| Sponges are common and many times dominant features of benthic marine communities, yet little is known about their role in the nutrient and material budgets of reefs. The major objective of this study was to determine the role sponges play in the cycling of nutrients and materials in two distinctly different reef communities: a Caribbean coral reef and a South Atlantic Bight hard bottom. Nine sponge species (Verongia (=Aplysina) Fistularis (VF), Ircinia sp. (ISP), I. strobilina (IS), I. compana (IC), Mycale laxissima (MY), Agelus sp. (AG), Neofibularia nolitangere (NF), and Condrilla nucula (CN) were studied as follows: (1) abundances and distributions of five common species on the fore-reef at Discovery Bay (VF, IS, MY, AG, and NF) were determined, (2) inorganic nitrogen and phosphorus, concentrations of incurrent and excurrent waters, and water transport rates, were determined in situ using SCUBA for fifty-seven colonies of the five species mentioned above, on the fore-reef in Discovery Bay, and (3) metabolism and inorganic nitrogen, phosphorus, and dissolved organic carbon uptake and release rates were determined for chamber-incubated, whole colonies of AF, IS, CN, IC and ISP at Gray's Reef National Marine Sanctuary (GRNMS) and the Berry Islands in the Bahamas in two seasons. All species examined in situ at Discovery Bay, released inorganic nitrogen (ammonium and nitrate). Two species released phosphate. Sponge community metabolic rates measured at GRNMS and the Bahamas, in October were generally higher for species at GRNMS than those in the Bahamas. Metabolic rates for species at GRNMS were significantly higher in summer-fall as compared with spring. Overall, inorganic nutrient release rates were highest for sponges in Jamaica, followed by those at GRNMS and the Bahamas. All sponge species examined using chambers removed dissolved organic carbon. Sponge nutrient releases accounted for 18-85% of the total benthic nutrient flux at GRNMS.;Sponge community metabolism of DOC-DON can quantitatively account for the inorganic nitrogen released. Nitrification of ammonium by the bacterial symbionts probably is responsible for much of the nitrate released. Sponges can be significant sources of inorganic nitrogen. |
