Project: RAPID: Hurricane Irma Impacts on Nitrogen Cycling in Florida Bay

NSF Award Abstract:
Availability of the nutrient element nitrogen generally limits the production of organic matter in Florida Bay and most other coastal ecosystems. In Florida Bay, approximately 90% of this primary production has been generated by seagrasses with another 10% generated by single celled algae and bacteria in the water column. Research completed prior to Hurricane Irma by the UNC-Chapel Hill team in collaboration with scientists at the Florida Fish and Wildlife Conservation Commission (FWC), has revealed that approximately half of the nitrogen needed by these primary producers is supplied by a huge sponge population that filters and decomposes freshly produced organic matter, then balances the nitrogen budget by efficiently recycling inorganic nitrogen back to the water column. The sponge community is capable of pumping and processing organic matter throughout the entire water volume of Florida Bay in less than a week, thus helping to maintain healthy seagrass communities and water clarity. The passage of Hurricane Irma may have profoundly altered the central Florida Bay ecosystem by causing tremendous losses of sponge and seagrass biomass and resulting changes associated with nitrogen cycling. This project will help to assess short- and long-term impacts of Irma through a quantitative assessment of sponge and seagrass biomass losses at representative locations, characterization of water column algal blooms, and measurement of changes to the nitrogen budget of Florida Bay.

The overall goal of the proposed new work is to quantify potentially major changes in Florida Bay nitrogen cycling and nitrogen budgets associated with the passage of Hurricane Irma, using a combination of pre- and post-storm data from established study sites. The proposed new work builds directly on the team's recently completed investigations of the role of sponges in the overall nitrogen budget of the Bay plus the catastrophic impacts of algal blooms on nitrogen cycling in its central basins that feature water column residence times of days to weeks. The results of this previous work have important implications for sponge-rich ecosystems throughout the Caribbean and tropical Pacific plus many other coastal regions including Antarctic shelf environments where sponges comprise a major component of the benthos. Pre-Irma results include multi-year nitrogen surveys and time-series data, sponge and seagrass biomass surveys at key sites and algal bloom meta-genomics and bacterial count surveys have been conducted. This research will benefit from new collaborations between scientists at UNC-Chapel Hill and FWC laboratories in Marathon (FWC-M), where post-Irma sponge surveys will be made and in St. Petersburg (FWC-SP), where algal bloom meta-genomic studies will be conducted. Data from the Pre-Irma studies includes extensive dissolved nitrogen (DIN and DON) water column concentration and time-series measurements, determination of the role of sponges in organic C and nitrogen recycling rates and the nitrogen budget, multi-year (2013-16) associated sponge biomass surveys at our study sites by FWC-M scientists (2013-15) and algal bloom meta-genomic plus bacterial count studies during a bloom at one of those sites led by FWC-SP. Two graduate and two undergraduate students will participate in this project.