Laure Vaitiare André
email: laure.andre@ird.fr

Simon Van Wynsberge

Mireille Chinain

Serge Andréfouët

Highlights

An appraisal of systematic conservation planning for Pacific Ocean Tropical Islands coastal environments

Keywords: Pacific Ocean Tropical Islands, Spatial planning, Marine Protected Area, Aichi Conservation Target, Coral Reef, Fishery

► Systematic conservation planning in the Pacific Ocean islands is growing.

► 34 case studies from 2000 to 2020 are reviewed.

► Melanesia (Fiji) is the most studied.

Introduction

The Pacific Ocean Tropical Islands (POTIs) of Polynesia, Micronesia and Melanesia are characterized by their socio-ecosystems with populations traditionally highly linked to their environment, and by their small sizes, high geographical dispersion and endangered biodiversity, both across terrestrial and marine systems [START_REF] Payri | Biodiversity, a pressing need for action in Oceania[END_REF]. As of 2019, population densities are strongly contrasted between the largest cities and the most remote islands or rural areas [START_REF] Andrew | Coastal proximity of populations in 22 Pacific Island Countries and Territories[END_REF]. Pacific islanders rely strongly on their marine environment for sustenance, income, culture, identity, exchanges with other islands, and coastal protection [START_REF] Bell | Planning the use of fish for food security in the Pacific[END_REF][START_REF] Friedlander | Marine conservation in Oceania : Past, present , and future[END_REF]. The livelihoods and incomes of local populations are thus particularly vulnerable to any change in the availability of these marine resources, notably with respect to climate change, shifting weather patterns, demographic growth and overexploitation, and degradation due to economic development [START_REF] Hanich | Small-scale fisheries under climate change in the Pacific Islands region[END_REF]. Islands are fragile, increasingly exposed to these threats, and increasingly face acute resource management and conservation issues [START_REF] Kueffer | What is the importance of islands to environmental conservation?[END_REF].

Conservation initiatives to mitigate various local and global threats are emerging. In some cases, they complement the customary management that is traditionally used to protect lagoon and reef areas as well as targeted species, with various levels of success [START_REF] Bartlett | Policy implications of protected area discourse in the Pacific islands[END_REF][START_REF] Hamilton | Community-based management fails to halt declines of bumphead parrotfish and humphead wrasse in Roviana Lagoon, Solomon Islands[END_REF][START_REF] Sangha | Recognising the role of local and Indigenous communities in managing natural resources for the greater public benefit: Case studies from Asia and Oceania region[END_REF]. National conservation initiatives are now also influenced by international guidelines on the conservation of biodiversity and ecosystem services, such as the Convention on Biological Diversity's Aichi Target 11, and the United Nations Sustainable Development Goal 14.

These international objectives are aimed at preserving at least 10% of coastal and marine areas by 2020, including "ecologically representative areas of particular importance for biodiversity and ecosystem services", with "management equity and effectiveness; connectivity and integration into wider landscape and seascape [START_REF] Rees | Defining the qualitative elements of Aichi Biodiversity Target 11 with regard to the marine and coastal environment in order to strengthen global efforts for marine biodiversity conservation outlined in the United Nations Sustainable Development Goal 14[END_REF], which are all aspects that can be relevant for POTIs.

To move conservation planning forward with increased effectiveness across different approaches requires Systematic Conservation Planning (SCP), a method that allows for a transparent, data-driven and objective decisions. SCP is based on prioritizing tools that identify optimal, or cost effective, priority conservation areas, by simultaneously setting conservation objectives around what to protect, with quantitative targets on how much to protect while minimizing the costs constraints of conservation (see Table 1). It relies on key concepts such as adequacy, comprehensiveness, representativeness, complementarity, vulnerability and/or efficiency [START_REF] Kukkala | Core concepts of spatial prioritisation in systematic conservation planning[END_REF]. SCP implements the overarching goals of, for instance, representativeness or connectivity of biodiversity features included in conservation areas, through a number of specific quantitative and locally relevant targets, which can be measured and monitored [START_REF] Margules | Systematic conservation planning[END_REF]Pressey and Bottril, 2009;[START_REF] Kukkala | Core concepts of spatial prioritisation in systematic conservation planning[END_REF]. Other approaches include conservation values aggregated across features and space [START_REF] Moilanen | Prioritizing multipleuse landscapes for conservation: Methods for large multi-species planning problems[END_REF]. Threats to biodiversity have often been used as surrogates for conservation costs, though this correlation is now challenged [START_REF] Sacre | Costs are not necessarily correlated with threats in conservation landscapes[END_REF]. Site selection is central to SCP and prioritisation can be calculated through mathematical models that balance objectives with the costs, providing sets of optimal and cost effective solutions.

Analysis can be carried out via software that is specific for marine SCP (mainly Marxan and its extensions, Zonation, ConsNet, C-Plan or PrioritizR) where the search for optimal solutions can be performed multiple times resulting in a range of solutions. The solutions can take the form of i) a 'best'-case solution (solution with the lowest cost or maximum benefits, depending on the approach) and ii) a selection frequency, or priority rank map showing how many times an area is selected. The best solution is not necessarily the only one to consider, as the overall set of solutions can provide interesting alternatives of site selections. In the past few years, marine SCP studies have evolved in terms of complexity, and can now include a wide variety of objectives and socio-economic costs, as well as new criteria related to climate change, ecological connectivity between marine populations, and linkages within broader island-scapes through land and sea connections [START_REF] Álvarez-Romero | Research advances and gaps in marine planning: towards a global database in systematic conservation planning[END_REF]. Beyond the core SCP prioritization step, additional stages in the conservation process take place such as involvement of stakeholders, integration of plans across governance levels, implementation of conservation actions, maintaining and monitoring conservation areas with long term commitment (Pressey and Bottril, 2009;Weeks et al., 2014a). The scope of this review focuses primarily on the core SCP prioritization step and the other steps are not considered here.

Term Definition

Conservation objective Qualitative goal, referring to general principles of conservation, such as international policy objectives, representativity objectives etc. It describes the type of feature to protect (e.g., geomorphic habitats, mangroves...), as used by [START_REF] Margules | Systematic conservation planning[END_REF].

Conservation target

Quantitative goal, to protect biodiversity. Often a percentage, between 10 and 30%, of the area of each feature that needs to be selected for conservation.

Cost

The constraint/negative outcome expected to be generated by the conservation objective and target. Cost is sought to be minimized in the design of SCP. Cost include acquisition costs, management costs, transaction costs or monetary (or in any other value) [START_REF] Naidoo | Integrating economic costs into conservation planning[END_REF]. It is usually measured through opportunity cost to fishers, but it could also be cultural or spiritual as well.

Opportunity cost What could have been gained but become foregone opportunities when a conservation plan is implemented [START_REF] Naidoo | Integrating economic costs into conservation planning[END_REF].

Spatial/planning domain The total area considered by the analysis.

Planning Unit

The geometric division of the overall spatial domain into individual regular spatial domain where management decision are applied. Planning units are classically either square or hexagonal shape. Their size can vary from less than 1 km² to hundreds of km², depending on the scale of the study.

Resolution

In SCP, it is used either as spatial resolution (minimum size on the ground of measured data), or thematic resolution (number of categories).

Scale

Can cover several meaning (see [START_REF] Cheok | Sympathy for the devil: Detailing the effects of planning-unit size, thematic resolution of reef classes, and socioeconomic costs on spatial priorities for marine conservation[END_REF]. Here, local-scale is used when the spatial domain includes one island or less; regional scale includes one or more archipelagos (which consist of at least two islands).

Scenario

A combination of all of the above, which defines the specific context of a SCP case study. Numerical modelling information also defines the SCP scenarios when performed with planning software, such as number of iterations.

Assessment

The design phase of conservation planning including spatial prioritization [START_REF] Álvarez-Romero | Research advances and gaps in marine planning: towards a global database in systematic conservation planning[END_REF].

Implementation

The translation of assessments into actions on the ground such as the implementation of protected areas [START_REF] Álvarez-Romero | Research advances and gaps in marine planning: towards a global database in systematic conservation planning[END_REF].

SCP is increasingly present in the Polynesian, Melanesian and Micronesian POTIs. Given the current theoretical advances in SCP and the POTIs specifics, we assessed how SCP was used, and identified different strengths, weaknesses and gaps in SCP applications that managers, stakeholders and scientists should be aware of. Here, the main features of the POTIs are first presented as background information and then the technical specificities of the SCP case studies are synthesized and critically examined. When relevant, case studies derived from islands located in other tropical regions are also considered for discussion to complement the examples from the Pacific Ocean. Lastly, our recommendations for new directions are highlighted.

The context of Pacific Ocean Tropical Islands 1/ Geographical dispersion and physical diversity

In the tropical and sub-tropical Pacific Ocean, the Islands are first characterized by their geographical isolation with vast ocean territories included in their Economic Exclusive Zone (EEZ), which typically stretches from the shoreline to 200 nautical miles and in which they have jurisdiction over natural resources. The boundaries of our study area expand from 32°N (Northern Hawaii EEZ) to 35°S

(Southern Kermadec Islands EEZ) and from 130°E (Palau) to 105°W (Easter Island). Our focus is primarily on tropical islands. We included several high latitude sub-tropical islands because they already harbor some tropical species in their waters, and this tendency is likely to increase with global warming [START_REF] Payri | Biodiversity, a pressing need for action in Oceania[END_REF].

POTIs are characterized by their physical diversity, ranging from large continental islands with complex and extensive coral reef formations, to geologically recent oceanic volcanic islands surrounded by a narrow fringing reef, partially subsided volcanic land masses surrounded by a lagoon and a barrier reef, and atolls. These tropical marine ecosystems of coral reefs and related are of particular interest for biodiversity conservation.

2/ Governance

Administratively, POTIs are managed at national and/or territorial levels: they are either fully independent or autonomous countries, or territories that remain strongly linked to their overseas metropoles, several of those nonetheless possess their own governments (Table 2). Several countries also have strong customary laws at a local level, which ultimately often control the local use of marine resources. Pacific countries and territories, their privileged metropole counterparts, and Asia-Pacific superpower countries also often promote regional cooperation to enhance sustainable development.

Governance and enforcement required to manage environmental, marine, coastal and reef resources vary widely within POTIs. Some have efficient and dedicated technical services managing the environment and marine resources, while others lack competent technical services, relying on international aid programs, foreign NGOs, private consultants, and frequent training and monitoring via external funding often managed by international organizations (Table 2). Some Islands have developed innovative models of multi-level governance, such as Palau where resource users, the national government, and NGOs all take part to the management process [START_REF] Gruby | Multi-level governance for large marine commons: Politics and polycentricity in Palau's protected area network[END_REF].

The lack of local available data and GIS facilities can make it difficult to compile local demography, environment and resource information (Table 2). This lack of spatial data can impact on requirements for SCP.

The small size of most islands implies that communities may have limited opportunities to replace any loss and damage to their natural resources, thus emphasizing the need for integrated management and conservation [START_REF] Wenger | Predicting the impact of logging activities on soil erosion and water quality in steep, forested tropical islands[END_REF].

3/ MPAs in the Pacific Ocean

Conservation areas, or Marine protected areas (MPAs), are defined as areas that are managed in order to reach the overall goal to protect biodiversity and manage marine resources. MPAs are important instruments for conservation and for sustaining marine resources for food security, particularly as POTIs have experienced considerable loss of biodiversity (Jupiter et al., 2014b;[START_REF] Payri | Biodiversity, a pressing need for action in Oceania[END_REF]. In POTIs, MPAs can be managed through diverse levels of management from institutional government-level with international registries of the MPAs (listed in Table 2), NGOs, locally managed marine areas based on traditional marine tenure (such as village-based, customary, and sometimes hybrid management), as well as diverse levels of protection (no-take zones, partial protection zones for nursery areas, rotating closures, tabu zones, rāhui zones) [START_REF] Friedlander | Marine conservation in Oceania : Past, present , and future[END_REF]Gairin and Andréfouët, 2020;Jupiter et al., 2014a;Smallhorn-West and Gowan, 2018).

