START_REF] Kumar-Roiné | Ability of certain plant extracts traditionally used to treat ciguatera fish poisoning to inhibit nitric oxide production in RAW 264.7 macrophages[END_REF] and rRBA [START_REF] Kumar-Roiné | Ability of certain plant extracts traditionally used to treat ciguatera fish poisoning to inhibit nitric oxide production in RAW 264.7 macrophages[END_REF]. Only extracts prepared from the roots of Pandanus tectorius and leaves of Vitex trifolia and H. foertherianum showed an ability to inhibit the binding of CTXs on site 5 of VGSCs [START_REF] Kumar-Roiné | Ability of certain plant extracts traditionally used to treat ciguatera fish poisoning to inhibit nitric oxide production in RAW 264.7 macrophages[END_REF]. These results were consistent with a previous study showing the ability of H. foertherianum extracts to inhibit spontaneous and repetitive discharges of the action potential as well as the swelling observed at the level of the frog myelinated axons induced by P-CTX1B [START_REF] Benoit | Reversal of pacific ciguatoxin-1B effects on myelinated axons by agents used in ciguatera treatment[END_REF]. Bio-guided fractionation carried out on leaf extracts of H. foertherianum further led to the formal identification of its main active principle, i.e., rosmarinic acid (RA), a compound widely known for its numerous biological properties (antioxidant, anti-inflammatory, bactericidal, fungicidal, and beneficial effects on the cardiovascular system and neurodegenerative diseases) [START_REF] Kumar-Roiné | Ability of certain plant extracts traditionally used to treat ciguatera fish poisoning to inhibit nitric oxide production in RAW 264.7 macrophages[END_REF].

Subsequent studies compared the effects of RA vs. a leaf decoction of tāhinu on the viability of neuroblastoma cells exposed to P-CTX1B, and allowed to confirm the beneficial effects of both extracts although the traditional remedy proved five-fold more active than RA alone, which suggests a possible synergistic action of the 24 co-occurring compounds identified in the extract of tāhinu leaves and whose chemical structures remain to be elucidated [START_REF] Rossi | Protective effect of Heliotropium foertherianum (Boraginaceae) folk remedy and its active compound, rosmarinic acid, against a Pacific ciguatoxin[END_REF]. The neuroprotective effects of RA on P-CTX1B in primary human neurons was also demonstrated by [START_REF] Braidy | Neuroprotective effects of rosmarinic acid on ciguatoxin in primary human neurons[END_REF]. It should be noted that a great variability in RA contents is observed from one site to another, certainly influenced by environmental factors but also by the composition of the soil or exposure to the sun and winds [START_REF] Rossi | Vers une valorisation industrielle d'un remède traditionnel pour le traitement des intoxications ciguatériques[END_REF]. This spatial variability in RA contents could partly explain why the effectiveness of the remedy varies between islands/archipelago.

In summary, although no clinical trial has been carried out to duly validate the effectiveness of this traditional remedy at a large scale, results already available clearly highlight the potential that exists around the tāhinu leaves traditional remedy. Further research efforts should examine the possibility of making concentrates of H. foertherianum commercially available in the form of infusion bags pre-dosed with active ingredients. In any case, this traditional remedy offers a promising alternative to symptomatic (palliative) treatment generally regarded as ineffective by most patients. However, to be effective, this remedy must be taken very quickly, i.e., within hours after the onset of clinical symptoms. Combined with early diagnosis of the disease, it may significantly help reduce the risk of developing chronic forms in ciguateric patients.

Risk assessment and management of ciguatera in the Pacific

The implementation of risk assessment and management programs in every PICT highly exposed to CP risk, should be regarded as a public health priority in the Pacific region. But to ensure sustainable results, any defined action plan should be considerate of the limited resources generally dedicated to the mitigation of this toxic threat by PICT national governments. This section will examine several management options readily implementable in PICTs, including: (i) the deployment on a routine basis of easy-to-use, low-cost fieldmonitoring devices to allow provision of timely advise on locations at risk of ciguatera; (ii) the selection of specific laboratory toxin detection tests well adapted to the context of ciguatera in PICTs (e.g., high endemicity); and (iii) the choice of appropriate communication and outreach strategies for increased awareness about ciguatera among local communities.

Detection tools

Gambierdiscus polynesiensis as a potential biomarker of ciguatera poisoning risk?

Management of CP is difficult, because its occurrence in reef ecosystems is generally associated with complex assemblages of multiple Gambierdiscus/Fukuyoa species characterized by highly divergent toxicities according to the suite of CTX congeners they produce, in addition to the amount [START_REF] Yogi | Determination of toxins involved in ciguatera fish poisoning in the Pacific by LC/MS[END_REF]Darius et al., 2018b). Gaining insights into the diversity and relative abundance of the different species of Gambierdiscus/Fukuyoa spp. present in a given locale can thus inform ciguatera hazard maps in CP-prone areas [START_REF] Smith | Molecular identification of Gambierdiscus and Fukuyoa (Dinophyceae) from environmental samples[END_REF]Darius et al., 2018b;[START_REF] Rhodes | Ciguatera fish poisoning: the risk from an Aotearoa/New Zealand perspective[END_REF], provided sampling designs properly address the issues of potential patchy distribution and/or substrate preferences and seasonal variations in cell abundance [START_REF] Parsons | Gambierdiscus and Ostreopsis: reassessment of the state of knowledge of their taxonomy, geography, ecophysiology, and toxicology[END_REF], for reviews and references therein; [START_REF] Chinain | Ciguatera-causing dinoflagellates in the genera Gambierdiscus and Fukuyoa: distribution, ecophysiology and toxicology[END_REF].

