PRODUCTION DYNAMICS OF HYALELLA-AZTECA (AMPHIPODA) AMONG DIFFERENT HABITATS IN A SMALL WETLAND IN THE SOUTHEASTERN USA

The life history, population dynamics, and secondary production of Hya lella azteca (Amphipoda) were studied in a small southeastern wetland pond. Habitat-specific sampling was used to estimate density, biomass, and production in each of 3 habitats (benthic, Nymphaea odorata leave s, and submerged wood). Laboratory experiments at different temperatur es (10, 15, 20, 25, and 30 degrees C) provided predictive equations fo r estimating growth rate and egg development times that could be appli ed to field populations. Size-frequency data from field sampling sugge sted that H. azteca had 2 major cohorts per year, but reproduction was continuous from spring through fall. Mean annual density and biomass were 904/ m(2) and 85 mg dry mass (DM)/m(2). Daily growth rate was a f unction of both individual mass and temperature. Annual production of somatic tissues as estimated by the instantaneous growth method (675 m g DM . m(-2). y(-1)) agreed well with that using the size-frequency me thod (714 mg DM . m(-2). y(-1)). Egg production (252 mg DM . m(-2). y( -1)) represented 27% of total production (927 mg DM . m(-2). y(-1)). A nnual production:biomass (P/B) was 7.8 without eggs and 9.8 with eggs. Habitat-specific estimates of density, biomass, and production were h ighest in the benthic habitat. The contribution of somatic production from Nymphaea leaves to total amphipod production was low (6.2%), but temporal patterns of production followed trends in leaf abundance. Pro duction on leaves reached 29% in September when leaves were most abund ant. Contributions of animals from submerged wood were consistently lo w (2.9%). Monthly densities and production peaked in May at the start of the summer cohort, decreased throughout summer, and showed a small increase in October at the start of the winter cohort. Although egg pr oduction and birth rates were highest in summer months, high death rat es were responsible for the late-summer declines in density and produc tion. These temporal trends in production suggest heavy predation or e nvironmental stress, or both, during summer months.