How disturbance patterns influence the composition and resilience of coral reef benthic communities

Background/Question/Methods

It is commonly accepted that coral reef ecosystems possess two dynamically stable states: one in which reef-building scleractinian corals dominate the benthic habitat and one in which macroalgae and turf algae dominate. The transition between these states has been linked to alterations of herbivores assemblages (e.g. fishing, marine protection), in addition to other environmental forcings. Importantly though, global climate change may impact the coral reef community without necessarily leading to the previously described phase shift. For example, drastic qualitative and quantitative changes of the coral community composition have been observed even though the coral cover ratio hardly changed. Since disturbances are spatially and temporarily diverse, the ecosystem will respond in a comparably diverse manner. An inventory of the possible responses of the coral community seems necessary to better encompass ecological consequences of varying disturbances. This work, by using a modeling approach, assesses how disturbance patterns could influence coral communities’ composition and characteristics, and thus coral reef ecosystem resilience. Two structurally different models of the benthic coral community have been used here to shed light on convergence between their respective outputs and thus increase the robustness of our results.

Results/Conclusions

Using a stereotypical representation of the major disturbances on coral reefs and their impacts, we demonstrate a clear heterogeneous response of coral communities to variations in the nature, frequency and magnitude of disturbance events. For example, an increase in the frequency of physical disturbance leads to a decrease in coral community diversity but not coral cover ratio. Indeed, such disturbance regimes select almost exclusively species with a high growth rate/high disturbance sensitivity profile, given their availability in the recruit pool, and increase the turnover of the coral population. The resilience capability of such communities is thus highly decreased. Other results suggest that disturbances causing whole-colony mortality, like bleaching events, lead to a more spatially clustered and more diverse community relative to the ones causing partial mortality, like some diseases. Overall, our theoretical approach allows us to track mechanisms underlying community responses and thus provide some clues about the functioning of the coral reef community reorganization driven by the climate global change.