The number of very large MPAs (VLMPAs, defined here as >100.000 km²) has increased in the past decade, allowing, on paper, a quick convergence towards the Convention on Biological Diversity Aichi target 11 on protected areas. Eight of the world's current thirty-five VLMPAs are located in the tropical Pacific Ocean (Table 2) (MPAtlas, 2020). The POTIs' considerable EEZ areas offered solutions to satisfy the political engagements, but the pros and cons of these engagements have generated important debates, about the relevance of EEZ to represent species and ecosystems, for instance (e.g. [START_REF] Ban | Social and ecological effectiveness of large marine protected areas[END_REF][START_REF] Devillers | Reinventing residual reserves in the sea: Are we favouring ease of establishment over need for protection?[END_REF][START_REF] Singleton | The contribution of very large marine protected areas to marine conservation: Giant leaps or smoke and mirrors?[END_REF]. There is considerable differences in how POTIs manage their MPAs, several VLMPAS with official designation can have limited management plans whilst others already have much stricter policies, such as no-take area, like the Phoenix Island Protected Area in Kiribati [START_REF] Rotjan | Establishment, Management, and Maintenance of the Phoenix Islands Protected Area[END_REF].

4/ Coastal and reef fisheries, and mariculture

Sustainable fishing (including of finfish and invertebrates) is a cornerstone of current protein supply and future food security of Pacific Ocean Islanders [START_REF] Bell | Planning the use of fish for food security in the Pacific[END_REF]. Despite many POTIs importing canned fish, most countries and territories still rely heavily on their local fisheries for economic development, revenue, job opportunities and food security, and islander livelihoods often depend on subsistence fishing, particularly from coral reefs (Bell et al., 2011b;[START_REF] Friedlander | Marine conservation in Oceania : Past, present , and future[END_REF]. For example, fish consumption is at least twice the World Health Organization recommended level in Tuvalu, Samoa, Niue, Wallis and Futuna, French Polynesia and the Federate States of Micronesia. Therefore, populations are vulnerable to any change in the status of these resources. [START_REF] Gillett | Fisherines in the Economies of Pacific Island Countries and Territories[END_REF] underlined a remarkable drop of production per capita of coastal fisheries in the 2007-2014 period, suggesting decreased stocks and unsustainable fishing by a growing human population. Management of fishing stocks to achieve long term sustainability is hence among the top priorities for many local governments and communities. Adaptation measures in the face of climate change will also be required on a short-term, which includes shifting consumption towards species less vulnerable to fishing pressure and environmental changes, like tunas [START_REF] Bell | Adaptations to maintain the contributions of small-scale fisheries to food security in the Pacific Islands[END_REF].

Mariculture production is not significant compared to other regions bordering the Pacific Ocean, especially Asia or South America [START_REF] Oyinlola | Global estimation of areas with suitable environmental conditions for mariculture species[END_REF]. At this time, 93% of the value of all mariculture is produced with both local and international markets in mind in two countries only [START_REF] Gillett | Fisherines in the Economies of Pacific Island Countries and Territories[END_REF]. In French Polynesia, mariculture is dominated by pearl oyster farming for the jewelry market, with 8250 ha of pearl farms in 2017, of which 74% located in the Tuamotu Islands [START_REF] Drmm | Bulletin Statistique, Synthèse des données de la pêche professionnelle, de l'aquaculture et de la perliculture[END_REF]. In New Caledonia, production is dominated by shrimp farming with 1252 t. produced in 2015 [START_REF] Dam | Pêches professionnelles maritimes et aquaculture, de 2006 à 2015[END_REF]. Mariculture remains a limited source of proteins for the local populations but is present in many places, at various development stages. It is often conducted at a small scale.

5/ Ciguatera poisoning

Ciguatera poisoning is widely present in the POTIs and results from the consumption of marine products that have accumulated lipid soluble toxins known as ciguatoxins. Yet, fish and also invertebrates highly prized by island communities such as bivalves (e.g. giant clams), echinoderms (e.g. sea urchins) and gastropods (e.g. trochus) have been found to be potential vectors [START_REF] Darius | Tectus niloticus (Tegulidae, Gastropod) as a Novel Vector of Ciguatera Poisoning : Detection of Pacific Ciguatoxins in Toxic Samples from Nuku Hiva Island (French Polynesia)[END_REF]. Ciguatoxins are produced by benthic dinoflagellates in the genera Gambierdiscus and Fukuyoa that grow preferentially within mixed algal turfs covering degraded coral substrates. Estimating the incidence of this disease is difficult because only 10-20% of cases are reported to public health or other authorities [START_REF] Friedman | An updated review of ciguatera fish poisoning: Clinical, epidemiological, environmental, and public health management[END_REF]. Across the Pacific islands, estimated true incidence rate reaches as much as 12,000 cases annually in the POTIs [START_REF] Chinain | Ciguatera poisoning: a global review of occurrences and trends[END_REF], with the highest rates for Tokelau and Cook Islands (1,576 and 1,437 cases per 100,000 inhabitants, respectively) [START_REF] Skinner | Ciguatera Fish Poisoning in the Pacific Islands (1998 to 2008)[END_REF]. Ciguatera poses an immediate threat to human health, but also to islander livelihoods in the long run in the case of jeopardized access to safe local resources. Indeed, ciguatera occurrences are dynamic and a link was found between the toxic microalgae development and environmental disturbances, such as coral reef damage due to cyclonic waves, elevation of sea surface temperature, and coastal development [START_REF] Bell | Planning the use of fish for food security in the Pacific[END_REF][START_REF] Chinain | Ciguatera risk management in French Polynesia: The case study of Raivavae Island (Australes Archipelago)[END_REF]. As ciguatera varies spatially, it might influence opportunities for conservation and be an interesting spatial feature for SCP.

6/ Exposure to climate change

Climate change is expected to affect the Pacific Ocean in different ways and to greatly impact islanders, exacerbated by the socio-economic vulnerability and dependence to marine resources of many islands [START_REF] Andrew | Coastal proximity of populations in 22 Pacific Island Countries and Territories[END_REF]Bell et al., 2011a;2011b;[START_REF] Hanich | Small-scale fisheries under climate change in the Pacific Islands region[END_REF][START_REF] Townhill | Communicating marine climate change impacts in the Caribbean and Pacific regions[END_REF]. Many threats arise due to changes in oceanic and atmospheric circulations, which are expected to affect marine and coastal ecosystems. Increased sea surface temperature can cause more frequent coral bleaching, spread of pathogens, and mass mortality events. Increased dissolved CO2 concentrations can lead to more acidic ocean with altered capacity of calcifying organisms to build skeletons and shells [START_REF] Kleypas | Coral Reefs and Ocean Acidification[END_REF]. Mariculture can also be impacted by these changes and adaptations, such as modification of the locations and diversification of production are required (Bell et al., 2011a). Rapid sea level rise could particularly affect reef islands and coastal environments, when the natural sediment production and dynamics are unable to compensate for the increased erosion of the soft-sediment coastlines [START_REF] Garcin | Lagoon islets as indicators of recent environmental changes in the South Pacific -The New Caledonian example[END_REF][START_REF] Tuck | Physical modelling of reef island topographic response to rising sea levels[END_REF]. Sea level rise could also have serious implications on populations living on low lying islands, with planned migration being required to move people to safer areas [START_REF] Weir | Social and cultural issues raised by climate change in Pacific Island countries: an overview[END_REF]. Climatic migrations, inducing land use change, could have important implications for conservation and could require spatial planning to manage this shift.

Literature review methods

To identify papers and reports on SCP applied to POTIs; literature searches were first performed from the Web Of Science® database with a variety of key-word combinations in the Title or Topic searched items. These combinations included: (1) the name of the targeted countries as displayed in Table 2;

(2) 'Pacific Ocean'; (3) 'systematic conservation planning'; (4) 'costs'; and (5) names of planning softwares (such as 'Marxan', 'ConsNet' or 'Zonation'). Then, additional searches in Google® and Google Scholar® were performed with the same key words to identify additional reports or conference papers. All searches were restricted to the period 2000-2019. The reference lists and appendices of each publication were also scrutinized to detect previously unseen references, especially from the grey literature. The SCP database by [START_REF] Álvarez-Romero | Research advances and gaps in marine planning: towards a global database in systematic conservation planning[END_REF] at http://database.conservationplanning.org was also checked.

The relevance of all references provided by online searches was further checked on the basis of their title, abstract, and content. The studies were categorized in three types, which were not necessarily exclusive: 'SCP case studies' (for all papers using SCP framework for an analysis of a concrete case study), 'POTIs context paper' (for all papers related to the context specific to POTIs, but not presenting SCP stricto sensu), and 'SCP concept paper' (for all papers enlightening concepts that are useful for SCP in POTIs, but that are not necessarily located in the POTI region). Other valuable inputs for general background were papers presenting new concepts, ideas or approaches for conservation and management not necessarily using SCP (e.g. [START_REF] Adams | Implementation strategies for systematic conservation planning[END_REF], and papers that delivered reviews that could be complementary of our own objectives (e.g., broader geographical scope, e.g., [START_REF] Álvarez-Romero | Research advances and gaps in marine planning: towards a global database in systematic conservation planning[END_REF][START_REF] Friedlander | Marine conservation in Oceania : Past, present , and future[END_REF]. Several 'SCP concept paper' or 'POTIs context paper' initially identified were removed from the analysis when too general or providing redundant information. Similarly, for some SCP case studies available as both report and peer-reviewed paper, the most detailed ones were kept.

Once selected and classified by types, the full text of each SCP case study was screened to extract further details regarding study objectives and locations, methods and results. This included, when relevant, (1) country, (2) main topics and questions addressed in the study, (3) the nature of the study (i.e. methodological versus applied study), ( 4) authorship (academics, government, NGOs), ( 5) conservation objectives, targets, and types of costs, ( 6) the nature and origin of data used, (7) size of the planning domain, (8) size considered for planning units, and ( 9) success rate or effectiveness (sensu [START_REF] Kukkala | Core concepts of spatial prioritisation in systematic conservation planning[END_REF]), which refers to the extent by which objectives have been met.

After the initial search specifically targeting the Pacific Ocean, we also identified and kept a number of SCP case studies for tropical or sub-tropical areas outside the Pacific if they were focusing on topics, ideas, methods and data that were not found in the previously screened studies but could also be relevant for the POTIs. To identify these supporting studies, the same aforementioned keywords were used but with 'Coral Triangle', 'South-East Asia', or 'Indian Ocean' instead of Pacific country names. Caribbean Islands' studies were not searched. This geographically-widened search aimed to identify some relevant papers that could complement the exhaustive tropical Pacific Ocean search, for discussion purpose only.

Results

This review collated 85 peer-reviewed papers and 10 reports. Among them, we found 34 studies describing POTI SCP case studies (SCP prioritization stricto sensu: describing the selected features, objectives, costs, software etc.), and providing a portfolio of different SCP objectives, methods, scale, and study sites, presented in Table 3. The topics addressed by these POTI SCP case studies have been itemized (Supplementary Material S1a). We also identified and short-listed a non-exhaustive list of 12 POTIs context papers and 28 SCP case studies for tropical or sub-tropical areas beyond POTIs, but focusing on topics that were relevant for the POTIs. The topics raised by these papers are also itemized (Supplementary Material S1b) and used for the discussion. seemed to be at almost-implementation stages. Some of these reports were consultancy reports for local governmental ministries and agencies (n=12) (e.g. Government of Papua New Guinea, 2015).

