DENSITY DEPENDENCE IN SUSPENSION-FEEDING AND DEPOSIT-FEEDING POPULATIONS OF THE BIVALVE MACOMA BALTHICA: A FIELD EXPERIMENT

SUMMARY (1) Levinton's hypothesis that populations in deposit-feeding communities are more often food-limited than those in filter-feeding communities was field tested using exclusion cages. (2) Densities of the bivalve, Macoma balthica, were varied experimentally in a sublittoral, exposed, sandy sediment and a sublittoral, sheltered, muddy, sand sediment. Densities varied from 0.25 to 4.0 x natural levels in the muddy, sand sediment and from 0.5 to 4.0 x natural levels in the sand sediment. The growth rates of individually marked (3) Macoma clams from the muddy sand sediment showed deposit-feeding in aquaria under simulated field conditions whereas clams from the sandy sediment were filter-feeding. Field experimental data also demonstrated that deposit-feeding predominated in the muddy sand sediment and suspension-feeding in the sand sediment. (4) The field experiments showed that growth of clams was density dependent in the muddy sand sediment, but no such effect could be demonstrated for clams in the sandy sediment. SUMMARY (1) Levinton's hypothesis that populations in deposit-feeding communities are more often food-limited than those in filter-feeding communities was field tested using exclusion cages. (2) Densities of the bivalve, Macoma balthica, were varied experimentally in a sublittoral, exposed, sandy sediment and a sublittoral, sheltered, muddy, sand sediment. Densities varied from 0.25 to 4.0 x natural levels in the muddy, sand sediment and from 0.5 to 4.0 x natural levels in the sand sediment. The growth rates of individually marked clams from each treatment were then measured. (3) Macoma clams from the muddy sand sediment showed deposit-feeding in aquaria under simulated field conditions whereas clams from the sandy sediment were filter-feeding. Field experimental data also demonstrated that deposit-feeding predominated in the muddy sand sediment and suspension-feeding in the sand sediment. (4) The field experiments showed that growth of clams was density dependent in the muddy sand sediment, but no such effect could be demonstrated for clams in the sandy sediment. SUMMARY (1) Levinton's hypothesis that populations in deposit-feeding communities are more often food-limited than those in filter-feeding communities was field tested using exclusion cages. (2) Densities of the bivalve, Macoma balthica, were varied experimentally in a sublittoral, exposed, sandy sediment and a sublittoral, sheltered, muddy, sand sediment. Densities varied from 0.25 to 4.0 x natural levels in the muddy, sand sediment and from 0.5 to 4.0 x natural levels in the sand sediment. The growth rates of individually marked SUMMARY (1) Levinton's hypothesis that populations in deposit-feeding communities are more often food-limited than those in filter-feeding communities was field tested using exclusion cages. (2) Densities of the bivalve, Macoma balthica, were varied experimentally in a sublittoral, exposed, sandy sediment and a sublittoral, sheltered, muddy, sand sediment. Densities varied from 0.25 to 4.0 x natural levels in the muddy, sand sediment and from 0.5 to 4.0 x natural levels in the sand sediment. The growth rates of individually marked clams from each treatment were then measured. (3) Macoma clams from the muddy sand sediment showed deposit-feeding in aquaria under simulated field conditions whereas clams from the sandy sediment were filter-feeding. Field experimental data also demonstrated that deposit-feeding predominated in the muddy sand sediment and suspension-feeding in the sand sediment. (4) The field experiments showed that growth of clams was density dependent in the muddy sand sediment, but no such effect could be demonstrated for clams in the sandy sediment.