In France, the presence of marine microalgae of the genus Ostreopsis has been identified repeatedly on the Mediterranean coast for several years, whereas on the French Basque coasts its presence is much more recent. In the summers of 2021 and 2022, major Ostreopsis flowering episodes were reported on the Basque coast, resulting in several hundred cases of intoxication among holidaymakers and residents. The main route of human exposure is inhalation of aerosols, although it is not yet known whether the agents responsible for poisoning are Ostreopsis cells, cell debris, known toxins produced by Ostreopsis, or other as yet unidentified compounds. Other routes of exposure (dermal contact, eye contact, ingestion of contaminated water or seafood) are also possible. Poisoning is manifested through various signs and symptoms, occurring within 48 hours of exposure (Neurosensory and neurological, respiratory, dermal and digestive). This document presents the opinion of the French Agency for Food, Environmental and Occupational Health & Safety (ANSES), established from the work of its WATER and ERCA Expert Committees. ANSES received a request from the Directorate General for Health (DGS) and the Directorate General for Food (DGAL) to update knowledge about Ostreopsis that had been reported in the Agency's opinions from 2007 and 2008 (ANSES, 2007 and 2008), and draw up specific recommendations for managing Ostreopsis proliferation on the Basque coast. The literature review conducted as part of this expert appraisal revealed that knowledge about the genus Ostreopsis (diversity, biology, ecology, toxins produced) is still too fragmentary to characterise the hazard and risk to human health. Nevertheless to help local authorities affected by Ostreopsis blooms, Agency proposes a surveillance and quality monitoring strategy based on collaboration between site managers and the regional health agencies (ARSs), applicable to sites currently subject to bathing water quality monitoring and water sports sites that meet the conditions below.

In April and May of 2020, a large phytoplankton bloom composed primarily of the dinoflagellate Lingulodinium polyedra reached historic levels in geographic expanse, duration, and density along the coast of southern California, United States, and Baja California Norte, Mexico. Here, we report the water quality parameters of dissolved oxygen and pH over the course of the red tide, as measured by multiple sensors deployed in various locations along San Diego County, and document the extent of mass organism mortality using field surveys and community science observations. We found that dissolved oxygen and pH corresponded with bloom dynamics, with extreme hypoxic and hyperoxic conditions occurring at multiple locations along the coast, most notably within select estuaries where dissolved oxygen reached 0 mg L−1 and hypoxia occurred for up to 254 consecutive hours, as well as along the inner shelf of the open coast where dissolved oxygen dropped as low as 0.05 mg L−1. Similarly, pH ranged widely (6.90–8.79) across the bloom over both space and time, largely corresponding with dissolved oxygen level. Extreme changes in dissolved oxygen and pH, in addition to changes to other water parameters that affect organismal health, ultimately led to documented mortalities of thousands of demersal and benthic fishes and invertebrates (primarily within estuarine and inner-shelf environments), and long-term surveys within one lagoon showed protracted changes to benthic infaunal density and species composition. In addition to field observations, we also quantified water quality parameters and organism mortalities from four local aquarium facilities, with varying levels of filtration and artificial oxygenation, and documented the morphological changes in the gills of captive-held Pacific sardine in response to the red tide. We show that multiple factors contributed to organismal stress, with hypoxia likely being the most widespread, but not the only, cause of mortality.