The analyses of the technical specificities of each SCP case study highlight that ( 1) there is a wide variety of scales for spatial domains: from few km² (28 km² in French Polynesia) up to country scales

(2,510,750 km² in Papua New Guinea) and for planning unit (PU) size (Table 3). Four groups can be distinguished. Studies used : PU size < 10,000 m² or even less (n=7), PU size: 10,000-100,000 m² (n=9), PU size: 100,000-1,000,000 m² (or 0,1-1 km²)(n=17), and few used PU size > 1 km² (n=6)

(counting the different values sometimes used in a single study). We found that PU sizes roughly grow with spatial domains, which is the same trend as reported globally by Álvarez-Romero et al.

(2018).

(2) The primary objective from which all results will depend on is often an Aichi 11 representation target: most plans (83%) were designed to target a given percent representation of habitats.

(3) There is a great discrepancy in country coverage. Specifically, while many POTIs have no identified studies (n=16/26; 47%; Figure 1), particularly in Polynesia, where 77% of the countries had no SCP case studies (Figure 2a), Fiji is by far the most represented country (n=14/34; 40% of all the studies). Melanesia thus accounts for 60% of studies (Figure 2b). ( 4) Many case studies relied on proxies and modelling (80%), and very few have specifically collected or validated new in situ data for their investigations (n=7) (Table 3). Several of these topics also emerged in a global review of the recent marine SCP literature [START_REF] Álvarez-Romero | Research advances and gaps in marine planning: towards a global database in systematic conservation planning[END_REF], which highlights that the same issues are of concern worldwide. However, there are POTI specific issues (see Discussion). Although the relatively limited number of case studies in this region impedes robust quantitative analysis, several patterns emerge (Figure 2). The geographical occurrence and abundance of studies vary over time between the three regions (Figure 2c). Among the analysed themes, most of them have been tackled mainly in Melanesia, and either in Micronesia or Polynesia, or both. Adaptive management has been discussed only for Melanesia, precisely in Fiji.

Discussion

This paper presents a summary of the current state of the art and SCP practices in POTIs, organized following the list of topics highlighted above. These topics include objectives and targets, gap analyses, cost functions and proxies, conservation network scaling, habitat map resolution and the integration of connectivity, resilience, climate change and adaptive planning. However, we also detected gaps in the SCP applications in POTIs. Avenues for improvements are discussed throughout, for each section and further discussion is made on issues such as data quality, planning unit size and shape, model validation, and missed opportunities. Examples from other regions outside the Pacific (Supplementary Material S1b) are used to highlight similar or alternative procedures, improvements and future developments also worthwhile to consider for POTIs. Note that we do not discuss here how much SCP has contributed in actually implementing conservation measures, due to the difficulty (i) to assess the actual degree of how much a SCP exercise could have influenced it, or even (ii) to assess reliably the number of MPAs in the POTIs (Smallhorn- [START_REF] Smallhorn-West | Towards reducing misrepresentation of national achievements in marine protected area targets[END_REF].

Setting (arbitrary) conservation objectives and targets

In the POTIs, most SCP case studies focus on protecting a certain proportion of biodiversity. This is generally achieved through the use of goals similar to the Aichi Target 11: by selecting areas that represent a given percent of the surface area of a number of key habitats that have been previously mapped, and thus are available in a spatial format unlike most other biodiversity data sets. These habitat maps act, in fact, as surrogates of biodiversity (see section Habitat). The targeted level of representation can vary greatly, typically between 10% and 30% depending on the studies. In South-East Asia, the Coral Triangle Initiative recommended 10% (Weeks et al., 2010a), or 20% [START_REF] Horigue | Benefits and challenges of scaling up expansion of marine protected area networks in the Verde Island Passage, Central Philippines[END_REF] representation of all habitats. This choice is actually rarely debated on even though it induces considerable spatial differences in terms of results (e.g. [START_REF] Hamel | Compromises between international habitat conservation guidelines and small-scale fisheries in Pacific island countries[END_REF]. It remains unknown, however, if these levels of habitat representation can achieve an exhaustive representation of biodiversity and its related services, or how much of it [START_REF] Dalleau | Use of Habitats as Surrogates of Biodiversity for Efficient Coral Reef Conservation Planning in Pacific Ocean Islands[END_REF].

In addition to habitat representation targets, some studies have tried to include qualitative objectives, notably by integrating representativeness, connectivity, and climate change considerations. For instance, targets are sometimes defined to be 10-100% protection of biodiversity features, 50-90% of connectivity pathways, 30-100% of areas resilient to global warming [START_REF] Magris | Integrated conservation planning for coral reefs: Designing conservation zones for multiple conservation objectives in spatial prioritisation[END_REF], 50% of critically important sites (e.g. fish spawning aggregations) or 95% of endangered turtles nesting beaches [START_REF] Lipsett-Moore | Ridges to Reefs Conservation Plan for Choiseul Province, Solomon Islands[END_REF]. These approaches can lead to Multiple-Criteria analyses. For example, both socio-economic equity and management effectiveness could be set as fishing activity costs. This has been proposed for transboundary Indian Ocean large domains (e.g.

from Kenya to South Africa, to east of Maldives and Chagos), to include 50% of reef areas in sustainable fishing areas and 20% in conservation zones [START_REF] Jones | Incorporating feasibility and collaboration into large-scale planning for regional recovery of coral reef fisheries[END_REF]. Other plans have proposed as an objective to include 10% of coral reef-associated habitats and an increasing percentage of fishing grounds remaining open for fishers, in the Philippines (Weeks et al., 2010b).

However, the problem is the same as for habitat representation: there is generally very little available rationale to select one percentage of representation over another for a given objective that management focus on, and guidelines for trade-offs are few. Within a fishery context, rationale for quantitative objectives of stock conservation, or important zones to sustain fish populations such as spawning areas, are lacking. The lack of clear thresholds is explained by the natural variability of the system and the consequences of different fishing levels.

Conservation gap analyses

Conservation and data gap analyses aim to identify the areas where data and conservation activities are lacking; these can be used to prioritize actions. As such, gap analysis is a critical preliminary step before SCP. To illustrate this point, two types of studies can be mentioned: one methodological paper based on metadata and habitat maps [START_REF] Andréfouët | Tropical islands quick data gap analysis guided by coral reef geomorphological maps[END_REF] and several case studies.

The latter encompass variable scales, methods, and goals. For instance, [START_REF] Cleguer | Spatial mismatch between marine protected areas and dugongs in New Caledonia[END_REF] focused on specific conservation gaps (for dugongs) in New Caledonia. Others identified broader data and conservation gap at national and ecosystem scales (e.g., Government of Papua New Guinea, 2015).

Various POTIs have been the subject of such assessments since 2000, including for instance the Marshall Islands, Solomon Islands, Papua New Guinea, and Fiji, often with the goal of generating SCP scenarios (Government of Papua New Guinea, 2015; [START_REF] Jupiter | Fiji Marine Ecological Gap Assessment: Interim Progress Report[END_REF][START_REF] Kool | Ridges to Reefs Conservation for Solomon Islands[END_REF]Reimaanlok National Planning Team, 2008). Data synthesis meant for ad hoc selection of conservation priority areas are less formalized, and often based on expert opinion. These correspond to ecoregional analysis (for New Caledonia for instance, [START_REF] Garrigue | Atelier d'identification d'aires de Conservation Prioritaires, Analyse écorégionale marine de Nouvelle-Calédonie[END_REF] or bioregionalisation [START_REF] Wendt | Marine Bioregions of Fiji[END_REF]) that also can be seen as a spatial planning approach different from SCP.

Importance of socio-economic costs and their proxies

Different types of costs, that planners aim to minimize, are relevant in SCP [START_REF] Naidoo | Integrating economic costs into conservation planning[END_REF].

However, our review showed that costs were most frequently defined as fishery opportunity costs (Table 3). Minimizing opportunity costs to fishers is assumed to increase their compliance and ensure their support with respect to MPA implementation, resulting in a more effective conservation plan (Weeks et al., 2010a). Costs are always recognized to greatly influence SCP outputs [START_REF] Cheok | Sympathy for the devil: Detailing the effects of planning-unit size, thematic resolution of reef classes, and socioeconomic costs on spatial priorities for marine conservation[END_REF][START_REF] Deas | Modulation of habitat-based conservation plans by fishery opportunity costs: A New Caledonia case study using fine-scale catch data[END_REF][START_REF] Gurney | Efficient and equitable design of marine protected areas in Fiji through inclusion of stakeholder-specific objectives in conservation planning[END_REF], and they are not free of incidental consequences impacting more stakeholders than fishers alone [START_REF] Hamel | The Importance of Fishing Grounds as Perceived by Local Communities Can be Undervalued by Measures of Socioeconomic Cost Used in Conservation Planning[END_REF]. Opportunity costs to fishers are most often incorporated using fishery data based on proxies, which can be crudely defined. In most papers, authors had no option but to use proxies because of the lack of socio-economic data and lack of resources to acquire such data [START_REF] Mills | A mismatch of scales: challenges in planning for implementation of marine protected areas in the Coral Triangle[END_REF]Weeks et al., 2010a). Indeed, it is worth noting that except for [START_REF] Deas | Modulation of habitat-based conservation plans by fishery opportunity costs: A New Caledonia case study using fine-scale catch data[END_REF], spatially explicit catch data have not been used to estimate opportunity costs although this would have been the most unbiased way to derive a fishery value.

The background data for [START_REF] Deas | Modulation of habitat-based conservation plans by fishery opportunity costs: A New Caledonia case study using fine-scale catch data[END_REF] were an atlas of the catches for a New Caledonia area (by weight, fishing gears, species, etc.) [START_REF] Guillemot | Atlas Pêche non professionnelle de poissons du lagon dans la zone de Vook-Koohnê-Pwëëbuu (Voh-Koné-Pouembout)[END_REF]. Unfortunately this type of coastal fishery atlas remains extremely rare as most socio-economic surveys are not translated into maps (e.g. the Procfish surveys, as in [START_REF] Kronen | Profils et résutats des enquêtes réalisées à Fakarava, Maatea, Mataiea, Raivavae et Tikehau, Polynésie Française (ProcFish/C/CoFish)[END_REF]), or offer only very coarse results [START_REF] Aswani | Incorporating Fishermen's Local Knowledge and Behavior into Geographical Information Systems (GIS) for Designing Marine Protected Areas in Oceania[END_REF]. As sustainable reef fisheries are a cornerstone of Pacific Ocean islander's food security and livelihood, it would be extremely valuable to create and update such fishery atlases, before running SCP scenarios.

When no fishery data are available, simple proxies are widely used as opportunity costs, such as population density or travelling distance [START_REF] Cheok | Sympathy for the devil: Detailing the effects of planning-unit size, thematic resolution of reef classes, and socioeconomic costs on spatial priorities for marine conservation[END_REF]. In that respect, the value of the chosen socio economic proxy is a key question [START_REF] Hamel | The Importance of Fishing Grounds as Perceived by Local Communities Can be Undervalued by Measures of Socioeconomic Cost Used in Conservation Planning[END_REF][START_REF] Maina | Designing climate-resilient marine protected area networks by combining remotely sensed coral reef habitat with coastal multi-use maps[END_REF], although its relevance and precision is rarely evaluated or put to the test. Weeks et al. (2010b) compared in a Philippines case study, spatially homogenous cost and population census data with empirical data and concluded that commonly used proxies poorly reflect fishery empirical costs that were estimated with surveys.

