Collaborative Research: The role of sponges in the coastal nitrogen cycle

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Sponges dramatically alter ecosystem water quality through the combination of extraordinary pumping rates and rapid, dynamic biogeochemical transformations. Sponge communities are ubiquitous in marine environments and can inhabit over 40% of the benthic area in tropical ecosystems. In this project, a research team from the University of North Carolina at Chapel Hill, the University of Hawaii at Manoa, and the University of Washington will continue their ongoing investigations of the importance of sponge nitrogen (N) transformations and fluxes in coastal environments through quantifying their role in the N cycle of Florida Bay, specifically the importance of these dominant benthic organisms in meeting the N demands of primary producers throughout the Bay. The team's previous research demonstrated that sponge dissolved inorganic nitrogen (DIN) flux to overlying waters at Conch Reef, Florida Keys, was larger than any other benthic nitrogen (N) source. In choosing Florida Bay as their study area, the team will benefit from the wealth of available data concerning N sources and recycling, including estimated values for new N inputs, and quantitative sponge benthic biomass. By performing in situ sponge N flux measurements they expect be able to contribute information about a potentially important recycled N source that has not previously been quantified in N budgets. The overarching goal of this research is to establish the importance of sponge-mediated N cycling processes in Florida Bay where sponges are abundant, their biomass has been quantified at hundreds of stations and their key role in water filtration has been established, by quantifying rates and mechanisms of transformations of both dissolved and particulate organic nitrogen to DIN and N2 (nitrogen gas) by key sponge species, and elucidating controls on N2 production by natural factors such as sponge tissue dissolved oxygen concentrations. Broader Impacts: Sponges play a crucial role in the nutrient balance of coastal environments because they are abundant in tropical, temperate and polar habitats, they process tremendous volumes of water, and many common species host abundant and active microbial populations. Their impact on biogeochemical cycling in most environments, however, remains largely unknown. During this study, graduate and undergraduate students and a postdoctoral fellow will learn in both laboratory and field settings a spectrum of state-of-the-art techniques and instrumentation firsthand and, when the results are ultimately synthesized for publication, they will benefit from participation in the exchange of ideas with established researchers from diverse fields.