This publication must be cited as: ICOD (2012). Round Table 2 of the International Conference on Ostreopsis Development: Environmental, Health and Economic management, state of the art and perspectives, Cryptogamie, Algologie 33(2) : 85–87.

The presence of dinoflagellates of the genus Ostreopsis along Mediterranean coasts was first observed in 1972, in the bay of Villefranche-sur-Mer. However, over the past ten years, harmful events related to this benthic dinoflagellate have been reported in Italian, Spanish, Greek, French, Tunisian and Algerian coastal areas. In France, during a hot period in August 2006, cases of dermatitis and respiratory problems were registered in Marseille area. At that time, a link to the proliferation of Ostreopsis was highlighted for the first time in that area. A specific monitoring was designed and implemented in the summer 2007. Two strains of Ostreopsis cf. ovata, collected in 2008 from Villefranche-sur-Mer and Morgiret coastal waters and grown in culture, were identified by molecular analysis and studied to characterise their growth and toxin profile. Liquid chromatography-mass spectrometry (LC-MS/MS) indicated that both strains produced ovatoxin-a (OVTX-a) as the major component (ca. 90%), and traces of palytoxin (PLTX). Toxin content was determined at the end of the exponential growth phase with highest concentration of 55 pg.cell^-1 of OVTX-a and 2.5 pg.cell^-1 of PLTX.

The complexity of effects exerted by palytoxin (PlTX) in biological systems is apparent from responses observed in different models. We have approached this complexity by proteomic analyses, to study responses induced by PlTX at a system level. The analysis of a sub-proteome of a human cell line has shown that PlTX causes changes in phosphorylation states of Hsp27 and the oxidation of DJ-1, supporting the conclusion that cell stress responses, including oxidative damage, participate to the cytotoxic effect of PlTX. A descriptive meta-analysis of proteomic data about toxic responses induced by other classes of microalgal toxins, such as okadaic acid and microcystins, reveals that several protein components participating to cell stress responses, particularly oxidative stress, are affected when the systems are exposed to effective doses of those toxins. Detected changes comprise either the total levels of individual proteins, or the relative proportions of isoforms distinguishable according to their post-translational modifications. A common set of protein effectors emerges from our analysis, suggesting that cytotoxic effects exerted by some biotoxins could share molecular processes executing cell death responses.

Bacteria associated to benthic dinoflagellate Ostreopsis cf. ovata cultures were removed to assess their effects on algal growth and toxins' production. Bacteria were removed using an antibiotic cocktail (streptomycin, ciprofloxacin, gentamicin and penicillin G). The actual axenic status of antibiotic treated cultures and bacterial growth in control cultures were assessed by epifluorescence microscopy using SYBR gold dye. The removal of bacteria unaffected algal growth, except conferring a higher cell number at mid stationary phase. Toxin profile and quantification of each toxin (PLTX, OVTX-a, -b, -c, -d, -e) were performed by HR LC-MS on both cell pellet and growth medium extracts. No changes in toxins' profile nor in cell and extra-cellular toxins' concentrations were found between bacteria-free and control cultures at the early stationary phase. Whereas, in late stationary phase axenic cultures showed significant lower cell toxins' concentrations and higher extra-cellular toxins' values, though not significantly (total cell toxins' concentrations: 39.3 and 24.9 pg cell—1; total extra-cellular toxins' concentrations: 23.8 and 28.3 μgL—1 for control and bacteria-free cultures, respectively).

Three strains of Ostreopsis ovata were isolated from sea water and algae collected either along the Tyrrhenian or the Adriatic Sea. Evaluation of growth profile of the three O. ovata strains in batch cultures were analyzed at four light intensities (10, 100, 400, 650 µmol m^-2 s^-1). Ostreopsis ovata cell densities increased at all light intensities except at 10 µmol m^-2 s^-1. The three strains showed growth rates with values from 0.24 to 0.56 day. The allelopathic effect of the filtrate of O. ovata culture on growth of Coscinodiscus granii, Prorocentrum minimum and Coolia monotis was studied. Filtrate from culture in exponential and senescent growth phase was considered. The results revealed a weak allelopathic effect on the growth of the three microalgae with an inhibition on the growth of C. monotis and P. minimum.

The tropical benthic dinoflagellate Ostreopsis cf. ovata recently occurred in the shallow coastal NW Mediterranean where blooms have caused health problems to humans. As part of the MediOs 2 project within the French research program Liteau III, we investigated the possible effects of this toxic microalga on the meiofauna (i.e. metazoans ranging from 40 µm to 1 mm in size) inhabiting the very common brown macroalga Halopteris scoparia. The macroalga was sampled in triplicate at 0.5 m depth in six stations along the French and Italian coasts on seven occasions in 2008. Ostreopsis bloomed in summer in three out of the six stations with abundances ranging from 2.5 to 6.6 10⁵ cells g^—1 macroalgal wet weight. Mean metazoan meiofauna densities ranged from 1274 to 9774 individuals g^—1 macroalgal spin-wet weight. Statistical analyses revealed that changes in the community structure were associated with high abundances of Ostreopsis. The most affected organisms were the nauplii suggesting a negative impact on harpacticoid copepod reproduction.