Likewise, [START_REF] Deas | Modulation of habitat-based conservation plans by fishery opportunity costs: A New Caledonia case study using fine-scale catch data[END_REF] showed that a poor choice of proxy could disadvantage fishers even more than a scenario constrained without any proxy of socio-economic costs to minimize. When no socioeconomic data are available, the proxy commonly used is the surface area. In a Madagascar case study, proxies of fishing pressure came from a combination of motorized and non-motorized coastal fishing units [START_REF] Allnutt | Comparison of marine spatial planning methods in madagascar demonstrates value of alternative approaches[END_REF]. Other studies developped more sophisticated proxies models in Fiji for instance, to represent food fish abundance and probability of catch, depending on fishing gear types and market values [START_REF] Adams | Improving social acceptability of marine protected area networks : A method for estimating opportunity costs to multiple gear types in both fished and currently unfished areas[END_REF]. Other fishery aspects related to the spatial and temporal dynamics of fishing pressure, never considered thus far, could be used. This includes the effects of the reserve on fishing effort displacement. This has already been assessed as critical when trying to conserve stocks [START_REF] Van Wynsberge | Best Management Strategies for Sustainable Giant Clam Fishery in French Polynesia Islands: Answers from a Spatial Modeling Approach[END_REF].

Costs are more often defined with fishers in mind, but the use of the marine domain in a variety of ways is a hallmark of POTI societies. An emergent recommendation is that it can be necessary to integrate in the design the interests of a variety of actors and how they value their environment [START_REF] Buijs | Lay People's Images of Nature: Comprehensive Frameworks of Values, Beliefs, and Value Orientations[END_REF][START_REF] Gurney | Efficient and equitable design of marine protected areas in Fiji through inclusion of stakeholder-specific objectives in conservation planning[END_REF][START_REF] Hamel | The Importance of Fishing Grounds as Perceived by Local Communities Can be Undervalued by Measures of Socioeconomic Cost Used in Conservation Planning[END_REF]Weeks et al., 2010b). Taking into account multiple stakeholder groups instead of a unique one is a sound path towards a more equitably distributed conservation cost.

Scaling conservation networks

'Scaling' reflects the dynamic two-way relationship that may exist between local and regional scales in terms of assessment and implementation. It is a complex series of topics that are strongly relevant for countries consisting of islands, such as the POTIs. It addresses for instance a MPA network extension from ad hoc local solutions to regional solutions [START_REF] Mills | Where do national and local conservation actions meet? Simulating the expansion of ad hoc and systematic approaches to conservation into the future in Fiji[END_REF], the frequency at which regional priorities need to be updated as local actions are implemented [START_REF] Cheok | The plans they are a-changin': More frequent iterative adjustment of regional priorities in the transition to local actions can benefit implementation[END_REF], or how conservation costs vary locally for a collection of local scenarios vs an overarching regional scenario [START_REF] Kabbadj | Scaling tropical island conservation planning to the regional level can lead to unbalanced ecological representation and poor social equity among islands[END_REF].

The question of extending existing networks of conservation areas has emerged as a scaling challenge in SCP. Very often, MPAs in developing countries are numerous but they are characterized by a very small size and were not designed to integrate, for instance, representativeness and connectivity. The challenge is especially acute in the POTIs, due to traditional management which is frequently dependent on local tenure. In Islands, local marine tenure and customary use of the sea have to be considered given their social importance, especially in Melanesia (Jupiter et al., 2014b).

However, a fragmented network of locally managed small protected areas are unlikely to protect effectively mobile species, nor represent all the ecological processes upon which local biological populations depend [START_REF] Léopold | Fish movements within community-managed fishery reserve networks: an acoustic survey of Lethrinus harak in Vanuatu[END_REF]. Locally managed areas can also be very vulnerable to local and global stressors if there are no nearby sources for the replenishment of populations. The growth, or scaling-up of the network in a coordinated manner is necessary to mitigate these problems. The case of Fiji is interesting here because it stands out with the highest number of case studies (Figures 1,2a; Table 3). This can be explained by the fact that the pre-existing qoliqoli traditional management areas needed to be integrated in overarching conservation projects, but also by a favorable context of science driven conservation NGOs and involved academics, who elaborated, step by step, a number of data layers and SCP scenarios, in cooperation with communities, private and state stakeholders.

Working on a larger domain can also theoretically spread the costs of conservation and can offer more flexibility when a range of solutions meeting the conservation objectives, are sought for. In practice, however, coordinating and merging in a conservation framework local tenures means that there will be overlap and interaction with other types of governance when the size of the targeted domain increases. These interactions are specific to each country and will depend on local administration entities and their competences [START_REF] Horigue | Benefits and challenges of scaling up expansion of marine protected area networks in the Verde Island Passage, Central Philippines[END_REF][START_REF] Mills | Linking regional planning and local action: Towards using social network analysis in systematic conservation planning[END_REF]2012;[START_REF] Weeks | Adaptive Comanagement of a Marine Protected Area Network in Fiji[END_REF]. These complex interactions can be a serious limiting factor for implementation.

For instance, in New Caledonia, lagoon and coral reefs conservation is a Provincial competence, hence there are not yet any marine trans-provincial conservation area despite the reef and lagoon continuum (Gairin and Andréfouët 2020). Furthermore, the small size and the isolation of POTIs are also critical limiting factors when spatially expanding conservation networks, as space is limited to find possible solutions.

There are both practical advantages and limitations of working at a regional or local scale [START_REF] Mills | A mismatch of scales: challenges in planning for implementation of marine protected areas in the Coral Triangle[END_REF]. Adequate understanding of scale-related issues and trade-offs can improve local conservation within regional plans, while promoting the implementation of ecologically functional networks [START_REF] Mills | A mismatch of scales: challenges in planning for implementation of marine protected areas in the Coral Triangle[END_REF], for instance by taking into account connectivity [START_REF] Margules | Systematic conservation planning[END_REF]. This argument, however, is valid only if there are enough data to characterize meaningfully and accurately these processes, which is often not the case. Some studies argue on the necessity of assessing data and provide data gap analysis to evaluate the availability and quality of the data before using it for SCP [START_REF] Andréfouët | Tropical islands quick data gap analysis guided by coral reef geomorphological maps[END_REF][START_REF] Geange | Integrating conservation and economic objectives in MPA network planning : A case study from New Zealand[END_REF]. This important issue of data quality will be further discussed in a next section. Conversely, working regionally may relax the need for high spatial resolution data that would be necessary for small local conservation areas.

Currently, there are no clear general recommendations for scaling-up an existing network, given the variety of configurations (geography, governance, existing networks, etc). General principles can be outlined, such as finding a trade-off between acceptability of costs and the ecological viability of many small reserves (Weeks et al., 2010a). For instance, it has been shown that spreading heterogeneously conservation costs throughout different tenures to meet an overarching regional conservation objective can easily generate inequities locally [START_REF] Kabbadj | Scaling tropical island conservation planning to the regional level can lead to unbalanced ecological representation and poor social equity among islands[END_REF]. Unequal outcomes and benefits can be a major reason to reject conservation programs [START_REF] Gurney | Efficient and equitable design of marine protected areas in Fiji through inclusion of stakeholder-specific objectives in conservation planning[END_REF].

Habitat data used in SCP scenarios

SCP scenarios often aim to protect a certain percentage of the surface of each habitat, in particular to obey an objective similar to a type of Aichi Target 11, i.e., habitat representation. Habitats are implicitly or explicitly used as a surrogate of biodiversity in conservation. In practice, habitat maps are used, and these data sets are the baseline for most scenarios (see above). Therefore, habitat map information, and understanding what is this information, should be critical.

The quality, and the relevance of a habitat map for a given conservation problem, is related principally to its thematic resolution (i.e., the number of habitats considered), thematic information, spatial resolution, coverage, and accuracy. There are trade-offs between all of these factors. For instance, a highly complex map of several tens of benthic habitat classes (high thematic resolution) at 1 to 4 m. resolution (very high spatial resolution), covering a full country (high coverage) and with an accuracy >95% for every habitat class (very high accuracy) probably do not exist, and are not doable without prohibitive ground-truthing campaign costs. It is necessary to make application-specific compromise between all these factors when creating habitat maps [START_REF] Andréfouët | Coral Reef Habitat Mapping using Remote Sensing: A User vs Producer Perspective[END_REF]. Furthermore, for a given site, many different types of maps can co-exist and all can be valuable in conservation context (e.g. for Wallis Island in [START_REF] Dalleau | Use of Habitats as Surrogates of Biodiversity for Efficient Coral Reef Conservation Planning in Pacific Ocean Islands[END_REF]. Eventually, SCP scenario results are very dependent on the set of maps used and on their characteristics, and this has been quite abundantly discussed [START_REF] Andréfouët | Distinction between effective pattern-based and selection-based biodiversity surrogates is essential: Caveats for managers[END_REF][START_REF] Deas | Modulation of habitat-based conservation plans by fishery opportunity costs: A New Caledonia case study using fine-scale catch data[END_REF][START_REF] Hamel | Compromises between international habitat conservation guidelines and small-scale fisheries in Pacific island countries[END_REF][START_REF] Hamel | Biodiversity-based propositions of conservation areas in Baa atoll, republic of maldives[END_REF][START_REF] Tulloch | Incorporating uncertainty associated with habitat data in marine reserve design[END_REF].

Several of the POTIs studies have used coral reef geomorphological habitat data from the Millennium

Coral Reef Mapping Project [START_REF] Andréfouët | Définition d'aires marines protégées pour la conservation de la biodiversité du système récifo-lagonaire de Wallis[END_REF][START_REF] Cheok | Sympathy for the devil: Detailing the effects of planning-unit size, thematic resolution of reef classes, and socioeconomic costs on spatial priorities for marine conservation[END_REF][START_REF] Deas | Modulation of habitat-based conservation plans by fishery opportunity costs: A New Caledonia case study using fine-scale catch data[END_REF][START_REF] Gurney | Efficient and equitable design of marine protected areas in Fiji through inclusion of stakeholder-specific objectives in conservation planning[END_REF][START_REF] Hamel | Compromises between international habitat conservation guidelines and small-scale fisheries in Pacific island countries[END_REF][START_REF] Horigue | Benefits and challenges of scaling up expansion of marine protected area networks in the Verde Island Passage, Central Philippines[END_REF][START_REF] Lipsett-Moore | Ridges to Reefs Conservation Plan for Choiseul Province, Solomon Islands[END_REF][START_REF] Tulloch | Improving conservation outcomes for coral reefs affected by future oil palm development in Papua New Guinea[END_REF][START_REF] Weeks | Using reef fish movement to inform marine reserve design[END_REF]. There are maps at high geomorphological thematic resolution, low spatial resolution (considered to be at 100m, as the products come from Landsat 7 ETM+ satellite image at 30m resolution), with full coverage of islands and countries. Some studies have added to this inventory of geomorphological reef habitats, maps of seagrass and mangroves [START_REF] Allnutt | Comparison of marine spatial planning methods in madagascar demonstrates value of alternative approaches[END_REF], intertidal areas (Makino et al., 2013b) and spawning and nesting sites [START_REF] Green | Designing a resilient network of marine protected areas for Kimbe Bay, Papua New Guinea[END_REF]. Other studies have used different benthic habitat maps created at much higher spatial resolution (few meters), at high thematic resolution (Deas et al., 2014 in New Caledonia), at local to national coverage (e.g. Maina et al., 2015 in Kenya) and with medium to good overall accuracy (60-95% depending on the classes) (Tulloch et al., 2013 in Fiji).

