Coral reefs on threshold of erosion

Many Caribbean coral reefs have stopped growing or are on the threshold of starting to erode, "alarming" new British evidence has revealed.

Scientists at the University of Exeter have discovered essential calcium carbonate produced and stored by the reefs is significantly below previous levels,

It comes after concerns were raised last year that carbon emissions are acidifying oceans at a faster rate than at any time in the past 300 million years, raising the prospect of ecological catastrophe in decades to come.

Coral reefs form some of the planet's most biologically diverse ecosystems and provide valuable services to humans and wildlife. However, their ability to maintain their structures and continue to grow depends on the fine balance between the retention and loss of those carbonates.

Scientists have long known that reef ecosystems are in decline and that the amount of live coral on reefs is dwindling. But the paper, published in Nature Communications, is the first evidence that these ecological changes are also impacting on the growth potential of reefs themselves.

Professor Chris Perry, who led the research, said: "Our estimates of current rates of reef growth in the Caribbean are extremely alarming. Our study goes beyond only examining how much coral there is to also look at the delicate balance of biological factors which determine whether coral reefs will continue to grow or will erode.

"Our findings clearly show that recent ecological declines are now suppressing the growth potential of reefs in the region, and that this will have major implications for their ability to respond positively to future sea level rises. It is most concerning that many coral reefs across the Caribbean have seemingly lost their capacity to produce enough carbonate to continue growing vertically, whilst others are already at a threshold where they may start to erode."

The research suggests that if these trends continue, reef erosion looks far more likely.

Last year, the Intergovernmental Panel on Climate Change said that when seawater becomes too acidic, corals and plankton at the bottom of the food chain cannot survive. The knock-on effects can lead to widespread mass extinction of marine species, and is believed to have done so in the past.

Commenting on the publication, Prof Perry said: "Urgent action to improve management of reef habitats and to limit global temperature increases is likely to be critical to reduce further deterioration of reef habitat."