TEMPORAL CHANGES IN THE BIOCHEMICAL-COMPOSITION AND NUTRITIONAL-VALUEOF THE PARTICULATE ORGANIC-MATTER AVAILABLE TO SURFACE DEPOSIT-FEEDERS - A 2-YEAR STUDY

Gross sedimentation rates (GSR) were monitored together with the main characteristics of the collected material (i.e. organic content, C, N, total proteins, Lipids, carbohydrates, available proteins and amino a cids) over a 2 yr cycle at a shallow station (18 m) of the bay of Bany uls, France. In addition, sediment pigment concentrations and meiofaun al densities were recorded monthly during a 1 yr period. GSR ranged be tween 0.6 and 317.8 g DW m(-2) d(-1). Spring and summer were character ized by relatively low and constant GSR whereas fall and winter were c haracterized by relatively high and highly variable GSR. There was a n egative relationship between GSR and the organic content of material c ollected within the sediment traps, suggesting the importance of resus pension in controlling GSR. Growth rates of the deposit-feeding bivalv e Abra ovata fed sediment trap material collected on 6 sampling dates were also measured. Significant changes in important nutrient componen ts (e.g. available proteins) of sedimenting materials from these diffe rent sampling dates correlated with growth differences and confirmed t he existence of temporal changes in the quality of the material collec ted in the sediment traps. The highest growth rate was obtained for th e material collected during May 1993, which coincided with maximal mei ofauna densities and maximal pigment concentrations at the surface of the sediment. The best description of growth was obtained when using a vailable proteins and total lipids as the independent variables of sim ple linear regression models. This supports the use of these parameter s as descriptors of food quality. The consequences of our results on t he parameterization of changes in food quality within models of contin ental shelf food webs are discussed, It is suggested that such changes should be simulated through control functions based on available prot ein contents.