It is believed that the ciguatoxicity in a given area depends primarily on the presence of selected highly toxic species of Gambierdiscus that may not be the numerically dominant species but which contribute disproportionately to the overall flux of CTXs in the environment [START_REF] Litaker | Global distribution of ciguatera causing dinoflagellates in the genus Gambierdiscus[END_REF][START_REF] Longo | Intraspecific variability in the toxin production and toxin profiles of in vitro cultures of Gambierdiscus polynesiensis (Dinophyceae) from French Polynesia[END_REF]. A vast majority of the Gambierdiscus and Fukuyoa species/strains identified as likely producers of CTXs or CTX-like compounds, actually exhibit very low toxicity, ranging from several femtograms to sub-picograms per cell [START_REF] Chinain | Ciguatera-causing dinoflagellates in the genera Gambierdiscus and Fukuyoa: distribution, ecophysiology and toxicology[END_REF], for a review and references therein). Only two species proved significantly more toxic than the others, producing pg amounts of CTXs: G. polynesiensis (Chinain et al., 2010a;[START_REF] Rhodes | Production of ciguatoxin and maitotoxin by strains of Gambierdiscus australes, G. pacificus and G. polynesiensis (Dinophyceae) isolated from Rarotonga, Cook Islands[END_REF][START_REF] Longo | Intraspecific variability in the toxin production and toxin profiles of in vitro cultures of Gambierdiscus polynesiensis (Dinophyceae) from French Polynesia[END_REF] and G. excentricus [START_REF] Fraga | Gambierdiscus excentricus sp. nov. (Dinophyceae), a benthic toxic dinoflagellate from the Canary Islands (NE Atlantic Ocean)[END_REF][START_REF] Litaker | Ciguatoxicity of Gambierdiscus and Fukuyoa species from the Caribbean and Gulf of Mexico[END_REF]Pisapia et al., 2017a), which are therefore recognized as important contributors to CP in the South Pacific and the Atlantic Oceans, respectively. Recent findings suggest that G. silvae possibly fill that role in the Caribbean region [START_REF] Robertson | Toxicity, chemistry, and implications of Gambierdiscus silvae: a ciguatoxin superbug in the Greater Caribbean Region[END_REF].

As an example, published toxicity records for G. polynesiensis range from 1.2 up to 18.2 pg.cell -1 , as determined by various analytical methods (Chinain et al., 2010a;[START_REF] Rhodes | Production of ciguatoxin and maitotoxin by strains of Gambierdiscus australes, G. pacificus and G. polynesiensis (Dinophyceae) isolated from Rarotonga, Cook Islands[END_REF][START_REF] Roué | Evidence of the bioaccumulation of ciguatoxins in giant clams (Tridacna maxima) exposed to Gambierdiscus spp. cells[END_REF]Darius et al., 2018b;[START_REF] Longo | Intraspecific variability in the toxin production and toxin profiles of in vitro cultures of Gambierdiscus polynesiensis (Dinophyceae) from French Polynesia[END_REF]. Of note, this species, which is currently only known from the Pacific Ocean, has been consistently described from locations reputed at high risk of ciguatera [START_REF] Skinner | Ciguatera fish poisoning in the Pacific Islands (1998 to 2008)[END_REF], such as French Polynesia (Darius et al., 2018b;[START_REF] Longo | Intraspecific variability in the toxin production and toxin profiles of in vitro cultures of Gambierdiscus polynesiensis (Dinophyceae) from French Polynesia[END_REF], the Cook Islands [START_REF] Rhodes | Production of ciguatoxin and maitotoxin by strains of Gambierdiscus australes, G. pacificus and G. polynesiensis (Dinophyceae) isolated from Rarotonga, Cook Islands[END_REF] and the Kingdom of Tonga [START_REF] Smith | Molecular identification of Gambierdiscus and Fukuyoa (Dinophyceae) from environmental samples[END_REF]. Therefore, the species G. polynesiensis may reasonable serve as a biomarker of elevated CP risk in routine cell-based risk assessment programs, as recently demonstrated in a historical ciguatera hotspot of Nuku Hiva Island (Marquesas archipelago, French Polynesia) (Darius et al., 2018b) (see section 5.1.2). However, one cannot exclude that other species with lower ciguatoxicity but wide geographical distribution can significantly contribute to the bioaccumulation of CTXs in marine food webs as well, as is the case for the species most frequently noted in the literature, i.e., G. australes [START_REF] Rhodes | Ciguatera fish poisoning: the risk from an Aotearoa/New Zealand perspective[END_REF]. Indeed, toxicity data currently available for this species clearly highlight a generally low CTX-like activity but the ability of certain strains to produce copious amounts of other ciguatera-related metabolites, such as MTXs congeners and two compounds in the gambierone group (Chinain et al., 1999a;Chinain et al., 2010a;[START_REF] Nishimura | Genetic diversity and distribution of the ciguatera causing dinoflagellate Gambierdiscus spp. (Dinophyceae) in coastal areas of Japan[END_REF][START_REF] Rhodes | Production of ciguatoxin and maitotoxin by strains of Gambierdiscus australes, G. pacificus and G. polynesiensis (Dinophyceae) isolated from Rarotonga, Cook Islands[END_REF][START_REF] Lewis | Rapid extraction and identification of maitotoxin and ciguatoxin-like toxins from Caribbean and Pacific Gambierdiscus using a new functional bioassay[END_REF][START_REF] Munday | Ciguatoxins and maitotoxins in extracts of sixteen Gambierdiscus isolates and one Fukuyoa isolate from the South Pacific and their toxicity to mice by intraperitoneal and oral administration[END_REF]Pisapia et al., 2017a;Rhodes et al., 2017b). Although MTXs are generally considered of lesser concern for CP than CTXs because of their low tendency to accumulate in fish flesh [START_REF] Yasumoto | Toxicity of the surgeonfishes. II. Properties of the principal water-soluble toxin[END_REF], their possible role in CP cannot be disregarded as eating noneviscerated fish is a common practice in many PICTs (Chateau-Degat et al., 2007b). Moreover, recent studies have provided evidence that gambierones may share similar biological activities with CTXs, although with much less potency [START_REF] Rodríguez | Gambierone, a ladder-shaped polyether from the dinoflagellate Gambierdiscus belizeanus[END_REF][START_REF] Boente-Juncal | Structure elucidation and biological evaluation of maitotoxin-3, a homologue of gambierone, from Gambierdiscus belizeanus[END_REF]. All these findings warrant further investigations to clarify the exact role of these compounds in CP, including their mode of action and targets in mammalian cells.

