Dissolved inorganic nitrogen fluxes from common Florida Bay (U.S.A.) sponges

Sponge biomass represents the largest heterotrophic component of benthic biota in the Florida Bay ecosystem. These organisms can significantly alter the water quality of their surrounding environment through biogeochemical transformations of nutrient elements resulting from their dynamic pumping, water filtration, and respiration processes. Ammonium (NH4 +) and nitrate plus nitrite (NO3 − + NO2 −; NOx −) fluxes were obtained for 11 ecologically important species at three sites within Florida Bay, Florida (U.S.A.) utilizing chamber incubations on undisturbed individual sponges. Significant dissolved inorganic nitrogen (DIN) effluxes ranging between 9.0 ± 2.2 μmol N h−1 Lsponge −1 and 141 ± 26 μmol N h−1 Lsponge −1 were observed for eight of the 11 tested sponges; specifically, from six of eight tested high-microbial abundance (HMA) sponges, and from two of three tested low-microbial abundance (LMA) sponges. The abundant HMA species Chondrilla nucula showed the highest, volume-normalized rate of DIN release. These fluxes represent a continuation of the previously observed dichotomy in the chemical speciation of DIN in exhalent waters of LMA and HMA sponges, with NH4 + and NOx − dominating their respective exhalent jets. Surprisingly, we found that dissolved organic matter (DOM) appeared to make a negligible contribution to the total released N, but we hypothesize that the lack of DOM utilization or production was due to methodological limitations. Our flux data combined with sponge biomass estimates indicate that sponges, particularly HMA species, are a large, and potentially dominant, source of inorganic nitrogen to Florida Bay waters