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Like Tropical rainforests, coral reefs are disappearing, but much faster than scientists had thought.
Marine ecologist John Bruno and graduate student Elizabeth Selig compiled and analyzed 6,001 scientific surveys of 2,667 coral reefs in the Pacific Ocean from Indonesia to Hawaii and discovered that nearly 600 square miles of these ecologically diverse underwater forests have disappeared per year since the late 1960s. That’s twice the rate of rainforest loss during the same span.
“We have already lost half of the world’s reef-building corals,” said Bruno, associate professor of marine ecology and conservation and lead author of the study that appeared in the online journal PLoS One.
The Indo-Pacific reefs account for 75 percent of the world’s coral reefs, which support thousands of fish species and other aquatic life. And coastal communities depend on healthy coral reefs for fisheries, tourism and protection from storm surges.
By analyzing scientific surveys from 1968 to 2004, Bruno and Selig tracked the decline of coral cover — how much coral covers the ocean floor in a given area, a key indicator of reef health, just as canopy cover is indicative of tropical rainforest health. Historically, reef-building coral have covered about 50 percent of the ocean floor where coral grows. But Bruno and Selig found that coral cover declined from 40 percent in the early 1980s to 20 percent by 2003. Today, only 2 percent of coral reefs in the Indo-Pacific come close to the 50 percent baseline.
And the researchers found this same decline in Hawaii, Indonesia, Australia and all points in between. This region-wide decline, Bruno said, is the most surprising result of their research because not all coral reefs face the same dangers. Some coral live in tight quarters, which means that viruses can more easily infect and kill nearby coral. Some reefs are over-fished and face more pollution and sediment runoff from coastal development and agriculture; other reefs are isolated and pristine, but are still dying.
The Great Barrier Reef off Australia’s northwest coast, for instance, is a protected area where humans tread lightly.
“But coral cover on the Great Barrier Reef was not significantly greater than reefs on the Philippines, which are often thought to be highly threatened and poorly managed,” Bruno said. Coral cover in Hawaii is just as good — or bad — as coral cover in Australia, despite the particular protection policies of the two areas and the fact that the Great Barrier Reef is much more ecologically diverse, which ecologists had assumed helped reef health and resiliency.
Also, ecologists had thought that the Indo-Pacific reefs were dying at a lower rate than say, Caribbean Sea reefs, which don’t support as many species and face many more threats from man-made pollution.
“We assumed that the Indo-Pacific was better off,” he said. “But it’s just not.”
All this leads to a troubling conclusion: Coral decline is likely due to large-scale stressors such as the warming of the oceans, which causes coral bleaching that can lead to coral death and also exacerbates coral disease outbreaks. Fossil fuel emissions are also increasing the acidity of the ocean, making it harder for corals to secrete their calcium carbonate skeletons, which they must constantly do to keep pace with erosion.
Most scientists agree that the warming of the oceans is one of the results of global warming, Bruno said.
“We need to deal with this at the national and global scale,” he said. “We can’t expect local reef managers to deal with this. Governments and corporations will need to do a far better job of developing technologies and implementing smart policies that will offset climate change.”
Writer: Mark Derewicz
Editor: Neil Caudle