Field-monitoring tools

Monitoring Gambierdiscus/Fukuyoa cell abundance in the environment is useful to inform CP risk assessment and management programs [START_REF] Litaker | Global distribution of ciguatera causing dinoflagellates in the genus Gambierdiscus[END_REF] as CP outbreaks are traditionally linked to blooms of these dinoflagellates. Such surveys are commonly based on the sampling of natural substrates, i.e., macrophytes [START_REF] Grzebyk | Ecology of ciguateric dinoflagellates in the coral reef complex of Mayotte Island (S.W. Indian Ocean)[END_REF]Chinain et al., 1999b;[START_REF] Rhodes | Toxic dinoflagellates (Dinophyceae) from Rarotonga, Cook Islands[END_REF][START_REF] Tester | Gambierdiscus (Dinophyceae) species diversity in the Flower Garden Banks National Marine Sanctuary, Northern Gulf of Mexico, USA[END_REF]Díaz-Asencio et al., 2019b). However, the obvious lack of standardization inherent to this method (variations in both cell densities across macroalgal hosts and substrate availability across sites and seasons) [START_REF] Bomber | Ecological studies of benthic dinoflagellates associated with ciguatera from the Florida Keys[END_REF][START_REF] Lobel | Assessment of ciguatera dinoflagellate populations: sample variability and algal substrate selection[END_REF] led researchers to explore the use of artificial substrates for the monitoring of various ciguatera-related benthic HAB species, including Gambierdiscus/Fukuyoa spp., Ostreopsis spp. and Prorocentrum spp. [START_REF] Kibler | A collection method for ciguatera-associated dinoflagellates[END_REF][START_REF] Tester | Sampling harmful benthic dinoflagellates: comparison of artificial and natural substrate methods[END_REF]. These artificial substrates generally consist of fiberglass window-screens (WS) floating freely above the sediment and deployed in the environment for 24h (Fig. 6A) [START_REF] Moreira | Guide for designing and implementing a plan to monitor toxin-producing microalgae[END_REF]. Over the past ten years, this method was tested in a number of studies worldwide which also examined the relevance of using different materials, sizes and deployment times [START_REF] Tan | Benthic harmful dinoflagellate assemblages in a fringing reef of Sampadi Island, Sarawak, Malaysia[END_REF][START_REF] Parsons | Assessing the use of artificial substrates to monitor Gambierdiscus populations in the Florida Keys[END_REF][START_REF] Ho | First report of Gambierdiscus caribaeus and G. carpenteri (Dinophyceae) from Nha Trang Bay, South Central Vietnam[END_REF][START_REF] Yong | Habitat complexity affects benthic harmful dinoflagellate assemblages in the fringing reef of Rawa Island, Malaysia[END_REF][START_REF] Fernández-Zabala | Benthic dinoflagellates: testing the reliability of the artificial substrate method in the Macaronesian region[END_REF][START_REF] González | Identification and monitoring of microalgal genera potentially capable of forming harmful algal blooms in Punta Galeta, Panama[END_REF]. This technique offers multiple advantages: it is user-friendly (devices can be easily deployed almost anywhere), costeffective and samples can be further analyzed by means of molecular identification techniques such as quantitative Polymerase Chain Reaction (qPCR) [START_REF] Vandersea | Development of semi-quantitative PCR assays for the detection and enumeration of Gambierdiscus species (Gonyaulacales, Dinophyceae)[END_REF][START_REF] Nishimura | Quantitative PCR assay for detection and enumeration of ciguatera-causing dinoflagellate Gambierdiscus spp. (Gonyaulacales) in coastal areas of Japan[END_REF]Kretzschmar et al., 2019b;[START_REF] Litaker | Species-specific PCR assays for Gambierdiscus excentricus and Gambierdiscus silvae (Gonyaulacales, Dinophyceae)[END_REF], Restriction Fragment Length Polymorphisms analysis [START_REF] Lyu | LSU rDNA based RFLP assays for the routine identification of Gambierdiscus species[END_REF], or high-throughput sequencing [START_REF] Sassenhagen | Microsatellite markers for the dinoflagellate Gambierdiscus caribaeus from high-throughput sequencing data[END_REF][START_REF] Smith | Molecular identification of Gambierdiscus and Fukuyoa (Dinophyceae) from environmental samples[END_REF] to obtain information on the diversity and relative abundance of ciguatera-related dinoflagellates in the sampling site. This information is particularly useful for an accurate evaluation of CP risk in a given location since Gambierdiscus and Fukuyoa species are known to show differential toxicity (see sections 2.1.2 and 5.1.1). These artificial substrates also provide clean cell samples useful for subsequent isolation and in vitro culturing experiments aiming at establishing an algal collection of strains of Gambierdiscus spp. most representative of CP hotspots in French Polynesia. Consequently, these devices are now used on a routine basis in risk monitoring programs currently conducted in French Polynesia. In some islands, this technology proved useful in determining some of the factors likely to influence CP risk in a given site, as was the case in Nuku Hiva Island (Marquesas archipelago) where these passive samplers were deployed in three different sites with contrasting CP risk. Species-specific qPCR assays allowed the detection of six species in this island, including G. australes, G. caribaeus, G. carpenteri, G. pacificus, G. polynesiensis and G. toxicus (Darius et al., 2018a;Darius et al., 2018b). Results also revealed that G. polynesiensis was the predominant species (82%) in Anaho Bay, a historical ciguatera hotspot, whereas G. carpenteri which is known as a low toxin producer for CTXs at a global scale (see section 2.1.2) [START_REF] Chinain | Ciguatera-causing dinoflagellates in the genera Gambierdiscus and Fukuyoa: distribution, ecophysiology and toxicology[END_REF], for a review and references therein) predominated in Taipivai and Taiohae Bays (90%), two spots regarded as at low-risk of CP (Darius et al., 2018b).

