Sylvaine Giakoumi
email: sylvaine.giakoumi1@gmail.com

Alexis Pey

Pierre Thiriet

Patrice Francour

Paolo Guidetti

Patterns of predation on native and invasive alien fish in Mediterranean protected and unprotected areas

Keywords: predators, invasive fish, Mediterranean, marine protected areas, no-take marine reserves, tethering experiment

Worldwide, the loss of predatory fish due to overexploitation has altered the structure of native communities and caused ecosystem shifts. Ecosystems deprived of high-level predators may be more vulnerable to invasive alien species as the latter are subject to reduced predation control. Marine protected areas (MPAs), and particularly no-take reserves where fishing is banned, can be effective tools for the restoration of predatory relationships within their boundaries. We explored whether the restoration of high-level predatory fish populations within Mediterranean MPAs can exert top-down control on alien fish. Fish tethering experiments, including native (Sardina pilchardus, Boops boops) and alien (Siganus rivulatus) dead specimens, were conducted to quantify predation within the no-take zones of three MPAs and in unprotected areas, and to assess potential differences in predation rates and prey type preferences. A subsample of experimental units was filmed to document predation events and related fish behavior. More high-level predators interacted with the tethered fish inside the MPAs than in unprotected areas. Yet we did not find significant differences in the consumption of alien or native fishes between MPAs and unprotected areas. The native S. pilchardus was consumed more in comparison to the other tethered fishes, regardless of protection status and location. Interestingly, the alien S. rivulatus was consumed by native predators in the western Mediterranean locations where this alien fish is not established.

Despite its limitations, our study provides evidence on the ability of some native predators to feed on and potentially control certain alien species without requiring 'adaptive' time-lag periods.

Introduction

High-level marine predators, including top (or apex) predators, are usually large-bodied longliving animals that occupy the highest trophic levels in food webs, and have a fundamental influence on the structure of marine communities and ecosystem functioning [START_REF] Ray | Large carnivores and the conservation of biodiversity[END_REF]. The effect of predators on prey populations and, via trophic webs, on entire communities (e.g. trophic cascades; [START_REF] Estes | Killer whale predation on sea otters linking oceanic and nearshore ecosystems[END_REF]) is a combination of lethal direct predation and non-lethal risk effects [START_REF] Heithaus | Predicting ecological consequences of marine top predator declines[END_REF]. Many prey species alter their behavior to avoid predation -the so called non-lethal risk effects -influencing their foraging patterns, growth and reproduction rates. The combined effects of predation exert top-down control on mesopredators and their prey, that may be as consequential, if not more so in some cases, than bottom-up forces [START_REF] Baum | Cascading top-down effects of changing oceanic predator abundances[END_REF].

High-level marine predators, including large finfish and sharks, have been intensively fished worldwide [START_REF] Pauly | Fishing down marine food webs[END_REF][START_REF] Christensen | a Hundred-year decline of North Atlantic predatory fishes[END_REF], leading to a dramatic decline in predatory fish biomass in the ocean by two thirds over the past 100 years [START_REF] Christensen | A century of fish biomass decline in the ocean[END_REF]. Depletion of predators has caused serious cascading effects in marine ecosystems, leading to regime shifts and alternative states of ecosystems [START_REF] Estes | Trophic downgrading of planet Earth[END_REF]. A classical example of a trophic cascade is the dramatic increase in sea urchin density and the subsequent deforestation of kelp beds because of the elimination of the sea-otter's keystone role [START_REF] Estes | Killer whale predation on sea otters linking oceanic and nearshore ecosystems[END_REF]. Another example is the decline of great sharks and the subsequent increase of their prey, mainly elasmobranchs of lower trophic levels, which in turn caused a decline in the mesopredators' prey populations, including the bay scallop (Argopecten irradians), leading to the collapse of the fishery [START_REF] Myers | Cascading effects of the loss of apex predatory sharks from a coastal ocean[END_REF]). Thus, the overexploitation of high-level predators and the reduction (or elimination) of top-down control can have important ecological, socio-economic and conservation implications as intermediate-level consumers (herbivores and mesopredators) become dominant, and the recovery of overexploited predators is jeopardized [START_REF] Baum | Cascading top-down effects of changing oceanic predator abundances[END_REF].

The loss of high-level predators not only produces effects that propagate throughout the food web, affecting native communities, but also makes ecosystems more vulnerable to invasion by alien species [START_REF] Carlsson | Native predators and exotic prey-an acquired taste?[END_REF][START_REF] Estes | Trophic downgrading of planet Earth[END_REF]. A key factor that allows alien species to successfully invade their new environment is the absence of their original predators and their release from top-down control [START_REF] Kolar | Progress in invasion biology: predicting invaders[END_REF]). Yet alien species may become prey of native predators in their new environment; these predators may adapt their diet to include alien prey, either rapidly, via existing phenotypic plasticity, or more slowly, via natural selection (Carlsson et al. 2009 and references therein). Alien species often become extremely abundant, outcompete and displace native prey species, and may eventually come to constitute the largest prey resource available to native predators. Native predators that feed on alien species will present a fitness advantage and might contribute to controlling both the abundance and distribution of alien species [START_REF] Carlsson | Native predators and exotic prey-an acquired taste?[END_REF]. For example, the alien European green crab (Carcinus maenas) is limited by the predation of two different native crab species, Callinectes sapidus in eastern North America [START_REF] Derivera | Biotic resistance to invasion: native predator limits abundance and distribution of an introduced crab[END_REF] and Cancer productus in southwestern North America [START_REF] Jensen | Biotic resistance to green crab, Carcinus maenas, in California bays[END_REF]). Thus, overharvesting native predators may compromise their ability to regulate invasive species either through predation, if the invasive species are of lower trophic levels, or through competition in the case of invasive and native species occupying the same trophic level.

Marine protected areas (MPAs), and particularly no-take marine reserves where extractive uses are not allowed, can be an effective tool for the recovery of large predatory fishes and the restoration of predatory relationships within their boundaries [START_REF] Shears | Marine reserves demonstrate top-down control of community structure on temperate reefs[END_REF][START_REF] Micheli | Trajectories and correlates of community change in no-take marine reserves[END_REF][START_REF] Guidetti | Marine reserves reestablish lost predatory interactions and cause community changes in rocky reefs[END_REF][START_REF] Bond | Reef sharks exhibit site-fidelity and higher relative abundance in marine reserves on the Mesoamerican Barrier Reef[END_REF]. A recent meta-analysis shows that the biomass of whole fish assemblages in no-take marine reserves is, on average, 6.7 times greater than in adjacent unprotected areas [START_REF] Sala | No-take marine reserves are the most effective protected areas in the ocean[END_REF]. This wide difference in biomass is primarily caused by the presence of large-bodied high-level predators inside marine reserves. The recovery of high-level predators in marine reserves and in other MPAs has the potential to control alien species spreading within their boundaries [START_REF] Francour | Mediterranean marine protected areas and nonindigenous fish spreading[END_REF]). In the Caribbean Sea, the density and biomass of the invasive lionfishes (Pterois volitans, P. miles) have been found to be lower in MPAs than in unprotected areas [START_REF] Mumby | Grouper as a natural biocontrol of invasive lionfish[END_REF][START_REF] Hackerott | Native predators do not influence invasion success of Pacific lionfish on Caribbean reefs[END_REF]). However, it remains unclear whether more and larger grouper inside the MPAs were able to control the lionfish populations [START_REF] Mumby | Grouper as a natural biocontrol of invasive lionfish[END_REF], or whether management measures adopted within MPAs, i.e. selective removal of lionfishes, was responsible for the lower values recorded therein [START_REF] Hackerott | Native predators do not influence invasion success of Pacific lionfish on Caribbean reefs[END_REF]. Experimental work that will complement observational studies is necessary to test the hypothesis of whether the restoration of high-level predators within MPAs and predator-driven biotic resistance can control biological invasions. So far, the available evidence is too limited to draw robust conclusions [START_REF] Burfeind | Performance of non-native species within marine reserves[END_REF][START_REF] Gelman | Assessing the effects of marine protected areas on biological invasions: a global review[END_REF].