Blooms of the dinoflagellate Ostreopsis cf. ovata are regularly associated with human intoxications that are attributed to ovatoxins (OVTXs), the main toxic compounds produced this organism and close analogs to palytoxin (PlTX). Unlike for PlTX, information on OVTXs'toxicity are scarce due to the absence of commercial standards. Extracts from two cultures of Mediterranean strains of O. cf. ovata (MCCV54 and MCCV55), two fractions containing or not OVTXs (prepared from the MCCV54 extract) and OVTX-a and -d (isolated from the MCCV55 extract) were generated. These chemical samples and PlTX were tested on a panel of cell types from several organs and tissues (skin, intestine, lung, liver and nervous system). The MCCV55 extract, containing a 2-fold higher amount of OVTXs than MCCV54 extract, was shown to be more cytotoxic on all the cell lines and more prone to increase interleukin-8 (IL-8) release in keratinocytes. The fraction containing OVTXs was also cytotoxic on the cell lines tested but induced IL-8 release only in liver cells. Unexpectedly, the cell lines tested showed the same sensitivity to the fraction that does not contain OVTXs. With this fraction, a pro-inflammatory effect was shown both in lung and liver cells. The level of cytotoxicity was similar for OVTX-a and –d, except on intestinal and skin cells where a weak difference of toxicity was observed. Among the 3 toxins, only PlTX induced a pro-inflammatory effect mostly on keratinocytes. These results suggest that the ubiquitous Na+/K+ ATPase target of PlTX is likely shared with OVTX-a and -d, although the differences in pro-inflammatory effect must be explained by other mechanisms.

Blooms of Ostreopsis cf. ovata pose an emerging health threat, causing respiratory disorders in various coastal regions. This dinoflagellate produce potent phycotoxins named ovatoxins that can be transferred from the seawater to the atmosphere. However, the biotic and abiotic conditions affecting their transfer are still unknown. In this study, we investigate the sea-to-air transfer of O. cf ovata phycotoxins using a process study in an aerosol reference tank (MART) and field observations. The process study exhibited a positive correlation between the phycotoxin content in sea spray aerosol (up to 832.59 ng m -3 ) and the particulate phycotoxin fraction in the water column and surface microlayer. In contrast, in the natural system, aerosolized phycotoxins were only observed in one out of six air collection (total toxins 0.59 ng m -3 ) despite optimal wind conditions. In both the process study and the natural system, ovatoxins represented only a minor fraction of the total toxin content, which was comprised of up to 90% liguriatoxins. In seawater, while no solubilized ovatoxins were detected, the concentration in dissolved liguriatoxin-a reached up to 19.07 μg L -1 . These results underscore the need for future research on the liguriatoxins, and on their toxicity to establish safe exposure thresholds for beachgoers.

Au cours des dernières décennies, les dinoflagellés du genre Ostreopsis ont été identifiés dans les eaux marines de plusieurs pays européens tels que l’Albanie, la Croatie, Chypre, l'Espagne, la France, la Grèce, l'Italie, Monaco et le Portugal . Ces microalgues sont principalement benthiques et vivent de préférence sur des substrats biotiques, comme des macrophytes (macroalgues et phanérogames marines). Elles peuvent néanmoins se retrouver en suspension dans l’eau (elles sont alors planctoniques) ou même former des agrégats en surface, on les nomme alors fleurs d’eau. Ces microalgues peuvent causer des intoxications humaines lorsque les cellules ou les toxines qu’elles produisent sont présentes dans l’eau de mer, dans les embruns et aérosols ou dans certains produits de la mer. L’exposition peut se faire : • par voie respiratoire (inhalation et/ou contact avec les aérosols lors de promenade, de surveillance des plages, des activités de baignade et nautiques, etc.) ; • par contact cutané avec de l’eau de mer ou des macrophytes, support d’Ostreopsis (lors des activités de baignade et/ou nautiques) ; • par ingestion d’eau de mer lors de la baignade ou de pratiques d’activités nautiques ou encore en cas de consommation de produits de la mer contaminés par des toxines produites par Ostreopsis spp. Des manifestations cliniques telles que toux, rhinorrhée, irritations de la sphère ORL et des yeux, céphalées, fièvre, difficultés respiratoires, nausées, vomissements, diarrhées, douleurs abdominales, myalgies, rougeurs ou démangeaisons sont alors observées chez les personnes exposées à Ostreopsis. En France, la présence d’Ostreopsis est identifiée de façon récurrente sur les côtes méditerranéennes depuis une quinzaine d’années. Plus récemment, 674 personnes ont développé des signes et des symptômes associés aux proliférations d’Ostreopsis sur la côte basque française durant l’été 2021. Le bilan épidémiologique de ces intoxications montre qu’il n’existe pas de différence clinique avec les effets observés lors des épisodes de prolifération d’Ostreopsis cf. ovata du pourtour méditerranéen. Les investigations menées par l’Ifremer ont mis en évidence sur la côte basque la présence de deux espèces de microalgues du genre Ostreopsis pendant les épisodes de proliférations de 2021 et 2022 : O. cf. siamensis et O. cf. ovata. Si la première, O. cf. siamensis, est présente sur cette côte depuis 2018, la seconde, O. cf. ovata, a été identifiée dans cette partie du golfe de Gascogne pour la première fois en 2021. Ostreopsis cf. ovata est connue pour produire des toxines dont la structure est proche de celle de la palytoxine (PLTX). Ces molécules pourraient être à l’origine des symptômes observés dans les populations humaines, d’autant plus que certaines d’entre elles ont été détectées dans les aérosols en Méditerranée.

