Evaluation of density and biomass of a bivalve population (Diplodon delodontus expansus) (Küster, 1856) in a small tropical reservoir

Abstract

Density and biomass of D. delodontus expansus (ICÜSTER, 1856) (Mollusca, Bivalvia) were estimafed in the Reservoir of fhe Rio Pardo (Botucatu, Sao Paulo, Brazil), in December, 1982. The average population densi$ of the bivalves in the reservoir was 36.62 specimens.m-2, ut 98 sampling stations. Tofal density in the reservoir was esfimated ut 5.8 million individuals. Average biomass tuas 347.27 gm-2 (alcohol ureight) ; 225.00 g.m-2 (shells dry ureighf) and 10.92 g.m-2 (bodies dry weight). Total biomass in the reservoir ruas estimated ut 55.0 tons (alcohol rveight), 35.6 tons (shells dry weight) and 1.7 tons (bodies dry weight). The granulomeIric analysis of fhe sediment showed that silt presented greater correlaiion with biomass and density (r = 0.16), ihough unsignificant. The other fractions of sediment (Sand and clay) showed lorver correlation coeficienfs with density and biomass of the bivalves. The granulometric composition of the sediment ulas not related wibh density ancl biomass of the animals. A revision of other ecological factors showed Chat fhere are no limiting facfors on the distribution and abundance of bivalves in fhe reservoir. This explains probably the high values of density and biomass. KEY