Modelling variations in corallite morphology of Galaxea fascicularis coral colonies with depth and light on coastal fringing reefs in the Wakatobi Marine National Park (S.E. Sulawesi, Indonesia)

Coastal environments in the tropics can suffer from high sedimentation and low light levels. Galaxea fascicularis is a hermatypic coral that is relatively resilient to stress from bleaching and from sedimentation. Corallite dimensions – width, height, corallite densities and inter-corallite distances – of Galaxea fascicularis colonies varied significantly with depth, and so with incident light at the Sampela reef in the Wakatobi Marine National Park, S.E. Sulawesi, Indonesia. Modelling studies based on our data showed that corallite width decreased with the amount of incident light, while corallite height increased with the amount of incident light (r2 values of 0.835 for width and 0.869 for height). In all colonies, inter-corallite distance decreased significantly with the amount of incident light (r2 = 0.89). Colony width/height ratio increased in a linear fashion with inter-corallite distance for all colonies studied (r2 = 0.65). Current flow as judged using tags did not appear to be a factor in variations of corallite dimensions. Our results suggest that under low light conditions, distribution and size of corallites may optimise heterotrophic nutrition, while in conditions where light is not limiting, distribution and size of corallites may be optimal for photosynthesis.