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Role of Sponges in Nitrogen Cycling and Total Respiration in Coral-Reef Ecosystems

Principal Investigator: Dr.Niels Lindquist, UNC Chapel Hill
Co-Principal Investigator: Dr. Chris Martens, UNC Chapel Hill
Training: September 8 — 12, 2008
Mission: September 16 — 25, 2008

The great abundance and diversity of sponges on Florida coral reefs can rival that of reef building and soft corals, but with recent declines in coral cover throughout the Caribbean, including the Florida Keys, many reefs have undergone dramatic shifts from coral to sponge and seaweed dominance. Corals must now live in environments in which the metabolisms of other abundant organisms, like sponges, dominate energy and nutrient flows on reefs thereby contributing substantially to the quality of reef water and its ability to promote coral survival and robust growth. The exceptional capacity of sponges to pump and filter seawater up to 100,000 times their own volumes each day potentially allows them to substantially alter concentrations of particulate and dissolved organic matter and nutrient elements in surrounding waters. For example, our UNCW-NURC and NSF funded research is showing that sponges metabolize to ammonium and nitrate much of the nitrogen in the particulate and dissolved organic matter they consume. Simultaneously, their high respiration rates substantially reduce levels of dissolved oxygen in the seawater they filter. Thus, the tremendous volumes of seawater many sponges exhale are hypoxic, rich in dissolved inorganic nitrogen, and likely sponge-produced toxins, all of which can harm corals both directly and indirectly.

Our 2008 studies will combine the expertise and talents of marine ecologists and chemists and physical oceanographers to examine nutrient element and chemical cycling for a greater number of coral reef sponges that differ in basic biological characteristics, such as the presence or absence of large, internally hosted populations of diverse microorganism that greatly expand the breadth of potential chemical transformations occurring within sponges. Using the exceptionally long underwater excursion times provided by the Aquarius Reef Base Observatory, we will deploy newly developed underwater systems for (i) continuously monitoring sponge pumping rates and changes in the concentrations of ecologically important chemicals in the seawater they filter, and (ii) tracking chemicals expelled by sponges as the chemicals mix and travel toward neighboring organisms. Field assays will also be conducted to examine how chemicals in seawater exhaled by sponges affect the growth, health and survival of neighboring corals and seaweeds. Because sponges are a major component of benthic communities in diverse tropical, temperate and polar marine habitats, a quantitative understanding of important chemical processes occurring within sponges and chemical fluxes between sponges and their surrounding communities are crucial for defining their roles in regulating the quality of critical marine habitats, such as coral reefs.