Within this context, the Mediterranean Sea is a particularly interesting system because: 1) it has one of longest recorded histories of marine resources overexploitation in the world [START_REF] Guidetti | Ancient art serving marine conservation[END_REF], 2) high-level predators show clear signs of recovery in wellenforced Mediterranean MPAs (Garcia Rubies et al. 2013;[START_REF] Guidetti | Large-scale assessment of Mediterranean marine protected areas effects on fish assemblages[END_REF]Giakoumi et al. 2017), and 3) it is a marine bioinvasion hotspot [START_REF] Rilov | Marine bioinvasions in the Mediterranean Sea -history, distribution and ecology[END_REF], with approx. 1000 marine alien species recorded (Zenetos et al. 2012). The Mediterranean Sea is currently characterized by a paucity of top predators compared to historical times [START_REF] Ferretti | Loss of large predatory sharks from the Mediterranean Sea[END_REF]; nevertheless, in long-established well-enforced marine reserves, the populations of large piscivorous fishes have been found to recover [START_REF] Prato | The importance of high-level predators in marine protected area management: Consequences of their decline and their potential recovery in the Mediterranean context[END_REF], which could exert top-down control on both native and invasive alien fish populations. The aim of the present study, therefore, is to provide evidence on whether the restoration of high-level fish predator populations within Mediterranean MPAs can trigger top-down control on invasive alien fishes.

Methods

Experiment locations

To test the hypothesis of whether the restoration of top-down regulation inside no-take MPAs enables the control of the spread of alien fish species, fish tethering experiments were conducted to quantify relative predation rates inside the no-take zones of three MPAs and in adjacent unprotected areas (i.e. open to professional and recreational fishing, according to national legislation). Two MPAs were situated in the Western Mediterranean, the Cabo de Palos MPA in Spain and the Tavolara MPA in Italy (Fig. 1), where invasive fishes rarely occur [START_REF] Guidetti | Large-scale assessment of Mediterranean marine protected areas effects on fish assemblages[END_REF]Giakoumi et al. 2019a). The third MPA was situated in the Eastern Mediterranean, the Kaş -Kekova MPA in Turkey (Fig. 1), where invasive alien fishes are abundant (Giakoumi et al. 2019a). This experimental approach enabled us to reconcile the contrasting facts that while the oldest and most effective MPAs are situated in the Western Mediterranean, the species richness and abundance of invasive fishes is much higher in the Eastern Mediterranean due to more favorable environmental conditions [START_REF] Guidetti | Large-scale assessment of Mediterranean marine protected areas effects on fish assemblages[END_REF]Giakoumi et al. 2019a). Evidence from previous studies [START_REF] Guidetti | Large-scale assessment of Mediterranean marine protected areas effects on fish assemblages[END_REF][START_REF] Hackradt | Response of rocky reef top predators (Serranidae: Epinephelinae) in and around marine protected areas in the Western Mediterranean Sea[END_REF][START_REF] Giakoumi | Ecological effects of full and partial protection in the crowded Mediterranean Sea: a regional meta-analysis[END_REF]Giakoumi et al. , 2019a) ) shows that the biomass and size of high-level predators are higher inside the no-take zone of the selected MPAs than in adjacent unprotected areas.

The experiments were performed within a narrow time window, in August and September 2017, to minimize temporal effects.

Experimental design

For each combination of 'location' (Cabo de Palos, Kaş -Kekova, or Tavolara) and 'protection level' (no-take vs unprotected area), we deployed 18 replicates of tethering experimental units.

In each experimental unit, three dead specimens were tethered: two specimens of native species (the sardine Sardina pilchardus and the bogue Boops boops) and one specimen of an alien species (the marbled spinefoot Siganus rivulatus). The species selected are part of the diet of native and invasive high-level predators (Andarolo and Pipitone 1997; [START_REF] Marengo | A review of biology, fisheries and population structure of Dentex dentex (Sparidae)[END_REF]Lopez and i Orvay 2005;[START_REF] Kalogirou | Diet of the invasive piscivorous fish Fistularia commersonii in a recently colonized area of the eastern Mediterranean[END_REF][START_REF] Bariche | Diet composition of the Lessepsian bluespotted cornetfish Fistularia commersonii in the eastern Mediterranean[END_REF]. The size of all specimens used in the experiment ranged between 8 and 12 cm TL, and in each unit the size of specimens of the three species was roughly equal. Fishes were bought from fish markets and transported frozen to the experimental locations. Experimental units were deployed two hours before sunset as at that time of day, some high-level predators are known to be particularly active [START_REF] Harmelin-Vivien | Ichtyofaune des herbiers de Posidonies du Parc National de Port-Cros: I. Composition et variations spatio-temporelles[END_REF].

A subsample of experimental units was equipped with HD cameras to get footage of the predation events and general fish behavior around the tethered fish (see example in the video provided as supplementary material). Overall, six replicates of video recordings were deployed for each location and protection level combination. Although the replication of video recordings was low due to logistical constraints, this complementary approach enabled us to get more precise information on the predators' identity, behavior and time of arrival.

Statistical analyses

Tethered fish consumption

In situ visual observations of the tethered fish enabled us to assess their status, 120 min after the deployment of the experimental units, as either consumed (i.e. we did not recover anything or less than half the tethered specimen) or not consumed (i.e. we recovered the whole specimen or more than half the tethered specimen). This provided a basis for assessment of the relative consumption rate. Video recordings enabled us to assess the tethered fish status from the 1 st minute until the 90 th minute after deployment of the experimental unit. The duration of the video recordings was constrained by the autonomy of the camera battery. The tethered fish status based on the video footage was assessed as: (1) unvisited, (2) visited, (3) partially consumed, or (4) completely consumed. The two latter categories (partially and completely consumed) were grouped within the status 'consumed'.

Respectively, the visiting fish behaviors observed within the experimental setup (during the 90 minutes) were classified into four categories: (1) present (i.e. species present around the experimental setup without showing specific interest in the tethered fishes), ( 2) interested (i.e. species being specifically interested in one or more tethered fish), (3) partial consumer (i.e. species biting one or more tethered fish), ( 4) consumer (i.e. species eating completely a tethered fish). Examples of each visiting fish behavior type are provided in Supplementary Video S1. Overall, 54 hours of video footage were recorded and analyzed.

To compare the consumption rate of tethered specimens (using the data either from in situ visual observations or from the video recordings) among locations and between protection levels, we used Generalized Linear Models for Multivariate Binomial Data (Wang et al. 2012). Terms included in the models were the factor 'protection' (fixed, 2 levels: NTZ vs OUT), the factor 'location' (fixed, 3 levels: CAB, KAS, TAV) and the interaction term (twoway crossed design). The factor 'location' was fixed to allow for the comparison of patterns among the three locations distributed along a longitudinal gradient. Significance of terms was assessed using analyses of deviance. P-values were calculated using 999 resampling iterations via PIT-trap resampling (to account for correlation in testing). Models and tests were carried out using the mvabund R package [START_REF] Wang | Alien species in the Mediterranean Sea by 2012. A contribution to the application of European Union's Marine Strategy Framework Directive (MSFD). Part 2. Introduction trends and pathways[END_REF]. Binomial confidence intervals of probabilities (of tethered fish being consumed) were calculated using Bayesian inference [START_REF] Gelman | Assessing the effects of marine protected areas on biological invasions: a global review[END_REF] with the binom R package (Dorai-Raj 2014).

Predator arrival time and interaction with tethered fish

When collecting data from the video footages, we also recorded the exact time of the first presence (arrival time) of a species within the experimental setup (i.e. within the camera field of view), and the time of the first predator-tethered fish interaction (i.e. when a visiting fish was interested, or a partial consumer or a consumer). For these two metrics (time of arrival and time of interaction), we produced accumulation curves and boxplots of the number of species within 90 mins from the deployment of the experimental unit.

