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Ostreopsis cells extruding exopolymeric substances from the ventral pore.
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... freely swimming in this mucilaginous matrix. Samples of living macroalgae collected during this event and placed in a large tank showed within a few minutes many reddish mucilaginous threads bridging drifting algae and the tank's walls. Light microscope observations showed Ostreopsis cells extruding exopolymeric substances from the ventral pore (Fig. 3) and cooperating in the rapid formation of the strings (Fig. 4). Small organisms were seen trapped in the newly formed networks, including potential predators of Ostreopsis (e.g. nematodes). At once and amazingly, hundreds of Ostreopsis cells jumped on the partially immobilised organisms (Fig. 5). Two available videos reveal the useless ...
Citations
... ovata extrude mucoid compounds and co-operate in rapid formation of larger mucus strings. This mucoid network, likely enriched with toxins (palytoxin-like compounds, [47]), entraps small organisms that are subsequently approached and attacked by Ostreopsis; it has been suggested that this "spider strategy" serves as a feeding aid [65,66]. In contrast to the delicate mucus traps of Prorocentrum, Ostreopsis mucilage has a complex and rigid structure made from a network of long trichocysts fibres in an amorphous matrix of acidic polysaccharides [47]. ...
Prorocentrum comprises a diverse group of bloom-forming dinophytes with a worldwide distribution. Although photosynthetic, mixoplanktonic phagotrophy has also been described. Recently, the small P. cf. balticum was shown to use a remarkable feeding strategy by crafting globular mucus traps to capture and immobilize potential prey. Here we present evidence showing that two additional related species, the recently described P. pervagatum and the cosmopolitan bloom-forming P. cordatum, also produce large (80–120 µm) mucus traps supporting their mixoplanktonic activity. Prey are captured within the traps either through passive entanglement upon contact with the outside surface, or through active water movement created by rotating Prorocentrum cells eddying particles to the inside surface where trapped live prey cells became immobilized. Entrapment in mucus assisted deployment into the prey of a peduncle extruded from the apical area of the Prorocentrum cell. Phagotrophy by P. pervagatum supported faster growth compared to unfed controls and time series quantification of food vacuoles revealed ingestion rates of ca. 10–12 Teleaulax prey cells day−1. Model calculations show clear advantages of deploying a mucus trap for increasing prey encounter rates. This study demonstrates that the large size and immobilization properties of mucus traps successfully increase the availability of prey for small Prorocentrum species, whose peduncle feeding mode impedes consumption of actively moving prey, and that this strategy is common among certain clades of small planktonic Prorocentrum species.
... ovata, a palitoxins-like producer giving airborne disease, were occasionally recorded in the samples of the column water during WFD and MSFD monitoring but it reached high abundance in the samples of the ad hoc BWD monitoring particularly in the shallow rocky coast sites. Hydrodynamic conditions are referred as the main factor affecting Ostreopsis bloom trends, highlighting that higher abundances are observed in sheltered sites compared with exposed ones (Barone, 2007;Shears and Ross, 2010;Totti et al., 2010;Mabrouk et al., 2012) and where high irradiance values and prolonged calm sea conditions occur (Ungaro et al., 2010;Accoroni and Totti, 2016). Potentially producer yessotoxins (YTXs, e.g. ...
The spatial distribution of harmful microalgal taxa along the coasts of the Apulia region (Mediterranean Sea) based on results of eight years (2012–2019) of routine monitoring program and a series of sporadic observations is presented. A total number of 69 potentially harmful taxa were found during the study period. Occurrence, abundance and richness of harmful taxa (toxic, potentially toxic and high biomass producers) varied along the Apulian coasts. The occurrence of harmful species was significantly higher where most of anthropogenic pressures overlap than only a few or no pressures existed. The physical alteration of coast is the most important pressure determining this pattern. Despite the variety and the abundances of the harmful microalgae, to our knowledge, no human health problems or risks have been ever recorded, nor were full-blown consequences on marine organisms such as fish kills during algal blooms. However, blooms coupled with water discoloration phenomena could become a big issue to tourism and recreational activities that have locally important socio-economic value.
