Stability of Caribbean coral-reef communities quantified by long-term monitoring and autoregressive models

Background/Question/Methods

Dramatic changes in coral-reef assemblages in the Caribbean have been observed over the past several decades.  Hurricanes, coral bleaching, sedimentation, herbivore die-offs, and ocean acidification are some of the biotic and abiotic phenomena thought to be challenging the health of coral-reef communities.  Will novel environmental conditions decimate coral-reef communities, or will new assemblages of coral species emerge that are more robust to the disturbances that future environments may hold?  To investigate this question, we fit autoregressive time-series models to data from 20 years of coral-reef monitoring in Great Lameshur Bay, St. John, USVI.  Data characterize cover of scleractinian corals, macroalgae, bare space, coralline algae and turf, and are available for three habitats experiencing similar disturbance regimes.  Model fits are used to quantify the temporal stability of each coral-reef community, and to characterize the impacts of hurricanes and bleaching events on coral cover.

Results/Conclusions

Model fits generate two measures of stability of coral-reef communities.  First, community stability can be measured by long-run variance in coral cover in each habitat.  Second, community resistance can be measured by changes in projected long-run average coral abundance under anticipated environments.   Model fits predict that overall coral cover will decline as oceans warm and hurricanes become more frequent, and that temporal variance in coral cover will increase.  More surprisingly, however, results suggest that the resistance of coral communities to both ocean warming and hurricane frequency vary considerably across habitats, even within a confined basin of several square km.  Local-scale differential resistances of coral assemblages to environmental challenges suggest that a regional-scale views of coral assemblages, whereby losses in one habitat have the potential to be balanced by larval recruitment from other habitats, may provide an ecologically felicitous framework for projecting regional responses of coral-reef communities to environmental change.