Benthic Primary Production on the South Atlantic Bight Continental Shelf -- Areal Efficiency of Light Utilization and Biogeochemical Significance

Skidaway Institute Of Oceanography, Savannah GA

Investigators

Abstract

This research program focuses on the contribution of benthic microalgae to the total primary productivity of a major continental shelf system, the South Atlantic Bight (SAB) off the southeastern United States. The work will focus on the proposition that biogeochemical cycling is intensified in the lower portion of the euphotic zone when the euphotic zone extends to the sand sediments of the shelf. In particular, it is hypothesized that the areal efficiency of light utilization for photosynthesis is enhanced as a result of the optical environment in the sands, high benthic microalgal biomass, and the internal cycling of nutrients within the surface layer of the permeable sands. Further, it is hypothesized that areal benthic primary production on the shelf may be estimated on a regional scale as a function of irradiance levels at the shelf sea floor. The study builds upon the results and experience obtained in a prior study that suggested that most of the sea floor of the broad SAB shelf is often within the euphotic zone. And, although the light intensity reaching the shelf sea floor averaged only some 4-7% of surface incident irradiance, microalgae could contribute about 40% of the total primary production (water column plus benthic) over the mid-shelf region of the SAB. To address the hypotheses stated above, the study will: 1) determine benthic primary production over the annual cycle in relation to regional environmental and bio-optical variability; 2) evaluate the areal efficiency of utilization for photosynthesis on the shelf, emphasizing on the sediment portion of the euphotic zone; 3) investigate key aspects of the physiological ecology of benthic diatoms, particularly those that could contribute to the maintenance of high benthic microalgal biomass (and high areal photosynthetic potential) in the shelf sediments. In the study, several approaches will be employed to obtain a robust estimate of benthic primary production as a function of incident irradiance. The biogeochemical and oceanographic scope of the proposed study will be expanded through association with other regional field programs currently in process.