Environmental controls on corallite morphology in the reef coral Montastraea annularis

Scleractinian reef-coral species display high phenotypic plasticity in skeletal morphology. Understanding environmental and physiologic controls on this variation is essential to explaining the distribution and abundance of coral species as well as understanding their susceptibility to pollution and global climate change. Here we assess phenotypic plasticity in the corallite morphology of genetically determined colonies of Montastraea annularis s.s. (Ellis and Solander, 1786) by analyzing the three-dimensional morphology of calical surfaces and the two-dimensional corallite morphology represented in transverse thin sections. Samples were collected along gradients of seawater depth and coastal influence on the island of Curaçao, Netherlands Antilles, and additionally compared to M. annularis and two closely related species, M. franksi (Gregory, 1895), and M. faveolata (Ellis and Solander, 1786), collected from Panama. Significant phenotypic plasticity was found between seawater depths and localities of Curaçao, as well as between the two geographic regions. Morphologic characters associated with calical surfaces were significantly more plastic than characters preserved in transverse thin sections. While characters preserved in thin section were more successful at classifying the three closely related species, characters associated with calical surfaces provide a basis for interpreting the adaptive significance of the observed differences between these three species.