... This mucilaginous matrix could facilitate the retention of chemical compounds (including toxins), leading to increased Ostreopsis competitiveness with other microalgae and bacteria (Ternon et al., 2018). It could also constitute a defence against Ostreopsis predators by embedding them into this mucus, or by avoiding dilution of (toxic) chemicals in the environment and allowing their ingestion in high quantity by predators (Barone 2007;Giussani et al., 2015;Pavaux et al., 2020a). In addition, the mucus could act as a deterrent agent against macroalgal grazers, thus resulting in a benefit for the benthic host. ...
This paper summarizes the research conducted by the partners of the EU co-funded CoCliME project to ascertain the ecological, human health and economic impacts of Ostreopsis (mainly O. cf. ovata) blooms in the NW Mediterranean coasts of France, Monaco and Spain. This knowledge is necessary to design strategies to prevent, mitigate and, if necessary, adapt to the impacts of these events in the future and in other regions.
Ostreopsis proliferations in the Mediterranean have been related to massive mortalities of benthic organisms and to symptoms of respiratory and cutaneous irritation in humans. A six-year epidemiologic study in a Ostreopsis hot spot in Catalonia and the accumulated experience of the French Mediterranean National Ostreopsis Surveillance Network confirm the main effects of these blooms on human health in the NW Mediterranean. The impacts are associated to direct exposure to seawater with high Ostreopsis cell concentrations and to inhalation of aerosols containing unknown irritative chemicals produced under certain circumstances during the blooms. A series of mild acute symptoms, affecting the entire body as well as the ophthalmic, digestive, respiratory and dermatologic systems have been identified. A main remaining challenge is to ascertain the effects of the chronic exposure to toxic Ostreopsis blooms.
Still, the mechanisms involved in the deletereous effects of Ostreopsis blooms are poorly understood. Characterizing the chemical nature of the harmful compounds synthesized by Ostreopsis as well as the role of the mucus by which cells attach to benthic surfaces, requires new technical approaches (e.g., metabolomics) and realistic and standardized ecotoxicology tests. It is also necessary to investigate how palytoxin analogues produced by O. cf. ovata could be transferred through the marine food webs, and to evaluate the real risk of seafood poisonings in the area. On the other hand, the implementation of beach monitoring and surveillance systems in the summer constitutes an effective strategy to prevent the impacts of Ostreopsis on human health.
In spite of the confirmed noxious effects, a survey of tourists and residents in Nice and Monaco to ascertain the socioeconomic costs of Ostreopsis blooms indicated that the occurrence of these events and their impacts are poorly known by the general public. In relationship with a plausible near future increase of Ostreopsis blooms in the NW Mediterranean coast, this survey showed that a substantial part of the population might continue to go to the beaches during Ostreopsis proliferations and thus could be exposed to health risks. In contrast, some people would not visit the affected areas, with the potential subsequent negative impacts on coastal recreational and touristic activities. However, at this stage, it is too early to accurately assess all the economic impacts that a potentially increasing frequency and biogeographic expansion of the events might cause in the future.
... Moderate hydrodynamics seems to favor O. cf. ovata cells to remain attached to the substrate (Vila et al., 2001;Barone, 2007;Shears and Ross, 2009;Totti et al., 2010) while rough seas and currents would disperse them. Relatively low wind intensities (2-4 m s − 1 ) were registered concurrently to some blooms in the NW Mediterranean (Vila et al., 2016). ...
... Data collected over the first two years of this monitoring program suggested a distinct pattern concerning the timing of the blooms and specific hydroclimatic conditions in that area ). Indeed, compared to 2008, 2007 was marked by a hot spring and a relatively cold summer and exhibited a strongly marked an earlier bloom episode ...
