Warming sea temperatures have scientists worried that the Caribbean could see a repeat this year of the widespread coral death that swept the region in 2005.
About 40 percent of coral died around parts of the U.S. Virgin Islands last year, and the coral that survived likely isn't healthy enough to survive another hot summer, U.S. Geological Survey biologist Caroline Rogers told The Associated Press.
"It worries me. It's looking so similar" to last year, said Rogers, who has studied coral in the U.S. Virgin Islands for 22 years. "It's impossible to overstate how important this is."
Bleached by warmer waters and infested with disease, coral in Puerto Rico and the U.S. Virgin Islands was especially hard hit last year.
"You don't know how scary it looks down there," said Zandy Starr, who monitors coral and sea turtles in St. Croix's national parks. "All of us thought that by now, with all the cooler temperatures in January and February, we would have seen recovery, but they're still sick."
Water hides the damage
A building block for undersea life, the coral reefs are a sheltered habitat for fish, lobsters and other animals to feed and breed. They also deflect storm waves that might otherwise wash away the Caribbean's famed beaches.
"People just don't know that much about coral because it's underwater," Rogers said. "If 40 percent of the trees in one of our national parks died, people would take notice."
Glassy, calm seas have permitted coral-killing ultraviolet rays to penetrate more easily to the ocean floor, raising sea temperatures and making the fragile undersea life more susceptible to disease, Starr said.
A record 9 percent of elkhorn coral — vital for reef building — died last year and much more was damaged, Rogers said. Elkhorn is one of the faster-growing corals at some 8 inches a year, compared with less than an inch for other varieties.
Scientists haven't pinpointed what caused the coral to become sick or led to the warm seas.
"We don't really have the data. You need a record over decades," said Alberto Sabat, a biology professor at the University of Puerto Rico. "There's a lot of research that needs to happen."
A shock for coral colonies
The rising temperatures appeared to be "something new that the corals aren't used to," said Tyler Smith, a marine researcher at the University of the Virgin Islands.
"I've seen some very large colonies — 100-year-old colonies — in the Virgin Islands that have completely died," he said.
The U.S. National Oceanic and Atmospheric Administration said waters were also warmer than usual in the South Pacific, mid-Atlantic and Indian oceans this month.
Millions of people visit the Caribbean each year to dive and snorkel over the region's coral reefs, part of a multibillion-dollar tourism industry.