An April–May 2020 bloom of the red tide microalga Lingulodinium polyedra developed to an unprecedented size, extending from northern Baja California to the Santa Barbara Channel. The L. polyedra strain is native to coastal California and is known to produce low levels of a toxic di-sulfated polyether named yessotoxin (YTX). In order to assess the evolution of the YTX content throughout the bloom and its transfer to water and aerosols, the concentration of YTX analogs was measured in the particulate and the dissolved organic matter of the sea surface water as well as in onshore sea spray aerosols. The YTX cell content was characteristic of Californian strains of L. polyedra. A lower production of YTX analogs by the cells at the peak of the bloom was detected, yielding total YTX content (particulate + dissolved) ranging from below the detection limit to 6.89 ng L−1 at that time. Yessotoxin and homo-yessotoxin were detected in sea spray aerosol measured onshore (from below detection limit to 20.67 ± 8.37 pg m−3), constituting the first detection of YTX analogs in coastal aerosols. The aerosolized YTX did not correlate with the seawater content but rather with westerly winds and higher tides. The presence of YTX in aerosols motivates further investigation into potential correlations with adverse effects in humans.

Au cours des dernières décennies, plusieurs espèces de dinoflagellés du genre Ostreopsis ont été identifiées dans les eaux marines de pays européens tels que l’Albanie, la Croatie, Chypre, l'Espagne, la France, la Grèce, l'Italie, Monaco et le Portugal. Ces microalgues peuvent causer des intoxications humaines lorsque les cellules ou les toxines qu’elles produisent sont présentes dans l’eau de mer, les aérosols ou dans certains produits de la mer. La voie principale d’exposition de l’Homme est l’inhalation d’aérosols sans que l’on sache actuellement si les agents à l’origine des intoxications sont les cellules d’Ostreopsis, les débris cellulaires, des toxines connues produites par Ostreopsis ou d’autres composés non encore identifiés. D’autres voies d’exposition (contact cutané, contact oculaire, ingestion d’eau ou de produits de la mer contaminés) sont possibles. Les intoxications se manifestent par divers signes et symptômes (survenant moins de 48h après l’exposition) : - neurosensoriels et neurologiques : paresthésies (sensation de fourmillements), dysesthésies (sensation de brûlure) et céphalées ; - respiratoires, de la sphère ORL et stomatologiques : dysgueusie à type de goût métallique, rhinorrhée, toux, gêne respiratoire ; - cutanés évoquant de l’urticaire ; - cardiaques : tachycardie, poussée hypertensive ; - digestifs : nausées, vomissements, diarrhée ; - systémiques : fièvre ; - locomoteurs : myalgies et arthralgies (douleurs musculaires et articulaires). Elles surviennent lors de diverses situations : - travail ou activités récréatives dans la mer (baigneurs, maîtres-nageurs, pêcheurs professionnels, surfeurs, etc.) ; - travail ou activités récréatives sur ou à proximité de la plage (estivants, secouristes, agents en charge du nettoyage des plages, restaurateurs, etc.) ; - séjour ou résidence à proximité immédiate du bord de mer ; - consommation de produits de la mer contaminés. En France, la présence d’Ostreopsis est identifiée de façon récurrente sur les côtes méditerranéennes depuis une quinzaine d’années alors qu’elle est beaucoup plus récente sur les côtes basques française et espagnole. Deux espèces ont été identifiées sur la côte basque : O. cf. siamensis et O. cf. ovata. Si la première, O. cf. siamensis, est observée sur cette côte depuis 2018, la seconde, O. cf. ovata, a été observée dans cette partie du golfe de Gascogne pour la première fois en 2021. Le bilan épidémiologique montre que près de 900 personnes ont développé des signes et des symptômes associés aux proliférations d’Ostreopsis sur la côte basque française depuis 2020. Ce bilan montre par ailleurs qu’il n’existe pas de différence clinique avec les effets observés lors des épisodes de prolifération d’Ostreopsis cf. ovata du pourtour méditerranéen. [Saisines liées n°2007-SA-0227 et 2007-SA-0303]