... It is generally agreed that O. cf. ovata blooms are favored by low hydrodynamic conditions, since the highest abundance levels are rather recorded in sheltered areas, even though blooms have also been observed in exposed sites (Barone, 2007;Totti et al., 2010;Accoroni and Totti, 2016). By comparing bloom events throughout the years, the PCA analysis in this present study showed no straight forward relation between environmental parameters and maximum annual growth rates of O. cf. ...
Blooms of the toxic benthic dinoflagellate Ostreopsis cf. ovata can induce ecological and human health issues in certain temperate areas. In order to prevent these negative effects, long-term monitoring studies of O. cf. ovata blooms have been conducted in several impacted areas to have a comprehensive understanding of bloom dynamics and efficient tools for risk management.
O. cf. ovata blooms were monitored every summer (from mid-June to the end of August) on five identified sites in Larvotto beach (Monaco, NW Mediterranean Sea), between 2007 and 2019. This time-series represents one of the largest time-series in the world describing blooms of this species.
Bloom phenological features (timing, duration, maximum cell abundance and growth rate), were found to be highly variable throughout the studied period, and were analyzed as a function of different hydroclimatic parameters, including sea surface temperature (SST). The highest net growth rates were related to temperatures ranging between 21°C and 25°C, and did not coincide with maximal temperature records (27.5°C). Such results suggest that, although global warming possibly influences the expansion of O. cf. ovata from tropical to temperate waters, the definite impact of temperature on bloom dynamics might be more complex than a simple facilitation factor for algal growth, at least in NW Mediterranean waters.
Furthermore, monthly SST anomalies calculated over this 13-year survey showed a strong positive correlation between spring SST positive anomalies and the bloom starting date, indicating that blooms occurred earlier in the season when spring SSTs were warmer than usual.
Overall results provide tools to modelers and managers who are facing crucial challenges to predict the distribution and phenology of O. cf. ovata blooms in European coastal waters, moreover in a context of global warming.
... However, the shape of the coast at these sampling stations (a cove at Prima Cala versus a linear seashore at Gavetone) may be one influencing factor because previous studies have reported greater blooms in protected sites than in exposed sites suggesting that hydrodynamic condition plays a key role in the blooming of O. cf. Ovata (Barone, 2007;Totti et al., 2010). In addition, due to lack of appropriate instrumentation, several factors have not been investigated. ...
The toxic benthic dinoflagellate Ostreopsis ovata causes harmful algal blooms. During five years, citizens have monitored blooms of O. cf. ovata along the coast of Molfetta city facing the Adriatic Sea. Coscinodiscus spp., Licmophora spp., Gyrosigma spp. and Achnantes spp. diatoms were also quantified. O. cf. ovata was detected from spring up to winter, however, blooms always occurred in summer. Correlation with nine weather parameters was relatively strong with seawater temperature, dew point and air temperature. Dew point has never been reported before as key parameter. Blooms of O. cf. ovata were preceded by lag period during which conditions permitted proliferation but no proliferation observed. Furthermore, dew point, seawater and air temperature only moderately correlated with proliferation of Coscinodiscus spp. However, correlation between blooms of O. cf. ovata and Coscinodiscus spp. was relatively strong. Correlation between proliferation of O. cf. ovata and Gyrosigma spp. was very weak, while moderate and negative with Licmophora spp. or Achnantes spp.
