A surprising discovery along the mangrove-rooted shores of Virgin Islands Coral Reef National Monument has, among other things, raised questions about how some coral reefs can tolerate higher water temperatures brought on by climate change.

It's said that coral reefs are more biologically diverse than rainforests. But in the case of those reefs that rim Virgin Islands National Park, which occupies roughly half of the island of St. John, that diversity is being threatened by warming seas, diseases, and human impacts. Forget what you might have heard about polar bears being the first species to gain Endangered Species Act protection due to climate change. Two species of coral can partially lay claim to that unfortunate distinction -- the Staghorn and Elkhorn corals.

On May 4, 2006, both of these coral species were officially designated as threatened under the ESA due to a variety of factors including disease, damage from hurricanes, human impacts, and bleaching.

Bleaching occurs when waters get too warm for the algal residents of corals, they die, and the corals turn white. In some situations, the corals themselves can die. At the present, the current state of affairs doesn't seem to be greatly impacting the fish that rely on the corals for habitat, although it could affect those that feed on the algae.

But dealing with the threat posed by rising ocean water temperatures is an altogether different, much more challenging, task. During the summer of 2005, when doldrums set in and the sea temperatures approached 90 degrees, there was widespread coral bleaching in the U.S. Virgin Islands -- more than 90 percent of the coral cover was affected, according to a U.S. Geological Survey report. A return to cooler temperatures helped some of the corals recover, but many others died.

The effects of bleaching and disease on coral reefs in the USVI (U.S. Virgin Islands) have been profound, and no other stressors have caused greater or more rapid coral cover declines on these reefs. These and other studies show that losses were similar for reefs inside and outside marine protected areas, including marine reserves. The anticipated benefits (for example, replenishment of fish and corals) from marine reserves (Virgin Islands Coral Reef National Monument and Buck Island Reef National Monument) established in the USVI in 2001 could be undermined by these significant declines in coral cover. No measurable recovery has been documented to date. The recovery of USVI coral reefs will depend on the severity and frequency of expected future bleaching and disease events.

How dire are things?

In December 2008 the International Union for Conservation of Nature estimated that nearly one-fifth of the world's coral reefs are in decline. This and related evidence led the IUCN to conclude that "unless the consequences of climate change (including temperature increases and increased ocean acidity levels from greenhouse gases), over-fishing, destructive fishing practices (such as dynamiting reefs), mining of coral, pollution, unchecked man-based development and a host of other factors are brought under control, the remaining reefs could be entirely wiped out by 2050."

Against this sobering news, a U.S. Geological Survey coral-reef ecologist has found a biologically rich collection of shallow-water coral reefs in mangrove stands at Virgin Islands Coral Reef National Monument that lies along the eastern shores of the national park. There within the waters little more than 3 feet deep and shaded by red mangrove trees are colorful collections of corals and sponges that in turn are supporting fisheries and anemones.

The area, known as Hurricane Hole, is thought to contain some of the best preserved and most pristine mangrove stands in the U.S. Virgin Islands, according to a USGS story about the discovery.

"The discovery of all of the corals in the mangroves is very exciting," Caroline Rogers said in the story. "Within Hurricane Hole, there are at least 30 coral species, some of which are rarely seen even in the nearby coral reefs."

The discovery means more than just another beautiful reef of marine life. If researchers can understand how this reef tolerates warming waters and other impacts that are threatening reefs elsewhere, it could have significant economic, geologic, and even biologic impacts.

Coral reef ecosystems are some of the most valuable ecosystems on Earth. They provide billions of dollars in economic and environmental services—food, protection for coasts, and tourism. As home to the richest marine biodiversity, coral reef ecosystems are beautiful and awe-inspiring. Coral reefs face serious threats, especially from the impacts of climate change (including ocean acidification), fishing, and land-based pollution. A 2008 Global Coral Reef Monitoring Network report says "The world has effectively lost 19 percent of the original area of coral reefs." Disappearing coral reefs means loss of underwater buffers that reduce wave strength during storms, loss of nature's nurseries for fish species that generate 200 million jobs and food for a billion people, and loss of the home for plants and animals used to treat cancer and HIV and other viruses. -- NOAA's Coral Reef Conservation Program

According to Ms. Rogers, the mangrove areas in and around Hurricane Hole contain at least 30 coral species.

"The diversity is remarkable and is not unique to the corals. We're seeing great diversity in the sponges as well. Many of the sponges are more typically found in coral reefs than in mangroves," she said.

To watch a slide show of photographs taken by the researcher, surf over to this site.

Or, watch this video filmed by Andrew Burnett: