Seawater DMS in a perturbed coastal ecosystem

Abstract

DMS concentrations, chlorophyll a concentrations, abiotic parameters of water quality and quantitative samples of plankton were carried out once a month from January to December 1997 into two zones of a semi-enclosed french littoral ecosystem (Toulon Bay, NW Mediterranean sea). This bay is divided into two subecosystems by an artificial breakwater: the inner bay (polluted zone, P) is largely influenced by anthropogenic perturbations and the outer bay (less polluted, LP) is much less polluted. We found greater concentrations of DMS and chlorophyll a, of phytoplankton and zooplankton densities and biomasses in the polluted zone (P) than in the less polluted zone (LP) of the bay. The DMS concentration and phytoplankton biomass were strongly correlated, and a high degree of eutrophication may contribute, in connection with other factors, to a greater production of phytoplankton which in turn enhances the DMS production. The DMS concentration in coastal polluted zones is then greatly higher than in open sea (around three times) and this greater production should be taken into account for the global estimation, at least on a local scale, of DMS production in seawater, which is a key factor for the biogenic sulfur cycle.