... L'influence d'autres paramètres physico-chimiques tels que la salinité (Parsons and Preskitt, 2007;Accoroni et al., 2015a;Blanfuné et al., 2015) et les nutriments (Shears and Ross, 2009;Cohu et al., 2011) (Honsell et al., 2013), le mucilage produit pourrait aussi avoir d'autres rôles liés à sa viscosité. Il pourrait, en particulier, avoir un intérêt allélopathique en créant une zone extracellulaire capable de concentrer les molécules bioactives (Barone, 2007;Giussani et al., 2015). Lorsque le mucus est produit en grande quantité, il piège également l'oxygène produit par les cellules lors de la photosynthèse, permettant l'accumulation de microbulles de gaz et (Jauzein et al., 2018), l'utilisation de plus en plus fréquente de substrats de type artificiels (Tester et al., 2014;Jauzein et al., 2016) ainsi que le développement de techniques moléculaires basées sur l'ADN environnemental (Penna et al., 2007;Battocchi et al., 2010;Casabianca et al., 2013;Vassalli et al., 2018) ont permis l'amélioration de l'effort de monitoring des microalgues benthiques nuisibles. ...
... The fact that in certain areas those episodes are observed in particular time periods of the year only suggests that specific environmental conditions are required for such blooms to occur. Studies showed the importance of hydrodynamics on Ostreopsis development (Barone, 2007;Shears and Ross, 2009;Totti et al., 2010). Low wave actions to moderately shaken waters seem to favor cells settlement (Vila et al., 2001), as strong winds and currents would favor cells dispersion and impact cell growth. ...
... It is admitted that blooms of Ostreopsis cf. ovata are generally favored by low levels of turbulence as highest abundances are recorded in sheltered sites, even though blooms also occur in exposed sites (Barone, 2007;Totti et al., 2010;Accoroni and Totti, 2016). ...
Les efflorescences algales nuisibles (HABs) associées aux dinoflagellés benthiques toxiques du genre Ostreopsis sont des phénomènes observés de plus en plus fréquemment à travers le monde et sont responsables de problèmes sanitaires, économiques et écologiques. L’augmentation du nombre d’observations de ce dinoflagellé depuis les dernières décennies laisse penser que les changements climatiques, et plus particulièrement le réchauffement des océans, seraient en partie responsable de son expansion, notamment dans les zones tempérées. Cependant, ce lien entre réchauffement des eaux et développement d’efflorescences d’Ostreopsis est difficile à prouver et certaines données concernant les aires de répartition ou la réponse des cellules aux variations thermiques sont encore manquantes. Ces travaux de thèse ont fourni des nouveaux éléments pour répondre à cette problématique en abordant trois thématiques principales : 1) la phénologie des efflorescences, 2) la distribution d’espèce le long d’un gradient latitudinal et 3) les adaptations physiologiques à un gradient de température. Ces questions ont été abordées en gardant l’effet de la température sur l’écologie des espèces étudiées comme fil conducteur principal et lien entre les trois questions posées. Les travaux ont été menés avec une approche multidisciplinaire incluant des analyses statistiques de jeux de données, des approches génétiques basées sur l’ADN environnemental, ainsi que des approches d’écophysiologie et d’écotoxicologie. Les données utilisées ont été acquises à la fois à partir de prélèvements de terrain et d’expériences en milieu contrôlé au laboratoire. Pour répondre au premier objectif, nous avons analysé la série temporelle issue du suivi d’efflorescences d’O. cf. ovata à Monaco, mis en place depuis 2007 et toujours poursuivi à ce jour, afin de mettre en relation la phénologie des efflorescences avec les paramètres environnementaux. Bien que, d’après nos analyses, aucun facteur physico-chimique mesuré ne soit en mesure d’expliquer la phénologie des efflorescences, une forte corrélation positive entre l’accumulation d’anomalies positives des températures de surface au printemps et la date de début des efflorescences a été mise en évidence, suggérant que plus les températures printanières seraient élevées, plus les efflorescences d’O. cf. ovata à Monaco seraient précoces. La deuxième question de la thèse a été abordée en analysant de nouveaux échantillons collectés dans le cadre d’une campagne d’échantillonnage conduite le long des côtes du Golfe de Gascogne en août-septembre 2018. Cette campagne avait pour objectif d’établir l’aire de répartition actuelle d’Ostreopsis spp. dans cette zone à fort gradient thermique sud-nord, afin de poser les bases pour l’analyse d’une possible future expansion en cas de réchauffement des eaux. Les résultats traités ont combiné une approche classique d’échantillonnage benthique, l’utilisation de substrats artificiels pour la collection d’ADN