To compare the arrival time and the time of predator-tethered fish interaction between protection levels and among locations, we performed univariate and multivariate Permutational Multivariate Analysis of Variance (PERMANOVA). The response variables used in the multivariate tests were: 1) the number of fish species sighted in the camera field of view at least once within 30min, 60min, and 90min, and 2) the number of fish species observed to interact with a tethered specimen (or multiple specimens) at least once within 30min, 60min and 90min, distinguishing visiting fish species by trophic level. We also ran the second analysis exclusively for Kaş, categorizing visiting fish species by trophic level and origin (native vs alien). Univariate tests were carried out for each response variable (i.e. each time period) separately. Euclidean distance was used in all tests. The design was two-way crossed, with the factor 'protection' (fixed, 2 levels: NTZ vs OUT) and the factor 'location' (fixed, 3 levels: CAB, KAS, TAV). The factor 'location' was fixed to allow for the comparison of patterns among the three locations distributed along a longitudinal gradient.

Results

Tethered fish consumption

Analyses of both in situ visual data and video footage did not reveal statistically significant differences in the mean consumption rates of the three tethered fish species between no-take zones and unprotected areas (Tables 1 &2). Based on in situ visual observations, specimens of S. pilchardus presented the highest consumption rate in both protected and unprotected sites (Fig. 2). The video footage revealed that native species were selected (partially or completely consumed) first, regardless of protection status and location (Fig. 2).

Based on the in situ visual observations, the mean consumption rate differed across locations (Dev = 18.113, p = 0.021, Table 1). More specifically, the consumption of S. pilchardus (the most consumed species) differed according to the factor 'location' (Dev = 11.628, p = 0.014, Table 1), and was particularly high at Tavolara.

Based on the video footage, the consumption rate of a specimen (i.e. partially or completely consumed) also differed among locations (Table 2, Fig. 3). Specimens of the three species tend to have higher consumption rates at Kaş, regardless of the protection status. Yet, this was statistically significant only for B. boops. The consumption rate of B. boops was significantly higher at Kaş for all time periods examined (i.e. within first 30mins, 60mins, or 90mins; Table 2).

In consistency with the fact that alien fish have rarely been recorded in the Western Mediterranean, we found that the estimated consumption rates of the tethered fish by alien species differed markedly among locations, being very high at Kaş, whereas at Cabo de Palos and Tavolara it was almost null (Table 3, Fig. 4a). Conversely, estimated consumption rates of tethered fish by native species did not vary among locations, except for B. boops for which the probability of being consumed by a native species was higher at Tavolara and Kaş. As a result, at Kaş, the consumption rates of all tethered specimens by alien predators (especially alien low-medium level predators; non-overlapping confidence interval in Fig. 4) were higher than the consumption rates by native predator fishes.

Predator arrival time and interaction with tethered fish

High-level predator species accumulation was higher in the no-take zone of the MPAs than in unprotected areas (pseudo-F = 18.365, p = 0.0001, Table S1; Fig. 5a) and was higher at Cabo de Palos than in the other two locations (pseudo-F = 3.9444, p = 0.0175, Table S1; Fig. 5a).

Moreover, in all locations, high-level predator species accumulated (i.e. arrived within the camera's field of view) faster in MPAs than in unprotected areas (Table S1, Fig. 5a).

Generally, high-level predator richness was higher in MPAs than in unprotected areas (Fig. 5b). Conversely, low-and medium-level predator accumulation was higher and faster in unprotected areas at Cabo de Palos and Tavolara, whereas the opposite pattern was observed at Kaş (pseudo-F = 5.2553, p = 0.0213 for protection, pseudo-F = 8.7447, p = 0.0005 for location, and pseudo-F = 5.8936, p = 0.0033 for their interaction, Table S1, Fig. 6).

Overall, a total of 19 species interacted with the tethered fishes (i.e. were interested or partial consumers or consumers). The list of species as well as the respective estimated consumption rates are provided in Table 4 and Fig. S1. Out of these species, ten were high-level predators whereas the others were low-and medium-level predators. In accordance with the results mentioned above, more high-level predators interacted with the tethered fish inside the MPAs, whereas more low-and medium-level predators interacted with the specimens outside the MPAs (pseudo-F = 24.331, p = 0.0001 for factor 'protection', Table S2; Fig. 6a).

In the two western locations (Cabo de Palos and Tavolara), all visiting fish interacting with the specimens were native species. At Kaş (Eastern Mediterranean), alien species also interacted with the tethered specimens, two were high-level (Fistularia commersonii and Lagocephalus sceleratus) and two medium-level predators (Sargocentron rubrum and Torquigener flavimaculatus). At Kaş, native high-level predators interacted more with the tethered fish inside the MPA than in unprotected areas (Fig. S2) over the entire period of video recording (pseudo-F = 20.714, p = 0.0019) and for each time interval (within 30mins: pseudo-F = 10, p = 0.05; within 60mins: pseudo-F = 15, p = 0.01, pseudo-F = 15, p = 0.01).

Discussion

The present study did not reveal differences in the average consumption rates of tethered alien or native fishes between the no-take zones of MPAs and adjacent unprotected areas. However, we found that more high-level predators interacted with the tethered fish inside the MPAs, whereas more low-and medium-level predators interacted with the tethered specimens outside the MPAs. This observation reinforces findings of previous studies demonstrating that the density and biomass of high-level predators in the no-take zones of the MPAs considered herein is higher than in adjacent fished sites (e.g. [START_REF] Hackradt | Response of rocky reef top predators (Serranidae: Epinephelinae) in and around marine protected areas in the Western Mediterranean Sea[END_REF][START_REF] Guidetti | Large-scale assessment of Mediterranean marine protected areas effects on fish assemblages[END_REF]Giakoumi et al. 2019a). The so called 'reserve effect' (i.e. increasing levels of density and size of individuals inside the reserve) of the Cabo de Palos and Tavolara MPAs, is further supported by the fact that the accumulation of high-level predator species was higher and faster in the MPAs, whereas low-and medium-level predators' accumulation was higher and faster in unprotected areas. This was not the case at Kaş, where the density and biomass of high-level predators is much lower than in the two western MPAs. The Kaş -Kekova MPA is relatively new, as it was only designated in 2012, and enforcement mechanisms are not wellestablished yet (Giakoumi et al. 2019a). In this MPA, large piscivorous predatory populations might need more time and more effective protection in order to increase in numbers and individual size that will allow them to exert top-down control on native and alien prey. Furthermore, our study showed a preference towards the native S. pilchardus, which was consumed more in comparison to the other tethered fish, regardless of protection status and location. Nevertheless, alien rabbitfish specimens were consumed by native predators (mostly by Muraena helena but also by Dentex dentex) in the locations where the alien species has never or rarely been observed (i.e. Cabo de Palos and Tavolara). This indicates that some native predators can feed on the alien species probably without requiring an 'adaptive' timelag period (see [START_REF] Carlsson | Native predators and exotic prey-an acquired taste?[END_REF]). The fact that the tethered fish were dead specimens may explain partly why some other predators were interested in the alien specimens (as well as in the native tethered fish) but did not bite or consume them. Piscivorous fish have predation strategies that may involve live fish to be ambushed, chased, stalked and caught [START_REF] Hobson | Interactions between piscivorous fishes and their prey. Predator-prey systems in fisheries management[END_REF]; thus, dead fish may be less attractive. In the recordings, we observed individuals of the species Seriola dumerili and D. dentex 'blowing water' on the tethered fish, potentially to test whether the 'prey' would try to escape (watch video provided as supplementary material).