Recurrent blooms of the toxic dinoflagellate Ostreopsis cf. ovata are frequently reported in the Northwestern Mediterranean Sea. The impact of these proliferations on other microalgal species inhabiting the same habitats is of interest from an ecological prospective. In vitro experiments were carried out to investigate the influence of O. cf. ovata on the growth of the co-occurring benthic diatoms Licmophora paradoxa, Navicula arenaria and the benthic dinoflagellates Prorocentrum lima and Coolia monotis. Overall, O. cf. ovata exhibited weak allelopathic effects towards these microalgal species, with a reduction in the cell abundance for L. paradoxa and P. lima only. Interestingly, dead cells of L. paradoxa and N. arenaria were observed embedded in the thick mucus surrounding O. cf. ovata cells, suggesting that the mucous layer could act as a toxic phycosphere, especially for non-motile cells. All competitors were further exposed for 24 h to ovatoxins, the major toxins produced by O. cf. ovata, and the maximum quantum yield efficiency of L. paradoxa, N. arenaria and P. lima was affected at a minimum concentration of 10 µg mL−1. We then hypothesized that the diffusion of solubilized ovatoxins in the culture medium affects only moderately the competitors’ growth, whereas their accumulation in the mucus would yield deleterious effects. More precisely, the competitors’ sensitivity to ovatoxins was enhanced in their stationary phase of growth and resulted from a rapid inhibition of an uncharacterized photosynthetic step downstream photosystem II. Altogether, these results emphasize the predominant role of the O. cf. ovata’s mucus in driving ecological interactions and suggest that it can affect the growth of several benthic microalgae by accumulating the potent ovatoxins.

Macroalgae constitute one of the preferred substrates of the benthic dinoflagellate Ostreopsis cf. ovata. Across the Mediterranean Sea, this toxic microalga has been shown to thrive on the surface of various species of macroalgae, including Chlorophyta, Rhodophyta, and Phaeophyceae. Interestingly, some Dictyotaceae are characterized by a low abundance of cells of O. cf. ovata on their surface. Based on the antifouling properties of some specialized metabolites produced by seaweeds, macroalgal metabolites have been proposed to contribute to the settlement and development of O. cf. ovata. To address this question, the composition of the surface of four Dictyotaceae, Dictyota dichotoma, Dictyota spiralis, Taonia atomaria, and Padina pavonica was investigated through an integrative approach combining the analysis of their eukaryotic diversity (18S rRNA gene metabarcoding), their surface metabolome (untargeted LC-MS-based metabolomics) as well as the bioactivity of their surface extracts on O. cf. ovata. Altogether, the data suggest an influence of the macroalgal surface chemistry on the growth of the dinoflagellate, with D. dichotoma being the most bioactive. Some metabolites are proposed to be involved in the observed bioactivity. Other biotic factors are also likely to be entailed in the control of the O. cf. ovata population and they may even prevail on the influence of the macroalgal surface chemistry.

