Geographically conserved rates of background mortality among common reef-building corals in Lhaviyani Atoll, Maldives, versus northern Great Barrier Reef, Australia

Abstract

Even in the absence of major disturbances (e.g., cyclones and bleaching), corals are consistently subject to high levels of background mortality, which under-mines individual fitness and resilience of coral colonies. Most studies of coral mortality however only focus on catastrophic mortality associated with major acute disturbance events, neglecting to consider background levels of chronic mortality that have a significant influence on population structure and turnover. If, for example, there are geo-graphic differences in the prevalence of injuries and rates of background mortality, coral communities may vary in their susceptibility to acute large-scale disturbances and environmental change. This study quantified the prevalence and severity of partial mortality for four dominant and widespread coral taxa (massive Porites, encrusting Montipora, Acropora hyacinthus,and branching Pocillopora) at Lhaviyani Atoll, Maldives, and on the northern Great Barrier Reef, Australia. The prevalence and severity of sublethal injuries varied greatly among taxa, but was generally similar between locations; on the Great Barrier Reef, 99.4 % Porites colonies, 66 % of A. hyacinthus, and 64 % of Pocillopora had conspicuous injuries, compared to 92.4 % of Porites, 47.5 % of A. hyacinthus, and 44 % of Pocillopora colonies in Lhaviyani Atoll. These results suggest that background rates of mortality and injury, and associated resilience of coral populations and communities to large-scale disturbances, are conserved at large geo-graphic scales, though adjacent colonies can have markedly different injury regimes, likely to lead to strong intraspecific variation in colony fitness and resilience.