CASTILLO, K.D.; HELMUTH, B; University of South Carolina: Effects of Elevated Seawater Temperature on Photosynthesis and Respiration in Scelractinian Coral Montastraea annularis – Southern Belize

Previous studies have shown that coral metabolism is closely related to ambient seawater temperature conditions, and that photosynthesis and respiration are accurate indicators of thermal stress. However, we still do not completely understand the roles of thermal history and rates of temperature change in driving coral stress. We compared the physiological response of the Caribbean scleractinain coral Montastraea annularis, when exposed to relatively rapid increases in seawater temperature, from inner lagoon reef sites and outer barrier reef sites in the Gulf of Honduras – Southern Belize, to test the hypothesis that differences in thermal history would be reflected by differences in responses to temperature change. Ambient seawater temperatures at 4-5 m were measured every 15 minutes at inner lagoon reef and outer barrier reef collection sites for a period of one year. Mean monthly maxima were higher at inner lagoon reef sites compared to outer barrier reef sites, and inner reef sites showed more variability in temperature than outer reef sites. These data, and temperatures recorded at other sites in Belize, further show that increases of several degrees can occur in a matter of hours. Measurements of M. annularis photosynthesis and respiration suggested that both photosynthesis and respiration increased with increasing temperatures but only up to a certain point. These preliminary results suggest that there may be significant difference in the photosynthetic stress responses of inner lagoon reef species versus outer barrier reef species of M. annularis when exposed to elevated seawater temperatures, and that the short-term changes in temperature observed in situ may have an impact on coral physiology.