Meeting Abstract

P3.63  Friday, Jan. 6  Pumping Activity and Nitrogen Cycling in the Giant Barrel Sponge, Xestospongia muta FIORE, Cara L*; LABRIE, Micheline; LESSER, Michael P; University of New Hampshire

The giant barrel sponge, Xestospongia muta, is one of the most prominent coral reef sponges in the Caribbean and its large size and high abundance provides habitat for a large number of macrofauna. Additionally, many sponges, including X. muta, are known to harbor various symbiotic microbes, which can influence sponge metabolism and the cycling of inorganic nitrogen, a limiting nutrient in tropical waters. Processes such as nitrogen fixation, nitrification and denitrification have been documented in a number of sponges and while nitrification has been documented in X. muta, it is not known whether other nitrogen transformations occur in this sponge. This study utilized stable isotopic techniques and nutrient analysis to assess which nitrogen transformations maybe occurring in this sponge. Sponges from three Caribbean locations were examined, and the flux of nitrogen to the surrounding reef was determined based on pumping activity and measurement of ambient and excurrent concentrations of inorganic nitrogen. Cyanobacterial and non-cyanobacterial nifH gene sequences were recovered in addition to archaeal amoA genes. Data from these experiments also suggests that anammox bacteria may be operating anaerobically in microhabitats within the sponge. Our data show the potential for nitrogen fixation, which may be an important source of 'new' nitrogen to the sponge and the reef given the large numbers of this species on coral reefs and high concentration of bacteria in their tissues. Future work will include investigating the molecular genetics of nitrogen cycling in X. muta under different environmental conditions.