Aurelie Blanfuné

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).

Unexpected abundance and long-term relative stability of the brown alga Cystoseira amentacea, hitherto regarded as a threatened species, in the north-western Mediterranean Sea.

Cystoseira amentacea is a Mediterranean endemic alga thriving on very shallow rocky substrates. It has been considered as a threatened species, having experienced a steady decline and is therefore protected by international conventions. The historical distribution of the species has been assessed along the French Mediterranean coast, on the basis of 467 articles and herbarium vouchers. We have produced an accurate map of its current distribution and abundance along 1832 km of coastline, through in situ surveys. C. amentacea was observed along 1125 km of shoreline, including 33% of almost continuous or continuous belt. In most of its range, there is no evidence of loss, except in 4 areas of Provence, French Riviera and Corsica. A significant relation was found between the absence or low abundance of C. amentacea and the vicinity of ports and large sewage outfalls. The status of conservation of the species should therefore be reassessed.

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.

Unexpected Temporal Stability of Cystoseira and Sargassum Forests in Port-Cros, one of the Oldest Mediterranean Marine National Parks

Abstract Fucales (Phaeophyceae, kingdom Stramenopiles) are ecosystem engineers and canopy forming seaweeds that are dramatically declining worldwide. In the Mediterranean Sea, Cystoseira spp. and Sargassum spp. have been shown to be locally extinct or locally functionally extinct, i.e. no longer forest forming, even in some Marine Protected Areas (MPAs). The patterns of change in the diversity and abundance of Fucales taxa within the Port-Cros Archipelago (Port-Cros National Park; PCNP) was studied by comparison of recent data (2005 to 2007) with previous data in order to measure the effects of protection since the creation of the park in 1963. Three taxa were reported before 1963, 10 between 1963 and 2005 and 17 between 2005 and 2007. Considering the biology of the species listed and the distance from the coast of the Port-Cros Archipelago, it is unlikely that this increase in species richness has resulted from colonisation events through the implementation and enforcement of effective protection of the area but is rather due to an increase in sampling effort. In contrast to other Mediterranean areas, the populations of Fucales are still highly diversified and stable. Only one species, C. brachycarpa var. brachycarpa, has declined in the 1-10-m depth zone in relation to the proliferation of herbivorous species, possibly enhanced by the PNPC conservation strategy. The overall good conservation of Fucales populations of the PCNP is probably the result of the absence of habitat destruction, high seawater quality and the regulation of human activities (fishing, tourism, diving).

Connectivity of populations of the seaweed Cystoseira amentacea within the Bay of Marseille (Mediterranean Sea): genetic structure and hydrodynamic connections

Abstract The brown alga Cystoseira amentacea (Phaeophyceae, kingdom Stramenopiles) constitutes an extensive belt in the shallowest horizon of the infralittoral (the infralittoral fringe), in the Mediterranean Sea. Hydrodynamic modelling was used to infer connectivity between populations of C. amentacea of the Bay of Marseille (Provence, France, NW Mediterranean) and to test the correlation between genetic and hydrodynamic connectivity. We genotyped 183 individuals from six populations at six microsatellite loci. Current fields were computed at a fine resolution by a 3D numerical model simultaneously utilizing the local winds, the Rhone River inputs and offshore circulation. The Lagrangian trajectories of the propagules (zygotes, or rafts) were computed with the ICHTHYOP software, for both NW and SE strong wind forcing (11–12 m·s-1). Cystoseira amentacea displayed a strong and significant genetic structure, not correlated with the geographic distance, i.e. a lack of isolation by distance (IBD). The pairs of sites with the lowest FST were those connected by the current patterns. The time needed for a zygote or a raft to travel from one location to another ranged from 4 to 18 h (i.e. within the survival time of a zygote) and for distances of up to 23 km. Despite the very low dispersal capability of the zygotes, long-distance dispersal is therefore possible. Several non-exclusive processes can account for the genetic structure of C. amentacea populations, such as step-by-step local dispersal, long-distance dispersal of zygotes and rafts by currents, during storms, and the “priority effect”, i.e. the importance of the timing of arrival of the propagules.

Distribution and abundance of Ostreopsis spp. and associated species (Dinophyceae) in the northwestern Mediterranean: the region and the macroalgal substrate matter

The range of Ostreopsis (Dinophyceae), a taxon harmful to both human health and ecosystems, has spread from a tropical and subtropical range of distribution to temperate areas, such as the Mediterranean Sea. This study has evidenced widespread summer occurrence in the northwestern Mediterranean, from French Catalonia to the French Riviera and Corsica. Ostreopsis spp. are usually associated with two other dinophycean taxa, Prorocentrum lima and Coolia spp. No obvious correlation (indicative of competition and/or facilitation) between the abundance of the three taxa was evidenced. In addition to local variability, we observed regional variability, with low abundance and local absence in French Catalonia and Languedoc, which contrasted with overall abundance and blooms in Provence, the French Riviera and Corsica, especially in late summer. Possible causes for this regional variability are discussed. Furthermore, the three taxa can grow on a variety of macroalgal substrates: 34 taxa belonging to the fleshy, bushy, flat and erect morpho-functional groups. Some macroalgal species were correlated with either high or low abundance of the studied dinophycean taxa and could therefore enhance or hinder their blooming.

An ecosystem-based approach to assess the status of Mediterranean algae-dominated shallow rocky reefs

A conceptual model was constructed for the functioning the algae-dominated rocky reef ecosystem of the Mediterranean Sea. The Ecosystem-Based Quality Index (reef-EBQI) is based upon this model. This index meets the objectives of the EU Marine Strategy Framework Directive. It is based upon (i) the weighting of each compartment, according to its importance in the functioning of the ecosystem; (ii) biological parameters assessing the state of each compartment; (iii) the aggregation of these parameters, assessing the quality of the ecosystem functioning, for each site; (iv) and a Confidence Index measuring the reliability of the index, for each site. The reef-EBQI was used at 40 sites in the northwestern Mediterranean. It constitutes an efficient tool, because it is based upon a wide set of functional compartments, rather than upon just a few species; it is easy and inexpensive to implement, robust and not redundant with regard to already existing indices.

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.

Where seaweed forests meet animal forests: the examples of macroalgae in coral reefs and the Mediterranean coralligene ecosystem

Where seaweed forests meet animal forests: the examples of macroalgae in coral reefs and the Mediterranean coralligene ecosystem