BENTHIC MICROALGAL PRODUCTION IN ONSLOW BAY, NORTH-CAROLINA, USA

Benthic microalgal production and sediment respiration were measured in situ at 8 locations in Onslow Bay, a portion of the North Carolina continental shelf, between 1984 and 1989, by measuring changes in dissolved oxygen concentrations inside clear and opaque benthic chambers placed by divers. Measurements were also made of water column productivity, phytoplankton biomass, benthic microalgal biomass, light flux, and temperature. Benthic production and respiration were measured from March through October at locations ranging from 14.6 to 41 m deep. Gross benthic microalgal production averaged 24.9 mg C m-2 h-1, compared to average integrated water column production of 27.4 mg C m-2 h-1. Sediment respiration rates averaged 18.1 mg C m-2 h-1, Benthic microalgal biomass averaged 36.4 mg chl a m-2, and always exceeded integrated phytoplankton biomass, which averaged 8.2 mg chl a m-2. Benthic microalgae had much lower average assimilation numbers than phytoplankton (0.8 vs 5.2 mg C (mg chl a)-1 h-1). Benthic microalgae make a significant contribution to total shelf production in Onslow Bay. Open sand bottom habitats in this ecosystem must now be viewed as productive, rather than relatively barren.