In parallel to this cell-based method, an easy-to-use toxin-based method, i.e., the Solid Phase Adsorption Toxin Tracking (SPATT) technology, has continuously gained in popularity since its first introduction in [START_REF] Mackenzie | Solid phase adsorption toxin tracking (SPATT): a new monitoring tool that simulates the biotoxin contamination of filter feeding bivalves[END_REF][START_REF] Mackenzie | Solid phase adsorption toxin tracking (SPATT): a new monitoring tool that simulates the biotoxin contamination of filter feeding bivalves[END_REF]. Known for their relatively low cost, SPATT samplers are also very simple to prepare, deploy, transport and store [START_REF] Mackenzie | In situ passive solid-phase adsorption of micro-algal biotoxins as a monitoring tool[END_REF]. They consist of a filter made of a porous synthetic resin (e.g., Diaion® HP20, so far the most used resin) capable of adsorbing dissolved toxins circulating in the water column, and is deployed in monitored areas for few hours to several days (Fig. 6B) [START_REF] Kudela | Passive sampling for freshwater and marine algal toxins[END_REF]Roué et al., 2018a, for reviews and references therein). The use of this passive sampling method, coupled with LC-MS/MS analyses performed in a multi-toxin screening format, has demonstrated its ability to detect a large array of lipophilic and hydrophilic toxins produced by various microalgae and cyanobacteria, in both marine and freshwater environments [START_REF] Kudela | Passive sampling for freshwater and marine algal toxins[END_REF]Roué et al., 2018a, for reviews and references therein). And in fact, this technology has been recently used with great success in routine monitoring programs conducted in French Polynesia: in Nuku Hiva Island, for instance, SPATT devices filled with HP20 resin and deployed for 24h to six days have allowed confirming the presence of dissolved P-CTXs, 44-methylgambierone (formerly known as MTX3, see section 2.1.2), okadaic acid (OA) and dinophysistoxin-1 (DTX1) in the ciguateric spot of Anaho Bay (Roué et al., 2018c, Roué et al, submitted).

Fig. 6

In summary, the complementary use of these two types of passive field-samplers has proved its efficiency in various French Polynesian study sites, including in remote, difficult to access and widely dispersed islands. Combined with analytical tools such as LC-MS/MS (available through a number of specialized laboratories in the region) they can allow early detection of a wide range of toxigenic organisms and related phycotoxins likely to emerge in a given location before their significant bioaccumulation in the food web. Therefore, extending this approach to other Pacific countries where CP is highly prevalent appears as a relevant strategy, since establishing random fish testing surveys on a regular basis in these endemic areas to prevent CP outbreaks seems unrealistic, and beyond the capacity of most of these island states. This management option also offers the possibility to involve local residents in the survey effort, e.g., in the framework of citizen science programs, to ensure sustainable results.

Laboratory detection tools

A common management practice to prevent unsafe products from being placed in the market is to establish a fish ban and/or maximum levels of CTXs in fish flesh [START_REF] Rodríguez | Canary Islands (NE Atlantic) as a biodiversity 'hotspot' of Gambierdiscus: implications for future trends of ciguatera in the area[END_REF]. But unlike other toxins routinely monitored for seafood safety purpose, CTXs are still not regulated due mainly to the lack of a validated reference method and the limited availability of reference CTX standards [START_REF] Daneshian | A roadmap for hazard monitoring and risk assessment of marine biotoxins on the basis of chemical and biological test systems[END_REF][START_REF] Nicolas | Marine neurotoxins: state of the art, bottlenecks, and perspectives for mode of action based methods of detection in seafood[END_REF][START_REF] Rodríguez | Canary Islands (NE Atlantic) as a biodiversity 'hotspot' of Gambierdiscus: implications for future trends of ciguatera in the area[END_REF][START_REF] Suzuki | Analytical challenges to ciguatoxins[END_REF]. Fortunately, purification efforts aiming at the production of reference material and/or quantified standards from cultures of highly toxic strains of Gambierdiscus and/or toxic fish material are currently underway in a few laboratories [START_REF] Kato | Quantification of representative ciguatoxins in the Pacific using quantitative nuclear magnetic resonance spectroscopy[END_REF]Chinain et al., 2018).

Several laboratory detection tests are currently available to assess CTX contents in fish samples, including functional assays (e.g., CBA-N2A, RBA), analytical methods (e.g., LC/MS-MS), and immunoassays based on antibodies recognition [START_REF] Daneshian | A roadmap for hazard monitoring and risk assessment of marine biotoxins on the basis of chemical and biological test systems[END_REF][START_REF] Nicolas | Marine neurotoxins: state of the art, bottlenecks, and perspectives for mode of action based methods of detection in seafood[END_REF][START_REF] Rodríguez | Canary Islands (NE Atlantic) as a biodiversity 'hotspot' of Gambierdiscus: implications for future trends of ciguatera in the area[END_REF][START_REF] Tsumuraya | Rationally designed synthetic haptens to generate anti-ciguatoxin monoclonal antibodies, and development of a practical sandwich ELISA to detect ciguatoxins[END_REF]. However, implementing sustainable monitoring programs necessarily involves selecting a test best suited to the context of PICTs, i.e., endemic ciguatera zones with often limited resources and technological capacities. In this respect, high throughput screening methods, or bioassays that can be easily transported, stored and used by island communities thus appear as the best candidates.

(a) RBA, F-RBA, CBA

Toxin assessment in seafood classically used the in vivo MBA, but due to ethical issues and questionable extrapolation of quantitative risk to humans, the use of an analytical method, i.e., LC-MS/MS, was recommended by the European Food Safety Authority (EFSA) in 2015 [START_REF] Daneshian | A roadmap for hazard monitoring and risk assessment of marine biotoxins on the basis of chemical and biological test systems[END_REF][START_REF] Nicolas | Marine neurotoxins: state of the art, bottlenecks, and perspectives for mode of action based methods of detection in seafood[END_REF]. Although LC-MS/MS is a very sensitive method and is helpful for confirming the identity of toxins, it does not allow the detection of currently unknown marine biotoxins. Thereby, alternative methods with high throughput capacity combined with high sensitivity, e.g., CBA-N2a and rRBA, were developed [START_REF] Daneshian | A roadmap for hazard monitoring and risk assessment of marine biotoxins on the basis of chemical and biological test systems[END_REF][START_REF] Nicolas | Marine neurotoxins: state of the art, bottlenecks, and perspectives for mode of action based methods of detection in seafood[END_REF].

