Distribution and Production of Two Crustaceans in a Wetland Pond

Abstract

Annual production of the isopod Asellus obtusus and the amphipod Crangonyx gracilis in a small wetland pond in northwest Georgia [USA] was estimated using the Hynes method. Both species were found in 2 distinct vegetation zones: a central Cephalanthus occidentalis zone and a marginal Nyssa biflora zone. In the Nyssa zone, the crustaceans occurred in the aufwuchs and benthos, but in the Cephalanthus zone, only in the aufwuchs. Five samples were taken each month in each of these 3 habitats during 1 yr to obtain life history and standing stock data. Although growth of each species was relatively asynchronous, they each appeared to have 1 generation/yr. Combined aufwuchs-benthos production in the Nyssa zone was 2.44 g/m2 dry wt for Crangonyx and 1.44 g/m2 for Asellus. Annual turnover ratios were 6.1 and 6.0, respectively. Aufwuchs production in the Cephalanthus zone was 1.63 g/m2 for Crangonyx and 0.65 g/m2 for Asellus. Annual turnover ratios were 6.8 and 8.1, respectively. Benthos in Nyssa contributed by far the greatest crustacean production to this zone based upon standing stock values, but aufwuchs populations were the only significant source of production in the Cephalanthus zone.