Due to increasing evidence of key chemically mediated interactions in marine ecosystems, a real interest in the characterization of the metabolites involved in such intra and interspecific interactions has emerged over the past decade. Nevertheless, only a small number of studies have succeeded in identifying the chemical structure of compounds of interest. One reason for this low success rate is the small size and extremely polar features of many of these chemical compounds. Indeed, a major challenge in the search for active metabolites is the extraction of small polar compounds from seawater. Yet, a full characterization of those metabolites is necessary to understand the interactions they mediate. In this context, the study presented here aims to provide a methodology for the characterization of highly polar, low molecular weight compounds in a seawater matrix that could provide guidance for marine ecologists in their efforts to identify active metabolites. This methodology was applied to the investigation of the chemical structure of an algicidal compound secreted by the bacteria Shewanella sp. IRI-160 that was previously shown to induce programmed cell death in dinoflagellates. The results suggest that the algicidal effects may be attributed to synergistic effects of small amines (ammonium, 4-aminobutanal) derived from the catabolization of putrescine produced in large quantities (0.05–6.5 fmol/cell) by Shewanella sp. IRI- 160.

Harmful algal blooms are a source of increasing concern within the health, economic and ecological sectors. In the Mediterranean Sea, severe blooms of the benthic dinoflagellate Ostreopsis cf. ovata have been occurring since the beginning of the century, causing human intoxications by inhalation of bio-aerosols or direct contact with cells. The toxicity of this dinoflagellate is attributed to the presence of palytoxin and several of its analogs called ovatoxins, palytoxin being one of the most potent marine toxins. While mass mortalities of marine invertebrates have already been reported in relation with O. cf. ovata blooms, the toxic effects of this dinoflagellate on benthic organisms is still poorly documented. In the present study, laboratory experiments were performed on a meiobenthic copepod (Sarsamphiascus cf. propinquus), which naturally lives on macrophytes in close contact to O. cf. ovata, in order to assess its potential toxic effects on mortality, fecal pellet production (as a proxy of feeding), as well as fecundity and fertility ratios. Both, O. cf. ovata as well as a non-toxic competitive diatom (Licmophora paradoxa), were used as food in the experiments. Regarding acute toxicity evaluation, this copepod proved to be the most tolerant organism to O. cf. ovata reported to date. Nevertheless, its fecundity and fertility ratios were lower when fed with the toxic dinoflagellate, indicating a possible reprotoxic effect. Moreover, although fecal pellet production decreased significantly when the copepod was fed with a mono-diet of O. cf. ovata, epifluorescence microscopy observations revealed the presence of the toxic cells inside the digestive track, hence suggesting that these primary grazers could be a vector of toxins through the marine food web.

For decades the microphytobenthos assemblage in the coastal Mediterranean Sea has been regularly colonized by the toxic benthic dinoflagellate Ostreopsis cf. ovata. This harmful algal species is a toxin producer and occupies the same ecological niche as various diatoms. Surprisingly, there are only few insights reported on the physiological responses of diatoms to blooms of O. cf. ovata The chemical interactions of O. cf. ovata with the co-occurring diatom Licmophora paradoxa was studied using a bioassay (measuring impact of cell-free culture filtrate) and a co-culture approach (separate by a membrane) to investigate the effects of the exometabolome and its mode of action. Bioassays highlighted a toxic effect of the exometabolome of O. cf. ovata on the diatom photosynthetic activity. However, the co-cultures revealed that these toxic effects do not occur through remote allelopathy. Contact or close interactions between cells of the two species is most likely needed to impair the diatom growth. Ovatoxins are suspected to be the toxic metabolites secreted by O. cf. ovata although the current set of data did not give confirmation of this assumption. Interestingly, the exometabolome of L. paradoxa impaired the growth and the photochemistry of O. cf. ovata in both bioassays and co-cultures. Some biomarkers possibly involved for the effect were identified using a metabolomic approach and may correspond to oxylipins, however a bacterial source of the bioactive metabolites is also considered.

