The view from Caroline Rogers’ office, on western St. John in Virgin Islands National Park, rivals a scene from a resort balcony. Looking north, she can see Scott Bay’s sapphire waters rimmed on the east by emerald green forest. Between the bay and the purplish-gray shape of Jost Van Dyke Island in the distance are a handful of uninhabited islands fringed by white sand beaches.

The view across the Caribbean from Caroline Rogers’ office. (Photo courtesy of Caroline Rogers).

As we talk on the phone on a late September afternoon, Rogers, a marine biologist with the U.S. Geological Survey, watches waves kicked up by a distant Hurricane Igor crashing on the shore. The view she describes is beautiful, but she doesn’t seem to be admiring it. Her attention is somewhere else.

The Caribbean Sea is unusually warm and predicted to stay that way through October, Rogers explains. The last time this happened, she says, was in 2005. Ninety percent of the corals in the park bleached, losing the symbiotic algae that produce much of their food—the coral version of “heat shock.” More than 60 percent died from disease over the next several months.

Corals are so slow-growing that little recovery has taken place in the years since, and the bleaching outlook from NOAA’s Coral ReefWatch Program indicates a high risk of heat stress in the Caribbean through the remainder of 2010. “I’m horrified to think that we could lose more coral here,” Rogers admits.

It’s hard to focus on the beauty out the window when a catastrophe might be unfolding beneath the waves.

Coral bleaching forecast for August–November 2010, issued by the NOAA Coral Reef Watch project. (Map by Dan Pisut, NOAA Environmental Visualization Lab).

Caribbean Coral Crisis
Coral reefs are to the ocean what tropical forests are to land: a lush habitat packed with a seemingly limitless number and variety of living creatures. Through fishing, tourism, and coastal protection from storm surges and beach erosion, reefs provide billions of dollars in ecosystem services each year.
Nearly everywhere around the world, coral reefs have been degraded by overfishing, boat anchors, sewage and other pollution, and runoff filled with dirt from agriculture, road-building, and other human activities. “The goal of protected areas like the park is to reduce as many of the direct human pressures as possible and allow reefs to recover to a more natural state,” says Rogers.

(Top) The Virgin Islands in the northeast Caribbean Sea. (Bottom) The U.S. Virgin Islands National Park protects the island of St. John (white outlined in top image of the U.S. and British Virgin Islands) as well as several thousand acres of adjacent waters. The island is surrounded by coral reefs. [Image and map by Hunter Allen, based on Landsat data (top) and benthic habitat data from Zitello et al., 2009 (bottom).]

Reefs also face threats beyond the park’s control: damage from hurricanes, disease, acidification (the drop in the pH of sea water as it absorbs excess carbon dioxide from the air), the possibility of stronger hurricanes, and of course, rising ocean temperatures. Sustained temperatures as little as 1° Celsius above what the corals are used to, especially during the warmest months of the year, are enough to cause bleaching.

Bleaching isn’t necessarily a death sentence for coral, but it can significantly weaken them. The microscopic algae that live in a coral’s tissues not only give healthy reefs their vibrant colors, but also produce much of the coral’s food. When the algae are stressed, the partnership falls apart, and the coral expel them. If the water stays warm, the surviving algae don’t reproduce, and eventually the corals may starve.

A bleached elkhorn coral (Acropora palmata) in the U.S. Virgin Islands in 2005 (left) compared to the species’ normal color (right, not same coral). Prior to 2005, there were no reported cases of bleaching in elkhorn coral in the region. [Photos courtesy Erinn Muller, Florida Institute of Technology (left), and NOAA Photo Library (right)].

The 2005 mass bleaching event was the worst ever seen in the Caribbean. Under stress, more than 60 percent of the coral in Virgin Islands National Park succumbed to disease and died over the next several months. The devastation was hard for Rogers to take.

“I’ll be honest,” she says. “Some of the places where I went snorkeling, when I saw the amount of coral mortality, it brought tears to my eyes, that’s how depressing it was. Within a national park, you feel that the reefs should be doing better, and you can’t help but think ‘If these can’t survive… .’”