SESTON DYNAMICS AND FOOD AVAILABILITY ON MUSSEL AND COCKLE BEDS

To provide a better understanding of seston dynamics in relation to fo od supply to the benthos, a series of 13-h tidal cycle sampling progra mmes was executed in the Oosterschelde estuary (The Netherlands). Samp les were taken near the surface and near the bottom on two subtidal mu ssel cultivation plots and on two intertidal cockle beds. Long-term an nual variablity of seston concentrations was lower than coefficients o f variance of the short-term tidal cycle seston data at the intertidal stations, and higher than at the subtidal stations. Near-bottom relat ive to surface concentrations were highest for suspended particulate m atter (SPM), followed by particulate organic carbon (POC), and chlorop hyll. There was no food depletion near the bottom but food quality was lower, presumably due to re-suspension of sediment, including low-qua lity biodeposits. Chlorophyll concentrations were lower in ebb than fl ood water at all stations, which was ascribed to feeding activity of t he bivalves. At the subtidal stations, SPM and POC concentrations were also lower during low water, owing to sedimentation. There was a posi tive correlation at the intertidal stations of seston quantity with wi nd speed and wave action. At a wave length exceeding twice the water d epth, re-suspension of low quality bottom material was observed and se ston quality decreased. It was concluded that food availability for be nthic suspension feeders was lower than suggested by routine monitorin g data. At the intertidal stations, food quality was further reduced d uring periods of increased wind velocities and wave action. The low ne ar-bottom food quality can partly be considered as an effect of the fe eding activity of the benthic suspension feeders. (C) 1997 Academic Pr ess Limited.