The CBA-N2a which uses a murine neuroblastoma (N2a) cell line offers multiple advantages: besides being a good alternative to the MBA when assessing the overall toxicity of a sample, it is also remarkably flexible in detecting a wide range of marine toxins: since its first introduction in the 1990s, this functional assay has been successfully applied to the detection of toxins acting on VGSC (e.g., saxitoxins, tetrodotoxin, CTXs, brevetoxins) [START_REF] Jellett | Paralytic shellfish poison (saxitoxin family) bioassays: automated endpoint determination and standardization of the in vitro tissue culture bioassay, and comparison with the standard mouse bioassay[END_REF], palytoxin [START_REF] Ledreux | Suitability of the Neuro-2a cell line for the detection of palytoxin and analogues (neurotoxic phycotoxins)[END_REF][START_REF] Pawlowiez | Evaluation of seafood toxicity in the Australes archipelago (French Polynesia) using the neuroblastoma cell-based assay[END_REF], MTXs [START_REF] Caillaud | Detection and quantification of maitotoxin-like compounds using a neuroblastoma (Neuro-2a) cell based assay. Application to the screening of maitotoxin-like compounds in Gambierdiscus spp[END_REF], okadaic acid, azaspiracids, pectenotoxins, yessotoxines and dinophysistoxins [START_REF] Sérandour | Collaborative study for the detection of toxic compounds in shellfish extracts using cell-based assays. Part I: screening strategy and prevalidation study with lipophilic marine toxins[END_REF]Bodero et al., 2018a;Bodero et al., 2018b). The CBA-N2a is also suitable for the detection of CTXs or CTX-like compounds in a variety of biological matrices including Gambierdiscus [START_REF] Caillaud | Cell-based assay coupled with chromatographic fractioning: a strategy for marine toxins detection in natural samples[END_REF][START_REF] Rhodes | Toxic dinoflagellates (Dinophyceae) from Rarotonga, Cook Islands[END_REF][START_REF] Pawlowiez | Evaluation of seafood toxicity in the Australes archipelago (French Polynesia) using the neuroblastoma cell-based assay[END_REF][START_REF] Xu | Distribution, abundance and diversity of Gambierdiscus spp. from a ciguatera-endemic area in Marakei, Republic of Kiribati[END_REF][START_REF] Roué | Evidence of the bioaccumulation of ciguatoxins in giant clams (Tridacna maxima) exposed to Gambierdiscus spp. cells[END_REF][START_REF] Catania | The prevalence of benthic dinoflagellates associated with ciguatera fish poisoning in the central Red Sea[END_REF][START_REF] Dai | Taxonomic assignment of the benthic toxigenic dinoflagellate Gambierdiscus sp. type 6 as Gambierdiscus balechii (Dinophyceae), including its distribution and ciguatoxicity[END_REF][START_REF] Litaker | Ciguatoxicity of Gambierdiscus and Fukuyoa species from the Caribbean and Gulf of Mexico[END_REF]Pisapia et al., 2017a;[START_REF] Clausing | Experimental evidence of dietary ciguatoxin accumulation in an herbivorous coral reef fish[END_REF][START_REF] Reverté | Assessment of cytotoxicity in ten strains of Gambierdiscus australes from Macaronesian Islands by neuro-2a cellbased assays[END_REF], cyanobacteria [START_REF] Kerbrat | Detection of ciguatoxin-like and paralysing toxins in Trichodesmium spp. from New Caledonia lagoon[END_REF][START_REF] Laurent | Ciguatera shellfish poisoning (CSP): a new ecotoxicological phenomenon from cyanobacteria to humans via giant clams[END_REF], fish [START_REF] Bienfang | Ciguatera fish poisoning: a synopsis from ecology to toxicity[END_REF][START_REF] Bienfang | Quantitative evaluation of commercially available test kit for ciguatera in fish[END_REF][START_REF] Chan | Spatial distribution of ciguateric fish in the Republic of Kiribati[END_REF][START_REF] Abraham | Caribbean ciguatoxin profile in raw and cooked fish implicated in ciguatera[END_REF][START_REF] Bienfang | Ciguatoxicity in the main Hawaiian Islands: spatial and temporal variability in the introduced reef carnivore Cephalopholis argus[END_REF][START_REF] Caillaud | Towards the standardisation of the neuroblastoma (neuro-2a) cell-based assay for ciguatoxin-like toxicity detection in fish: application to fish caught in the Canary Islands[END_REF][START_REF] Jiang | Proteomic analysis of hepatic tissue of ciguatoxin (CTX) contaminated coral reef fish Cephalopholis argus and moray eel Gymnothorax undulatus[END_REF][START_REF] O'toole | Linking ciguatera poisoning to spatial ecology of fish: a novel approach to examining the distribution of biotoxin levels in the great barracuda by combining non-lethal blood sampling and biotelemetry[END_REF][START_REF] Mak | Pacific ciguatoxins in food web components of coral reef systems in the Republic of Kiribati[END_REF][START_REF] Robertson | Invasive lionfish (Pterois volitans): a potential human health threat for ciguatera fish poisoning in tropical waters[END_REF][START_REF] Bravo | Ciguatera, an emerging human poisoning in Europe[END_REF][START_REF] Hossen | Contribution to the risk characterization of ciguatoxins: LOAEL estimated from eight ciguatera fish poisoning events in Guadeloupe (French West Indies)[END_REF][START_REF] Soliño | Prevalence of ciguatoxins in lionfish (Pterois spp.) from Guadeloupe, Saint Martin, and Saint Barthélmy Islands (Caribbean)[END_REF][START_REF] Hardison | Fluorescent receptor binding assay for detecting ciguatoxins in fish[END_REF][START_REF] Hardison | Investigation of ciguatoxins in invasive lionfish from the greater caribbean region: implications for fishery development[END_REF][START_REF] Loeffler | Ciguatoxin prevalence in 4 commercial fish species along an oceanic exposure gradient in the US Virgin Islands[END_REF]Díaz-Asencio et al., 2019a;[START_REF] Estevez | An attempt to characterize the ciguatoxin profile in Seriola fasciata causing ciguatera fish poisoning in[END_REF][START_REF] Loeffler | Fish hybridization leads to uncertainty regarding ciguatera fish poisoning risk; confirmation of hybridization and ciguatoxin accumulation with implications for stakeholders[END_REF][START_REF] Sanchez-Henao | Predictive score and probability of CTX-like toxicity in fish samples from the official control of ciguatera in the Canary Islands[END_REF][START_REF] Sanchez-Henao | Presence of CTXs in moray eels and dusky groupers in the marine environment of the Canary Islands[END_REF], giant clams [START_REF] Laurent | Ciguatera shellfish poisoning (CSP): a new ecotoxicological phenomenon from cyanobacteria to humans via giant clams[END_REF][START_REF] Roué | Evidence of the bioaccumulation of ciguatoxins in giant clams (Tridacna maxima) exposed to Gambierdiscus spp. cells[END_REF]Roué et al., 2018b), gastropods (Darius et al., 2018b), sea urchins [START_REF] Pawlowiez | Evaluation of seafood toxicity in the Australes archipelago (French Polynesia) using the neuroblastoma cell-based assay[END_REF]Darius et al., 2018a), lobsters and crabs [START_REF] Mak | Pacific ciguatoxins in food web components of coral reef systems in the Republic of Kiribati[END_REF], sharks [START_REF] Diogène | Identification of ciguatoxins in a shark involved in a fatal food poisoning in the Indian Ocean[END_REF], and even samples derived from passive sampling devices [START_REF] Caillaud | Monitoring of dissolved ciguatoxin and maitotoxin using solid-phase adsorption toxin tracking devices: application to Gambierdiscus pacificus in culture[END_REF]Roué et al., 2018c).

