S. Cohu

Trends in Ostreopsis proliferation along the Northern Mediterranean coasts

Harmful benthic microalgae blooms represent an emergent phenomenon in temperate zones, causing health, ecological and economic concern. The main goal of this work was to compile records of Ostreopsis at large temporal and spatial scales, in order to study the relationship between cell abundances, the periodicity and intensity of the blooms and the role of sea water temperature in 14 Spanish, French, Monegasque and Italian sites located along the northern limits of the Mediterranean Sea. General trends were observed in the two considered basins: the north-western Mediterranean Sea, in which higher cell abundances were mostly recorded in mid-summer (end of July), and the northern Adriatic Sea where they occur in early fall (end of September). The sea-water temperature does not seem to be a primary driver, and the maximal abundance periods were site and year specific. Such results represent an important step in the understanding of harmful benthic microalgae blooms in temperate areas, and provide a good base for policy makers and managers in the attempt to monitor and forecast benthic harmful microalgae blooms.

Occurrence of the toxic dinoflagellate Ostreopsis cf. ovata in relation with environmental factors in Monaco (NW Mediterranean)

To study environment characteristics favoring the toxic benthic dinoflagellate Ostreopsis cf. ovata, a survey was conducted in Monaco (NW Mediterranean Sea), in summers 2007 and 2008. Epiphytic and planktonic blooms occurred almost simultaneously and a high variation of abundances at low spatial scales was observed. An early and very marked bloom occurred in 2007, compared to a later and less abundant development in 2008. These distinct patterns in bloom timing corresponded with very different hydroclimatic scenarios in 2007 (hot spring and relatively cold summer) and 2008 (standard year compared to the median year profile estimated with data from 1995 to 2008). No clear impacts of summer seawater temperature, rainfall or nutrient concentrations were evident. Strong wind may favor the dispersal of benthic and planktonic cells. Our study suggests that further investigations are needed to examine the potential role of Ostreopsis nutritional mode (i.e. autotrophy vs. mixotrophy).

Interactions between scientists, managers and policy makers in the framework of the French MediOs project on Ostreopsis (2008-2010)

Abstract 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.

Preliminary Assessments of the Impact of Ostreopsis cf. ovata (Dinophyceae) Development on Macroinvertebrates in the North Western Mediterranean Sea

Abstract 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.