Coral reef ecosystems depend on water movement at all levels. Water movement delivers prey to corals and enhances uptake and exchange of nutrients, oxygen, carbon dioxide, bicarbonate and other ions. It also affects coral competition, larval dispersal, fragmentation, activity of predators, and sedimentation, thus having a large potential impact on coral distribution. Flow micro-habitats on reefs differ substantially, even over a few meters or less, causing measurable differences in coral growth rates. The contribution of zooxanthellae (photosynthesis) to coral energetics is most strongly affected by diffusional limitations at the lower extremes of flow, modified by changes in irradiance. Flow at the smallest scale affects the processes of respiration, productivity and suspension feeding by corals, the escape behavior of zooplankton encountering corals, and the ultimate success of particular polyp, tentacle, and colony morphologies. Over an entire reef, there is a characteristic gradient from high velocity oscillatory (wave-induced) flow in shallow reef zones, to unidirectional flows of lower velocity in deep reef and lagoonal habitats. Such flow regimes affect benthic-pelagic fluxes and dispersal of gametes and larvae of reef dwelling species. Corals vary in polyp size, tentacle form and colony structure; coral growth forms in each reef zone reflect adaptations to local flow and light regimes at the polyp and colony levels. In this project Dr. Sebens, collaborators and students will investigate the effects of water movement on the feeding biology, energetics, and nutrition of reef corals. Attempts to model energy, carbon and nitrogen budgets have suffered from a lack of information on prey capture rates and have generally not considered flow effects adequately. Past studies along with new data on the contributions of sediment ingestion and inorganic nutrient uptake to energy, carbon, and nitrogen requirements will be used to construct energy, carbon, and nitrogen budgets for at least six coral species. Effects of water flow on each input and output process will be incorporated into this model budget. The project will continue to measure small scale water flow around corals in the field. Self-contained underwater flowmeters with fine spatial resolution have been constructed for this research. The data collected will be used to characterize the general flow regime, providing new information about the flow environment of coral reefs in Jamaica, Florida, Belize and other sites in the Caribbean. This new information on coral feeding with flow will extend the current conceptual model to encompass a diversity of colony forms, tentacle morphologies, and nematocyst compositions. Zooplankton feeding by coral reef cnidarians is necessary for their survival, yet most studies have focused on the autotrophic contribution from their endosymbiotic zooxanthellae. This research will increase our understanding of energy and nutrient fluxes in coral reef environments, which are among the most productive and endangered marine habitats.
