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University of Richmond

Publication Date

Fall 2009

Program Name

Australia: Natural and Cultural Ecology


Climate change currently represents the most significant and increasing threat to coral reef ecosystems worldwide as sea surface temperatures are predicted to increase by up to 4oC by the year 2099. Sponges that rely on strong microbial symbioses are particularly sensitive to elevations in seawater temperature. In this study, the impacts of elevated seawater temperature on feeding behavior in the tropical marine sponge Rhopaloeides odorabile were assessed. Sponges were exposed to temperatures ranging between 27 and 32oC. At four time points, filtration rate and volume flow rate of each sponge were measured, and feeding efficiencies on both heterotrophic and phototrophic bacteria were determined. No differences in volume flow rate or feeding efficiencies on both bacterial types were detected in 27 and 30oC treatments. In contrast, sponges exposed to 31oC exhibited significantly reduced volume flow rates and feeding efficiency on heterotrophic bacteria after 24 hours but maintained normal feeding efficiency on phototrophic bacteria through 3 days. Sponges exposed to 32oC exhibited major cellular necrosis and dramatically reduced volume flow rates and feeding efficiencies on both bacterial types after 24 hours. The threshold for normal sponge feeding behavior was 31oC, and the shift in feeding efficiencies at 31oC is clear evidence of selective filtration of phototrophic bacteria by R. odorabile in response to thermal stress. This thermal threshold is identical to the symbiosis threshold for corals and their zooxanthellae, indicating that sponges may be similarly threatened by climate change.



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