Most marine sponges are known to produce a large array of low molecular-weight metabolites which have applications in the pharmaceutical industry. The production of so-called specialized metabolites may be closely related to environmental factors. In this context, assessing the contribution of factors like temperature, nutrients or light to the metabolomes of sponges provides relevant insights into their chemical ecology as well as the supply issue of natural sponge products. The sponge Crambe crambe was chosen as a model due to its high content of specialized metabolites belonging to polycyclic guanidine alkaloids (PGA). First results were obtained with field data of both wild and farmed specimens collected in two seasons and geographic areas of the North-Western Mediterranean. Then, further insights into factors responsible for changes in the metabolism were gained with sponges cultivated under controlled conditions in an aquarium. Comparative metabolomics showed a clear influence of the seasons and to a lesser extent of the geography while no effect of depth or farming was observed. Interestingly, sponge farming did not limit the production of PGA, while ex situ experiments did not show significant effects of several abiotic factors on the specialized metabolome at a one-month time scale. Some hypotheses were finally proposed to explain the very limited variations of PGA in C. crambe placed under different environmental conditions.

Ecological interactions in the marine environment are now recognized to be partly held by chemical cues produced by marine organisms. In particular, sponges are sessile animals thought to rely on the bioactive substances they synthesize to ensure their development and defense. However, the mechanisms leading the sponges to use their specialized metabolites as chemical cues remain unknown. Here we report the constant release of bioactive polycyclic guanidinic alkaloids by the Mediterranean sponge Crambe crambe into the dissolved and the particulate phases using a targeted metabolomics study. These compounds were proven to be stored into already described specialized (spherulous) sponge cells and dispersed into the water column after release through the sponge exhaling channels (oscula), leading to a chemical shield surrounding the sponge. Low concentrations of these compounds were demonstrated to have teratogenic effects on embryos of a common sea squirt (ascidian). This mechanism of action called spherulization may therefore contribute to the ecological success of encrusting sponges that need to extend their substrate cover to expand.

The Mediterranean marine sponge Crambe crambe is the source of two families of guanidine alkaloids known as crambescins and crambescidins. Some of the biological effects of crambescidins have been previously reported while crambescins have undergone little study. Taking this into account, we performed comparative transcriptome analysis to examine the effect of crambescin-C1 (CC1) on human tumor hepatocarcinoma cells HepG2 followed by validation experiments to confirm its predicted biological activities. We report herein that, while crambescin-A1 has a minor effect on these cells, CC1 protects them against oxidative injury by means of metallothionein induction even at low concentrations. Additionally, at high doses, CC1 arrests the HepG2 cell cycle in G0/G1 and thus inhibits tumor cell proliferation. The findings presented here provide the first detailed approach regarding the different effects of crambescins on tumor cells and provide a basis for future studies on other possible cellular mechanisms related to these bioactivities.

Dans les régions océaniques hauturières oligotrophes LNLC, comme la Méditerranée, l’atmosphère constitue la principale source d’éléments nutritifs. En 2008, l’atmosphère estivale était constituée d’un « bruit de fond » relativement uniforme spatialement, mélange d’aérosols naturels et anthropiques. Les éléments nutritifs libérés par la dissolution des aérosols stimulent l’activité autotrophe avec une même intensité dans le cas d’un dépôt mixte ou saharien naturel : la labilité des éléments nutritifs associés aux aérosols mixtes est plus importante. Bien que stimulée par un dépôt atmosphérique, l’activité diazotrophe en été est restée faible. Le carbone organique induit par l’augmentation de l’activité biologique suite à un dépôt mixte, est exporté sous forme de POC, augmentant l’efficacité de l’export de carbone en période estivale. L’implication des évènements sahariens dans le cycle du carbone se réalise aussi à travers la formation « d’évènements lithogéniques » : fort export associé de POC – particules lithogéniques suite à des phénomènes d’agrégation en surface. Ces évènements sont générés (1) en hiver, du fait de l’approfondissement de la couche de mélange, (2) en lien avec des évènements sahariens extrêmes. L’export de carbone résultant peut représenter jusqu’à 2 fois celui mesuré en période de bloom, pic annuel de l’activité biologique. Les dépôts atmosphériques, et en particulier les évènements sahariens extrêmes, jouent donc un rôle prépondérant dans le cycle du carbone en Méditerranée et doivent être pris en compte dans la modélisation écosystémique de façon à pouvoir appréhender l’impact de leur évolution, en lien avec le changements environnementaux actuels