Responses of pelagic microorganisms to contamination by polluted sediments – RISCO

It is now well recognized that the risk of environmental contamination by chemical pollutants is particularly high in coastal environments where past, present and forecasted demographic increases, are amplifying the pressures in these ecosystems. Unraveling the links between contamination pressure and living organisms is a key feature in environmental management of anthropogenic ecosystems. In coastal seas and lagoons, sediment act as a sink for contaminants, however, this storage is not definitive, particulate-bound pollutants may be remobilized into the water column. This potential of remobilization for pollutants is a major problem for an anthropogenic ecosystem because even the anthropogenic source of pollution is identified and stopped; contaminated sediments represent a non-negligible pollution source that can severely affect the ecosystemic services. It is therefore a major of concern to take into account this potential source of pollution in the management of coastal anthropogenic ecosystems. During a resuspension of contaminated sediments, a trail of pollutants can be released (metals, organic compounds, nutrients), sometimes in trace levels; which nevertheless may have significant effects on diversity and function for the pelagic communities.
The aim of RISCO project is to determine the consequences of pollution from contaminated sediments on the diversity and function of pelagic microbial communities, the first levels of the trophic chain. For this purpose, bacterioplankton and phytoplankton communities, sampled in a Mediterranean coastal ecosystem, the Bizerte lagoon (Tunisia), will be exposed to pollutants in realistic situations reflecting the doses and the exposure conditions observed during sediment resuspension to take into account the interactions (antagonism, synergism...) between contaminants for a rigorous evaluation of their toxicity. RISCO will study the mechanisms of adaptation, structural and functional, developed by bacterioplankton and phytoplankton to cope with contaminants at different level of organization, from the organism with the detection of specific genes to the community scale with the identification of contaminant tolerant populations. The mechanisms of adaptation will be determined as a function of the selection pressure exerted by contaminants and the environmental conditions.
Results of RISCO will not be restricted to the Bizerte lagoon, but will allow providing pertinent indicators for a better understanding of the functioning and the management of similar shallow water ecosystems more or less anthropized such as the 632 lagoons inventoried in the Mediterranean basin.