Pollution killing world's coral reefs

By Jason Lange

CANCUN, Mexico (Reuters) - Dainty blue fish dart around coral shaped like moose antlers near the Mexican resort of Cancun, but sickly brown spots are appearing where pollution threatens one of the world's largest reefs.

Parts of the reef, nestled in turquoise waters, have died and algae -- which feed on sewage residues flowing out of the fast-growing resort city -- has taken over.

Coral reefs like Chitales, near the northern tip of a Caribbean reef chain stretching from Mexico to Honduras, are dying around the world as people and cities put more stress on the environment.

Climate change alone could trigger a global coral die-off by 2100 because carbon emissions warm oceans and make them more acidic, according to a study published in December.

But local environmental problems like sewage, farm runoff and overfishing could kill off much of the world's reefs decades before global warming does, said Roberto Iglesias, a biologist from UNAM university's marine sciences station near Cancun.

"The net effect of pollution is as bad or maybe worse than the effects of global warming," said Iglesias, a co-author of the study in the journal Science on how climate change affects reefs.

Human waste like that from Cancun's hotels and night spots aggravates threats to coral worldwide like overzealous fishing which hurts stocks of fish that eat reef-damaging algae.

Coral reefs, underwater structures that look like rocky gardens, are covered with tiny animals called coral polyps.

The polyps build the reefs by slowly secreting calcium carbonate over thousands of years, creating structures that can dull the blow hurricanes deal to coastal cities and are vital nurseries for fish.

The polyps also give the reefs their dazzling shades of pink and purple that delight scuba divers and boost tourism from the Great Barrier Reef of Australia to the Florida Keys.

Economically, reefs generate billions of dollars a year worldwide in tourism and fishing, the Nature Conservancy environmental group says.

Across the Caribbean, the amount of reef surface covered by live coral has fallen about 80 percent in the last three decades, the Global Coral Reef Monitoring Network says.

In the Pacific between Hawaii and Indonesia, reefs have been losing about 1 percent of their coral coverage annually over the last 25 years.

It is hard to tell how much of that damage was caused by global warming and how much by local factors like pollution.

Some scuba diving instructors around Cancun are worried about the future of their trade. Jorge Olivieri, who has been taking tourists out diving in the area for the last 16 years, says some reefs are so damaged he would not take an experienced diver to see them.