Marine Reserves Enhance the Recovery of Corals on Caribbean Reefs

TLDR

Marine reserves protect fisheries and biodiversity, and herbivorous fish are increasingly viewed as a tool to aid ecosystem recovery from climate change, especially for coral reefs, yet evidence that reserves accelerate coral recovery has been lacking. The study tests whether reserve‑induced reductions in macroalgae by parrotfishes speed coral recovery compared to fished areas. Ten sites inside and outside a Bahamian marine reserve were surveyed over 2.5 years, and coral cover gains were significantly greater within the reserve. Reserve sites showed a significant negative correlation between macroalgal cover and coral gain, and coral cover increased from a heavily degraded state, indicating that limiting herbivore exploitation benefits reef recovery and supports ecosystem‑based management.

Abstract

The fisheries and biodiversity benefits of marine reserves are widely recognised but there is mounting interest in exploiting the importance of herbivorous fishes as a tool to help ecosystems recover from climate change impacts. This approach might be particularly suitable for coral reefs, which are acutely threatened by climate change, yet the trophic cascades generated by reserves are strong enough that they might theoretically enhance the rate of coral recovery after disturbance. However, evidence for reserves facilitating coral recovery has been lacking. Here we investigate whether reductions in macroalgal cover, caused by recovery of herbivorous parrotfishes within a reserve, have resulted in a faster rate of coral recovery than in areas subject to fishing. Surveys of ten sites inside and outside a Bahamian marine reserve over a 2.5-year period demonstrated that increases in coral cover, including adjustments for the initial size-distribution of corals, were significantly higher at reserve sites than those in non-reserve sites. Furthermore, macroalgal cover was significantly negatively correlated with the change in total coral cover over time. Recovery rates of individual species were generally consistent with small-scale manipulations on coral-macroalgal interactions, but also revealed differences that demonstrate the difficulties of translating experiments across spatial scales. Size-frequency data indicated that species which were particularly affected by high abundances of macroalgae outside the reserve had a population bottleneck restricting the supply of smaller corals to larger size classes. Importantly, because coral cover increased from a heavily degraded state, and recovery from such states has not previously been described, similar or better outcomes should be expected for many reefs in the region. Reducing herbivore exploitation as part of an ecosystem-based management strategy for coral reefs appears to be justified.