Sponges represent a major source of inorganic nitrogen in Florida Bay (U.S.A.)

Abstract

AbstractFlorida Bay nutrient budgets have shown that the majority of existing and influent nitrogen (N) is in organic forms. Consequently, local remineralization processes have been found to regulate the supply of dissolved inorganic nitrogen (DIN). Sponges have dominated benthic animal biomass in Florida Bay and are known to influence local DIN concentrations through remineralization organic matter, yet the role of these organisms in local N budgets is largely unaddressed. We quantified the role of sponges in N cycling in Florida Bay during 2012–2013 by constructing an N budget for a sponge‐rich basin. Surveys of sponge biomass conducted in Mystery Basin found sponges at 57 of the 59 assessed stations. Sponge population maxima reached 21 individuals m−2 and biomass contributions as high as 4.4 Lsponge m−2. We estimated an average areal DIN contribution from total sponge biomass of 0.59 ± 0.28 mmol N m−2 d−1. However, calculated fluxes from the 59 stations exhibited significant spatial variability associated with changes in the size and species composition of the sponge community; peak N fluxes reached 3.5 ± 0.9 mmol N m−2 d−1 in areas with large populations of high microbial abundance sponges. The average flux from the sponge community was the largest of the estimated sources of DIN to Mystery Basin, representing roughly half of the overall N sourcing. This N satisfied more than half of the demand by primary productivity. These results indicate that sponges are important sources of inorganic N to Florida Bay environments.