The development of Ostreopsis cf. ovata, a toxic benthic dinoflagellate has increased in the North Western Mediterranean Sea, causing health, ecological and economical concerns. In order to understand the ecological impact on macroinvertebrates, a preliminary study was carried on edible grazers, the sea urchin Paracentrotus lividus and the limpet Patella spp. Their densities were followed toward the abundance of O. cf. ovata. Thus, in 2008, we performed a monthly field survey in scuba-diving in three sites of the North Western Mediterranean Sea (Genoa, Nice and Villefranche-sur-Mer) at the sea surface and at 1 and 3 m depth. Results showed that at 1 m and 3 m depth, the density of P. lividus was not clearly affected by a strong development of Ostreopsis. Decrease in P. lividus abundance may be due to natural variation or to fishing activities especially in France. Regarding the density of Patella spp., only one significant decrease was observed between July and August 2008 in Genoa. Patella species are living in the interdital zone, we could therefore hypothese that the limpets were intoxicated either by direct ingestion of O. cf ovata by grazing and/or by the toxins released in the surrounding water.

The main goal of the multidisciplinary MediOs project was to acquire and analyze pertinent scientific knowledge in fields as diverse as ecology, biology, chemistry, epidemiology or socio-economics concerning the occurrence of species belonging to genus Ostreopsis (toxic benthic dinoflagellates) in the Mediterranean. The economic impact of Ostreopsis was estimated, based on the intensity and frequency of blooms. Results obtained allowed science-based recommendations concerning the management of risk, with suggestions to optimize environmental surveys, to initiate a food risk survey, and to structure actions at the national level.

As shown in this report, the integration of a research project with a monitoring program improves the detection and management of Ostreopsis blooms in Catalonia. The research project benefits from information previously obtained from several localities by the monitoring program, which in turn profits from the specific findings and conclusions contributed by the research project.

This study reports some recent phylogeographical considerations on the genus Ostreopsis distribution worldwide, with particular attention to the Mediterranean Sea, and new recent advances on the quali-quantitiative detection of Ostreopsis species along coastal areas of the Mediterranean Sea based on the PCR and quantitative real time PCR (qrt-PCR) assays. It was found that O. cf. ovata is widely dispersed throughout tropical and warm temperate coastal areas. In the Atlantic/Mediterranean region it represents a panmictic population that is highly divergent from Indo-Pacific populations. Furthermore, we demonstrated that the developed qrt-PCR assay is specific, robust and high sample throughput for the quantification of the toxic O. cf. ovata in the environmental samples. This molecular approach may be considered alternative to traditional methods of microscopy and applied for the survey of benthic toxic microalgal species in marine ecosystems.

In the last decades, blooms of Ostreopsis ovata are increasingly frequent in several Mediterranean coastal areas, sometimes causing problems to the public health. The quantification of O. ovata abundances is generally performed by quantifying the number of cells per gram of macroalga, often preventing the comparison of abundances from different sites if cell quantifications are performed on different algal species. In this paper we propose a sampling method based on the use of a modified plastic syringe designed to quantify benthic cells abundances independently from the type of substratum. The method was tested in the O. ovata monitoring carried out in the Gulf of La Spezia (Ligurian Sea) and along the Apulian coasts (Southern Italy) since 2007. In 2009 the “syringe” method was compared with the classic methodology used in national monitoring of O. ovata. The syringe method seems interesting in terms of time costs and effectiveness, both for sample collection and processing, allowing quick and simple sampling of several sites along the coastline. The technique turned out to be adequate when a fast and reliable estimate of O. ovata “reservoir” near the bottom was required, in order to forecast toxic algal blooms in coastal areas.

Both benthic and planktic dinoflagellates can produce harmful algal blooms. However most of the studies conducted so far emphasized on planktic species. In the present review, we assessed the main ecological factors affecting the population dynamics of bloomforming benthic dinoflagellates, with particular emphasis on Ostreopsis and Gambierdiscus. Based on the basic equation of population dynamics, we mainly focused on growth, predation, mortality, immigration and dispersion. Factors determining the dynamics of benthic dinoflagellate populations are very different from the well-studied case of planktic dinoflagellates. The relative movement of cells and water is the main difference as benthic dinoflagellates depend on a fixed substratum while planktic dinoflagellates depend on a water body. Any alteration in the substratum will affect benthic dinoflagellate populations, as for example the changes in seaweeds concentrations due to predation by sea urchins. We also evaluated the impact of global changes on dinoflagellates bloom occurrence.

