THE MORPHOMETRICS OF PHENOTYPIC PLASTICITY

Zooxanthellate corals (Order: Scleractinia) form the backbone of the most diverse marine ecosystems. Corals have been put under growing pressure from increased ocean temperature swings, pollution, and ocean acidification. Scleractinian corals are known to show phenotypic plasticity at the colony level in response to a myriad of environmental factors including water depth, light intensity, water movement, and nutrient levels. The response of individual corallites to changing environmental conditions is more poorly understood. Examining how both colonies and corallites change in response to environmental conditions can help examine the variability of species for purposes of taxonomy and provide clues as to the environment within fossil assemblages. In order to better understand how individual corallites change in response to environmental factors this study employed 2D and 3D geometric morphometrics on experimental, lab-grown corallites. Controls were put in place to account for genetic effects and the experimental corals were grown under three different light intensities in one experimental series and three different ambient temperatures in a second experimental series to examine their plastic response to these conditions. Colonies of Dipsastraea speciosa and Caulastraea furcata were chosen for these experiments due to their hardiness and availability. The amount of morphological variation differed by species. Dipsastraea speciosa displayed a small change in morphology when exposed to differences in light levels, but did not show significant difference between the tested ambient temperature treatments. Caulastraea furcata displayed significant changes in morphology to both differences in light levels and in response to different ambient temperatures. The amount of morphological changes caused by differing levels of light intensity was more noticeable than the changes in skeletal morphology attributed to variation in ambient temperature. The results of this study suggest that light intensity is a more important factor in skeletal growth than ambient temperature as long as the ambient temperature remained within a hospitable range.