Living corals on Australia's Great Barrier Reef face a bleak future if current ocean warming trends continue and could fall to unprecedented low levels, a study suggests.
Coral cover, defined as the percentage of the ocean floor covered by living coral, is considered an indicator of both ocean and reef health. Environmental change has caused the loss of more than half the world's reef-building corals, researchers say, with the percentage of the globe's seafloor covered with living coral down to between 10 percent and 20 percent.
The Great Barrier Reef, previously considered one of the most pristine and healthy of global reef systems, has lost around half of its coral cover in just the last 27 years, they say, and living coral cover could decline to less than 10 percent with ongoing environmental change.
In time, the researchers say, moderate ocean warming of 1 to 2 degrees Celsius could drive coral cover to below that 10 percent figure, considered a number vital to maintain reef growth.
The study looked at quantitative measurements of 46 reef habitats over the 10 years from 1996-2006 to arrive at a statistical model.
"If our model is correct the Great Barrier Reef will begin to look very different as ocean temperatures increase," says study lead author Jennifer K. Cooper, a graduate student in marine biology at James Cook University.
In addition to rising ocean temperatures, reefs are being damaged by human-caused threats such as coastal development, over-fishing and pollution, the researchers say.
"Even the massive, remote, and intensely managed Great Barrier Reef is being degraded by human activities," says study co-author John Bruno, a marine ecologist from the University of North Carolina, Chapel Hill.
"Losing the GBR and other reefs would be a massive blow to marine biodiversity and to the people that depend on healthy reefs for food, tourism, and protection from storms," he says.
The Great Barrier Reef is the world's largest coral reef system, covering an area about the size of Japan, stretching for almost 1,400 miles along the majority of the coastline of Australia's Queensland state.
Comprised of more than 2,900 individual reefs and around 900 islands, it houses 400 kinds of coral and 1,500 species of fish, many of them listed as vulnerable or endangered.
It was declared a World Heritage site in 1981 by the United Nations, which is considering it for inclusion on its List of World Heritage in Danger this year.
