Did corals recover faster inside a marine reserve?

Details

Marine reserves are widely recognized for fisheries and biodiversity benefits, and interest is growing in using herbivorous fish to help ecosystems recover from climate change impacts. This could be particularly useful for coral reefs, which are acutely threatened by climate change: the trophic cascades generated by reserves could theoretically speed coral recovery after disturbance. But evidence that reserves facilitate coral recovery had been lacking.

Researchers investigated whether reduced macroalgal cover, caused by the recovery of herbivorous parrotfishes inside a reserve, had resulted in faster coral recovery than in areas subject to fishing. Surveys of ten sites inside and outside a Bahamian marine reserve over 2.5 years found significantly greater increases in coral cover at reserve sites, including after adjustment for the corals’ initial size distribution. Macroalgal cover was significantly negatively correlated with the change in total coral cover over time.

Recovery rates of individual coral species generally agreed with small-scale manipulations of coral–macroalgal interactions, but differences also showed the difficulty of translating experiments across spatial scales. Size-frequency data indicated that species particularly affected by high macroalgal abundance outside the reserve experienced a population bottleneck that restricted the supply of smaller corals to larger size classes.

Coral cover increased from a heavily degraded state, and recovery from such states had not previously been described. The researchers therefore suggested that similar or better outcomes should be expected for many reefs in the region. They concluded that reducing herbivore exploitation as part of an ecosystem-based management strategy for coral reefs appears justified.