Seasonal variations in suspended particulate matter in the Marennes-Oleron Bay, France, using lipids as biomarkers

In the most important oyster-producing area in France, an investigation was conducted to determine the origin of particulate organic matter (POM) of the size, < 100 mu m, available to oysters. Suspended particulate matter (SPM) was sampled monthly over 1 year at one estuarine station in the Bay, Fort Boyard, and at one river station in the Charente at St. Savinien. Lipid-class and fatty-acid profiles were determined in the SPM. At Fort Boyard, variations in amounts of SPM and its ratio of both POC:Chlorophyll a and C:N were associated with changes in river discharge rates, local resuspension and phytoplankton proliferation. High concentrations of mineral and detrital particles were observed in winter, and low levels during the rest of the year, when phytoplankton blooms occur frequently. Lipid-class and fatty-acid profiles varied in relation to seasonal changes in both weather and hydrology. The terrestrial contribution to SPM was highest in winter, when river outflow and resuspension in the Bay were also maximal. High bacterial biomass occurred in association not only with river detritus, but also with early-spring blooms. Microalgal fatty acids were predominant from spring to autumn and, by using compounds shown to be of taxonomic significance, the presence of diatoms could be discerned from that of other microalgae. In winter, the estuarine and freshwater stations showed similar lipid compositions, with dominance by terrestrial and bacterial biomarkers. In summer, however, fatty-acid profiles were very different at the two sites, showing clear temporal variations, which suggest that the Bay and the River then function as separate systems and follow different biological patterns. (C) 1996 Academic Press Limited