environnemental analysés via des outils moléculaires (rt-qPCR) ainsi qu’une approche de modélisation Lagrangienne visant à établir la connectivité physique entre différents sites de prélèvement. Nous avons pu montrer que seule l’espèce O. cf. siamensis était présente dans le Golfe, et que celle-ci pouvait être retrouvée jusqu’à l’entrée de La Manche, bien que les populations formant des efflorescences n’aient été observées que dans la partie sud-est du Golfe. Cette étude nous a permis d’identifier des zones sentinelles le long du Golfe de Gascogne où il serait intéressant de mettre en place de nouveaux suivis à long terme afin d’observer la potentielle expansion vers le nord d’O. cf. siamensis. La réponse d’Ostreopsis spp. face à des changements de température a été étudiée en termes de capacité de croissance, d’adaptations physiologiques et de toxicité, au cours d’une expérience d’acclimatation thermique. Différentes souches monoclonales ont été comparées [...]
... However, there is very limited information on the relationships between nutrient concentrations and the occurrence of Ostreopsis blooms. Several studies considered hydrodynamic condition as a main factor affecting Ostreopsis bloom trends, highlighting that higher abundances are observed in sheltered sites compared to exposed ones (Barone, 2007;Totti et al., 2010). However, effects of hydrodynamics and turbulence may lead to opposite effects in each bloom phase. ...
Ostreopsis cf. ovata, a benthic toxic marine dinoflagellate, has been recorded along Italian coasts since the '90, but large bloom events have been reported only in recent years. In 2005, a monitoring programme started along the Ligurian coast (North-western Mediterranean), where time series of cell abundances have been collected for several sites, together with a range of related environmental variables. Data of cell abundances in 15 sites, together with environmental data provided by meteo-marine forecasting models used by the Regional Environmental Agency (ARPAL), have been used to implement a predictive modelling tool, able to forecast Ostreopsis cells concentration threshold exceedance as a function of meteo-marine forecasts. Starting from the experience of the predictive model implemented in 2015, the Quantile Regression Forest (QRF) has been applied: the model has been trained on past data (from 2015 until 2017) and tested with data taken during the two last available years (2018 and 2019). The use of this extremely adaptable regression model to evaluate threshold exceedance has shown a good capacity to predict overcoming events at a given spatial location. This tool can help the Regional Agency in the decision making process, providing an alert when/where a given alarm threshold is exceeded in order to trigger the emergency procedures. This is a first step in defining a predictive sampling strategy able to better capture bloom events.
... However, there is very limited information on the relationships between nutrient concentrations and the occurrence of Ostreopsis blooms. Several studies considered hydrodynamic condition as a main factor affecting Ostreopsis bloom trends, highlighting that higher abundances are observed in sheltered sites compared to exposed ones (Barone, 2007;Totti et al., 2010). However, effects of hydrodynamics and turbulence may lead to opposite effects in each bloom phase. ...
Ostreopsis cf. ovata, a benthic toxic marine dinoflagellate, has been recorded along Italian coasts since the '90, but large bloom events have been reported only in recent years. In 2005, a monitoring programme started along the Ligurian coast (North-western Mediterranean), where time series of cell abundances have been collected for several sites, together with a range of related environmental variables. Data of cell abundances in 15 sites, together with environmental data provided by meteo-marine forecasting models used by the Regional Environmental Agency (ARPAL), have been used to implement a predictive modelling tool, able to forecast Ostreopsis cells concentration threshold exceedance as a function of meteo-marine forecasts. Starting from the experience of the predictive model implemented in 2015, the Quantile Regression Forest (QRF) has been applied: the model has been trained on past data (from 2015 until 2017) and tested with data taken during the two last available years (2018 and 2019). The use of this extremely adaptable regression model to evaluate threshold exceedance has shown a good capacity to predict overcoming events at a given spatial location. This tool can help the Regional Agency in the decision making process, providing an alert when/where a given alarm threshold is exceeded in order to trigger the emergency procedures. This is a first step in defining a predictive sampling strategy able to better capture bloom events.
