Examining the independent and combined effects of ocean warming and acidification on the corallite morphology of the Caribbean coral Siderastrea siderea

Anthropogenic increases in atmospheric carbon dioxide (CO2) are predicted to cause sea surface temperature to increase by 1 to 4°C and sea surface pH to decrease by 0.1 to 0.3 pH units. These ramifications of global change reduce calcification rates in a variety of coral species; however, little work has been done to investigate the underlying aspects of corallite morphology that influence observed calcification responses under these global-scale stressors. In this study, stereomicroscopy was used to investigate the independent and combined effects of ocean warming (28 and 31°C) and ocean acidification (ca. 280, 400, 700, 3200 µatm pCO2) on two aspects of corallite morphology, corallite height and corallite infilling, of Siderastrea siderea coral samples reared for 93 days in a controlled laboratory experiment. While neither corallite height nor corallite infilling were significantly impacted by elevated temperature or pCO2, trends suggest that corals in the elevated temperature show decreased height and infilling with increasing pCO2, indicating that the combination of increased temperature and pCO2 may have a greater impact on corallite infilling than either stressor alone. Corals from the inshore environment were found to have significantly taller corallite heights than those from the offshore environment in the control temperature treatments, but not at the elevated temperature; corallite infilling was not significantly different between reef environments. Together, these results indicate that S. siderea corals, especially colonies from inshore environments, may be robust and continue to calcify under projected end-of-century conditions, but that continued increases in temperature and pCO2 will ultimately decrease corallite height and corallite infilling. These changes in skeletal morphology may alter the growth patterns of S. siderea, potentially compromising skeletal function and overall reef presence.Bachelor of Scienc