Other studies do not use habitat as a conservation objective but rather use it as a base to infer features related to marine resources, such as the distribution of focal reef species [START_REF] Weeks | Using reef fish movement to inform marine reserve design[END_REF], giant clam density, biomass and recruitment [START_REF] Kabbadj | Scaling tropical island conservation planning to the regional level can lead to unbalanced ecological representation and poor social equity among islands[END_REF], catch per unit effort [START_REF] Gurney | Efficient and equitable design of marine protected areas in Fiji through inclusion of stakeholder-specific objectives in conservation planning[END_REF], fishing pressure [START_REF] Van Wynsberge | Conservation and resource management in small tropical islands: Trade-offs between planning unit size, data redundancy and data loss[END_REF], exposure to thermal stress, biological richness [START_REF] Hamel | Biodiversity-based propositions of conservation areas in Baa atoll, republic of maldives[END_REF], biodiversity value [START_REF] Allnutt | Comparison of marine spatial planning methods in madagascar demonstrates value of alternative approaches[END_REF], reef class resilience score [START_REF] Weeks | Adaptive Comanagement of a Marine Protected Area Network in Fiji[END_REF], and resilience to climate change [START_REF] Lipsett-Moore | Ridges to Reefs Conservation Plan for Choiseul Province, Solomon Islands[END_REF].

Sensitivity analysis of SCP solutions to different habitat map characteristics should be more systematic, although there are already some examples. [START_REF] Andréfouët | Définition d'aires marines protégées pour la conservation de la biodiversité du système récifo-lagonaire de Wallis[END_REF], [START_REF] Deas | Modulation of habitat-based conservation plans by fishery opportunity costs: A New Caledonia case study using fine-scale catch data[END_REF], [START_REF] Hamel | Compromises between international habitat conservation guidelines and small-scale fisheries in Pacific island countries[END_REF] and [START_REF] Mills | A mismatch of scales: challenges in planning for implementation of marine protected areas in the Coral Triangle[END_REF] all found that thematic and spatial resolution of habitat maps influence the results. [START_REF] Deas | Modulation of habitat-based conservation plans by fishery opportunity costs: A New Caledonia case study using fine-scale catch data[END_REF] compared SCP solutions generated from geomorphological maps and from benthic habitat maps, and confirmed that high thematic resolution increases the fragmentation of the solution network, and can limit management effectiveness. [START_REF] Mills | A mismatch of scales: challenges in planning for implementation of marine protected areas in the Coral Triangle[END_REF] recommended to use available data -often only available at a coarse-resolution -as a first step, and then to acquire new fine-resolution data. Finally, [START_REF] Tulloch | Incorporating uncertainty associated with habitat data in marine reserve design[END_REF] specifically looked at the influence of map accuracy on reserve network design. Solutions were easily influenced if prioritizations accounted for habitat map accuracy. However, in the case of known poorly accurate map, it may be simply advised not to use such maps.

Planning unit size and shape

The type of planning units and their sizes impact the resulting design. Rationales for selecting PU sizes are listed in [START_REF] Álvarez-Romero | Research advances and gaps in marine planning: towards a global database in systematic conservation planning[END_REF]. From the POTI SCP case studies, a very wide range of size is used while overall, there are few sensitivity analysis to this important parameter (but see [START_REF] Cheok | Sympathy for the devil: Detailing the effects of planning-unit size, thematic resolution of reef classes, and socioeconomic costs on spatial priorities for marine conservation[END_REF]. [START_REF] Hamel | Compromises between international habitat conservation guidelines and small-scale fisheries in Pacific island countries[END_REF] showed that the PU size was a preponderant criteria when trying to optimize trade-offs between conservation objectives and costs, around Wallis, Futuna and Alofi Islands. Sizes can vary greatly between studies but the trend is that choosing small planning unit size allows for more satisfying trade-offs [START_REF] Van Wynsberge | Conservation and resource management in small tropical islands: Trade-offs between planning unit size, data redundancy and data loss[END_REF]. In terms of shape, PUs are frequently square or hexagonal. Most of the time, the choice of the shape is rather arbitrary and not justified. [START_REF] Van Wynsberge | Conservation and resource management in small tropical islands: Trade-offs between planning unit size, data redundancy and data loss[END_REF] compared two designs for small islands and concluded that an irregular shape PU network (that are equally acceptable as input for the SCP softwares), based on coral reef geomorphology and data availability, was more suitable because data quality was less impacted, compared to the necessary spatial averaging to match the spatial format of a regular grid.

Towards more complex scenarios: representativity, connectivity, resilience, climate change and adaptive planning

International guidelines recommend the integration of a number of qualitative objectives to optimize a network of ecologically or biologically significant marine areas (EBSAs). These core concepts include representativity, connectivity replicated ecological features, adequate and viable sites, and more [START_REF] Kukkala | Core concepts of spatial prioritisation in systematic conservation planning[END_REF][START_REF] Rees | Defining the qualitative elements of Aichi Biodiversity Target 11 with regard to the marine and coastal environment in order to strengthen global efforts for marine biodiversity conservation outlined in the United Nations Sustainable Development Goal 14[END_REF]. Indeed, it is widely recognized that area-based objectives alone are not sufficient to identify optimal areas to sustain marine ecosystems processes and services [START_REF] Rees | Defining the qualitative elements of Aichi Biodiversity Target 11 with regard to the marine and coastal environment in order to strengthen global efforts for marine biodiversity conservation outlined in the United Nations Sustainable Development Goal 14[END_REF]. Representativity is a key concept in SCP and is defined by the Convention on Biological Diversity Parties as being 'captured in a network when it consists of areas representing the different biogeographical subdivisions of the global oceans and regional seas that reasonably reflect the full range of ecosystems' (UNEP/CBD/COP/DEC/IX/20/Annex II). It is a core concept of prioritization, found in all SCP scenarios at different biological levels (species, communities, habitats, etc.). Conversely, resilience and connectivity are criteria that have been considered more recently, including for POTIs, to refine scenarios and represent key dynamic ecological processes and functions in a network, generally at a fairly wide scale.

Resilience is the capacity of an entity to resist to disturbances or recover and bounce back after disturbances [START_REF] O'leary | The Resilience of Marine Ecosystems to Climatic Disturbances[END_REF]. Maximizing resilience within a network can be an objective in SCP, but naturally resilient areas can be seen as low priority conservation areas compared to degraded ones. Since [START_REF] West | Resistance and Resilience to Coral Bleaching: Implications for Coral Reef Conservation and Management[END_REF], principles for designing MPA networks to maximize resilience have been developed including i) replicate major habitats to spread risks, ii) incorporate patterns of connectivity, iii) include critical habitats, and iv) reduce the overall level of threats (marine or land pollution, unsustainable or destructive fishing, coastal development, etc.). POTI examples of resilience-based networks exist in Papua New Guinea [START_REF] Green | Designing a resilient network of marine protected areas for Kimbe Bay, Papua New Guinea[END_REF] and Fiji [START_REF] Weeks | Adaptive Comanagement of a Marine Protected Area Network in Fiji[END_REF]. In Indonesian Islands, Torres-Pulliza et al., ( 2013) also built on these principles and ensured that coral reefs, mangroves and seagrass beds would be enough replicated at close distance. In practice, the applications of resilience-based principles on any given site are strongly limited by the lack of knowledge, even for the most studied ones (see section on data quality and modelling). Instead, rules of thumb, and proxies, are usually applied [START_REF] Green | Designing a resilient network of marine protected areas for Kimbe Bay, Papua New Guinea[END_REF], for instance by taking into account the longest and shortest dispersal distances, thus with a minimum size per MPA and a maximum spacing distance between different MPAs (Mora et al., 2006).

However, similar to other type of modeling and choice of proxies, there are virtually no validation data to justify the choices for most of the sites. [START_REF] Weeks | Adaptive Comanagement of a Marine Protected Area Network in Fiji[END_REF] recognized that without a large disturbance event, it would be impossible to measure whether the resilience of their targeted area increases with the suggested MPA network.

Connectivity is a core process of landscape ecology and population dynamics as it depicts how populations are linked, with the movements of larvae, recruits, juveniles or adults [START_REF] Pinsky | Open and closed seascapes: Where does habitat patchiness create populations with high fractions of self-recruitment?[END_REF]. Connectivity is seen as a key factor of resilience and recovery, mitigating the impacts of stressors in the long term, including climate change. Pathways of larvae and adults, as well as reproduction sites are therefore included in SCP plans in the form of specific representation objectives to maximize connectivity in the network of solutions. Within marine ecosystems, there is a considerable degree of functional and spatial connectivity depending on species, locations, and scales [START_REF] Rees | Defining the qualitative elements of Aichi Biodiversity Target 11 with regard to the marine and coastal environment in order to strengthen global efforts for marine biodiversity conservation outlined in the United Nations Sustainable Development Goal 14[END_REF]. It is however, difficult to set general parameterization for connectivity considering there are often many species of interest with varying dispersal patterns [START_REF] Magris | Integrating multiple species connectivity and habitat quality into conservation planning for coral reefs[END_REF]. Instead, specific objectives are needed for demonstration [START_REF] Weeks | Using reef fish movement to inform marine reserve design[END_REF], but the solutions can be inherently very specific to the selected species and contexts, and possibly of limited practical relevance for real-world implementation if the biodiversity conservation objectives are broad.

Another approach related to connectivity and rising in the POTIs and worldwide (Álvarez-Romero et al., 2018), is to adopt a "ridge to reef" logic and take into consideration that land has an impact on streams, rivers, shores and the surrounding marine ecosystems with soil runoffs, nutrients, pathogens, and sediment plumes. Some studies are fairly simple based on coastal watershed, rivers, and forest cover or types [START_REF] Comeros-Raynal | Applying a ridge-to-reef framework to support watershed, water quality, and community-based fisheries management in American Samoa[END_REF][START_REF] Klein | Setting conservation priorities in Fiji: Decision science versus additive scoring systems[END_REF][START_REF] Lipsett-Moore | Ridges to Reefs Conservation Plan for Choiseul Province, Solomon Islands[END_REF][START_REF] Tsang | Identifying high value areas for conservation: Accounting for connections among terrestrial, freshwater, and marine habitats in a tropical island system[END_REF]. In Fiji (Makino et al., 2013a) and in Hawaii [START_REF] Tsang | Identifying high value areas for conservation: Accounting for connections among terrestrial, freshwater, and marine habitats in a tropical island system[END_REF]) studies compared SCP without connectivity and with different types of connectivity, including land-sea connectivity.

They concluded that connectivity had a huge influence on the solutions computed for habitat representation objectives. Some have modelled the future watershed based-pollution as projected with future land uses such as logging [START_REF] Wenger | Predicting the impact of logging activities on soil erosion and water quality in steep, forested tropical islands[END_REF], in the Solomon islands) or agriculture, in particular oil palm development in Indonesia, with a wide number of parameters to estimate erosion and pollutant sources, coastal transport plume model etc. [START_REF] Tulloch | Improving conservation outcomes for coral reefs affected by future oil palm development in Papua New Guinea[END_REF]. While it seems that high islands only would be concerned by a ridge-to-reef approach, in fact, low-lying atolls can also have significant land-based pollution that have triggered ecological shifts in some lagoons [START_REF] Andréfouët | The timing and the scale of the proliferation of Sargassum polycystum in Funafuti Atoll, Tuvalu[END_REF]. While the type of data and model would be very different for an atoll from for a high-island, land-sea linkages remain a concern for atolls too. Further, in the implementation stage, the success of integrated land-sea management is largely subject to the type of governance, as demonstrated for three islands in the POTIs [START_REF] Jupiter | Opportunities and constraints for implementing integrated land-sea management on Islands[END_REF].

