Benthic microalgal biomass and irradiance at the sea floor on the continental shelf of the South Atlantic Bight: Spatial and temporal variability andstorm effects

Variables relating to the potential for benthic microalgal primary producti on on the continental shelf of the South Atlantic Eight (SAB) were characte rized over a depth range of 14-40 m off Georgia and 20-40 m off northeaster n Florida. The areal concentration of chlorophyll a in the surface 0.5 cm o f the sand sediments generally exceeded the depth-integrated chlorophyll in the entire overlying water column, often by a factor of 4-6. Visible irrad iance at the sediment surface was often 4-8% of surface levels over much of the region, and exceeded 10% of surface levels on occasion (mid-summer at 14-30 m depth). HPLC pigment analyses and qualitative microscopy indicate t hat sediment chlorophyll is associated with a distinct benthic microflora d ominated by diatoms. Relatively high concentrations of diatom pigments exte nd to at least 2-3 cm in the sediments, apparently associated with intact c ells. At small spatial scales, variability in benthic microalgal biomass ma y be related to bioturbation and grazing by benthic fauna. Intense storms c an strongly affect the potential for benthic primary production on the shel f by physical disturbance of sediments and by resuspension of fine particle s, which limits light penetration to the sediment surface. (C) 1999 Elsevie r Science Ltd. All rights reserved.