The effects of periodic fishery closures on reefs that switch between coral and macroalgal dominance

Background/Question/Methods

: Fishing sustains coastal communities across the globe, but can produce undesirable effects on ecosystems. In particular, fishing removes herbivores from coral reefs, enabling macroalgae to outcompete coral. Further, coral reef ecosystems can exhibit alternate stable states, in which the transition from coral-dominated to macroalgae-dominated states can be difficult to anticipate or reverse. These transitions can cause loss of ecosystem services and the long-term decline of the reef.Spatial fishing closures are commonly used to combat this degradation, usually in the form of fixed marine protected areas that permanently prohibit fishing in an area. However, periodic closures, in which fishing is sequentially prohibited and permitted in a recurring pattern, are often preferred by fishing communities and are a common management tool on coral reefs in the South Pacific. Previous research has explored how these periodic closures affect fisheries outcomes, but surprisingly, has not evaluated their potential effects on corals. Here we ask how periodic closures will perform in systems with the potential to switch between alternative stable states. We analyze a suite of ecological models and predict how periodic closures will affect coral cover as a function of initial ecosystem state, closure area and closure duration.

Results/Conclusions

: We found that short-period closures had little effect on the benthic community; rapidly cycling between permitting and prohibiting fishing has no net effect on the fish community and thus did not change coral or macroalgae. Longer-period closures can have significant effects on coral and macroalgal dynamics, and importantly these effects differ from predictions of prior studies which focused only on fish populations. A system initially dominated by coral can only lose coral as a result of periodic closures, and is more vulnerable to larger closures that concentrate fishing effort into the remaining open areas. By contrast, periodic closures can help coral recover in a system that has already shifted to macroalgal dominance, with more extensive closures typically resulting in better coral recovery. We find that periodic closures can outperform marine protected areas of similar coverage under certain scenarios. These results provide important guidance to managers considering periodic closures and emphasize their potential utility and pitfalls.