Pumping rates of the giant barrel sponge Xestospongia muta on Caribbean reefs: size scaling, envionmental controls, and bleaching effects.

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Sponges are among the dominant organisms on coral reefs in terms of diversity, numerical abundance, and biomass. Their ability to filter particles (e.g. viruses, bacteria, phytoplankton) from the water column contributes to both water clarity, which is necessary to support corals and other coral reef organisms, and for the transport of carbon from the water column to the benthos, also known as benthic-pelagic coupling. Despite their acknowledged importance, there are only a few mechanistic studies that have quantified sponge filtration rates. This proposal addresses part of that gap in our knowledge by measuring the pumping rates of the most conspicuous sponge on Caribbean reefs, the giant barrel sponge, Xestospongia muta. Specimens of X. muta can comprise up to 60% of sponge biomass on Caribbean reefs, and exhibit a size range (diameter) that spans three orders of magnitude. These sponges, like corals, can be affected by increases in seawater temperature that result in the ?bleaching? of the sponges and the loss of their symbionts. Up to 25% of the X. muta population can be affected by thermal bleaching with unknown consequences for both individual and population level filtration rates. Accurate measurements of pumping rate, and therefore water column filtration rates, are important to assess because sponges have such a profound influence on energy flow on coral reefs. The principal objectives of this proposal are to; (1) measure the excurrent velocities of water from sponges in order to calculate volumetric flow rates; (2) to quantify the scaling relationships between pumping and tissue volume to account for the changes in sponge pumping due to size differences within a population; (3) to describe the temporal patterns of pumping and its relationship to environmental variables; and (4) to determine the effects of sponge bleaching on pumping rates relative to healthy sponges. To address these critical needs in our understanding of sponge biology and reef ecology the principal investigator will take field measurements of pumping rates from sponges using an Acoustic Doppler Velocimeter (ADV). An ADV uses shifts in the frequency of sound waves to measure water flow velocities and can accurately measure these velocities across the diameter of sponges over both short time scales of pumping (10 minutes), and also during longer term pumping measurements of 24 hr or more. These measurements will be made concurrently with water quality measurements to assess temporal trends and environmental controls of sponge pumping. This project will contribute significantly to our understanding of the role(s) of sponges on coral reefs and enhance the development of research and education infrastructure at the University of North Carolina at Wilmington (UNCW). When not in use for this project, the the principal investigator will make available the ADVs for use in education or research. The principal investigator is a new faculty member at UNCW and is currently updating courses in Marine Biology (undergraduate) and Biological Oceanography (graduate), and is involved in the training and education of undergraduates and graduate students. These students will also have the opportunity to participate in highly collaborative, international research cruises. Participation in these cruises represents an unparalleled opportunity for these students to develop international collaborations and broaden their research interests.