Light-induced morphological plasticity in the scleractinian coral Goniastrea pectinata and its functional significance

Environment-induced i.e., phenotypically plastic, changes in morphology, are potentially an important life-history component of sessile corals. Previous reciprocal transplant experiments have demonstrated depth-related responses in various coral species, but the potential adaptive significance is rarely investigated. To test for small-scale morphological plasticity in the massive coral Goniastrea pectinata Ehrenberg 1834, fragments from five colonies were reciprocally transplanted between two depths at Raffles Lighthouse (Pulau Satumu), Singapore. After 163 days, all fragments were collected, cleared of tissue, and examined. Reaction norms and multivariate analysis of variance describe light-induced changes in corallite architecture and genotype x environment interactions. In fragments transplanted to the shallow station, calices were deeper, and septa were shorter than in fragments transplanted to the deep station. To explore the functional significance of this plasticity, a two-dimensional model of corallite shape was constructed. The induced calice morphology of the shallow-water transplants was efficient at shading, possibly to protect tissue from excess radiation, whereas the calice morphology found in the deep-water transplants was more efficient at capturing light when irradiance was low.