Moreover, some of the interested predators might need to slightly change their behavior, life history or morphology to incorporate alien species into their diet. Phenotypic plasticity can occur during the lifetime of an individual or across generations [START_REF] Padilla | A systematic review of phenotypic plasticity in marine invertebrate and plant systems[END_REF], and thus the potential for control of the alien population can occur either within short or longer time periods [START_REF] Carlsson | Native predators and exotic prey-an acquired taste?[END_REF]. In more southeastern locations in the Mediterranean Sea, such as Lebanon, where S. rivulatus has been present for almost a century [START_REF] Golani | Distribution of Lessepsian migrant fish in the Mediterranean[END_REF], specimens have been found as items in the stomachs of several native highlevel predator fishes including grouper (Epinephelus spp.), the greater amberjack (Seriola dumerili), and the bluefish (Pomatomus saltatrix) (Guidetti P. and Fatfat S., unpublished data). This evidence suggests that native predators could potentially exert predation pressure and regulate invasive fish populations.

The population of invasive alien species could also be regulated by the predatory activity of higher trophic level alien species that have been introduced in the recipient environment at the same or a different time period. According to the video recordings data, the consumption probability of the tethered specimen (both native and alien) differed across locations and was generally higher at Kaş, triggered by the predation activity of alien predators (especially, L. sceleratus and T. flavimaculatus). Evidence from studies exploring the difference in the impact of native and alien predators on native terrestrial vertebrates shows that alien predators can have a more severe impact on native species populations compared to native predators [START_REF] Salo | Alien predators are more dangerous than native predators to prey populations[END_REF]). In the marine environment, the invasive lionfish Pterois volitans appears to have a stronger ecological impact on native prey in northwestern Atlantic coral reefs than native piscivores of similar size [START_REF] Albins | Effects of invasive Pacific red lionfish Pterois volitans versus a native predator on Bahamian coral-reef fish communities[END_REF]. Our recordings demonstrate that the invasive pufferfish L. sceleratus and T. flavimaculatus are voracious predators that consume indistinctively native and alien fishes. These two species appear to be well adapted to their new environment, and their predation activity may have a major impact on both native and alien species in the host environment. Evidence shows that the high-level predator L. sceleratus can cause a major negative impact on native communities [START_REF] Kalogirou | Ecological characteristics of the invasive pufferfish Lagocephalus sceleratus (Gmelin, 1789) in the eastern Mediterranean Sea -a case study from Rhodes[END_REF], fisheries (Ünal et al. 2015) and human health [START_REF] Beköz | Consequences of the increasing prevalence of the poisonous Lagocephalus sceleratus in southern Turkey[END_REF]. Despite its negative ecological and socio-ecological impact, L. sceleratus could control other invasive species populations through predation or competition. The ability of L. sceleratus to resist the venom of its prey [START_REF] Kalogirou | Ecological characteristics of the invasive pufferfish Lagocephalus sceleratus (Gmelin, 1789) in the eastern Mediterranean Sea -a case study from Rhodes[END_REF]) makes it a fit predator for many invasive alien species, including rabbitfish and lionfish that are venomous. The cornet fish F. commersonii is another invasive high-level predator that feeds on rabbitfish, among other alien species [START_REF] Bariche | Diet composition of the Lessepsian bluespotted cornetfish Fistularia commersonii in the eastern Mediterranean[END_REF], and thus could exert control on alien species of lower trophic levels. Besides exploring the impact of alien high-level predators on native fishes, future research should also investigate the direct impact of alien high-level predators on alien species and associated trophic cascades (see [START_REF] Kindinger | Consumptive and non-consumptive effects of an invasive marine predator on native coral-reef herbivores[END_REF].

Our study presents some limitations in assessing the predation rates inside MPAs versus adjacent unprotected areas, and thus in providing evidence on whether the restoration of highlevel predator populations within Mediterranean MPAs can potentially exert top-down control on invasive alien fish. First, we fully acknowledge that this type of experiment cannot be used to estimate predation rates as they occur in nature, but rather to compare relative predation rates under different conditions; here, to compare predation rates in areas under different fishing regulations. Moreover, our experiment suffers from the bias associated with all tethering experiments regarding alterations in predator behavior and, most importantly, reduction in the effectiveness of the escape responses of the prey [START_REF] Aronson | Measuring predation with tethering experiments[END_REF][START_REF] Mills | Bias in lobster tethering experiments conducted for selecting low-predation release sites[END_REF]). In our experiment, these important sources of bias were even greater as the tethered fish were dead specimens. Logistical, legal, and ethical issues ruled out the use of living specimens; introducing living alien specimens into an MPA where the species does not occur would be at least reckless, if not unethical. The exposure time of the tethered fish might also have been shorter than appropriate, but logistical reasons (e.g. camera battery autonomy, transfer to remote locations, loss of equipment at sites with high diving activity) prevented us from further extending the duration of the experiment. Lastly, short-term snapshot studies may be insufficient to assess the long-term regulatory potential of native predators as there may be a long time-lag before native predators become effective at controlling an alien population [START_REF] Carlsson | Native predators and exotic prey-an acquired taste?[END_REF].

Despite its limitations, the present study contributes to a research topic -the relationships between MPAs and biological invasions -for which empirical evidence is scarce [START_REF] Burfeind | Performance of non-native species within marine reserves[END_REF][START_REF] Gelman | Assessing the effects of marine protected areas on biological invasions: a global review[END_REF]. Our finding that some native predators consumed specimens of S. rivulatus shows a potential ability of native predator populations to control certain alien species populations. The approach we followed, i.e. complementing the tethering experiments with video recordings, enabled us to observe species interactions that could be suggestive of potentially higher predation rates within MPAs. The higher density, size and biomass of high-level (including piscivorous) predators in the no-take zones of the MPAs than in adjacent unprotected sites (as documented by [START_REF] Hackradt | Response of rocky reef top predators (Serranidae: Epinephelinae) in and around marine protected areas in the Western Mediterranean Sea[END_REF][START_REF] Guidetti | Large-scale assessment of Mediterranean marine protected areas effects on fish assemblages[END_REF]Giakoumi et al. 2019a) can result from different predation behavior patterns and/or higher predation pressure (Vergès et al. 2012). The potential higher predation pressure exerted in the MPAs may lead to higher consumption of alien species within their boundaries than in unprotected areas. However, as there are plentiful and diverse food resources in well-enforced MPAs (especially in no-take zones), the native predators might prefer native over alien species (as our results indicate), and thus consume alien species in smaller quantities. To support or reject the hypothesis that higher predation pressure can trigger alien population control, experimental studies and stomach content analyses should be conducted examining prey preferences of native high-level predators. Finally, our findings suggest that the predation activity of alien predators may play an important role in shaping food webs in the host environment. Currently, evidence on the impact of invasive alien predators on both native and (particularly) alien species is very limited [START_REF] Katsanevakis | Impacts of invasive alien marine species on ecosystem services and biodiversity: a pan-European review[END_REF]). Filling such knowledge gaps is critical for the effective control of alien populations (Giakoumi et al. 2019b) and for marine conservation decision-making.

Fig. 1

 1 Fig. 1 Study locations. Two locations are situated in the Western Mediterranean, including the Cabo de Palos MPA in Spain and the Tavolara MPA in Italy. The third location is situated in the Eastern Mediterranean, including the Kaş -Kekova MPA in Turkey.

Fig. 2

 2 Fig.2Mean rate (and 95% confidence interval) of consumption of tethered fish 120 min after the experimental unit was deployed. The estimation of the consumption rate was based on in situ visual observations from the tethering experiment. The red line corresponds to values in the no-take zone (NTZ) of the MPAs and the turquoise line to values in unprotected areas (OUT). Refer to Table1for location and species abbreviations.

