The next time Caribbean snorkelers peer down into the water, there may not be much for them to see, new research finds.

Due to local pressures such as overfishing and excessive coastal pollution, coral cover in the Caribbean has declined by more than 50 percent since the 1970s, according to a comprehensive study released today by the Global Coral Reef Monitoring Network (GCRMN), the International Union for Conservation of Nature (IUCN) and the U.N. Environment Programme (UNEP).

Unless governments promptly implement measures to mitigate the threats posed by fisheries, tourism and coastal development, "Caribbean coral reefs and their associated resources will virtually disappear within just a few decades," the authors write.

The report points to scientific evidence that ocean acidification is restricting coral growth over time and that coral bleaching caused by extreme heat events has already caused mass coral mortality. For instance, an intense bleaching event at St. John in the U.S. Virgin Islands in 2005 caused some reefs to lose up to 60 percent of their coral cover.

"We know that these things will be more and more critical as time goes on and humanity burns more coal and oil and puts more CO2 into the atmosphere," said Jeremy Jackson, lead author of the report and scientific director of GCRMN. "But when you look at the entire region, it's something else other than extreme heating events has been a much more important driver of the lost corals."

The report challenges conventional wisdom about the relative importance of global climate change versus local impacts as the primary driver of coral reef degradation to date. It finds that while climate change poses a threat to corals, local stressors—particularly ones that threaten crucial algae-eating species—have been the main determinant of coral health in the Caribbean to date.

Protected areas the key?

The study was produced by 90 experts over the course of three years. It contains data from more than 35,000 surveys of corals and other sea life conducted at 90 different Caribbean locations since 1970.

The Caribbean is an environmentally and economically significant region. It's home to 9 percent of the world's coral reefs and some of the most diverse ecosystems. These reefs also span 38 countries and serve as a vital economic driver, generating more than $3 billion annually from tourism and fisheries.

According to the report, the loss of the Caribbean's two main underwater grazers—parrotfish and sea urchins—has been the key driver of coral decline. Without these species to feed on algae, the algae can grow to smother and kill the coral.

An unidentified disease led to the mass mortality of sea urchins in the Caribbean in 1983. But it was unregulated fishing throughout the 20th century that brought parrotfish to populations in some areas to the brink of extinction. Places where parrotfish don't have protection have seen some of the greatest coral declines, including parts of Florida and the U.S. Virgin Islands.

But Jackson said the study is a good news story. The report shows that restoring parrotfish populations and restricting coastal development could help reefs recover more quickly and make them more resilient to future climate change impacts.

Some of the healthiest Caribbean coral reefs that exist today are in protected areas. For instance, the U.S. Flower Garden Banks National Marine Sanctuary in the northern Gulf of Mexico, Bermuda and Bonaire have already restricted or banned certain fishing practices and are already seeing corals bounce back from extreme heat events.

Jackson said the report debunks arguments for inaction in the face of climate change.

Some people think that if coral reefs are doomed anyway, why not continue to fish and make some money in the meantime, he said. "We hope our report will convince some people that that's not true," he said.

"Climate change is scary. It may eventually bring coral reefs down, but it hasn't been doing that; it hasn't been having the negative effects we think of on reefs in the few places that are protected," Jackson added. "So why don't we protect every place? If we do, corals would have a lot more protection as the effects of climate change ratchet up."

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500