Here in the West Indies, a highlight of any visit to Virgin Islands National Park is exploring the sea life that resides just beneath the Caribbean Sea's surface. Whether you choose to snorkel or prefer going deeper and longer with scuba gear, the world viewed through a mask is incredible.

Schools of shimmering fish in hues of yellow, orange, blue, black and red flit about. You've got (neon) blue tangs, black-and-yellow striped sergeant majors, moray eels, sting-rays, yellowtail damsel fish, cocoa damselfish, grunts, jewfish, parrot fish, yellowtail snappers, and more.

There are beautiful purple-hued sea fans waving in the currents, brain corals that look, well, like brains, Staghorn corals, Elkhorn corals, Pillar corals, and sponges. Silvery barracudas prowl the waters. Leatherback and green turtles graze on the vegetation. Spiny Sea Urchins appear as over-stuffed pin cushions with their long, black -- and sharp -- spines. Coral reefs blossom in greens, blues, oranges and reds thanks to their algal residents.

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.

So, why worry if the sea life remains after corals are bleached? Because eventually as more and more corals die the reefs break down -- disintegrate, really -- wiping out valuable habitat for fish, sponges, eels, and other sea life. Additionally, the barriers that the reefs form to blunt incoming waves disappear and the waves can lead to heightened beach erosion.

In November 2008, recognizing the plight facing corals, the National Marine Fisheries Service designated "critical habitat" for Staghorn and Elkhorn corals in four areas -- Florida, Puerto Rico, St. John/St. Thomas, and St. Croix.

Actions can be taken to mitigate human impacts. At the Virgin Islands in parts of the national park's waters the National Park Service has worked to protect reefs by educating divers on the impacts they can cause by touching corals or inadvertently kicking them with their flippers. Since careless anchoring can also damage reefs, the NPS has marked areas where boats are not supposed to anchor.

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?

This past December 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."

The good news?

Well, in the waters in and around Virgin Islands National Park and the associated Virgin Islands Coral Reef National Monument the rate of the coral die-off has leveled off. For now. Even with that news, though, snorkeling and diving on the reefs in the park's waters are not as colorful as they once were. Not nearly.

What can you do?

If you visit the park or monument and head into the water, be careful what you touch and where you stand. As the Park Service puts it, "If it's not sand, don't stand." If you're boating, be careful where you drop anchor. And overall, do what you can to reduce greenhouse gas emissions, and let your congressional representatives know how important it is to you that the country as a whole do the same.