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Ciguatoxins (CTXs), potent neurotoxins produced by dinoflagellates of the genera Gambierdiscus and Fukuyoa, accumulate in commonly consumed fish species, causing human ciguatera poisoning. Field collections of Pacific reef fish reveal that consumed CTXs undergo oxidative biotransformations, resulting in numerous, often toxified analogs. Following our study showing rapid CTX accumulation in flesh of an herbivorous fish, we used the same laboratory model to examine the tissue distribution and metabolization of Pacific CTXs following long-term dietary exposure. Naso brevirostris consumed cells of Gambierdiscus polynesiensis in a gel food matrix over 16 weeks at a constant dose rate of 0.36 ng CTX3C equiv g−1 fish d−1. CTX toxicity determination of fish tissues showed CTX activity in all tissues of exposed fish (eight tissues plus the carcass), with the highest concentrations in the spleen. Muscle tissue retained the largest proportion of CTXs, with 44% of the total tissue burden. Moreover, relative to our previous study, we found that larger fish with slower growth rates assimilated a higher proportion of ingested toxin in their flesh (13% vs. 2%). Analysis of muscle extracts revealed the presence of CTX3C and CTX3B as well as a biotransformed product showing the m/z transitions of 2,3-dihydroxyCTX3C. This is the first experimental evidence of oxidative transformation of an algal CTX in a model consumer and known vector of CTX into the fish food web. These findings that the flesh intended for human consumption carries the majority of the toxin load, and that growth rates can influence the relationship between exposure and accumulation, have significant implications in risk assessment and the development of regulatory measures aimed at ensuring seafood safety.

Harmful algal blooms (HABs) are natural events that can also be fostered by anthropogenic pressures on aquatic ecosystems. Some HABs affect aquatic fauna (including wild and cultured fish and the habitat) with subsequent impacts on human well-being. Other HABs are caused by species producing natural toxins that cause human health problems due to the ingestion of contaminated seafood, direct contact with water, or inhalation of the aerosolized toxins. Monitoring the HAB causative organisms and their toxins is essential for deciding closures of harvesting and commercialization of sea products or allowing access to beaches in order to avoid human illness. Interdisciplinary research contributes to predictions of the occurrence of many blooms. Time series analyses indicate that some HABs may increase and intensify with global change in certain areas. The sustainable use of natural resources is mandatory to minimize this trend, for the health of humanity and the oceans

In comparison to planktonic species, the distribution and ecology of harmful benthic dinoflagellates (BHABs) are poorly understood. Much of this uncertainty is attributable to the complex habitats in which benthic dinoflagellates live – neither suspended in the water column nor buried in the sediment. The benthic species are instead associated with three-dimensional biotic and abiotic substrates or with the sediment–water interface (Figure 3.1). Two genera of BHABs are of special concern because they produce toxins that affect marine food-webs and human health. The increased numbers of adverse incidents associated with both Gambierdiscus and Ostreopsis species have generated strong research interests since the beginning of the twenty-first century, particularly with regard to taxonomy, toxin characterization and protocols for cell-based monitoring systems. Information on species, toxins and cell abundance can serve as early warnings of human health risks

Gambierdiscus and Fukuyoa dinoflagellates produce a suite of secondary metabolites, including ciguatoxins (CTXs), which bioaccumulate and are further biotransformed in fish and marine invertebrates, causing ciguatera poisoning when consumed by humans. This study is the first to compare the performance of the fluorescent receptor binding assay (fRBA), neuroblastoma cell-based assay (CBA-N2a), and liquid chromatography tandem mass spectrometry (LC-MS/MS) for the quantitative estimation of CTX contents in 30 samples, obtained from four French Polynesian strains of Gambierdiscus polynesiensis. fRBA was applied to Gambierdiscus matrix for the first time, and several parameters of the fRBA protocol were refined. Following liquid/liquid partitioning to separate CTXs from other algal compounds, the variability of CTX contents was estimated using these three methods in three independent experiments. All three assays were significantly correlated with each other, with the highest correlation coefficient (r2 = 0.841) found between fRBA and LC-MS/MS. The CBA-N2a was more sensitive than LC-MS/MS and fRBA, with all assays showing good repeatability. The combined use of fRBA and/or CBA-N2a for screening purposes and LC-MS/MS for confirmation purposes allows for efficient CTX evaluation in Gambierdiscus. These findings, which support future collaborative studies for the inter-laboratory validation of CTX detection methods, will help improve ciguatera risk assessment and management.

In small islands, the potential for new coastal activities and management options are often spatially limited. To reduce dependence on external factors and increase the resilience of populations to global changes and fluctuations in international markets, a recommended pathway is to diversify activities. We used a systematic prioritization tool with single and multiobjective zoning to explore the feasibility of scenarios at various levels of spatial diversification in the Gambier lagoon (French Polynesia), where black pearl culture is economically and spatially dominant. Local managers are committed to economic, livelihood, and environmental sustainability and agree that prioritizing both artisanal fisheries, which provide local food security, and ecosystem conservation should also be considered. Diversification options included the optimized reallocation of farming concessions and the identification of different types of conservation areas while taking into account traditional management areas. The scenarios were set to minimize surface areas and loss of access to existing fishing grounds. The solutions were compared between the scenarios with different cost metrics, allowing further discussions with stakeholders and managers. The Gambier case study shows that exploring diversification options in small islands using systematic prioritization tools can provide local managers with tailor-made plans adapted to island development questions

Ciguatera poisoning (CP) results from the consumption of coral reef fish or marine invertebrates contaminated with potent marine polyether compounds, namely ciguatoxins. In French Polynesia, 220 fish specimens belonging to parrotfish (Chlorurus microrhinos, Scarus forsteni, and Scarus ghobban), surgeonfish (Naso lituratus), and groupers (Epinephelus polyphekadion) were collected from two sites with contrasted risk of CP, i.e., Kaukura Atoll versus Mangareva Island. Fish age and growth were assessed from otoliths’ yearly increments and their ciguatoxic status (negative, suspect, or positive) was evaluated by neuroblastoma cell-based assay. Using permutational multivariate analyses of variance, no significant differences in size and weight were found between negative and suspect specimens while positive specimens showed significantly greater size and weight particularly for E. polyphekadion and S. ghobban. However, eating small or low-weight specimens remains risky due to the high variability in size and weight of positive fish. Overall, no relationship could be evidenced between fish ciguatoxicity and age and growth characteristics. In conclusion, size, weight, age, and growth are not reliable determinants of fish ciguatoxicity which appears to be rather species and/or site-specific, although larger fish pose an increased risk of poisoning. Such findings have important implications in current CP risk management programs.

Blooms of the benthic genus Ostreopsis are increasing from tropical to temperate latitudes, becoming recurrent in some beaches (especially in the Mediterranean coasts) and appearing in new zones. The main threats posed by Ostreopsis blooms on human health include respiratory and other problems associated with the aerosolization of toxic compounds produced by Ostreopsis, and potential (not clarified yet) food borne poisoning. To prevent the impacts on human health, scientists, stakeholders, and public authorities have been coordinating efforts in different Mediterranean countries via the International Agreement RAMOGE to monitor Ostreopsis blooms in summer periods. The gained knowledge and successful experience constitute an Early Warning System that can be translated to other BHAB cases

The increased numbers of adverse incidents associated with benthic harmful algae blooms (BHABs) has generated strong research interests in the last decade and calls for early warning system that provide warnings and reduce risk to human health. The complex habitats of BHABS make many detection methods difficult or unfeasible so case studies of bloom management, like the one we present here, are especially helpful