Climate change stressors and resulting changes on communities have been taken into account in a variety of designs in islands and tropical coasts worldwide [START_REF] Allnutt | Comparison of marine spatial planning methods in madagascar demonstrates value of alternative approaches[END_REF][START_REF] Álvarez-Romero | Research advances and gaps in marine planning: towards a global database in systematic conservation planning[END_REF][START_REF] Kabbadj | Scaling tropical island conservation planning to the regional level can lead to unbalanced ecological representation and poor social equity among islands[END_REF][START_REF] Levy | A method for incorporating climate change modelling into marine conservation planning: An Indo-west Pacific example[END_REF][START_REF] Maina | Designing climate-resilient marine protected area networks by combining remotely sensed coral reef habitat with coastal multi-use maps[END_REF][START_REF] Makino | Spatio-temporal marine conservation planning to support high-latitude coral range expansion under climate change[END_REF]. Principles to include climate change projections in SCP designs in the POTIs have been first discussed by Levy & Ban (2013) at regional scale. They used sea surface temperature historical patterns, one coupled atmospheric-ocean general circulation models (CAOGCM) and one emission scenario to infer future anomalies and vulnerability to climate stress. However, this pilot study needs to be enhanced. In particular, CAOGCM are notoriously inaccurate for the central Pacific and specific approaches are needed to meaningfully downscale and characterize anomalies for islands [START_REF] Andréfouët | Mass mortality events in atoll lagoons: Environmental control and increased future vulnerability[END_REF][START_REF] Dutheil | Impact of surface temperature biases on climate change projections of the South Pacific Convergence Zone[END_REF]. These precautions are required to identify suitable robust areas with SCP. This is only one of the challenges. Understanding capacities to adapt over present ranges of environmental conditions is critical [START_REF] Kleypas | Environmental Limits to Coral Reef Development: Where Do We Draw the Line?[END_REF]. The location of possible refugia might be also a key resilience question, and there are, for instance, limited knowledge on the resilience potential of mesophotic areas on the deep areas around most islands [START_REF] Slattery | Connectivity and stability of mesophotic coral reefs[END_REF].

Finally, adaptive planning is a relevant concept for islands facing climate change, resources collapse or socio-economic changes [START_REF] Mills | Real-world progress in overcoming the challenges of adaptive spatial planning in marine protected areas[END_REF]. Adaptive planning means that new data, socioecosystem changes, natural disasters and so on may call for new decisions, assessment and implementation. For instance, the poleward, or latitudinal, shift of communities and habitats is a process already occurring (in Japan and Australia at least) [START_REF] Nimbs | Beyond Capricornia: Tropical Sea Slugs (Gastropoda, Heterobranchia) Extend Their Distributions into the Tasman Sea[END_REF], that certainly calls for re-assessment and adaptive planning in the future [START_REF] Makino | Spatio-temporal marine conservation planning to support high-latitude coral range expansion under climate change[END_REF]. The concept is also inherent to the amount of time required between regional assessment and local implementation, which may call for frequent re-assessment, and changes of objectives [START_REF] Álvarez-Romero | Research advances and gaps in marine planning: towards a global database in systematic conservation planning[END_REF]. In the POTIs, adaptive planning has been emphasized for Fijian coral reefs [START_REF] Weeks | Adaptive Comanagement of a Marine Protected Area Network in Fiji[END_REF] but not all the challenges could be overcome in this case [START_REF] Mills | Real-world progress in overcoming the challenges of adaptive spatial planning in marine protected areas[END_REF]. On the ground, there are

several POTIs examples of zoning plans that have been revisited in the past although without using SCP (e.g., Moorea lagoon in French Polynesia, about 15 years after the first zoning). It is most likely that many existing conservation plans will have to be modified, perhaps at a frequency of 10-15 years. The technical challenges are the same as for a one-time conservation evaluation, but are multiplied by the need to understand the natural or anthropogenic triggers for adaptation, convince stakeholders that changes are needed, evaluate the effectiveness of the previous plans, and so forth.

Despite the challenges, anticipating the almost unavoidable needs to update plans should be a methodological priority in SCP for POTIs.

House of cards: modelling without validation, and the issue of data quality

Looking at the chronology of the various studies (Supplementary Material S1a), there is a clear trend towards more complex scenarios with time, both in the POTIs and globally [START_REF] Álvarez-Romero | Research advances and gaps in marine planning: towards a global database in systematic conservation planning[END_REF]. This is likely partly due to academic objectives (publications having to introduce novelties) and not necessarily driven by the most urgent manager needs. In parallel with more complex questions, more complex modelling is being developed for SCP inputs, but is often not based on new in situ validation data, and does not always take into account the adequacy of used data sets (in scale, content and accuracies). It seems that in many cases, working out a new idea is by itself a justification to conduct an exercise, regardless of data quality. This is even more worrisome when model outputs are 'stacked' together in order to include complex modelled layers such as vulnerability to climate change, soil erosion, land cover maps, sediment transport pathways, lagoon hydrodynamics, ecological behaviors (such as fish movements), socio-economic information (such as fishing patterns), etc. (e.g. Klein et al., 2014b;[START_REF] Levy | A method for incorporating climate change modelling into marine conservation planning: An Indo-west Pacific example[END_REF][START_REF] Tulloch | Incorporating uncertainty associated with habitat data in marine reserve design[END_REF][START_REF] Weeks | Using reef fish movement to inform marine reserve design[END_REF]. While the management problems at stake are certainly relevant, the methodology of the study can suffer from serious shortcomings in the absence of any clear model validation. Inferences for management recommendations should be avoided when there are no proofs that the model outputs are robust and accurate, or without in-depth sensitivity analyses. Obviously, collecting the right and validated information can be a time-consuming expensive effort, but it should not be forgotten for real applications. On the other hand, there also are many POTIs studies that have carefully modelled new data layers which can be useful for conservation (e.g. [START_REF] Knudby | Mapping Fish Community Variables by Integrating Field and Satellite Data, Object-Based Image Analysis and Modeling in a Traditional Fijian Fisheries Management Area[END_REF].

We recommend that i) model validation should be imperative before management conclusions are drawn and ii) that adequate quality data must be collected for validation purposes.

A possible effect of complex modelling papers used for new conceptual developments is that managers may believe that without extensive complex scenarios and complex data layers, they cannot achieve sound spatial planning through SCP tools and use its guidance potential. Similar misconception also occurred, for instance, in habitat mapping using remote sensing that was often seen as a high-tech endeavor [START_REF] Andréfouët | Coral Reef Habitat Mapping using Remote Sensing: A User vs Producer Perspective[END_REF]. Conversely, and perhaps because it is not original anymore, very useful studies for management that make basic uses of the SCP tools are poorly represented in the list of recent SCP publications. For instance, sensitivity studies identifying tradeoffs between solution performances and socio-economic costs remain extremely useful, even in simple fishery contexts (e.g. [START_REF] Hamel | Compromises between international habitat conservation guidelines and small-scale fisheries in Pacific island countries[END_REF][START_REF] Oyafuso | Evaluating bioeconomic tradeoffs of fishing reserves via spatial optimization[END_REF].

Another data-related issue also highlighted by [START_REF] Álvarez-Romero | Research advances and gaps in marine planning: towards a global database in systematic conservation planning[END_REF] in their review, is the lack of proper documentation on the parameterization and setting of SCP software options, such as Boundary Length Modifier and Species Penalty Factor used by Marxan. These options influence the solutions and their documentation contributes to data quality improvement. Detailed reports in this regard are often more useful than the typically concise peer-reviewed papers (e.g., for Palau, [START_REF] Hinchley | Biodiversity Planning for Palau's Protected Areas Network -An Ecoregional Assessment[END_REF].

Missed POTI opportunities for SCP, and perspectives

Overall, two types of studies could be clearly outlined in the present review. First, academic-driven studies are dominant, without much of a manager involvement, which seems to push SCP towards more complex scenarios and assess the feasibility to integrate new constraints and paradigms (adaptive planning, climate change, resilience, ridge-to-reef continuum, genetics models, etc.). The second type of papers are case studies which are more in line with the founding SCP concepts of evaluating conservation gaps and comparing objectives vs cost trade-offs, especially for fishery and stock conservation. Similar trends were also noted globally by [START_REF] Álvarez-Romero | Research advances and gaps in marine planning: towards a global database in systematic conservation planning[END_REF]. The latter, simpler, types of applications are also more in line with the main basic priorities, often put forward by island managers. Indeed, they often primarily have to deal with balancing marine resource conservation and food security with other types of activities (tourism, coastal development, mining, etc.). As such, it is likely that the simplest types of SCP scenarios will continue to be used to provide a sound foundation for decision making in partnership with various stakeholders. However, when comparing island specifics and criteria used in SCP scenarios, we suggest that seven important gaps, or missed opportunities, emerge, which we believe should shortly require some attention from SCP practitioners.

First, biodiversity criteria (either as objectives, costs of exploitation, or biological processes) are often limited to habitats (see above) or biased towards fishes. Yet, from the POTIs context, there is a variety of potential relevant criteria. To our knowledge, there are almost no SCP studies built around echinoderms, crustaceans, mollusks (but see [START_REF] Kabbadj | Scaling tropical island conservation planning to the regional level can lead to unbalanced ecological representation and poor social equity among islands[END_REF], or marine mammals though scientists, NGOs and government acknowledge that these are also priorities for management [START_REF] Weeks | Research priorities for conservation and natural resource management in Oceania's small-island developing states[END_REF]. For instance, sea cucumber fisheries are significant in many archipelagoes, and while the status and management of this resource is frequently debated (Andréfouët et al., 2019b;[START_REF] Bosserelle | The status of sea cucumbers at Pohnpei Island and Ant Atoll , Federated States of Micronesia[END_REF][START_REF] Purcell | Sea cucumber fisheries: global analysis of stocks, management measures and drivers of overfishing[END_REF], no SCP studies have focused on this taxa, or used population data. Similarly, several critically endangered species, such as dugong in New Caledonia, are the focus of many conservation projects (e.g., [START_REF] Cleguer | Spatial mismatch between marine protected areas and dugongs in New Caledonia[END_REF]), yet, relevant information such as feeding and reproduction areas, or migration pathways, have not been used in SCP scenarios, except for turtle nesting beaches (e.g., [START_REF] Green | Designing a resilient network of marine protected areas for Kimbe Bay, Papua New Guinea[END_REF]. Lack of spatialised data readily available likely hinder the development of appropriate scenarios.

Second, mariculture has never been used in any SCP scenario in the POTIs, either within a conservation or fisheries management approach. Outside the POTI region, Indonesia brings an example of mariculture integrated to SCP, with seaweed and pearl farming [START_REF] Grantham | A comparison of zoning analyses to inform the planning of a marine protected area network in Raja Ampat, Indonesia[END_REF].

Mariculture in island lagoons or coastal areas is at various stages of development in many Pacific

Ocean places and have often only occurred at small scale in the past decades [START_REF] Adams | Current status of aquaculture in the Pacific Islands[END_REF]. In the past 20 years, black pearl farming in French Polynesia, Cook Islands and Fiji, or shrimp farming in New Caledonia have developed over large areas and have become economically significant. For instance, black pearl farming in French Polynesia is the 2 nd source of income for the country with activities in about 35 islands [START_REF] Andréfouët | French Polynesia[END_REF]. A most likely path for development in the POTIs is the aquarium trade, for which areas for valuable specimen collection, spat collection, or rearing are increasing (e.g., Teitelbaum and Friedman, 2008, for giant clams). Even if mariculture remains today marginal in many countries, the future needs for local stock enhancement, the proximity of the Asian seafood and jewelry market, the extent of shallow lagoons offering suitable locations, the possibility to grow high value products in small areas with simple technology, and an interest for local populations to work with marine resources, could increase the need to account for mariculture in future SCP scenarios. For instance, given the extent of black pearl farming activities in many French Polynesian lagoons, it is likely that specific SCP scenarios for optimal zoning according to this activity will emerge soon. These could also take advantage of hydrodynamic 3D models implemented to compute connectivity matrices for pearl oyster larval dispersal [START_REF] Dumas | Tidal flushing and wind driven circulation of Ahe atoll lagoon (Tuamotu Archipelago, French Polynesia) from in situ observations and numerical modelling[END_REF][START_REF] Thomas | Larval connectivity of pearl oyster through biophysical modelling; evidence of food limitation and broodstock effect[END_REF], as well as genetics study that can help mapping populations and larval dispersal source and sinks [START_REF] Reisser | Population Connectivity and Genetic Assessment of Exploited and Natural Populations of Pearl Oysters within a French Polynesian Atoll Lagoon[END_REF]. In the context of different uses and zones that require ad hoc management, such as mariculture, fishing and conservation zones specific SCP tools can help, such as Marxan with Zones.

