In situ measurements of flow effects on primary production and dark respiration in reef corals

The effects of flow on the physiological ecology of Montastrea annularis , an important frame‐building species of Caribbean coral reefs, were investigated in situ with a recirculating flow respirometry system deployed from an underwater habitat. For this species, primary production and respiration rates increase with increasing water motion. The slope of a nondimensional Sherwood ‐Reynolds(Re) number plot indicates that forced convection increases dark respiration in a manner consistent with oxygen transfer through a turbulent boundary layer . A similar analysis for maximal photosynthetic rate yields a lower but significant slope A simple conceptual model of diffusional depletion in the boundary layer over the coral fits the data and accounts for the distribution of zooxanthellae. Calculations of phototrophic capacity for this species indicate that water motion can enhance the local productivity of the reef.