Award: OCE-1132155

Sponges can 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 and other ecosystems including under Antarctic ice in the Southern Ocean. The primary goal of this present research project was to ascertain the importance of sponges in coastal environments through quantifying their role in the N cycle of Florida Bay (FL Bay). Specifically we wished to document the importance of sponges in meeting the N demands of seagrasses and plankton in these environments through sponge and associated microbial transformations of Particulate Organic Matter (POM) and Dissolved Organic Matter (DOM). In choosing FL Bay, we particularly benefitted from an existing wealth of available data concerning other N sources and the FL Bay N budget. By performing in situ sponge N release measurements in association with measuring their respiration rates and C cycling at selected FL Bay sites, we were able to quantify a potentially important recycled N source that has not previously been quantified in FL Bay N budgets. We performed most of our research at two nearshore sites with easy access from land but focused the work on establishing tthe role of sponges in the N budget of an enclosed basin, Mystery Basin, located in central FL Bay. The restricted water exchange in Mystery Basin, coupled with abundant sponge biomass, improved our capability to quantify the importance of recycled N from these organisms in the overall nutrient budget. The species-specific estimates of sponge N release allowed us to calculate the importance of the DIN flux from the sponge community in satifying the majority of local photosynthetic N demand. We quantitatively demonstrated that the impact of the observed C and N transformations was largely dependent upon the size and composition of the sponge community. Sponge-recycled N represented 45 ± 24 % of the total N sources at our sites, approximately half of the calculated N demand by primary producers. We also measured total DON fluxes at the Mystery Basin sites and calculated the total N flux from sponges in both inorganic and organic N. Our results indicate that sponges have the capacity to alter local water quality through the observed C and N transformations mediated by the sponge holobiont (sponge animal and associated microbiome). The quantification of these processes across environmental gradients further suggests that sponges should play a significant role in most coastal ecosystems, particularly where their populations dominate. The proven role of sponges in nitrogen cycling suggests that their contributions to nutrient cycles should be incorporated into biogeochemical models for sponge-rich ecosystems throughout the Caribbean and many other coastal systems. Our results are critical for ecosystem managers with the Everglades National Park, where a furthered understanding of internal estuarine processes is essential to predicting the trajectory of ecosystem change, particularly in response to anthropogenic disturbance. The response of Mystery Basin to a harmful algal bloom during our project allowed us to determine how sponge-rich areas within Florida Bay may respond to and possibly modulate recurring bloom phenomena. These results have implications for the management of the now frequent occurrence of blooms in sponge-rich areas as the presence of these organisms may not only apply top-down pressure regulating cyanobacterial populations through normal filtration but their mortality under bloom conditions may fuel explosive expansion of those populations. Last Modified: 12/02/2015 Submitted by: Christopher S Martens