Patch Reef Degradation in Subtropics, San Salvador Island, Bahamas

Patch reefs are small isolated reefs commonly found on modern carbonate banks, and in (sub)tropical lagoons. To better understand the modern degradation of patch reefs, this study, based on a field survey of patch reefs and peri-reefal sediments by scuba diving, explores the biota and the processes influencing the preservation of patch reefs on East Beach, San Salvador Island, the Bahamas. Brown algae are the most abundant organisms generally covering > 95% of the top surface of some patch reefs. Stony coral cover is < 5%, with Diploria and Porites being the most abundant genera, whereas the estimated soft coral cover can get up to 10% on some reefs. Green (predominantly Halimeda) and red algae are common on and around all studied reefs. Comparison to previous studies shows that the studied reefs have significantly declined over the last three decades, with the present-day predominance of fleshy seaweeds and a decrease in crustose red algae and coral abundance. The latter also exhibit a shift from historically dominant reef-building acroporids to more opportunistic, stress-tolerant, non-framework-building coral species. Macroalgae have likely reached abundance beyond the grazing capacity of herbivores and have drastically reduced space for coral settlement and recruitment, which in turn has compromised the patch reef resilience on the island.