Grazing of Natural Particulates by Bivalve Molluscs: A Spatial and Temporal Perspective

Abstract

The production of suspension feeders may be limited by processes ranging from cm to km scales, and time periods from seasonal changes in temperature to tidal cycle changes in the seston flux. Field observations have shown that the processing of phytoplankton, organic detritus and inorganic particulates by shellfish beds results in kilometer scale effects on particle concentration which can be simulated by computer modelling. A four-year study (1986--1990) (Newell 1991) at four commercial mussel bottom lease sites in Maine, USA, examined oceanographic and biological processes in a variety of field experiments. The data were used to build and test mussel production models for determination of carrying capacity and optimal seeding density. Seven key factors in the benthicpelagic coupling were studied:Height of the mussel feeding zoneFine vertical gradients (0--50 cm) in the food supplyVariations in mussel pumping rates over tidal cyclesDifferential feeding of mussels on phytoplankton and silt particlesClearance of different phytoplankton species and effects of food quality on growth.Density-dependent growth of mussels within patchesSpatial variations in water volume flux, and benthic boundary layer particle flux, as determined with physical flow models forced by tide, and influenced by local bathymetry and boundary layer roughness