EFFECTS OF MORPHOLOGY AND WATER MOTION ON CARBON DELIVERY AND PRODUCTIVITY IN THE REEF CORAL, POCILLOPORA-DAMICORNIS (LINNAEUS) - DIFFUSION-BARRIERS, INORGANIC CARBON LIMITATION, AND BIOCHEMICAL PLASTICITY

Colonies of the reef coral Pocillopora damicomis (Linnaeus) taken from high and low flow habitats at the same depth and light regime show significant differences in colony morphology but not Reynolds numbers. Because Reynolds numbers are similar, dynamic similarity predicts that the flow patterns, and thickness of the diffusional boundary layer are quantitatively identical. Measurements of chlorophyll content per cell, antioxidant enzymes, and carbonic anhydrase all indicate similar levels of productivity between corals from high and low flow environments. When specimens of P. damicornis exhibiting the high flow morphology were placed in microcosms and allowed to acclimatize for 13 days to different flow regimes they exhibited a significant increase in the activities of all antioxidant enzymes, photosynthesis, and respiration with increasing water velocity. A non-dimensional analysis using Sherwood/Reynolds number plots also showed a significant augmentation of net photosynthesis with increasing water flow. Carbonic anhydrase in the host tissues showed an inverse relationship with water velocity, while the productivity and specific activities of ribulose bisphosphate carboxylase oxygenase of the zooxanthellae show a direct relationship with water velocity. These results suggest that: (1) morphological plasticity of the coral skeleton under different flow regimes provides a mechanism that minimizes diffusional boundary layer thickness and maximizes carbon delivery to the site of fixation under different flow regimes, and (2) when a coral with a fixed skeletal morphology is exposed to a new flow regime, physiological and biochemical plasticity can augment the delivery of carbon to the site of assimilation.