Decoupled Seasonal Stress as an Indication of Chronic Stress in <i>Montastraea cavernosa</i> and <i>Porites astreoides</i> Inhabiting the Florida Reef Tract

Abstract

Although mass mortality from disease and climate anomalies are largely to blame for rapid losses in coral cover along the Florida reef tract, the failure of extant populations to recolonize the offshore zone is puzzling given improvements to water quality and narrower range in seawater temperature compared to the inshore patch reef zone. Using existing data from the Coral Reef Environmental Monitoring Program (CREMP) and from an inshore and offshore site established to compliment this dataset we identified significantly increased abundance and diversity of scleractinian coral from inshore to offshore across the Florida reef tract. Applying exploratory statistical methods we identified two abundant species, Montastraea cavernosa and Porites astreoides , inhabiting both zones to varying degrees. Following reciprocal transplantation of conspecifics between a representative offshore and inshore reef (6 m depth), we monitored monthly coral colony brightness (a measurement related to endosymbiotic dinoflagellate density) over a two-year period to examine symbiont loss, a common stress response in scleractinian corals. Although species-specific stress patterns were not identified, zone-specific variation was evident. Trigonometric regression of stress level by month revealed a significant relationship supporting an annual stress and recovery period at the inshore patch reef zone. Contrary to this result, conspecifics transplanted to the offshore zone did not display recovery resulting in a continued chronically bleached state over the two-year period. Our results implicate alleviation or decreased stress at inshore sites and the importance of extending greater protection to reefs within this zone.