In contrast to the upper stretches of the Great Barrier Reef, the southern third saw coral cover drop from 38 percent to 34 percent year on year. Scientists blamed the decline on an outbreak of crown-of-thorns starfish, which prey on corals. The starfish
grow faster and
eat more in warmer, more acidic waters, and carbon emissions are both raising ocean temperatures and turning waters more acidic.
In areas where coral cover expanded, it was mostly fast-growing Acropora corals driving the growth, a potentially troubling prospect given that Acropora are particularly vulnerable to strong waves generated by tropical cyclones, highly susceptible to bleaching, and the preferred target of crown-of-thorns starfish.