Fig. 3

 3 Fig. 3 Mean estimated rate (and 95% confidence interval) of a tethered fish being bitten within a) 30 minutes, b) 60 minutes, and c) 90 minutes after the experimental unit was deployed. The estimated rates were assessed based on video recording data. The red line corresponds to values in the no-take zone (NTZ) of the MPAs and the turquoise line to values in unprotected areas (OUT). Refer toTable 1 for location and species

Fig. 4

 4 Fig.4Mean probability (and 95% confidence interval) of a tethered fish being bitten within 90 minutes after the experimental unit was deployed a) distinguishing predators based on origin (alien vs native fish), and b) distinguishing predators based on origin and trophic level (high vs low-medium). The red line corresponds to alien species and the turquoise line to native species. Refer to Table1for location and species

Fig. 5

 5 Fig. 5 Fish arrival time in the camera field of view represented in a) species accumulation curves through time, and b) box plots of number of species after 90 min of video deployment. In both panel figures the predators are distinguished by trophic level (High vs Low-Medium trophic level predators), location (CAB, TAV, KAS) and protection level (no-take zone: NTZ, unprotected areas: OUT). Solid lines in (a) are smoothed conditional means (method LOESS), and grey envelopes are the 95% Confidence Intervals. Dashed lines are site-specific curves (see also Table1). The red

Fig. 6

 6 Fig. 6 Time of first predator -tethered fish interaction (predator approaching the tethered fish with eventual partial or complete consumption) represented by a) species accumulation curves through time, and b) Box Plots of number of species after 90 min of video deployment. In both panel figures the predators are distinguished by trophic

Table 2 :

 2 Analyses of DevianceTable of the multivariate and univariate Generalized Linear Model fits on the estimated rates of tethered fishes to be bitten (partially or completly consumed) within 30 minutes (upper panel), 60 minutes (central panel) and 90 minutes (lower panel). The multivariate GLM fit considers the 3 tethered fish species. Univariate fits consider one species at a time. Full tests and pairwise comparisons among pairs of levels of the Location factors. Refer to Table 1 for location and species abbreviations.

			Res. Df Df. diff		Dev	p	Dev	p	Dev	p	Dev	p
	LOCATION	105	2	18.113	0.021	5.917	0.116 11.628	0.014	0.568	0.729
	PROTECTION	104	1		2.194	0.541	1.129	0.642	0.687	0.671	0.379	0.671
	LOCATION X PROTECTION	102	2	13.009	0.091	3.549	0.411	1.203	0.586	8.256	0.080
	CAB vs TAV	70	2	15.049	0.003	3.339	0.143 11.551	0.002	0.159	0.704
	CAB vs KAS	70	2		8.129	0.075	5.623	0.064	2.379	0.230	0.127	0.782
	TAV vs KAS	70	2		4.475	0.243	0.322	0.688	3.585	0.180	0.568	0.688
						Multivariate	BOO.BOO.	SAR.PIL.	SIG.RIV.
			Res. Df Df. diff	Dev	p	Dev	p	Dev	p	Dev	p
		LOCATION	33	2	26.456	0.001 16.920	0.001	4.834	0.194	4.702	0.194
		PROTECTIO N	32	1	5.022	0.240	0.000	0.914	4.765	0.106	0.257	0.909
		LOCATION
	Within 30 min	X PROTECTIO N	30	2	2.616	0.779	1.928	0.743	0.494	0.920	0.194	0.920
		CAB vs TAV	22	2	4.379	0.304	1.247	0.561	0.178	0.706	2.955	0.319
		CAB vs KAS	22	2	24.327	0.003 15.407	0.001	4.332	0.089	4.589	0.089
		TAV vs KAS	22	2	11.853	0.028	8.795	0.020	2.805	0.221	0.254	0.635
		LOCATION	33	2	29.303	0.001 16.920	0.001	4.029	0.147	8.353	0.046
		PROTECTIO N	32	1	5.083	0.232	0.000	0.921	4.864	0.119	0.219	0.921
		LOCATION
	Within 60 min	X PROTECTIO N	30	2	3.084	0.675	1.928	0.699	1.030	0.776	0.126	0.776
		CAB vs TAV	22	2	4.201	0.323	1.247	0.563	0.000	0.904	2.955	0.330
		CAB vs KAS	22	2	26.773	0.001 15.407	0.002	3.104	0.084	8.263	0.015
		TAV vs KAS	22	2	13.759	0.009	8.795	0.015	3.104	0.190	1.860	0.190
		LOCATION	33	2	25.425	0.001 15.928	0.001	3.342	0.229	6.155	0.132
	Within 90 min	PROTECTIO N LOCATION	32	1	3.752	0.353	0.191	0.923	3.381	0.244	0.180	0.923
			X	30	2	5.441	0.500	1.286	0.751	1.498	0.751	2.657	0.637
		PROTECTIO

Table 3 :

 3 Analyses of DevianceTable of the multivariate and univariate Generalized Linear 616 Model fits on the estimated rates of tethered fish to be partially or completly consumed after 617 90 min. The multivariate GLM fit considers the 3 tethered fish species. Univariate fits 618 consider one species at a time. Full tests and pairwise comparisons among pairs of levels of 619 the Location factors. Refer to Table 1 for location and species abbreviations.

	620
					Multivariate		BOO.BOO.		SAR.PIL.		SIG.RIV.
			Res. Df	Df. diff	Dev	p	Dev	p	Dev	p	Dev	p
		LOCATION	33	2	79.259 0.001 31.727 0.001 31.727 0.001 15.805 0.001
	Alien	CAB vs TAV	22	2	<0.001 1.000 <0.001 1.000 <0.001 1.000 <0.001 1.000
		CAB vs KAS	22	2	53.932 0.001 21.788 0.001 21.788 0.001 10.357 0.005
		TAV vs KAS	22	2	53.932 0.001 21.788 0.001 21.788 0.001 10.357 0.006
		LOCATION	33	2	14.958 0.034 6.851 0.114 5.152 0.132 2.955 0.394
	Native	CAB vs TAV	22	2	2.959 0.478 2.403 0.436 0.168 0.797 0.387 0.797
		CAB vs KAS	22	2	5.963 0.096 1.430 0.304 3.104 0.127 1.430 0.304
		TAV vs KAS	22	2	13.946 0.005 6.351 0.044 4.641 0.052 2.955 0.112
	Alien
	High Trophic	LOCATION	33	2	6.890 0.154 0.000 1.000 4.635 0.093 2.255 0.191
	level
	Alien	LOCATION	33	2	71.430 0.001 31.727 0.001 26.992 0.001 12.711 0.002
	Low-Medium Trophic	CAB vs TAV CAB vs KAS	22 22	2 2	<0.001 1.000 <0.001 1.000 <0.001 1.000 <0.001 1.000 48.310 0.001 21.788 0.001 18.259 0.001 8.263 0.010
	level	TAV vs KAS	22	2	48.310 0.001 21.788 0.001 18.259 0.001 8.263 0.013
	Native
	High Trophic	LOCATION	33	2	9.269 0.226 4.635 0.340 2.955 0.410 1.680 0.739
	level
	Native	LOCATION	33	2	14.597 0.021 4.736 0.127 7.607 0.042 2.255 0.422
	Low-Medium Trophic	CAB vs TAV CAB vs KAS	22 22	2 2	3.346 0.397 1.247 0.758 0.670 0.758 1.430 0.758 5.237 0.065 1.430 0.156 3.807 0.076 -0.000 1.000
	level	TAV vs KAS	22	2	13.387 0.009 4.589 0.074 7.368 0.025 1.430 0.307

Table 4 :

 4 List of species that interacted with the tethered fish per site. Species are distinguished by their behavior i.e. whether they were interested in the tethered fish or were consumers (including both partial and full consumers), their trophic level (low & medium vs high), and their origin (N = native, A = alien).

		Cabo de Palos	Tavolara		Kaş
		Interested Consumer Interested	Consumer	Interested	Consumer
	Low & medium TL
	Diplodus annularis (N)	x	x	x	x
	Diplodus sargus (N)	x		x	x	x
	Diplodus vulgaris (N)	x		x	x	x
	Sargocentron rubrum (A)					x	x
	Serranus cabrilla (N)	x		x	x	x	x
	Serranus scriba (N)	x	x	x	x	x
	Sparus aurata (N)			x		x
	Spondyliosoma cantharus (N)	x		x	x
	Torquigener					x	x
	flavimaculatus (A)
	High TL
	Dentex dentex (N)	x	x	x
	Epinephelus costae (N)	x				x
	Epinephelus marginatus (N)	x		x		x
	Fistularia commersonii (A)					x
	Lagocephalus sceleratus (A)					x	x
	Muraena helena (N)	x	x	x	x	x	x
	Mycteroperca rubra (N)	x
	Pomatomus saltatrix (N)			x
	Seriola dumerili (N)	x		x		x
	Sphyraena sphyraena (N)	x		x		x

  Table 1 for location and species abbreviations.

