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 investigatio n was conducted to determine the origin of particulate organic matter (POM) of the size, < 100 mu m, available to oysters. Suspended particu late matter (SPM) was sampled monthly over 1 year at one estuarine sta tion 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 riv er 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 phytoplank ton blooms occur frequently. Lipid-class and fatty-acid profiles varie d in relation to seasonal changes in both weather and hydrology. The t errestrial contribution to SPM was highest in winter, when river outfl ow and resuspension in the Bay were also maximal. High bacterial bioma ss occurred in association not only with river detritus, but also with early-spring blooms. Microalgal fatty acids were predominant from spr ing to autumn and, by using compounds shown to be of taxonomic signifi cance, the presence of diatoms could be discerned from that of other m icroalgae. In winter, the estuarine and freshwater stations showed sim ilar lipid compositions, with dominance by terrestrial and bacterial b iomarkers. In summer, however, fatty-acid profiles were very different at the two sites, showing clear temporal variations, which suggest th at the Bay and the River then function as separate systems and follow different biological patterns. (C) 1996 Academic Press Limited