Food limitation in cockles ( Cerastoderma edule (L.)): Influences of location on tidal flat and of nearby presence of mussel beds

Abstract

Dilution of phytoplankton concentrations by suspension-feeding organisms, and local reduction in current velocity, may lower food supply for other suspension feeders, and consequently affect their growth. Influences of food supply on stomach contents and growth of the suspension-feeding bivalve Cerastoderma edule were studied in two situations: (a) inside and outside an experimental mussel bed in a basin with a natural seawater supply, and (b) along tidal creeks in the field. Cockles showed a lower increase in shell length, body weight and condition inside the experimental mussel bed than outside. In the field, phytoplankton concentrations in the water were lower at upper than at lower tidal-creek sites. At these upper creek sites, cockles were smaller, as were their growth rates and stomach contents, compared to the lower creek sites. Largest reductions of phytoplankton concentration in the water were observed at sites near a mussel bed. It is concluded that phytoplankton uptake by suspension feeders (particularly in mussel beds), as well as relatively low current velocities, negatively affects food supply, stomach contents and growth of C. edule.