  Table 1 for location and species abbreviations.

  Table 1 for location and species abbreviations.

  Table 1). The red colour corresponds to values in the no-take zone (NTZ) of the MPAs and the turquoise colour to values in unprotected areas (OUT). Refer to Table 1 for location and species abbreviations.

Acknowledgements

This work is a contribution of the project "PAVIS: Assessing the relationships between marine protected areas and invasive species" funded by the French National Agency for Research (Project No. ANR-16-ACHN-0016-01). We thank all the MPA authorities that granted permission to conduct fieldwork within their jurisdiction. Special thanks for operational and field assistance to V. Gerovasileiou, M.F. Huseyinoglu, Y. Arda, M. Draman, E. Desidera, A. Cuardos, and J.A. Garcia Charton. We also thank R. Stantz for inspiring the tethering experiment performed in this study.

level (High vs Low-Medium), location (CAB, TAV, KAS) and protection level (notake zone: NTZ, unprotected areas: OUT). Solid lines in (a) are smoothed conditional means (method LOESS), and grey envelopes are 95% Confidence Intervals. Dashed lines are site-specific curves (see also Table 2). The red colour corresponds to values in the no-take zone (NTZ) of the MPAs and the turquoise colour to values in unprotected areas (OUT). Refer to Table 1 for location and species abbreviations.


Agnes Beaugendre

Charlotte Lemesle

Séverine Bellayer

Stephanie Degoutin

Sophie Duquesne

Mathilde Casetta

Christel Pierlot

Fabian Jaime

Taejin Kim

Maude Jimenez

Elaheh Rohani Rad

Henri Vahabi

Agustin Rios De Anda

Dr Mohammad Reza Saeb

Prof. Sabu Thomas
email: sabuthomas@mgu.ac.in

Flame retardant and weathering resistant self-layering epoxy-silicone coatings for plastics

Keywords: Bio-based epoxy resin, Flame retardancy, Thermoset composites

Bio-epoxy versus conventional petroleum-based epoxy

Epoxy resins offer versatile integrated features such as outstanding mechanical properties, chemical resistance, and shape integrity in harsh conditions. These functional properties are the result of a crosslinked 3D network obtained by the chemical reaction between an epoxy monomer and a curing agent [START_REF] Jin | Synthesis and application of epoxy resins: A review[END_REF][START_REF] Fink | 3 -Epoxy Resins[END_REF]. The use of epoxy thermosets has been surged over the last decade in a wide range of applications such as coatings, adhesives, solar cells, electronic apparels, as well as in automotive and aerospace industries [START_REF] Kothmann | Fatigue crack propagation behaviour of epoxy resins modified with silica-nanoparticles[END_REF][START_REF] Kenig | Processing of Polymer Nanocomposites[END_REF]. Such applications are expected to receive more attention in the near future. Petroleum-based diglycidyl ether bisphenol A (DGEBA) accounts for ca. 90% of the epoxy resin worldwide usage. This monomer is produced from the reaction between bisphenol A (BPA) and epichlorohydrin (ECH) in sodium hydroxide media (NaOH) [START_REF] Shibata | Fully biobased epoxy resin systems composed of a vanillin-derived epoxy resin and renewable phenolic hardeners[END_REF]. Although DGEBA displays fascinating properties such as chemical resistance, good adhesion, and superior mechanical properties, the use of this monomers encounters several barriers [START_REF] Kumar | Synthesis and characterization of petroleum and biobased epoxy resins: a review[END_REF] summarized as follows:

(I)

It has been proved that DGEBA has severed effects on living organisms due to the toxicity of BPA [START_REF] Huang | Bisphenol A (BPA) in China: a review of sources, environmental levels, and potential human health impacts[END_REF]. Since BPA has been involved in the manufacture of many products, especially in epoxy resin thermosets, concerns about exposure to high dosages of BPA that might be harmful for human have consequently risen. Given this, legislation in many countries has banned use of BPA in infant-related products [START_REF] Valentino | Bisphenol A environmental exposure and the detrimental effects on human metabolic health: is it necessary to revise the risk assessment in vulnerable population?[END_REF].

(II) From an economic point of view, as DGEBA is derived from petroleum, it has experienced a rise in raw materials prices that have had a negative effect on the market.

(III) Emitted CO2 from fossil fuels is the major suspect for recent global warming, which has encouraged researchers to substitute petroleum-based products with renewable green products. In addition, unreacted BPA might be released during products production and ageing, and hence be rejected to the environment. [START_REF] Corrales | Global assessment of bisphenol A in the environment: review and analysis of its occurrence and bioaccumulation[END_REF].

Thus, taking into consideration of the worldwide volume of DGEBA usage, a great deal of work has been devoted to explore bio-based epoxy resins from renewable resources such as plant oils [START_REF] Das | Vegetable oil-based flame retardant epoxy/clay nanocomposites[END_REF][START_REF] Jin | Thermomechanical behavior of epoxy resins modified with epoxidized vegetable oils[END_REF], lignin [START_REF] Malutan | Lignin modification by epoxidation[END_REF], rosin acids [START_REF] Atta | Epoxy resins from rosin acids: synthesis and characterization[END_REF], tannins [START_REF] Benyahya | Functionalized green tea tannins as phenolic prepolymers for bio-based epoxy resins[END_REF], cardanol [START_REF] Kanehashi | Preparation and characterization of cardanol-based epoxy resin for coating at room temperature curing[END_REF], and itaconic acid [START_REF] Ma | Bio-based epoxy resin from itaconic acid and its thermosets cured with anhydride and comonomers[END_REF] to replace traditional petroleum-based DGEBA. Rapid development in the synthesis of bio-epoxy resins and their outstanding characteristics nominate them as powerful building blocks to possible overtake commercial DGEBA market [START_REF] Chrysanthos | Preparation and properties of bio-based epoxy networks derived from isosorbide diglycidyl ether[END_REF][START_REF] Aouf | Multi-functionalization of gallic acid. Synthesis of a novel bio-based epoxy resin[END_REF]. In terms of curing potential, substantial attempts have been made in our group to define, quantify, and explain mechanism of network formation in thermoset systems [START_REF] Saeb | Highly curable epoxy/MWCNTs nanocomposites: an effective approach to functionalization of carbon nanotubes[END_REF][START_REF] Saeb | Cure kinetics of epoxy nanocomposites affected by MWCNTs functionalization: a review[END_REF][START_REF] Puglia | Cure kinetics of epoxy/MWCNTs nanocomposites: isothermal calorimetric and rheological analyses[END_REF]. However, potential curability of bio-epoxy resins are lower than the commercial DGEBA, which needs to be studied because of the fact that almost the whole ultimate properties of thermosets strongly depend on the epoxy curing state [START_REF] Sari | Epoxy/starch-modified nano-zinc oxide transparent nanocomposite coatings: A showcase of superior curing behavior[END_REF][START_REF] Rastin | Transparent nanocomposite coatings based on epoxy and layered double hydroxide: Nonisothermal cure kinetics and viscoelastic behavior assessments[END_REF]. Analysis of mechanical properties revealed that bio-epoxy resins derived from rigid chemical structures such as diphenolic acid, rosin acid, and 2,5furandicarboxylic acid (FDCA) show mechanical properties comparable to DGEBA [START_REF] Deng | Synthesis and properties of a bio-based epoxy resin from 2, 5-furandicarboxylic acid (FDCA)[END_REF][START_REF] Liu | Preparation of a bio-based epoxy with comparable properties to those of petroleum-based counterparts[END_REF].