Third, ciguatera spatial risk has never been integrated into SCP. For islands where there are ciguatera-endemic areas, it can be stated that these areas are de facto protected as no take (or 'less take') areas, since they tend to be avoided by fishers. Hence, SCP scenarios could take advantage of the situation by maximizing the inclusion of areas known to be ciguateric, to decrease the fisher opportunity costs. Several other factors obviously need to be considered, including i) the habitat quality and its suitability as a conservation objective, in case ciguatera was due to coastal degradation, and ii) the availability of spatially-explicit ciguatera toxicity data, which are difficult and costly to collect and spatialize. If this information could be collected from fishers, who should care about and know ciguatera spatial patterns, even approximately, it could benefit to SCP and might influence opportunities for conservation. We can generalize this point about ciguatera to any factors (environmental, cultural or historical) that transform areas into de facto no take areas for local populations.

Fourth, molecular data are increasingly available for POTIs and have long served conservation (Von der Heyden et al., 2014), but methods to include genetics and genomics data in SCP have only been emerging recently [START_REF] Beger | Evolving coral reef conservation with genetic information[END_REF] and, to our knowledge, no example is available for the POTIs, yet. Molecular data are necessary to understand connectivity at population and evolutionary time scales and validate connectivity models [START_REF] Treml | The emergent geography of biophysical dispersal barriers across the Indo-West Pacific[END_REF][START_REF] Reisser | Population Connectivity and Genetic Assessment of Exploited and Natural Populations of Pearl Oysters within a French Polynesian Atoll Lagoon[END_REF], which could improve SCP to a great extent, depending on the scale of the exercise. However, considering the cost of sampling and analysis especially for population genetics, investigations can only be performed for a limited number of species, and the choice of candidate species is not trivial if the conservation objective is general and not specific to those species. Multi-species modelling could be a solution, as discussed for South Africa [START_REF] Nielsen | Multispecies genetic objectives in spatial conservation planning[END_REF]. However, other limitations arise, such as differences in the density of samples per planning domain or planning unit, especially for multiple island exercises.

Other island-specific aspects have already emerged in SCP scenarios but still remain understudied or underrepresented and could define future additional roadmaps for POTIs scenarios as highlighted below.

Fifth, while the need to consider customary management has been emphasized in several SCP scenarios with, for instance, locked-in areas [START_REF] Adams | Improving social acceptability of marine protected area networks : A method for estimating opportunity costs to multiple gear types in both fished and currently unfished areas[END_REF][START_REF] Green | Designing a resilient network of marine protected areas for Kimbe Bay, Papua New Guinea[END_REF][START_REF] Horigue | Benefits and challenges of scaling up expansion of marine protected area networks in the Verde Island Passage, Central Philippines[END_REF], there is also a large amount of work to be done about the scaling of conservation network, especially in several of the POTIs that have not been yet the object of SCP studies. In Vanuatu for instance, traditional micro-managed areas are the norm, are plentiful [START_REF] Dumas | Effectiveness of village-based marine reserves on reef invertebrates in Emau, Vanuatu[END_REF] and will not be easily abandoned for other schemes. Understanding how to maximize the benefits of existing initiatives is a priority. In Polynesia region, existing protected tapu (or tabu, taboo) or rāhui (temporal closures) areas, have also been ignored thus far by SCP studies, while some local initiatives have recently revitalized these traditional practices (e.g. in French Polynesia: [START_REF] Bambridge | Communs et Océan, Le rāhui en Polynésie[END_REF].

Nevertheless, in the context of sessile or sedentary fishery management, the effectiveness of temporal, rotating or permanent closures compared to other measures such as catch size limits and quotas, is still debated [START_REF] Carvalho | Optimized fishing through periodically harvested closures[END_REF][START_REF] Plagányi | Crop rotations in the sea: Increasing returns and reducing risk of collapse in sea cucumber fisheries[END_REF][START_REF] Purcell | Rotational harvesting is a risky strategy for vulnerable marine animals[END_REF][START_REF] Van Wynsberge | Best Management Strategies for Sustainable Giant Clam Fishery in French Polynesia Islands: Answers from a Spatial Modeling Approach[END_REF]. Cultural values are still strongly anchored in many island societies despite the fast evolution towards a westernized, globalized, modern way of life [START_REF] Buijs | Lay People's Images of Nature: Comprehensive Frameworks of Values, Beliefs, and Value Orientations[END_REF][START_REF] Mcfarlane | Ecosystem services for human health in Oceania[END_REF]. However, cultural values remain poorly considered in POTI SCP scenarios [START_REF] Hamel | The Importance of Fishing Grounds as Perceived by Local Communities Can be Undervalued by Measures of Socioeconomic Cost Used in Conservation Planning[END_REF] although they could be difficult to integrate due to ongoing change, varied tenure and governance systems, and strong bottom-up approaches to management. Interestingly in Fiji, mixed co-management systems exist, including for joint land-sea managed areas (Jupiter et al., 2014a;[START_REF] Weeks | Incorporating seascape connectivity in conservation prioritisation[END_REF]. Anthropology studies have characterized how local communities can value their marine environment for reasons that are beyond just access to food, identifying locations of high symbolic value [START_REF] Foale | Tenure and taboos: origins and implications for fisheries in the Pacific[END_REF], but this information is often not spatialized though it would be valuable for SCP.

Sixth, SCP has never been used for the zonation of VLMPAs in the POTIs (listed in Table 2). Even globally, the only example is the rezoning plan of Great Barrier Reef Marine Park Authority in Australia [START_REF] Fernandes | Establishing Representative No-Take Areas in the Great Barrier Reef: Large-Scale Implementation of Theory on Marine Protected Areas[END_REF]. In POTIs, none of the boundaries or zoning plans (if any) of the VLMPAs or sanctuaries were designed using SCP methodology. Political decisions were made without much of spatial planning scientific prioritization. Considering the sizes of these MPAs, and the limited amount of conflicting stakeholder activities (if no fishing license or seabed mining), a SCP driven selection was often not justified. However, most need to define zoning plans and a SCP approach has been recommended for their definitions as well as for the identification of new VLMPAs (Davies et al., 2017;[START_REF] Devillers | Reinventing residual reserves in the sea: Are we favouring ease of establishment over need for protection?[END_REF]. It is likely that SCP will play a role for this, although the biggest challenges remain collecting suitable biological data across wide expanses of ocean, to build relevant and robust scenarios. Biodiversity models have been used at the scale of VLMPAs (e.g., [START_REF] Davies | Large marine protected areas represent biodiversity now and under climate change[END_REF], but, again, data quality remains an issue and it might be better to focus on the representation of bio-physical regions defined by mapped physical and geomorphological features [START_REF] Devillers | Reinventing residual reserves in the sea: Are we favouring ease of establishment over need for protection?[END_REF]. It is likely that in the near future, the problems inherent to optimizing conservation vs costs, and inferring management plans for these VLMPAs, will be under the scrutiny of the SCP community.

Recent studies have proposed new definitions for bioregions in the Pacific Ocean [START_REF] Beger | National-scale marine bioregions for the Southwest Pacific[END_REF][START_REF] Garcia | Scale-dependency of the environmental influence on fish β-diversity: Implications for ecoregionalization and conservation[END_REF], that could help refining VLMPAs planning, based on representativity, but the relevance of these bioregion definitions remain data quality-dependent.

Seventh, and last, POTIs are highly vulnerable to climate change. While some island examples of climate change-driven SCP scenarios emerge from this review (Hawaii, French Polynesia and Fiji, respectively with [START_REF] Chung | Building Coral reef resilience through spatial herbivore management[END_REF][START_REF] Kabbadj | Scaling tropical island conservation planning to the regional level can lead to unbalanced ecological representation and poor social equity among islands[END_REF][START_REF] Weeks | Adaptive Comanagement of a Marine Protected Area Network in Fiji[END_REF], their number is not congruent with the threats that represent warming, changes in cyclone activities and potentially sea level rise [START_REF] Payri | Biodiversity, a pressing need for action in Oceania[END_REF]. Adaptive planning would also have to be considered if SCP considers climate change effects at various time scale. For instance, while the effects of sea level rise on low lying islands are still scientifically debated [START_REF] Tuck | Physical modelling of reef island topographic response to rising sea levels[END_REF][START_REF] Masselink | Coral reef islands can accrete vertically in response to sea level rise[END_REF], this process could accentuate the effects of poor land use [START_REF] Yamano | Atoll island vulnerability to flooding and inundation revealed by historical reconstruction: Fongafale Islet, Funafuti Atoll, Tuvalu[END_REF] and of tectonic activities that are also a feature of several POTIs, such as Vanuatu [START_REF] Ballu | Comparing the role of absolute sea-level rise and vertical tectonic motions in coastal flooding, Torres Islands (Vanuatu)[END_REF]. Increased occurrences of flooding could trigger population migrations, which raise important questions on potential destinations, availability of land and tenure [START_REF] Connell | Last days in the Carteret Islands? Climate change, livelihoods and migration on coral atolls[END_REF][START_REF] Donner | The legacy of migration in response to climate stress: learning from the Gilbertese resettlement in the Solomon Islands[END_REF], including a change on the use of resources and potential for conservation. SCP could be useful to plan these migrations that could occur in the future at different spatial scales (within and between islands).

The main recommendations emerging from this review on POTI SCP are summarised in Table 4.

Several recommendations echo previous reviews not specific to POTIs [START_REF] Álvarez-Romero | Research advances and gaps in marine planning: towards a global database in systematic conservation planning[END_REF].

However, they are reinforced from the present review. Furthermore, we also emphasised both thematic and methodological priorities, namely the need to still consider basic SCP applications, document well the projects, conduct sensitivity analyses and, most importantly, use accurate data to, at least, validate the proxies or model outputs used for SCP. Among the most critical recommendations inferred from this study, adaptive planning concepts should be part of the long term implementation of conservation plans, even for the most basic ones. Islands and populations are inherently dynamic in the present context of climate change and increased resource exploitation, thus revisiting conservation plans will necessarily be mandatory, at least every decade or more often.

'Plan for new plans' as we could put it, is essential.

Conclusion

Systematic conservation planning is a mature scientific tool that has demonstrated high flexibility in the accommodation of a variety of data, features and processes relevant to conserve and sustain ecosystems while minimizing the impacts for stakeholders. It is only one part of the conservation toolbox and other approaches can also work quite well for assessment and implementation. For instance, expert-driven ad hoc solutions can emerge more easily and simplify the work of managers, though this approach has limitations [START_REF] Allnutt | Comparison of marine spatial planning methods in madagascar demonstrates value of alternative approaches[END_REF][START_REF] Keppel | The importance of expert knowledge in conservation planning -Comment to an article by C[END_REF][START_REF] Keppel | Conservation in tropical Pacific Island countries: Why most current approaches are failing[END_REF]Klein et al., 2014a). The potential, pros, and cons of the various approaches remain a matter of debate and this will likely continue in the future, however, SCP provides useful advantages.

