DAINTY blue fish still dart around coral shaped like antlers near the Mexican resort of Cancun, but pollution is threatening 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 hotels in the tourist city – has taken over.
Coral in areas such as Chitales, near the northern tip of a Caribbean
reef chain stretching from Mexico to Honduras, are dying as people and cities put more stress on the environment.
Climate change alone could trigger a global coral extinction by 2100 because carbon emissions warm oceans and make them more acidic, according to a recent study.
But local environmental problems, such as sewage, farm run-off and over-fishing, could kill 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.
Human waste, like that from Cancun's hotels and night spots, aggravates threats to coral worldwide, such as overzealous fishing, which hurts stocks of fish that eat reef-damaging algae. Coral reefs are covered with tiny animals called coral polyps,
which build the reefs by slowly secreting calcium carbonate over thousands of years, creating structures that can dull the blow hurricanes deal to coastal cities. The polyps also give the reefs their dazzling shades of pink and purple.
Across the Caribbean, the amount of reef surface covered by live coral has fallen about 80% in the past 30 years, the Global Coral Reef Monitoring Network says.
In the Pacific, between Hawaii and Indonesia, reefs have been losing about 1% of their coral coverage annually over the past 25 years.
It is hard to tell how much of that damage was caused by global warming and how much by local factors such as 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 past 16 years, says some reefs are so damaged he would not take an experienced diver to see them. "There are still fish and coral, but it isn't like it used to be," he said.
Fixing problems like poor sewage treatment and over-fishing are among the few things that countries and cities can do to help their reefs.
"The local factors are the only things we can manage at this point and they are absolutely critical," said Drew Harvell, a biologist at Cornell University.
In the late 1960s, Cancun was barely inhabited.
Then Mexican bureaucrats, hungry for foreign currency and armed with statistics on sunshine, hatched a plan to turn the area into a tourist area. Today millions of people each year pack into hotels running the length of the strip.
