Rising sea levels threaten coral reefs

Researchers believe that the predicted rise could also spur different varieties

Already endangered by agricultural runoff and sewer line leaks, the world's coral reefs also face the threat of a projected rise in sea levels, according to a preliminary study by government scientists.

Initial findings by scientists from the U.S. Geological Survey studying the south shore of the Hawaiian island of Molokai reveal that higher waters likely will lead to larger waves and larger currents, endangering the health of fringe reefs.

The U.N.-backed Intergovernmental Panel on Climate Change has predicted sea levels will rise by a foot and a half by 2100, said Curt Storlazzi, a research oceanographer with the survey.

The panel has attributed much of that projected rise to an increase in temperatures around the globe and a continuing loss of glaciers and ice caps.

"We're trying to answer this question over the next couple of years -- what is that rise in sea level? How is that going to affect the processes on the reefs?" Storlazzi said last week during the biannual ocean sciences meeting of the American Geophysical Union.

Deeper water could help keep the reefs cool, but the faster currents will stir up soil and pollution washed down into the waters closer to shore and pull it out to blanket the "fore reefs" further out, where the ecosystem diversity is at its greatest, the scientists found.

Studies show a lot of sediment can cause coral bleaching, and can also prompt algae blooms, Storlazzi said.

The result, he said, "is smothered, dead, bleached corals," he said.

Brian Lapointe, a researcher with the Harbor Branch Oceanographic Institution in the Florida Keys, has been documenting the local effects of land-based sediments and pollution rich in the nutrients nitrogen and phosphorus for the past 20 years.

Lapointe has documented dramatic die-offs of native corals from disease and being overwhelmed by invasive species of algae that flourish in the nutrient-saturated water.

Almost all of the Keys' elkhorn coral is lost, said Lapointe, who is also reporting on his latest findings at the meeting.

Both Storlazzi and Lapointe said that the reefs will survive the current threats to their environments.

Storlazzi said corals have in the past survived higher levels of carbon dioxide and higher water temperatures. Both factors are being connected by researchers to coral reef damage today.

In the future, communities of coral will likely change to contain a different variety of coral species, he said.

However, the threat to the world's current ecosystems, including coral reefs, is also a threat to the survival of humanity, Lapointe said.

In waters being studied off Looe Key, the number of fish that eat plant life, such as algae, have gone up as the numbers of species of fish caught by commercial fishermen have gone down, he said.

"This is a no-take zone, so we can't blame this on fisherman," he said. "So I think at this point this really gives the whole issue a ... seriousness that we haven't had with us before."