However, natural oil-based resins display inferior mechanical and thermal properties due to their long aliphatic chains, and because of their lower crosslinking density [START_REF] Liu | Preparation of a bio-based epoxy with comparable properties to those of petroleum-based counterparts[END_REF]. Furthermore, it was documented that the analysis of kinetics of epoxy curing provides a practical tool to compare the reactivity of bio-epoxy monomers with flame retardant additives [START_REF] Mashouf Roudsari | Study of the curing kinetics of epoxy resins with biobased hardener and epoxidized soybean oil[END_REF]. Flame Retardancy Index was recently defined to quantitatively study flame retardancy potential of polymer composites, but revisiting must be applied for inherently bio-epoxy systems [START_REF] Vahabi | Flame Retardancy Index for Thermoplastic Composites[END_REF].

Incorporation of flame retardant additives impedes the curing reaction and consequently lower the matrices' mechanical properties. Such an influence can also be detected by another useful criterion, namely Cure Index [START_REF] Jouyandeh | Cure Index' for thermoset composites[END_REF].

Table 1 presents the main class of bio-based epoxy resins derived from sustainable resources.

Overall, epoxy resins derived from renewable resources benefit from identical properties to those of commercial DGEBA, while eliminating the environmental and production drawbacks. However, like petroleum-based epoxies, bio-epoxy resins suffer from high flammability, which is a crucial prerequisite for many applications such as transportation, construction, and electronic appliances [START_REF] Vahabi | Flame retardant epoxy/halloysite nanotubes nanocomposite coatings: Exploring low-concentration threshold for flammability compared to expandable graphite as superior fire retardant[END_REF][START_REF] Vahabi | Short-lasting fire in partially and completely cured epoxy coatings containing expandable graphite and halloysite nanotube additives[END_REF][START_REF] Rakotomalala | Recent developments in halogen free flame retardants for epoxy resins for electrical and electronic applications[END_REF][START_REF] Perret | Novel DOPO-based flame retardants in high-performance carbon fibre epoxy composites for aviation[END_REF][START_REF] Wang | Flame retardancy and thermal degradation mechanism of epoxy resin composites based on a DOPO substituted organophosphorus oligomer[END_REF]. Overall, two strategies can be used to achieve an adequate level of flame retardancy performance.

(I)

The starting of using epoxy monomers with high char content and low combustion energy, which impart flame retardancy to the structure of epoxy building blocks [START_REF] Benyahya | Functionalized green tea tannins as phenolic prepolymers for bio-based epoxy resins[END_REF].

(II)

The strategy of incorporation of flame retardant (FR) to the epoxy matrix is based on chemical bonding of FR's to epoxy monomers or physical blending with epoxy resins [START_REF] Ménard | Synthesis of biobased phosphoruscontaining flame retardants for epoxy thermosets comparison of additive and reactive approaches[END_REF]. Even if the physical blending of FR's is still a cheaper method from an industrial point of view, it remains challenging due to the difference in chemical structures between the FR's and the epoxy matrix. This leads to poor miscibility and difficult handling of the epoxy filled with flame retardant formulations [START_REF] Lligadas | Development of novel phosphorus-containing epoxy resins from renewable resources[END_REF]. In addition, migration or leaching of FR's during life cycle, as well as a negative effect of additives on the epoxies crosslinking density [START_REF] Vahabi | Short-lasting fire in partially and completely cured epoxy coatings containing expandable graphite and halloysite nanotube additives[END_REF] and consequently a loss of mechanical properties remain as unresolved issues. However, a means to overcome all these issues is to chemically bond FR's to epoxy monomers so as to obtain captive FR's in the polymer network.

In addition, two parallel fields of research, as regards the development of the bio-based epoxy resin and the bio-based flame retardant are at cutting edge. Thus, both approaches need to meet on a common ground to benefit the design of fully bio-epoxy resins with high biomass content [START_REF] Costes | Bio-based flame retardants: When nature meets fire protection[END_REF][START_REF] Ménard | From a bio-based phosphoruscontaining epoxy monomer to fully bio-based flame-retardant thermosets[END_REF][START_REF] Mauldin | Synthesis and characterization of isosorbide-based polyphosphonates as biobased flame-retardants[END_REF][START_REF] Marosi | Fire-retardant recyclable and biobased polymer composites[END_REF][START_REF] Liang | Recent developments in flame retardant polymeric coatings[END_REF]. However, to the best of our knowledge, only few works reported the synthesis of fully bio-epoxy resins with flame retardancy properties. In this sense, this short mini-review aims to highlight the current development of flame retardant bio-based epoxy resins. Even though several review papers have been published to cover the bio-based epoxy resin [START_REF] Kumar | Synthesis and characterization of petroleum and biobased epoxy resins: a review[END_REF][START_REF] Ramon | A Review of Recent Research on Bio-Based Epoxy Systems for Engineering Applications and Potentialities in the Aviation Sector[END_REF] and bio-based flame retardants [START_REF] Hobbs | Recent Advances in Bio-Based Flame Retardant Additives for Synthetic Polymeric Materials[END_REF], the area of inherently flame retardant epoxy resins from sustainable resources remains largely intact.

Table 1. Chemical structure and main sources of bio-epoxy resins [START_REF] Ramon | A Review of Recent Research on Bio-Based Epoxy Systems for Engineering Applications and Potentialities in the Aviation Sector[END_REF]. Cone calorimetry and burning analysis of TPEU-EP provided concrete evidence for potential application of TPEU-EP as an alternative for DGEBA of the synthesis route of TPEU-EP was economic-friendly for large scale production. Literature survey suggests that synthesis of flame retardant bio-epoxy experiences an early stage flourishing period, while chemically embedded FR elements in bio-epoxy were alternatives for inherent flame retardant bio-epoxy.

Class

FR elements chemically embedded in bio-epoxy backbone

Silicon-containing FR

Silicon compounds improve flame retardancy of epoxy resins as a result of formation of residue in the condensed phase as well as the presence of radicals in vapour phase [START_REF] Kausar | Recent developments in different types of flame retardants and effect on fire retardancy of epoxy composite[END_REF][START_REF] Wang | Characterization and properties of new siliconecontaining epoxy resin[END_REF][START_REF] Franchini | Influence of POSS structure on the fire retardant properties of epoxy hybrid networks[END_REF]. Li et al. [START_REF] Li | Biobased epoxy resin with low electrical permissivity and flame retardancy: from environmental friendly high-throughput synthesis to properties[END_REF] linked epoxidized eugenol bio-epoxy (EPEU) with silicon-containing bridges with different lengths and chemical structures. It was found that the flammability of the prepared silicon-containing bio-epoxy resin was significantly improved in comparison to the commercial DGEBA. The value of LOI reported for DGEBA was 22.8%, which was improved up to 31% for phenyl siloxane-containing bio-epoxy resins. This was explained by the carbonation of phenyl groups as well as the migration of Si-O to the surface, which formed an ablative layer that avoided the penetration of oxygen and fuel through the combustion layer. Moreover, the viscosity of the prepared silicon-containing bio-epoxy decreased when the length of siloxane linker increased, which eased epoxy curing reaction.

The authors did not report on the mechanical and thermal properties of the prepared systems.

Phosphorous-containing FR

There are numerous works reporting the flame retardancy effect of phosphorous-containing compounds, which mainly benefit from char formation in the condensed phase [START_REF] Kausar | Recent developments in different types of flame retardants and effect on fire retardancy of epoxy composite[END_REF][START_REF] Velencoso | Molecular firefighting-how modern phosphorus chemistry can help solve the challenge of flame retardancy[END_REF].

