METABOLIC CONSEQUENCES OF PHENOTYPIC PLASTICITY IN THE CORAL MADRACIS-MIRABILIS (DUCHASSAING AND MICHELOTTI) - THE EFFECT OF MORPHOLOGY ANDWATER-FLOW ON AGGREGATE RESPIRATION

Phenotypic plasticity has been documented in a number of reef coral sp ecies fora variety of morphological traits, but its ecological importa nce is not well understood. In the branching coral Madracis mirabilis (Duchassaing and Michelotti) spacing among branches varies across envi ronmental gradients and in general is inversely related to the rate of water movement. This polymorphism is due in part to variation in bran ch diameter which is phenotypically plastic in this species. Branch sp acing can affect biomechanical processes such as the surface roughness of aggregated branches and flow dynamics within an aggregate, both of which could affect colony metabolism. We examined the metabolic conse quences of variation in branch spacing and flow speed on small M. mira bilis aggregates to determine if plasticity for this trait could be be neficial. The dark respiration of aggregates with different amounts of branch spacing was measured under three flow speeds (3.1, 4.7 and 8.4 cm s(-1)) in respiration chambers. Aggregates with the greatest branc h spacing had the highest respiration rates in all three flow conditio ns and the respiration of each morphology increased with flow speed. I ncreased branch spacing may decrease the thickness of the diffusive bo undary layer, thereby maintaining mass transport and hence high respir ation rates in low flow. This and previous studies suggest that phenot ypically plastic branch spacing may represent an important adaptation in M. mirabilis, enabling aggregates to tolerate a variety of flow con ditions. (C) 1998 Elsevier Science B.V. All rights reserved.