Resilience of coral communities on an isolated system of reefs following catastrophic mass-bleaching

Abstract

As a result of climate change, sea-water temperatures around the world are expected to increase, potentially causing more frequent and severe episodes of coral bleaching. In this study, the impact of elevated water temperatures at an isolated system of reefs was assessed by quantifying the changes in benthic communities over almost 10 years. Mass-coral bleaching in 1998 dramatically altered the community structure of the reefs, including a >80% relative decrease in the cover of hard and soft corals and a twofold increase in the cover of algae, but which did not include macroalgae. The magnitude of the impact varied among the different sites according to their initial cover and community structure, largely due to the differing susceptibilities of the dominant groups of hard corals. Subsequent increase in the cover of these groups varied according to their life history traits, such as modes of reproduction and rates of growth. Additionally, the increase in cover was strongly correlated with the magnitude of the impact at the different sites, suggesting that recovery was driven by processes acting over local scales. Six years after the bleaching, the hard corals had returned to approximately 40% of their pre-bleaching cover, but there was little change in the cover of soft corals, and the structure of most hard coral communities remained very different to that prior to the bleaching. These data provides insights into the degree to which coral communities are resilient to catastrophic disturbances, when they are isolated from other reef systems but not exposed to some of the chronic stressors affecting many reefs around the world.