Pierre-Yves Pascal

The toxicological interaction between ocean acidity and metals in coastal meiobenthic copepods.

Increased atmospheric CO(2) concentrations are causing greater dissolution of CO(2) into seawater, and are ultimately responsible for todays ongoing ocean acidification. We manipulated seawater acidity by addition of HCl and by increasing CO(2) concentration and observed that two coastal harpacticoid copepods, Amphiascoides atopus and Schizopera knabeni were both more sensitive to increased acidity when generated by CO(2). The present study indicates that copepods living in environments more prone to hypercapnia, such as mudflats where S. knabeni lives, may be less sensitive to future acidification. Ocean acidification is also expected to alter the toxicity of waterborne metals by influencing their speciation in seawater. CO(2) enrichment did not affect the free-ion concentration of Cd but did increase the free-ion concentration of Cu. Antagonistic toxicities were observed between CO(2) with Cd, Cu and Cu free-ion in A. atopus. This interaction could be due to a competition for H(+) and metals for binding sites.

Key features of intertidal food webs that support migratory shorebirds.

The migratory shorebirds of the East Atlantic flyway land in huge numbers during a migratory stopover or wintering on the French Atlantic coast. The Brouage bare mudflat (Marennes-Oléron Bay, NE Atlantic) is one of the major stopover sites in France. The particular structure and function of a food web affects the efficiency of carbon transfer. The structure and functioning of the Brouage food web is crucial for the conservation of species landing within this area because it provides sufficient food, which allows shorebirds to reach the north of Europe where they nest. The aim of this study was to describe and understand which food web characteristics support nutritional needs of birds. Two food-web models were constructed, based on in situ measurements that were made in February 2008 (the presence of birds) and July 2008 (absence of birds). To complete the models, allometric relationships and additional data from the literature were used. The missing flow values of the food web models were estimated by Monte Carlo Markov Chain – Linear Inverse Modelling. The flow solutions obtained were used to calculate the ecological network analysis indices, which estimate the emergent properties of the functioning of a food-web. The total activities of the Brouage ecosystem in February and July are significantly different. The specialisation of the trophic links within the ecosystem does not appear to differ between the two models. In spite of a large export of carbon from the primary producer and detritus in winter, the higher recycling leads to a similar retention of carbon for the two seasons. It can be concluded that in February, the higher activity of the ecosystem coupled with a higher cycling and a mean internal organization, ensure the sufficient feeding of the migratory shorebirds.

What Is the Relative Importance of Phytoplankton and Attached Macroalgae and Epiphytes to Food Webs on Offshore Oil Platforms

Abstract Offshore oil platforms function as artificial reefs, but little is known about the food webs that fuel platform-dwelling biota. Here, we use carbon and nitrogen isotopes in tissues of biota from two offshore oil platforms to estimate the importance of phytoplankton and platform-associated macroalgae and epiphytic microalgae to the diets of platform-dwelling consumers. Although the consumption of macroalgae was indicated for small, mobile consumers including crabs, amphipods, and harpacticoid copepods, both a Bayesian mixing model and temporal changes in isotope composition identified phytoplankton as the most important basal resource for these consumers. Sessile suspension-feeding barnacles and oysters consumed phytoplankton and epiphytes, and probably redirected large amounts of pelagic production to other consumers. Secondary consumers including syllid polychaetes and the blennies, Molly Miller Scartella cristata and Tessellated Blenny Hypsoblennius invemar, exhibited a distinct contribution from epiphytes although large ranges in all potential basal resources were observed. Elemental and isotope analysis of the gut contents of individuals indicated that the nektonic Gray Triggerfish Balistes capriscus was omnivorous, directly consuming reef-derived macroalgae and epiphytes as well as animal tissue. Although we found that reef-derived resources entered benthic and nektonic food webs surrounding platforms, phytoplankton was the dominant basal resource fueling platform-dwelling communities at the time of our study, and no consumer studied specialized on a diet of red macroalgae. If these findings are generally representative, platform-derived benthic algae would not be integral to food-web function on artificial reefs, and reef function should be similar in areas both favorable to and unfavorable to in situ algal growth.

Persistent benthic communities in the extreme dynamic intertidal mudflats of the Amazonian coast: an overview of the Tanaidacea (Crustacea, Peracarida)

The extreme dynamics of the Amazonian coast and associated mudbanks raises questions about their unknown resistant infauna. In order to fill the gap, we investigated the seasonal variations of species composition, abundance and population structure of Tanaidacea in two dynamic mudbanks near the coast of French Guiana. Despite the low species richness recorded for this taxon, the very high densities and biomass of tanaids constituted a potential plentiful trophic resource for many coastal species, such as shorebirds, fish, shrimps, and crabs. The estuarine habitat at Sinnamary presented more tanaid species than the bare marine mudflat at Awala-Yalimapo. All species showed strong female-biased sex ratios and differed in range of total length and stage of maturity. The species with smaller body size with sexual maturity occurring at an earlier stage were dominant and widely distributed. Pore water salinity and predator pressure may be considered key factors driving seasonal variations of tanaid abundance and population structure. This study gives a novel insight into the macrobenthos communities along the highly dynamic Amazonian coast.