Temporal changes in the biochemical composition and nutritional value of the particulate organic matter available to surface deposit-feeders:a two year study

Abstract

Gross sedimentation rates (GSR) were monitored together with the main characteristics of the collected matenal (i.e. organic content, C, N, total proteins, lipids, carbohydrates, available proteins and amino acids) over a 2 yr cycle at a shallow station (18 m) of the bay of Banyuls, France. In addition, sediment pigment concentrations and meiofaunal densit~es were recorded monthly during a 1 yr period. GSR ranged between 0.6 and 317.8 g DW m ' cl'' Spring and summer were characterized by relatively low and constant GSR whereas fall and wlnter were characterized by relat~vely high and hlghly variable GSR. There was a negatlve relationship between GSR and the organic content of material collected within the sediment traps, suggesting the importance of resuspension in controlling GSR. Growth rates of the deposit-feeding bivalve Abra ovata fed sediment trap material collected on 6 sampling dates were also measured. Significant changes in important nutrient components (e.g. available proteins) of sedimenting materials from these different sampling dates correlated with growth differences and confirmed the existence of temporal changes in the quality of the material collected in the sediment traps. The highest growth rate was obtained for the material collected during May 1993, which coincided with maximal meiofauna densities and maximal pigment concentrations at the surface of the sediment. The best descript.ion of growth was obtained when using available proteins and total lipids as the independent variables of simple linear regression models. This supports the use of these parameters as descriptors of food quality. The consequences of our results on the parameterization of changes in food quality within models of continental shelf food webs are discussed. It is suggested that such changes should be simulated through control functions based on available protein contents.