Corals at risk – and we're to blame

A THIRD of the world's reef corals are at risk because of climate change and other human activities, scientists have warned.

Carbon dioxide levels, coastal development, sewage discharge and overfishing are all putting coral species at the threat of extinction.

Scientists said urgent conservation measures were needed or there could be mass biodiversity loss, and an impact on the hundreds of millions of people who rely on reef fish for food.

The authors of a study published in the journal Science assessed 845 tropical reef-building species and found that, of the 704 for which sufficient information existed to judge the risks they faced, 231 or 33 per cent, were under threat of extinction.

When this was broadened out to include species that were "near threatened", 407 species – more than half of those assessed by the scientists – were at risk.

The report's authors warned: "Our results emphasise the widespread plight of coral reefs and the urgent need to enact conservation measures."

They said the results showed the extinction risks for corals had increased dramatically over the past decade and now exceeded those for all terrestrial animal groups, apart from amphibians.

The Caribbean has the largest proportion of species in the high extinction risk categories, the study said, while the Coral Triangle in the western Pacific has the highest proportion of species in all categories of extinction risk.

The scientists said the threats were the result of rising levels associated with climate change, as well as local human impacts.

The raised levels of had increased sea surface temperatures, leading to the "bleaching" of corals, and made the oceans more acidic, which harms the coral's ability to build its skeleton.

The Intergovernmental Panel on Climate Change has predicted increased acidification of the oceans by the end of the century, and Dr Alex Rogers, one of the study's authors, said this presented "disastrous scenarios" for corals.

The research warned destructive fishing, sewage, coastal development and the use of agricultural chemicals were all reducing the ability of corals to withstand the threats caused by climate change and to rebuild reefs.

Dr Rogers, a senior research fellow at the Zoological Society of London's Institute of Zoology, said: "The resilience of corals to bleaching and ability to recover is heavily influenced by other stresses the corals are under, such as overfishing or destructive fishing, declining water quality and nutrient loading from agrochemicals."

While coral reefs cover no more than 0.2 per cent of the earth's surface, they host to up to two million species, with a quarter of all marine fish species found there.

"In terms of humans, they are massively important as a source of food, and globally it is estimated they deliver ecosystem services of £15.2 billion," Dr Rogers said. "They also have major effects on coastal protection from storms and flooding."

The study concluded that whether corals become extinct this century will depend on the severity of climate change, the extent of other environmental disturbances and the ability of corals to adapt.

"If corals cannot adapt, the cascading effects of the functional loss of reef ecosystems will threaten the geologic structure of reefs and their coastal protection function, and have huge effects on food security for hundreds of millions of people dependent on reef fish," it warned.