Another key advantage of the CBA-N2a concerns the possibility to use a cost effective approach when the testing of a high number of samples is required: first, the sample extracts are tested for the presence or absence of CTXs (qualitative random screening) which allows to classify them into negative, suspect or positive samples. Second, a quantitative analysis can then be carried out only on suspect and positive samples, thus saving time and effort.

The rRBA is based on the competitive binding between CTXs and radiolabeled brevetoxin on site 5 of VGSCs, thus allowing the specific detection of any toxin able to interfere with this labeled brevetoxin [START_REF] Dechraoui | Ciguatoxins and brevetoxins, neurotoxic polyether compounds active on sodium channels[END_REF][START_REF] Darius | Ciguatera risk assessment in two toxic sites of French Polynesia using the receptor-binding assay[END_REF][START_REF] Nicolas | Marine neurotoxins: state of the art, bottlenecks, and perspectives for mode of action based methods of detection in seafood[END_REF][START_REF] Dechraoui Bottein | Receptor-binding assay for the analysis of marine toxins: detection and mode of action[END_REF][START_REF] Díaz-Asencio | A radioligand receptor binding assay for ciguatoxin monitoring in environmental samples: method development and determination of quality control criteria[END_REF]. So far, the rRBA has been successfully applied to the detection of CTXs or CTX-like compounds in Gambierdiscus [START_REF] Darius | Ciguatera risk assessment in two toxic sites of French Polynesia using the receptor-binding assay[END_REF]Chinain et al., 2010a;Chinain et al., 2010b;Pawlowiez et al., 2013;Díaz-Asencio et al., 2019a;Díaz-Asencio et al., 2019b), cyanobacteria [START_REF] Laurent | Are cyanobacteria involved in ciguatera fish poisoning-like outbreaks in New Caledonia?[END_REF][START_REF] Laurent | Ciguatera shellfish poisoning (CSP): a new ecotoxicological phenomenon from cyanobacteria to humans via giant clams[END_REF], fish [START_REF] Darius | Ciguatera risk assessment in two toxic sites of French Polynesia using the receptor-binding assay[END_REF][START_REF] Laurent | Ciguatera shellfish poisoning (CSP): a new ecotoxicological phenomenon from cyanobacteria to humans via giant clams[END_REF][START_REF] Darius | Use of folk tests to detect ciguateric fish: a scientific evaluation of their effectiveness in Raivavae Island (Australes, French Polynesia)[END_REF][START_REF] Gaboriau | Ciguatera fish toxicity in French Polynesia : size does not always matter[END_REF][START_REF] Clausing | Guide for designing and implementing a plan to monitor toxin-producing microalgae[END_REF][START_REF] Clausing | Experimental evidence of dietary ciguatoxin accumulation in an herbivorous coral reef fish[END_REF]Díaz-Asencio et al., 2019a) and giant clams [START_REF] Laurent | Ciguatera shellfish poisoning (CSP): a new ecotoxicological phenomenon from cyanobacteria to humans via giant clams[END_REF]. Of note, the rRBA was recently developed into a high throughput testing format (microplates) by [START_REF] Díaz-Asencio | A radioligand receptor binding assay for ciguatoxin monitoring in environmental samples: method development and determination of quality control criteria[END_REF]Díaz-Asencio et al., 2019a;Díaz-Asencio et al., 2019b). However, license requirements and restrictive regulations pertaining to radioisotope utilization represent major issues that can significantly limit the applicability of the rRBA in certain laboratories, especially in PICTs where radioactive waste management could be unaffordable. A fluorescence-based RBA (fRBA) was recently developed as an alternative method for the screening of CTXs in fish samples [START_REF] Mccall | Development of a competitive fluorescence-based synaptosome binding assay for brevetoxins[END_REF][START_REF] Mccall | Development and utilization of a fluorescence-based receptor-binding assay for the site 5 voltage-sensitive sodium channel ligands brevetoxin and ciguatoxin[END_REF], then successfully applied to the detection of CTXs in Caribbean fish [START_REF] Hardison | Fluorescent receptor binding assay for detecting ciguatoxins in fish[END_REF][START_REF] Hardison | Investigation of ciguatoxins in invasive lionfish from the greater caribbean region: implications for fishery development[END_REF]. The fRBA shows clear advantages as compared to the rRBA, such as easier manipulation, shorter testing time and a high throughput testing capacity.

