Reefs losing their lustre

Mass bleaching threatens world’s corals.

A massive coral bleaching event currently ravaging coral reefs across the globe could destroy thousands of square kilometres of coral cover forever, US government scientists have said.

Scientists from the US National Oceanic and Atmospheric Administration ( Noaa) said about 12% of the world’s reefs have suffered bleaching in the last year. Just under half of these, an area of 12,000sqkm of coral, may be lost forever.

But the devastation is only getting started. The event could continue well into 2016. Noaa said that the western Atlantic is about to heat up, turning the corals of the Caribbean bone white. When this occurs, bleaching will have hit every tropical ocean basin on Earth since June last year.

In all, scientists forecast a total of 15,000sqkm of reef may not recover and losses to the world’s remaining coral reefs would be a devastating 6%.

Dr Mark Eakin, the co- ordinator of Noaa’s Coral Reef Watch programme, said that given uncertainties around how long the event will continue it was very difficult to predict exactly how much reef would be wiped out. “It probably won’t be as big as 1998, so we’re probably talking hopefully no more than 10%. Even if we’re talking one to 10% of the coral reefs around the world that’s a huge amount of coral reef area,” he said.

Global bleaching events have been recorded twice before, in 1998 and 2010. In 1998, a massive El Niño ( an upwelling of warm water in the Pacific) set off a chain of warming events in oceans across the world that killed off 16% to 19% of the world’s coral reefs. Eakin said this year’s El Niño was playing a part, but “it’s almost certainly being driven largely by global warming”.

A huge patch of climate change- generated hot water, known as “the blob”, has been wobbling across the northern Pacific since this time last year. Corals can only tolerate a narrow range of temperatures. If the water around them warms by just 1° C and this lasts more than a week, they are likely to bleach. After a mild warming event it is possible for polyps to regain their colour. But under extreme warming, the corals will die, meaning new colonies will have to grow.

Research from James Cook University found 40% of reefs in the Seychelles that were bleached in 1998 had now been replaced by weed and algae.

University of Queensland professor Ove Hoegh- Guldberg said the background warming of climate change could hamper recovery. After a warming event, corals that stayed stressed by even slightly warmer than normal temperatures recover more slowly.

There are measures that can assist the chance of reef recovery for the time being. When a coral bleaches, it loses its ability to clean itself of algae. Once algae cover the surface, it is impossible for coral to repopulate. Herbivorous fish graze the coral and help keep it algae free. In polluted water, algae grow faster.

“Pollution and over- fishing, if you’ve got a lot of that going on then coral reefs don’t recover very quickly. But if you can control those other factors you can improve the ability of corals to bounce back,” said HoeghGuldberg. – Guardian News & Media