FILTRATION AND RESUSPENSION OF PARTICULATE MATTER AND PHYTOPLANKTON ON AN INTERTIDAL MUSSEL BED IN THE OOSTERSCHELDE ESTUARY (SW NETHERLANDS)

In situ measurements were carried out on an intertidal mussel bed in t he Oosterschelde estuary, SW Netherlands. Exchange of suspended partic ulate matter and phytoplankton between the water column and the mussel bed was measured with a Benthic Ecosystem Tunnel. In situ clearance r ates of the mussel bed were compared to clearance rates of individual mussels measured in a field station under ambient conditions. Concentr ations of suspended particulate matter (SPM) and particulate organic c arbon (POC) in the water column above the tidal flat were affected by wind-induced resuspension. Chlorophyll a concentrations were higher du ring flood tides than during ebb tides, and were not affected by wind- induced resuspension. Clearance rates of the mussel bed ranged from 1. 3 to 7.1 m(3) m(-2) h(-1). In situ measured clearance rates generally were comparable to rates observed in measurements with individual muss els in a field station. Uptake of SPM and POC by the mussel bed was hi ghly variable. Under calm weather conditions, uptake rates were correl ated with inflow concentrations. Net uptake of phytoplankton was relat ively higher than the uptake of POC, indicating that a major part of t he POC was resuspended and exported from the mussel bed after filtrati on. In addition, wind stress induced considerable resuspension and exp ort of SPM and POC from the mussel bed. Chlorophyll a uptake was less influenced by wind, and high rates of uptake, caused by mussel filtrat ion, were observed. The result of filtration and resuspension processe s was a net uptake by the mussel bed of particulate matter containing a relatively high proportion of phytoplankton: the mussel bed acted as a selective filter for phytoplankton.