Variability in skeletal bulk densities of common hard corals in Southeast Asia

Skeletal density, a measure of a coral's investment in its structure and a known proxy for climate history, can potentially be used to enhance the precision of reef accretion models and benefit reef management strategies. However, trait data and an understanding of how it may vary are limited, especially for Southeast Asia's coral reefs where information is available for only a few species. To fill this knowledge gap, we quantified the skeletal densities of 11 common species from four reefs in Singapore. Skeletal density was best explained by a model that included species, depth, colony size, sedimentation rate, water motion, as well as an interaction between depth and colony size. Mean skeletal densities ranged from 0.99 to 2.01 g cm(-3), and species with massive growth forms (e.g. Platygyra sinensis) were least dense, while a branching coral (Pocillopora acuta) was densest. Skeletal density was influenced positively by water motion and negatively by sedimentation and colony size. The depth-size interaction also indicated that large colonies in deeper areas were denser compared to shallow colonies. Our findings suggest that environmental conditions at local scales play important roles in affecting coral skeletal density and provide an indication of the relative vulnerability among taxa and locations to physical disturbances. The need for baseline information on the skeletal properties of more species is further underscored if habitat conservation is to be effective in a changing climate.