In summary, both CBA-N2a and rRBA have been widely used in risk assessment and management programs conducted in French Polynesian lagoons [START_REF] Darius | Ciguatera risk assessment in two toxic sites of French Polynesia using the receptor-binding assay[END_REF]Chinain et al., 2010b;[START_REF] Laurent | Ciguatera shellfish poisoning (CSP): a new ecotoxicological phenomenon from cyanobacteria to humans via giant clams[END_REF][START_REF] Pawlowiez | Evaluation of seafood toxicity in the Australes archipelago (French Polynesia) using the neuroblastoma cell-based assay[END_REF]. Of note, toxicity data yielded at these occasions were consistent with the epidemiological data and the local knowledge of local populations with regard to risky fish species and areas. These observations clearly highlight the benefit of incorporating these two functional assays into routine ciguatera risk monitoring programs for increased food safety in PICTs.

(b) Newly developed cell-based functional tests

Recent research efforts have focused on the development of biosensors based on either mammalian cells or yeast cells, whose potentialities are impressive [START_REF] Gupta | Cell-based biosensors: recent trends, challenges and future perspectives[END_REF]. [START_REF] Lewis | Rapid extraction and identification of maitotoxin and ciguatoxin-like toxins from Caribbean and Pacific Gambierdiscus using a new functional bioassay[END_REF] recently developed a new functional bioassay based on the monitoring of changes in the intracellular Ca 2+ ions levels of SH-SY5Y cells (human neuroblastoma cells) in response to exposure to potentially contaminated samples. This bioassay was successfully applied to the detection of MTXs and CTX-like compounds, even at low levels. These authors also proposed a simplified extraction procedure to isolate toxins present in Gambierdiscus samples making the whole process easier and faster.

Cardiomyocytes represent another interesting cell type: the high number of ion channels present in their membranes renders them highly sensitive to toxins acting on ion channels, while their stable beating signal can be used to quantitatively analyze toxicity. Based on this idea, Wang et al. (2015b) developed a novel functional method for the detection of saxitoxin and tetrodotoxin using a cardiomyocyte-based impedance biosensor able to monitor cardiomyocyte growth and beating status in real time. This biosensor was further developed into a robust portable system in 96 wells microplates with high consistency and long-term lifespan (Wang et al., 2015a), which appears promising for the field of marine toxin detection in general due to its high sensitivity, possible high-throughput screening applications and its potential applicability to the detection of CTXs provided specific adaptations are achieved.

In addition to mammalian cell-based assays, microbial biosensors have also been developed and are currently used for the monitoring of marine environment [START_REF] Balootaki | Microbial biosensor for marine environments[END_REF], for review and references therein). These "whole cells" biosensors classically use different types of microorganisms -bacteria or fungi -which can be genetically modified in various ways in order to increase their sensitivity or to incorporate different reporter and transducer capacity [START_REF] Han | Redesigning of microbial cell surface and its application to whole-cell biocatalysis and biosensors[END_REF]. However, eukaryotic cellular models present several relevant advantages. Among them yeasts are especially interesting since they are very resistant to drastic environmental conditions, and very well-known at both genetic and technological levels [START_REF] Walmsley | The eukaryote alternative: advantages of using yeasts in place of bacteria in microbial biosensor development[END_REF]. Yeasts also share most cellular features and molecular mechanisms with mammalian cells including signaling pathways relevant to sensing various environmental stimuli. Hence, several bioassays and biosensors based on yeast cells are presently in use in various domains of applications including food safety and HABs monitoring. As an example, [START_REF] Richter | Detection of marine microalgal biotoxins using bioassays based on functional expression of tunicate xenobiotic receptors in yeast[END_REF] have reported the development of recombinant Saccharomyces cerevisiae strains able to detect structurally complex marine biotoxins such as okadaic acid, pectenotoxin-11 and portimine. These recombinant yeast strains can be set-up in robust and inexpensive high-throughput screens for microalgal biotoxins and novel marine bioactive chemicals [START_REF] Richter | Detection of marine microalgal biotoxins using bioassays based on functional expression of tunicate xenobiotic receptors in yeast[END_REF]. Recently, taking advantage of the existence in the model yeast S. cerevisiae of a close homolog of the targets of CTXs -mammalian VGSCs -new recombinant yeast strains able to detect CTXs produced by Gambierdiscus and Fukuoya spp. have also been developed [START_REF] Martin-Yken | Ciguatoxins activate the calcineurin signalling pathway in yeasts: potential for development of an alternative detection tool?[END_REF]. These strains need now to be optimized and coupled to a detection system as simple as possible. Provided their suitability as biosensors is confirmed, they offer promising prospects for the development of a low cost field-test in the near future.

(c) Tests based on the effects of ciguatoxins on fish

The detection of CTXs in fish samples not only requires time-consuming extraction and purification steps, but also quantitative analyses carried out on high-tech equipments and by trained and skilled personnel. Hence, alternative strategies aiming at, e.g., the development of biomarkers that reflect the effects of fish exposure to high concentrations of CTXs have been explored by researchers. Results of proteomic and transcriptomic studies conducted on either CP-prone (Naso brevirostris, Cephalopholis argus, Gymnothorax javanicus) or amphidromous (Oryzias latipes) fish species revealed a strong signal of differential gene expression between toxic and non-toxic individuals, with genes involved, e.g., in detoxification, and immune defense processes [START_REF] Jiang | Proteomic analysis of hepatic tissue of ciguatoxin (CTX) contaminated coral reef fish Cephalopholis argus and moray eel Gymnothorax undulatus[END_REF][START_REF] Yan | Developmental toxicity and molecular responses of marine medaka (Oryzias melastigma) embryos to ciguatoxin P-CTX-1 exposure[END_REF][START_REF] Nuel | Transcriptomic signature of long-term CTX exposure in Naso brevirostris, 18 th International Conference on Harmful Algae[END_REF]. Of note, a similar approach has also been applied to mouse primary cortical neurons as a model for mammalian neuronal cells [START_REF] Rubiolo | Transcriptomic analysis of ciguatoxin-induced changes in gene expression in primary cultures of mice cortical neurons[END_REF] and to the blood of CP patients with the idea of developing a potential diagnostic tool [START_REF] Ryan | Transcriptomic signatures in whole blood of patients who acquire a chronic inflammatory response syndrome (CIRS) following an exposure to the marine toxin ciguatoxin[END_REF].

