The Uptake of Organic Matter and the Release of Inorganic Nutrients by Bivalve Suspension Feeder Beds

Abstract

In many estuarine and coastal ecosystems, bivalve suspension feeders, such as mussels, oysters, cockles and various species of clams, occur in high densities. They are often concentrated in beds and reefs (Wolff 1983). Feeding is performed by pumping and filtering large volumes of water through the gills, and results in a continuous flux of particulate matter from the water column to the bivalve beds. Particles of a size larger than 2 μm in diameter are effectively retained by most species (Jørgensen 1990). In various ecosystems, depletion of organic matter, bacteria and phytoplankton in the overlying water, due to the filtration activity of bivalves, has been observed (Wright et al 1982; Carlson et al 1984; Fréchette and Bourget 1985; Nichols 1985; Peterson and Black 1987; Navarro et al 1991). Observations in San Francisco Bay gave rise to the hypothesis that benthic filter feeding kept the algal biomass at a low level (Cloern 1982; Alpine and Cloern 1992), and could act as eutrophication control (Officer et al 1982). This idea was based on extrapolation of individual clearance rates, taken from the literature, to the total Bay volume.