NOAA Warns: Caribbean's Coral Reefs In Danger This Year

The Caribbean’s vibrant coral reefs could be in for another devastating year as the world's oceans experience some of their warmest surface temperatures on record, scientists warn.

The National Oceanic and Atmospheric Administration released its 2009 outlook for the world's coral reefs this week, and the results are disturbing.

The temperature patterns and heat stress that scientists are seeing, particularly in the Caribbean, are reminiscent of 2005. That year set records for coral deaths. Across the Caribbean, 25 to 95 percent of the coral colonies were affected. In the U.S. Virgin Islands, nearly 52 percent of the corals died. In Trinidad and Tobago, 73 percent of all Colpophyllia and Diploria brain coral colonies were wiped out.

The damage goes beyond the corals themselves. Reefs provide habitats and ecosystems for tens of thousands of organisms, and they support the fisheries and tourism that some 100 million people worldwide depend on for their livelihoods.

“There’s a lot of similarly between what we’re seeing now and what hindcasts of 2005 showed,” said C. Mark Eakin, coordinator of NOAA’s Coral Reef Watch. “We can’t say whether it’s going to be worse or how they’re going to compare, but we’re looking at the potential for conditions that could lead to coral bleaching.”

In 2005, parts of the Caribbean were hit by a double-whammy: high surface temperatures and a lack of tropic storm activity that could have cooled the water. This year, the global ocean surface temperature reached a record 0.62 degrees Celsius above the 20th century average in July, and the warmer water is accompanied by a storm forecast for the Caribbean that promises little rain or cloud cover.

The arrival of El Nino raises further concerns, starting in the central and eastern Pacific later this year and worsening conditions for corals in the Caribbean in 2010.

There isn’t much scientists can do at this point but monitor the reef ecosystems, learn from what they see and hope for the best. That’s because the primary source of the problem is global warming: Human activities have pumped more carbon dioxide into the air than the oceans can handle and raised the oceans' temperatures in the process.

When carbon dioxide mixes with seawater it forms carbonic acid, lowering the pH of the water. As the pH falls, so do levels of carbonate ions, which are essential to the creation of corals' calcium carbonate skeletons.

Add heat stress from rising surface temperatures to creatures with weakened skeletons, and scientists discover mass coral bleachings.

Corals that are under stress lose their color, known as bleaching, because they expel microscopic algae from their systems. They rely on that algae for food, and without it, they slowly starve. In mild events, they can recover quickly. In more severe events, they can die.

“Even if you don’t visibly see the corals bleach, they’re still under a lot of stress and you tend to see aspects of infectious disease,” Eakin said. “These diseases are also more active at higher water temperatures.”

The worst years to date for corals were 1998, when about 16 percent of world’s coral reefs died, and 2005, which held the record for global sea surface temperature until this year.