Although promising, these innovative approaches have not yet allowed the characterization of biomarkers specific to CTX exposure.

Outreach and communication strategies for an effective management of ciguatera: example from French Polynesia

Since 2007, numerous field campaigns have been conducted in various French Polynesian lagoons in the framework of risk assessment and management programs (Chinain et al., 2010b;[START_REF] Pawlowiez | Evaluation of seafood toxicity in the Australes archipelago (French Polynesia) using the neuroblastoma cell-based assay[END_REF]Darius et al., 2018b). They are useful to investigate the etiology of novel poisoning syndromes especially those involving atypical symptoms, or to provide local populations with risk maps of their lagoon, i.e., assist them in identifying (i) infected reef vs. low risk fishing sites; and (ii) fish species or marine invertebrates deemed not edible. The integrated approach routinely used in these field campaigns combines environmental investigations (see section 5.1.2) and toxicological analyses which target a variety of marine products most representative of the food web, and the population's food preferences and local fishing habits (see section 5.1.3a). If exceptional measures are required, fishing bans and/or ciguatera alerts can be issued in close coordination with local authorities (Fig. 7A). In addition to these field investigations, community outreach interventions are also conducted in the form of public meetings (Fig. 7B). At these occasions, recommendations to systematically report CP incidents to the local medical staff are strongly emphasized to the population.

Fig. 7

Other outreach and communication strategies are also currently considered for a more effective prevention of CP risk in French Polynesia. Based on our long-time experience with local communities, providing regular information and warnings about ciguatera all year round appears critical for increased awareness and sustainable results. This is achieved through the dissemination of guide books, flyers and posters made available in French and native language that are displayed at various strategic spots of each island, such as town halls, medical centers, schools, etc. (Fig. 8A).

In parallel, information and education actions targeted at the healthcare workers occupational group are also carried out: in 2018, an online survey was conducted among 88 healthcare professionals in duty in the five islands that compose French Polynesia, in order to identify potential gaps and weaknesses in the existing reporting network. It provided useful information on their level of knowledge about ciguatera (source, symptoms, diagnosis, patient' scare including the potential use of traditional remedy, etc.), and commitment to the reporting program. As a result, a medical information kit along with flyers intended for patients were produced and made available in paper and numeric formats (https://www.service-public.pf/dsp) (Fig. 8B).

Finally, educational interventions are also conducted on a regular basis in the frame of citizen science initiatives, school interventions, "week of science" workshops, etc.

Fig. 8 6 Conclusion

Very few countries in the Pacific region currently have a defined action plan in response to the health threat represented by ciguatera. Among the major obstacles to the implementation of sustainable monitoring and mitigation programs is the lack of sufficient resources due to competing priorities, and technical training on HAB sciences. However, the recent globalization of ciguatera has led to a resurgence of interest within the scientific community and regulatory agencies. As a result, voices have raised for more international coordinated research efforts in the field of ciguatera, as attested by the emergence of regional programs such as the Pace-Net Plus project funded by the European Commission to reinforce EU-Pacific cooperation on Science, Technology, and Innovation (http://plus.pacenet.eu.s3-website-eu-west-1.amazonaws.com/), the SafeFish National Ciguatera Poisoning Research Strategy (http://safefish.com.au/reports/technicalreports/ciguatera-research-strategy), as well as recent international initiatives such as the International Atomic Energy Agency (IAEA) technical cooperation projects, and the Intergovernmental Oceanographic Commission (IOC) of UNESCO, IAEA, FAO, and World Health Organization (WHO) Interagency Global Ciguatera Strategy (http://www.iocunesco.org/index.php?option=com_oe&task=viewDocumentRecord&docID=15111/). It is also highly encouraging that at the 32 th session of the Codex Committee on Fisheries and Fishery Products (Food and Agricultural Organization of the United Nations (FAO) and World Health Organization (WHO), 2016), CP was raised by the Pacific Nations as an issue that increasingly affects the tropical and subtropical regions of the Pacific Ocean, Indian Ocean, and Caribbean Sea, resulting in a joint data call on ciguatera by both FAO and WHO (http://www.fao.org/fileadmin/user_upload/agns/pdf/Call_for_data_experts/CALL_FOR_DA TA_CFP_final-1.pdf). All these initiatives should eventually benefit PICTs by fostering and/or accelerating the implementation of risk assessment and management programs in PICTs.

However, several issues specific to PICTs remained to be addressed: for instance, in PICTs composed of widely dispersed islands, there is an urgent need to establish effective tracking systems to quickly trace fish from harvest locations to retail outlets in the eventuality of a major toxic outbreak, in order to minimize the health impact and economic losses. Additionally, since a significant reduction in IRs was observed on numerous occasions following information and community-outreach interventions [START_REF] Pawlowiez | Evaluation of seafood toxicity in the Australes archipelago (French Polynesia) using the neuroblastoma cell-based assay[END_REF], the implementation of country-wide prevention programs also represent a good management option, especially in communities where a high level of risk-taking behavior is frequently reported. Similarly, regular training in CP diagnosis among health professionals should be promoted to improve patients' care [START_REF] Pearn | Ciguatera : dilemnas in clinicla recognition, presentation and management[END_REF][START_REF] Friedman | An updated review of ciguatera fish poisoning: clinical, epidemiological, environmental, and public health management[END_REF] and to compensate for the high turn-over of the medical personnel generally observed in PICTs. Finally, despite the extensive studies conducted in the Pacific over the past decade, high quality time-series data are still lacking for the region, making this area an ideal playground for scientists where appropriate observer (sentinel) sites can be identified for long-term monitoring programs [START_REF] Tester | Climate change and harmful benthic microalgae[END_REF].

Improved networking at a regional and international level aroused by the renewed interest in ciguatera will hopefully assist in the implementation of a global response to a global issue.