Keywords: classification, regression, machine learning, environmental data, Ostreopsis
... The role of this mucilaginous matrix in mixotrophic behavior was also suggested (Barone, 2007). Mixotrophy is a common way of nutrition in harmful algal species (Burkholder et al., 2008) and several studies have investigated this nutritional capacity in Ostreopsis, although not completely demonstrated yet. ...
The genus Ostreopsis includes some species that produce high biomass blooms and/or synthesize toxic compounds that can be transferred through the marine food webs or aerosolized causing ecological, human health and socio-economic impacts. Ostreopsis species are increasing their biogeographic distribution from tropical to more temperate waters and causing recurrent blooms in certain coastal areas, thus constituting an emerging concern worldwide. The proliferation capacity of Ostreopsis is due to a complex and poorly understood combination of multiple factors, and may be a paradigm of chemical ecology reviewed here. A first section summarizes the basic knowledge on the different Ostreopsis species, the toxins they produce and the described foodborne and airborne effects of Ostreopsis toxins on humans. Secondly, direct and indirect interactions between Ostreopsis species and their environment are reviewed. Mucopolysaccharide substances produced by the cells to attach to different substrates appear to be a key element on the chemical ecology and requires further study. However, this research is challenged by technical limitations to conduct ecologically realistic and harmonized studies where organisms can be in direct contact with Ostreopsis cells, their mucus and/or the released extracellular toxic compounds. Understanding the transfer mechanisms of these substances within the food web, potentially affecting humans is critical and requires further study with new analytical tools. Still, the progress in knowledge achieved in the last years, combined with experimental and field studies using cutting edge methods will facilitate to address the open questions on the chemical ecology of Ostreopsis and understand its bloom dynamics now, and under future climate and anthropogenic change scenarios.
... In addition, there was a positive correlation between wind speed and benthic abundances of O. fattorussoi at TRI; as water agitation at each site could be influenced by local winds, these results suggest that the species might prefer some agitation, as also observed for Ostreopsis spp. in other studies (Selina et al., 2014;Vila et al., 2001). The effects of water agitation on blooms of Ostreopsis spp. in the Mediterranean Sea might be variable, as it has been suggested that has a negative effect as higher abundances are found in sheltered or calm areas (Accoroni et al., 2012;Barone, 2007;Mangialajo et al., 2008;Totti et al., 2010), as wind and waves could disperse the bloom (Cohu et al., 2011, Accoroni andTotti, 2016). A single environmental parameter did not solely influence the development of O. fattorussoi, but it is a combination of several factors; the PCA did not highlight the influence of a specific environmental factor on its abundance. ...
This study involves monitoring both benthic and planktonic abundances of the toxic dinoflagellate Ostreopsis fattorussoi in 5 stations along the Lebanese coast (Eastern Mediterranean); it extended from June 2014 to July 2016 and aims to study the dynamics of its development. Results revealed its presence year round along the coast, presenting seasonal blooms, both epiphytic and planktonic. A major bloom (maximum of 880 694 cells/g FW and 18 000 cells/L) occurred early in the summer (June–July), followed by a minor one in the fall (October–November) (≤ 50 000 cell/g FW). Its development seemed influenced by a combination of multiple environmental parameters. Water temperature seemed to play a major role in its development, as it appeared to be a thermophilic species, with maximum abundances per site reached between 27 °C and 30.5 °C. Its development could be facilitated by some agitation resulting from winds. Results concerning the role of nutrients and other environmental parameters remain inconclusive.
