Animal abundance and food availability in coastal lagoons and intertidal marine sediments

The relationships between the standing stocks of deposit-feeding benthic invertebrates and benthic chlorophyll-a, phaeopigment and total combustible organic matter were investigated at a series of coastal lagoons and in the type of intertidal soft-sediment sites from which the lagoons originated. Across all the sites, in Norfolk, UK, an inverse relationship occurred between (a) the amounts of chlorophyll-a and of other potential food materials and (b) the degree of coverage by water. The biomass of consumers also decreased with increased water coverage, so that the lagoons supported less biomass than the adjacent high-level intertidal sites. Further, the deposit-feeder biomass supported by unit food decreased with extent of water coverage. There was no evidence of any relationship between deposit-feeder and food biomass within any single site, in spite of the study period being selected to be that in which there was maximum likelihood of competition for microphytobenthic food. Whilst chlorophyll concentrations may set the maximum achievable level of consumer biomass at these sites, including in the deeper lagoons setting very low potential maximum population densities, the seasonal abundance patterns of the deposit feeders appear to be determined by other factor(s).