Menard et al. [START_REF] Ménard | From a bio-based phosphoruscontaining epoxy monomer to fully bio-based flame-retardant thermosets[END_REF] embedded diglycidyl mono-phosphonated phloroglucinol reactive flame retardant derived from renewable resources of phloroglucinol in triglycidyl phloroglucinol (P3EP), and reported that the phosphorous flame retardant embedded in P3EP deteriorated thermal stability of epoxy resin; Such a behavior was explained by the plasticizing role of the flame retardant. However, the flammability of phosphorous flame retardants embedded in bio-epoxy was improved significantly, as confirmed by pyrolysis combustion flow calorimetry (PCFC) data together with char content measurements. Nevertheless, it should be noticed that the complementary flammability tests were principally needed to be conducted for this system to fully comprehend the flame behaviour of system.

Elsewhere [START_REF] Ma | Synthesis and properties of phosphorus-containing bio-based epoxy resin from itaconic acid[END_REF], a phosphorus-containing bio-epoxy resin (EADI) was prepared based on itaconic acid (IA) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO), then it was used as bio-based flame retardant in DGEBA system. Mechanical and thermal properties of DGEBA/EADI were found to be as good as those of DGEBA systems, with a significant improvement flame retardancy in of bio-based system in terms of LOI, char content and burning time.

In search for bio-epoxy resins, Lligadas et al. [START_REF] Lligadas | Development of novel phosphorus-containing epoxy resins from renewable resources[END_REF] synthesized two different epoxidized monomers including 10-undecenoyl triglyceride (UDTGE) and methyl 3,4,5-tris(10undecenoyloxy) benzoate (UDBME) from fatty acids. To improve their flame retardancy properties,10-[2',5'-bis(9-oxiranyl-nonayloxy)phenyl]-9,10-dihydro-9-oxa-10phosphaphenanthrene-10 oxide (DOPO-III) and bis(m-aminophenyl) methylphosphine oxide (BAMPO) were added to the structure of epoxy resin as flame retardant and curing agent, respectively. It was found that the Tg of UDBME-based resin was higher than that of UDTGE due to the presence of aromatic groups in the chemical structure of UDBME. However, Tg decreased upon addition of phosphorous-containing FR due to a lower crosslinking density.

From a flammability point of view, LOI values and charring residue were both improved upon addition of phosphorous-containing DOPO-III and BAMPO. However, more accurate and reliable tests were required to fully analyse the flame behavior performance of the proposed system.

Concluding remarks and recommendations for future works

DGEBA is the most sought epoxy resin in industrial applications thanks to its remarkable features. However, high volume usage of this monomer in various applications has risen increasing environmental concerns. By contrast, bio-epoxy resins produced from sustainable resources promise a green alternative for DGEBA. Such resins possess comparable properties to commercial DGEBA in terms of mechanical and thermal properties. Yet, bio-based epoxy resins suffer from high flammability, which jeopardize their potential application in many technical fields. Flammability of bio-epoxy resins has been addressed mainly through the incorporation of flame retardant elements or synthesis of bio-epoxy monomers with high char yield.

Up to date, seldom investigations have highlighted the flammability of bio-epoxy resins, which are summarized in Table 2. For most cases, inadequate flame resistance of the proposed bio-epoxy systems has been highlighted by the investigators, which needs further investigations. On the other hand, flame retardancy of polyphenols derived from sustainable resources offer a great potential for fabrication of fully bio-epoxy resin, and this deserve to be considered for future works. For instance, Qi et al. [START_REF] Qi | Epoxidized soybean oil cured with tannic acid for fully bio-based epoxy resin[END_REF] cured epoxidized soybean oil (ESO)

with Tannic acid (TA) and histidine (His) as the curing agent and accelerator, respectively.

The curing reaction between ESO and TA is relatively slow, but the addition of His improves the curing rate significantly, which was evident by nonisothermal analysis of curing kinetics.

In addition, ESO/TA resins are thermally stable with an initial decomposition at 270 °C.

However, the flame behaviour of this system has not been fully addressed yet. We believe that polyphenols with numerous hydroxyl groups provide a great substrate to link with the listed bio-epoxy resins observed in Table 1. Thus, this mini-review has aimed its focus on the importance of the study and development of fully bio-epoxy resins with fire retardancy properties by highlighting the importance of synthesis of flame resistant bio-epoxy resins.

2 .

 2 Inherently flame retardant bio-epoxy resinsSynthesis of flame retardant bio-epoxy resins from renewable resources capable of giving adequate mechanical properties, comparable to that of DGEBA is of a prime importance in developing bio-based formulations.Miao et al.[START_REF] Miao | Biobased heat resistant epoxy resin with extremely high biomass content from 2, 5-furandicarboxylic acid and eugenol[END_REF] compared the flammability of bio-based bis(2-methoxy-4-(oxiran-2ylmethyl)phenyl)furan-2,5-dicarboxylate (EUFU-EP) with the commercial DGEBA cured with methyl hexahydrophthalic anhydride (MHHPA) in terms of time to ignition (TTI), peak of heat release rate (pHRR) and total heat release (THR). Aside from identical TTI values for both systems, EUFU-EP had lower pHRR and THR values, which were indicative of higher flame retardancy performance for EUFU-EP. This was mainly explained by the presence of a packed aromatic structure in EUFU-EP resin, which reflected in higher char content and glass transition temperature (Tg). Although the crosslinking density of EUFU-EP/MHHPA was lower than that of the EUFU-EP/MHHPA system, the mechanical properties of EUFU-EP/MHHPA were improved due to the presence of furan and aromatic structures in the EUFU-EP backbone.Likewise, Dai et al.[START_REF] Dai | High-performing and fire-resistant biobased epoxy resin from renewable sources[END_REF] revealed that bio-based diglycidyl ether of daidzein (DGED) cured with 4,4'-diaminodiphenylmethane (DDM) was more reactive than the petroleum-based DGEBA. Such a higher reactivity was attributed to the additional unsaturated double bonds in DGED structure involved in the course of curing reaction. Consequently, the viscosity of DGED increased faster than that of DGEBA and; thus, the thermo-mechanical properties of DGED/DDM stand over DGEBA/DDM systems. From the flammability point of view, DGED formed char at the surface during combustion, which protected the bottom layers form heat transfer leading to self-extinguish in just 3 s with a very smaller flame. Since no complementary flame tests such as cone calorimetry were conducted, it appears difficult to understand the flame behaviour of the proposed system taking into account the resistance of material contributed from condensed phase.Wan et al.[START_REF] Wan | A sustainable, eugenol-derived epoxy resin with high biobased content, modulus, hardness and low flammability: synthesis, curing kinetics and structure-property relationship[END_REF] synthesized bio-epoxy resins by making linked two eugenol molecules together followed by epoxidation of terminal groups (DEU-EP), which resulted in a product with very high bio-based content of ca. 70 wt.%. This monomer was cured with DDM. The authors studied cure kinetics mechanism of bio-epoxy using model-free isoconversional approach and reported that addition of eugenol building blocks in the chain backbone as well as and their arrangement greatly affected cure behavior of DEU-EP/DDM systems. As a result, mechanical properties and high-temperature charring ability and flammability resistance were enhanced. It was also reported that DEU-EP/DDM resin left 38% char at 800 °C, which was almost twice the amount left by the DGEBA/DDM system. Moreover, pHRR (201 kW/m 2 ) and THR (16.3 kJ/m 2 ) for DEU-EP were much lower than the values obtained for DGEBA. Eventually, self-extinguishing DEU-EP was attained in 10 s, which proved an inherent flame retardancy behavior. However, the storage modulus of DEU-EP dropped suddenly at higher temperatures where glass transition temperature occurred at 114 °C due to an increase in free volume and molecular mobility of DEU-EP polymer chains. Later, this group[START_REF] Wan | A novel biobased epoxy resin with high mechanical stiffness and low flammability: synthesis, characterization and properties[END_REF] developed eugenol-based bifunctional epoxy resins (TPEU-EP) with improved flame retardancy thanks to the full aromatic ester backbone of TPEU-EP. Despite lower crosslinking density of TPEU-EP compared to commercial DGEBA, an enhanced mechanical property was observed, which again was attributed to the aromatic structure of TPEU-EP.