PHYSIOLOGICAL AND ISOTOPIC RESPONSES OF THE CORAL STYLOPHORA PISTILLATA TO FUTURE COASTAL OCEAN CONDITIONS

Corals are increasingly at risk of bleaching and bleaching-induced mortality due to rising global temperatures. However, there is evidence to suggest that high nutritional input (i.e., feeding) and lower light levels may provide some protection from elevated temperature stress. We measured the individual and interactive effects of temperature (27°C, 31°C), light (ambient light-200 mol photons, high light-400 mol photons), and nutrition (fed brine shrimp, not fed brine shrimp) on the physiology and biogeochemistry of the coral species Stylophora pistillata. Calcification, photosynthesis, respiration, and feeding rates were measured as well as the nitrogen (δ¹⁵N) and carbon (δ¹³C) isotopic compositions of the whole coral tissue. Overall, calcification and photosynthesis decreased as temperature increased, independent of feeding. This indicates that the corals were bleached and allocated fewer resources to calcification. However, this negative temperature effect on calcification was offset at higher light levels. δ¹³C increased as temperature and light increased, which suggests that corals were decreasing the amount of isotopically depleted dissolved and particulate organic carbon in their diets. δ¹⁵N increased as feeding and light increased. This shows the importance of heterotrophy in coral tissue growth and the enhancement of light in nitrogen assimilation. However, overall, lower light and heterotrophic feeding did not appear to mediate the negative of effects elevated temperature as was hypothesized. Additional results of the δ¹⁵N and δ¹³C of the endosymbiontic algae and the coral animal host will be presented.