Environmental Variation in Skeletal Morphology within the Caribbean Reef Corals Montastraea Annularis and Siderastrea Siderea

Environmental variation within the scleractinian species, Montastraea annularis and Siderastrea siderea, has been described quantitatively between populations collected in a range of environments within a limited geographic area near Discovery Bay, Jamaica. Characters studied in each species consist of linear measurements on the dimensions and spacing of corallites, the thickness and arrangement of vertical and horizontal structures constructing corallites, and the size and shape of coenosteal voids. Highly variable characters in M. annularis describe the size of corallites, the porosity of the coenosteum, and the thickness of columellae and endothecal dissepiments. Highly variable characters in S. siderea describe the size and arrangement of synapticulae, the thickness of columellae, and the spacing of dissepiments. In both species, the variation of each character is continuous. Different characters have different amounts and different patterns of variation. The magnitude of interpopulation variation is generally less than or equal to that of intracolony variation.

Comparisons between species show that the same character often varies to differing degrees and has different patterns of interpopulation variation. Growth rate varies more in S. siderea, whereas corallite dimensions vary more in M. annularis. Vertical and horizontal corallite structures vary equally in the two species. In general, variation is correlated with light intensity and food supply in M. annularis and with sedimentation rate in S. siderea. These results show that environmental variation is an important attribute of the species and suggest that variation is related to the magnitude and type of energy sources used by species. M. annularis may be deriving energy largely from products of zooxanthellae photosynthesis while S. siderea may be deriving energy from organic particles in fine sediment.