Effects of water flow on growth and energetics of the scleractinian coral Agaricia tenuifolia in Belize

The branching scleractinian coral Agaricia tenuifolia is abundant on reefs in Belize, over an excep tionally broad range of depth, flow regime, and irradiance. Photosynthesis and respiration of coral branches were measured over a range of irradiance and unidirectional flow speeds (1-10 cm s(-1)) using a small-volume respirometry chamber designed for flat coral branches. Respiration rate increased significantly with flow speed; however, there was no significant effect of flow on either alpha or P-max, indicating that this coral could thus carry out maximum photosynthesis even at very low flow. This result contrasts with published results for other coral species that experience a significant increase in net photosynthesis with flow speed. Growth rates of A. tenuifolia were measured using branch fragments in a variety of reef habitats, over a range of water flow speeds. Growth rates were comparable over most habitat types, across a depth range of 1-15 m. Compared to 1 m, flow and irradiance at 15 in decreased to less than 20% and less than 50%, respectively. Reduced growth was observed only at 24-m depth, and in low-flow microhabitats (concavities) at 15 m. Transplants to 1 m, in the surf zone, also had reduced growth and were the only group to suffer significant colony mortality. At 8- and 15-m depth, growth rate of flat coral branches was not affected by orientation (parallel or perpendicular to flow) or shading. Compared with studies of other species, A. tenuifolia displays an ability to utilize a greater range of habitats and flow speeds, suggesting that it may have specific adaptations that allow it to tolerate very low flow conditions.