The tropical genus Ostreopsis has been recorded along Italian coasts of the Mediterranean Sea since the ‘90s, but large bloom events have been reported only in recent years. In order to describe O. ovata bloom dynamics and provide a better understanding of environmental variables involved in triggering blooms, we collected a time series of data in Genoa (North Western Mediterranean) from 2006 to 2010. Cell abundances in the water column and epiphyte on the macroalgae were assessed during the summer months. Water and meteorological variables were concurrently collected.

We elaborated a meaningful explanatory model, performing multiple correlations between bloom magnitude (maximum cell concentration) and length (extent of the bloom event) and water/meteorological features. Such a model highlights a significant role of water temperature, barometric pressure and wind speed in affecting bloom dynamics. It represents a good base for managers in the attempt of forecasting O. ovata blooms and, specifically, toxic events, in an ecological, economic and sanitary perspective.

The ecology of Ostreopsis cf. ovata blooms was investigated to evaluate the role of environmental factors (temperature, hydrodynamism, nutrient concentrations, depth and substratum) on the bloom dynamics. This paper reports the present knowledge on O. cf. ovata blooms along the Conero Riviera (NW Adriatic Sea), on the basis of samplings carried out from 2006 to 2010. The annual maximum of benthic cell abundance was always observed in late-summer, reaching the order of magnitude of 10⁶ cells g^-1 fw (corresponding to 10⁷ cells g^-1 dw and 10⁴ cells cm^-2) on macrophyte samples. Comparing the mean abundances settled on seaweeds with those growing on hard substrata, significantly higher abundances were observed on the latter. Hydrodynamism plays a major role in Ostreopsis blooms, as significantly higher abundances were observed in sheltered sites compared with exposed ones. The abundances of O. cf. ovata showed a marked decrease with depth. Temperature and nutrients do not seem to play an important effect on the O. cf. ovata blooms. High levels of ovatoxins were recorded in natural samples; episodes of death of both benthic invertebrates (limpets, sea urchins and mussels) and macroalgae were commonly observed during O. cf. ovata blooms.

An extensive sampling program was performed in the Atlantic side of the Iberian Peninsula on 17 sites during 2010 and 2011 summers, in order to characterize the distributional pattern of potential toxic dinoflagellates of the genus Ostreopsis. The study area presents a discontinuity in the species distribution in a pattern that parallels that of summer water temperature. Ostreopsis was not found in a relatively wide fringe of the Northwest side of the Peninsula, as water temperature is markedly lower than that in the Northeast and Southwest extremes where Ostreopsis has been found. Comparing the observed distribution of Ostreopsis on the Atlantic coast of the Peninsula with different sea surface temperature (SST) percentiles, it is notable that neither minimum nor maximum temperatures observed in the range of the study area can explain the species distribution but presumably is the length of the warm period what limits the genus presence. Thus we hypothesize that for Ostreopsis to be present in a certain area three continuous months with SST above 19.5°C may be necessary.

This work describes the first toxic event (human intoxications and sea urchin mortality) related to Ostreopsis bloom in Algerian coastal waters. The distribution of Ostreopsis is presented in three rocky beaches of Algiers Wilaya, where several cases of human intoxications were registered during July 2009. The maximum abundances attained by Ostreopsis in other stations of the network established by the Agency for the Protection and Promotion of Algiers Wilaya coasts (APPL) for monitoring HABs species are also presented. We discuss some of the factors that could explain this toxic episode.

In order to investigate the identity, abundance and toxicity of a distinctive Ostreopsis species present in the southern-central coast of Cuba, Ostreopsis field populations were examined during January-September of 2010. The morphological and partial LSU phylogenetic data suggested the presence of O. lenticularis, although a very close species like O. labens could not be discarded. Results indicated the presence of palytoxin-like molecules in a natural extract at concentration of 0.12 pg/cell. Ostreopsis populations were very stable through the course of the study, and a maximum of 7.9 × 10⁴ cells/g of macroalgae fresh weight was recorded on June.

Harmful events caused by benthic microalgae have recently garnered a high level of attention in temperate areas, upon reports of Ostreopsis species causing fauna damage, food intoxication and respiratory illness. A resurgence of interest has also occurred in ciguatera fish poisoning (CFP), a syndrome associated with the consumption of reef fish contaminated by ciguatoxins produced by the dinoflagellate genus Gambierdiscus in tropical and subtropical areas. To foster research on events caused by benthic microalgae, the SCOR-IOC Global Ecology and Oceanography on Harmful Algal Blooms (GEOHAB) program started a Core Research Project on Benthic Harmful Algal Blooms (BHABs). During an Open Science Meeting (OSM) in 2010, scientists studying benthic and planktonic microalgae identified the main gaps of knowledge and the research, technology and infrastructure needs in the field of the ecology and oceanography of BHABs. The issues addressed during the OSM covered the state of taxonomy, sampling methods, biogeography, genetic diversity, ecology and ecophysiology of BHABs, along with the identification of research priorities and approaches to be taken in order to improve understanding and prediction of BHABs.