This review of SCP application in POTIs shows strong potential despite limited uptake in POTIs [START_REF] Álvarez-Romero | Research advances and gaps in marine planning: towards a global database in systematic conservation planning[END_REF][START_REF] Margules | Systematic conservation planning[END_REF]. In terms of geographic polarisation, the present analysis is consistent with the conclusions from Álvarez-Romero et al. ( 2018): studies are concentrated within a few areas; in particular in Fiji at the POTI's scale analysis. In other countries, there might be shortage of technical competences and initiatives as those found in Fiji. In some countries, conservation took the path of implementing Very Large Marine Protected Areas, a path that is not necessarily exclusive of smaller local initiatives, but has dominated the political, if not the technical, conservation agenda.

In the future, understanding the reasons why SCP has not emerged in some places will also help conservation agendas, along with adequate data collection, storage and management.

The present review points to several possible bottlenecks that are expected to drastically limit the generalization of the more complex scenarios and adaptive planning. First, good data sets are limited. There are no shortage of research questions useful to enhance conservation and SCP [START_REF] Weeks | Research priorities for conservation and natural resource management in Oceania's small-island developing states[END_REF], but a lack of data and knowledge to provide answers to those questions.

Modelling and proxies are often used to fill data gaps, but there are shortcomings due to the inherent limitations of models and proxies. Collection for any scenarios of relevant accurate 'hard' data of known errors is therefore highly recommended here. Enough resources should be allocated for initial data collection, especially for baseline data that often seemed to be granted, such as habitat maps, biodiversity, or fishery data. For instance, a systematization of the spatialisation of the socio-economic surveys, especially those related to fisheries (such as in [START_REF] Léopold | A framework for mapping small-scale coastal fisheries using fishers' knowledge[END_REF], should be a priority.

Figure 1 .

 1 Figure 1. Map of the POTI Exclusive Economic Zones and the census of reviewed systematic conservation planning case studies conducted for each one, from 2000 to 2019. For each value, the number of POTIs concerned is given in brackets.

Figure 2 .

 2 Figure 2. a. All the Pacific Ocean tropical Islands (POTIs) classified by region (POTIs in Polynesia = 50% as there are 13/26 POTIs that are located in Polynesia), and the proportion of POTIs that have been subject to SCP are indicated in colour, POTIs not subject to SCP in blank; b. All the reviewed POTI SCP case studies classified by regions; c. Number of SCP case studies through time, with a coloured indication for each region, and case studies concerning Fiji highlighted by a grey frame; d. Summary of the SCP case studies organised according to their regions and the themes tackled. Themes are presented with key words here, they are further developed in the result section.

Table 1 .

 1 Definition of SCP vocabulary.

Table 2 .

 2 The POTIs main features.SPC= Pacific Community, FFA= Pacific Islands Forum Fisheries Agency, WCPFC= Western and Central Pacific Fisheries Commission (Y* for Participating territory, not member), Environmental/fishery technical services (Y* for existing services but few/no specific information available), SCP= Systematic conservation planning, MPA= Marine protected areas, VLMPA: very large MPA, WHS= UNESCO World Heritage Site, MAB= UNESCO Man and Biosphere Reserve. NC= New Caledonia, NZ= New Zealand; USA=United States of America; UK=United Kingdom. MPA= all categories, including IUCN ones.

						Political levels
				Regional level
	Group	Countries or	SPC FFA WCPFC	Status	Env/fishery	National	SCP	MPA, VLMPA, shark/marine mammal
		territories					technical	marine GIS	case studies	sanctuaries (sanct.), UNESCO WHS and
							services	database		MAB (area in km²)
	Melanesia	Papua New	Y	Y	Y	Independent	Y*	N	4	MPA; Whale sanctuary
		Guinea
	Melanesia	Solomon Isl.	Y	Y	Y	Independent	Y*	N	3	MPA;
										WHS: East Rennell (370)
	Melanesia	Vanuatu	Y	Y	Y	Independent	Y	N	0	MPA; Marine Mammal sanct.
	Melanesia	New Caledonia	Y	N	Y*	French overseas	Y	Y	1	VLMPA: Natural Park of the Coral Sea
						territory				(1,368,806); WHS: Lagoons of NC (15,740) ;
										Shark sanct.; Whale sanct.
	Melanesia	Fiji	Y	Y	Y	Independent	Y	N	14	MPA
	Micronesia	Palau	Y	Y	Y	Independent	Y*	N	1	MPA; VLMPA: Palau Nat'l Marine Sanct.
										(475,000);
										MAB: Ngaremeduu (137);
										WHS: Rock isl Southern Lagoon (1002);
										Shark sanct.; Marine Mammal sanct.
	Micronesia	Federated States	Y	Y	Y	Independent	N	N	4	MPA;
		of Micronesia								VLMPA: Micronesia MPA (184,948);
										MAB: Utwe (18); And Atoll (10); Shark sanct.
	Micronesia	Guam	Y	N	Y*	Unincorporated territory	Y	Y	0
						of the USA				MPA
	Micronesia	Commonwealth	Y	N	Y*	Unincorporated territory	Y	Y	0	MPA; VLMPA: Marianas Trench Marine Nat'l
		of the Northern				of the USA				Monument: (250,000);
		Mariana Isl.								Shark sanct.
	Micronesia	Marshall Isl.	Y	Y	Y	Independent	Y	N	1	MPA; Shark sanct.
	Micronesia	Nauru	Y	Y	Y	Independent	N	N	0	N
	Micronesia	Kiribati	Y	Y	Y	Independent	Y	Y	0	MPA; Shark sanct.;
										VLMPA-WHS: Phoenix Island protected area
										(408,250)
	-	USA Minor	N	N	Y	Unorganized territories	Y	Y	0	VLMPA: Pacific Remote Isl. Nat'l Monument,
		Outlying Isl.				of the USA				(1,270,000)

Table 3 .

 3 Review of the technical features of 31 SCP case studies on POTIs. PU= Planning units, DDPU= data driven planning units, BLM= Boundary Length Modifier, CSM= Connectivity strength modifier, CPUE= catch per unit effort, PNG= Papua New Guinea. FSM= Federated States of Micronesia, NGO=non-governmental organization. MCRMP= Millennium Coral Reef Mapping Project, LMMA= locally managed marine areas,MPA= marine protected area, nb= number, min.= minimum, max.=maximum, obj=objective(s), cons.= conservation, hab.= habitats, ecosyst.= ecosystem, comm= community/ies, sp.= species, gov.= government, spag= spawning aggregation sites. For Success rate of objectives, only the quantitative results clearly presented are provided.

	Date Authors	Country	Methodo	Institutional	Marine	Origin of the	Conservati	Costs: Proxies?	Other	SCP	Spatial	PU size (m²)	Success rate of
		or	logical/	context	conservation obj	map	on targets	Validation?	constraints	software +	domain	(shape), BLM	objectives
		Territory	Applied		ectives (nb)		(%)			version	(km²)	(y/n)
			paper
			(M/A)
	TNC	FSM	A	NGO	Ecological	-	20-30%	-	-	-	29,175	-38% sites are
					systems, comm.								protected
					& species (53)
	Hinchley et al.	Palau	A	Academic	Ecosystems,	1:25,000	30-100%	28 socio-	Existing	SPOT +	3114	15,000 m²	NA
				with NGO &	hab., species &	USGS,		economic factors	reserves	Marxan		BLM
				gov.	special areas (39)	Landsat7
	Reimaanlok Nat'l	Marshall	A	Academic &	Coarse scale	IKONOS,	30-100%	Socio-economic	Existing	-	14,067	-30-100%
	Planning Team	Isl.		gov.	(hab./ ecosyst.)	Quickbird,		costs, distributed	reserves
					(10), fine scale	LandSat &		among comm.
					(sp./ rare comm./	ASTER;
					cultural point)	Landsat7 for
					(6), sp. (21)	coral reefs
	Andréfouët et al.	Wallis	M, A	Academic &	Geomorphic hab.	MCRMP	20%	Management	-	R	269	250,000	NA
				gov.	(MCRMP, level			costs (minimal				1,000,000 &
					5) + benthic map			size of the MPA;				4,000,000 m²
					(56). 9 biological			cost = BML)				BLM
					inventories
	Green et al.	PNG	A	Academic		-	-	15 data layers	-	Marxan	13,000	100,000 m²	NA
				with NGO				combined to				(hexagon).
								derive a total cost				BLM
								layer (detailed				Min. size of
								socio-economic				MPA ; Max
								surveys)				spacing dist.
	Lipsett-Moore et	Solomon	A	Academic &	Marine cons.	MCRMP	10-95%	PU area minus	Existing,	Marxan &	7 894	500,000 m²	NA
	al.	Isl.		NGO with	features (114)	(coral reef		PU proportion of	proposed,	Zonae cogito		BLM
				Tribal	(47 coral reefs	types);		rapid inclusion in	protected or
				Communities	derived by 4	experts		the protected	managed
					bioregions)	(bioregions)		area network.	areas
	Jupiter et al.	Fiji	M, A	Academic &	Hab. (11) & sp.	Workshop	25-100%	-	LMMAs	-	-	-NA
				NGO		participants
	Kool et al.	Solomon	A	Academic,	Functional hab.	MCRMP	10-50%	No costs for the	Reserves	Marxan	60,638	2,500,000 m²	NA
		Isl.		NGO + gov.	types (8)			marine part				BLM

Table 4 .

 4 Technical and thematical recommendations emerging from the analysis of the POTI SCP literature. Promote the assessment and implementation of simple SCP scenario, not only complex scenarioSensitivity analysis2. Perform sensitivity analysis to representation conservation targets, to counteract the arbitrary levels of representation frequently used in SCP 3. Conduct systematic sensitivity analysis of SCP solutions to the key parameters (habitat map characteristics, biodiversity inventories, PU size, etc.)Data quality4. Promote and fund collection of relevant data to limit the use of proxies, or at least to validate them Documentation 5. Improve documentation on i) the parameterization and set-up of SCP software options used; ii) the results of sensitivity analysis. Fishery 6. Promote and fund fishery atlases to better define fishery-related opportunity costs and fishery-related conservation objectives 7. Consider invertebrate resources, not only fish, for fishery based objectives or costsCosts8. Define and map opportunity costs beyond just fishers, including islanders' socio-cultural value and islanders' range of economic activity in particular mariculture and tourism 9. Collaborate with local or national managers to determine these objectives and costs

	Scenario for islands
	1.

Integration of complex processes, with adequate data

  10. Consider ridge to reefs approaches to include land-based criteria (threats, assets, costs, etc.) relevant for marine protection 11. Promote and implement connectivity and resilience concepts, with adequate data acquisition, including, but not limiting to genetic data 12. Use adequate downscaling techniques to infer island vulnerability to climate change

	Scaling up networks
	13. Scale-up conservation networks by taking into account customary reserves, while enhancing their
	ecological performances
	Adaptive planning
	14. 'Plan for new plans', with adaptive planning strategies

Acknowledgements

The study was funded by the MANA (Management of Atolls) project (grant ANR-16-CE32-0004) and by the PANGEA project (grant from Délégation à la Recherche de Polynésie française to Institut Louis Malardé, Conv. N° 06575/MED of September 28 th , 2018), and by a doctoral fellowship from Sorbonne Université to LA. We are grateful to Emma Gairin for her edits of English language on the initial version. Three anonymous reviewers and Michelle Devlin (Guest Editor) are acknowledged for their numerous comments and suggestions that enhanced the manuscript.