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This week, the Government Accountability Office criticized the Bush administration for not doing enough about global climate change. One of the places the GAO's report examined is the Florida Keys National Marine Sanctuary, home to North America's only living coral reef.

To see the effects of global warming there, you need only swim several feet below the ocean surface. Marine scientists say warming ocean temperatures are taking a toll on the reef and underwater ecosystem that stretches from Palm Beach through the Florida Keys.

NPR's Greg Allen has this report on coral bleaching.

GREG ALLEN: Rowena Garcia is a marine biologist with the Nature Conservancy based in the Florida Keys. She heads the project that, for the last three years, has been conducting surveys of Florida's coral reefs. It's an effort that involves dive teams from a dozen different research groups and government agencies. On this day, she's heading out to a small patch reef, about a half-mile offshore with two Nature Conservancy staffers and one reporter.

Coral reefs are sensitive to rising temperatures. The increase of just one or two degrees over a few weeks can lead them to expel the colorful algae that live in a symbiotic relationship inside their tissue. Garcia says when that happens the coral loses its color, becoming pure white.

Ms. ROWENA GARCIA (Marine Biologist, Nature Conservancy): In essence, what you are seeing is the skeleton of the coral. The tissue of the coral becomes very translucent so that enough that you will see their coral skeleton. So that's really what we call coral bleaching.

ALLEN: Now, even though the coral did turn white, it actually doesn't die, though?

Ms. GARCIA: In a lot of instances, it does not die. But what we have been starting to see is once they are in this bleached state, they are weakened, and that the disease comes in.

ALLEN: Nature Conservancy marine specialist Meaghan Johnson pilots the boat to a reef she has visited several times over the past few years.

Ms. MEAGHAN JOHNSON (Marine Specialist, Nature Conservancy): We've got a GPS point that we're looking for, and I'm just going directly to that. We're just east of Munson Rocks, which is right over there, and we're in the inshore zone.

This is fine, Jess.

(Soundbite of anchor dropping)

ALLEN: As they drop anchor, we look over the side of the boat. We can see the reef through the clear Florida Atlantic. Even from the surface, much of the coral stands out - a stark, white color.

Jess Snook, puts on her dive gear and gets the other tools she needs to measure and record the condition of the reef.

Ms. JESS SNOOK (Staff Member, Nature Conservancy): We just look for what coral is there. We identify it, we measure how big it is, and we look to see whether it's bleaching or if it has any kind of disease or anything.

Ms. JOHNSON: Are you ready to go in?

ALLEN: Sure.

(Soundbite of water splashing)

ALLEN: We all go over the side to get a closer look - Meaghan and Jess in dive gear, Rowena and me with snorkels. It doesn't take long to see how warmer ocean temperatures have affected this reef - as much as one-fifth of it is already bleached out.

ALLEN: So Rowena, we just came out of the water. I saw a lot of bleached coral down there. That big boulder of coral really made an impression on me. Is with - how's this site compare to what you've seen normally?

Ms. GARCIA: Normally, this site wouldn't have all those boulder corals bleached. A lot of them would have color. You would see them kind of a mustard brown color of instead of being white. Also, we saw some diseased corals in there - black band. It's a fairly common disease down here. Inside that ring was - dead. It was basically dead from, I would assume, from the disease.

ALLEN: Coral bleaching is a growing problem, not just here in Florida, but also around the world. And it's a problem scientists say is clearly linked with rising ocean temperatures.

Bleaching itself isn't devastating to a reef. Given enough time and cooler water temperatures, the coral bounces back, capturing new algae and regaining its color. That happened here in Florida after the hurricanes of 2005 helped lower temperatures in the Atlantic.

But because bleaching makes coral susceptible to disease, it can lead to its death. Scientists worry that persistent warm temperatures may have a lasting impact on coral reefs here in Florida and around the world.

Greg Allen, NPR News, Miami.

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