Baseline Levels of <i>Siderastrea siderea</i> Bleaching under Normal Environmental Conditions in Little Cayman

Abstract

This study describes the health status of Siderastrea siderea in Little Cayman before, during, and after the 2015 Caribbean-wide elevated temperature anomaly. Colony color was used as a proxy for health during snorkel and scuba surveys of shallow (<2 m depth) and deep (6 - 16 m depth) reefs. Baseline demographics indicated that 6% of this species were pale or blue pre-disturbance. When seawater temperatures exceeded 30.5 ° C, S. siderea were early indicators of reef stress and among the first corals to bleach. Depth and site resilience did not significantly impact temperature susceptibility; however, smaller colonies (<200 cm 2 surface area) were more likely to change color than the larger size classes. Little Cayman’s S. siderea were capable of surviving large-scale (>80%) bleaching: mortality was observed for only one colony. Resilience rates varied considerably: one-third of the impacted population returned to the normal brown color within two months, one-third required 3 - 9 months to recover, and the fates of the remaining one-third remain to be determined. If the return to normal color is indicative of resistance to reef disturbances, S. siderea may be among the “winning” coral species following elevated temperature anomalies which are predicted to occur with increasing frequency and severity as a result of climate change.