POPULATION-DYNAMICS, GROWTH, AND PRODUCTION OF THE ASIATIC CLAM, CORBICULA-FLUMINEA, IN A BLACKWATER RIVER

In a sixth-order blackwater river (Lower Coastal Plain of Georgia, USA), the average life span of Corbicula fluminea (Muller) was 3-4 years, with shell length reaching only 18-20 mm by the third year. Mean density was usually < 200/m(2) over a 43-month period, but > 1000/m(2) in population centers. Mean biomass (dry mass of soft tissue) was consistently 1-5 g/m(2), but averaged 11 g/m(2) in population centers. Biomass growth rates of clams reared in situ were highest in late spring and were inversely related to clam mass. Production ranged from 0.18 g . m(-2). year(-1) at a main-channel site to 3.2 in a backwater and averaged 1.2-1.7 for 2 consecutive years. In population centers, production reached 9-23 g . m(-2). year(-1). Production was highest in spring and fell to zero in winter when growth ceased. Annual production/biomass values were about 4-8 for first-year individuals, but ranged from 0.51 to 1.78 overall. Individual size, growth rates, and production all indicated that this blackwater river was a stressful environment for Corbicula, probably due to low alkalinity (< 30 mg/L as CaCO3). Unlike its effect in many other systems, the clam appears to play a minor role in the trophic dynamics of this river.