Resilience in a coral reef ecosystem: Initiation of a long-term experiment to determine the effects of multiple disturbances
Documenting the trajectories of ecological communities following a disturbance represents one of the five core research themes central to LTER network science. Quantifying degrees of resilience, here defined as the time needed for a community to return to a previous steady or quasi-steady state following a disturbance, can be especially challenging when ecosystems experience multiple perturbations that, in combination, can cause complex, non-linear community responses. Understanding what influences resilience is becoming ever more critical in light of forecasted alterations in disturbance regimes (pulse events) and environmental drivers (press events) associated with global climate change. Global environmental change not only is altering the intensity of press events, it also is changing the frequency and strength of pulse disturbances. Given these complexities, the ability to forecast how ecosystems will respond to or recover from projected changes in pulse and press events is an important scientific challenge.
Coral reefs frequently experience both short-term “pulse” and long-term “press” disturbances. As an example, the coral reefs surrounding the island of Moorea, French Polynesia experienced multiple pulse disturbances in the early to mid-1980s in the form of several cyclones and an outbreak of the crown-of-thorns seastar (Acanthaster planci)as well as a continuing disturbance in the form of low to moderate levels of overfishing. An unanticipated natural disturbance that is now occurring at the Moorea Coral Reef LTER site provides an opportunity to resolve several key questions regarding resilience, including the trajectory of the system following disturbances that affect different components of the ecosystem, and the existence and strength of positive feedbacks that might produce alternate persistent states. The source of the current disturbance is an outbreak of crown-of-thorns seastars on the reefs surrounding Moorea that has reduced the cover of living coral from ~60% to ~5% cover over large areas. The widespread elimination of just living coral tissue (with coral skeletal structure left intact) provides an opportunity to manipulate additional features to mimic qualitatively different types of disturbances, and to cross these treatments with various combinations of other environmental stressors. MCR investigators will conduct surveys and carry out a large field experiment to explore how and why resilience is affected by structural heterogeneity, grazing, corallivory and composition of the microbial community.