Community metabolism and nutrient cycling at Gray's Reef, a hard bottom habitat in the Georgia Bight

Abstract

Sediment organic carbon content increased from <0.2% of dry weight in sandy regions to an epifaunal biomass >77 g C m-2 on rock outcrops. Sponges and corals accounted for a large percentage of macrofaunal biomass when sands were shallow. Benthic metabolism and nutrient regeneration were positively related to the spatial distribution of epifaunal biomass. In regions of high epifaunal biomass respiration exceeded 133 mg C m-2 d-1 and nutrient flux amounted to 23 mmol inorganic N, 1.8 mmol inorganic P, and 24 and 0.4 mmol m-2 d-1 dissolved organic N and P, respectively. The benthic community was markedly heterotrophic, consuming almost twice as much organic matter as was produced on the bottom (production:respiration = 0.52:1). Community respiration in the water column exceeded by c30% a fairly high level of pelagic primary production of 2.15 g C m-2 d-1. The overall Gray's Reef system was heterotrophic and strongly dependent on allochthonous organic carbon for support of almost 1/3 of its total respiratory requirements (production:respiration = 0.68:1). Over 50% of system biomass and respiration was attributable to filter-feeding organisms which are largely ungrazed, including corals and sponges. -from Authors