What drove coral cover loss on the Great Barrier Reef?

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Coral reefs worldwide are being degraded, and reducing local pressures to offset growing global pressures is widely recognized as necessary. This study examined how coral cover changed across the Great Barrier Reef over space and time, identified the main drivers of coral mortality, and estimated potential recovery rates.

The researchers used what the abstract describes as the world’s most extensive time series of reef condition: 2,258 surveys of 214 reefs from 1985 to 2012. Coral cover declined from 28.0% to 13.8%, at 0.53% per year, a loss of 50.7% of the initial cover. Tropical cyclones, coral predation by crown-of-thorns starfish (COTS), and coral bleaching accounted for 48%, 42%, and 10% of the respective estimated losses, amounting to a mortality rate of 3.38% per year. The relatively pristine northern region showed no overall decline.

The estimated increase in coral cover in the absence of cyclones, COTS, and bleaching was 2.85% per year, indicating substantial recovery capacity. Without COTS, coral cover was estimated to increase by 0.89% per year despite continuing losses from cyclones and bleaching. The researchers concluded that reducing COTS populations through improved water quality and alternative control measures could prevent further coral decline and improve the reef’s outlook. They noted, however, that such strategies can succeed only if climatic conditions stabilize; otherwise, losses from bleaching and cyclones will increase.