University of Hawai'i researchers have found that higher levels of carbon dioxide in the ocean could significantly slow the growth of coral.

Scientists at the Hawai'i Institute of Marine Biology at Coconut Island studied the effects of carbon dioxide on two species of coral living in Kane'ohe Bay.

The results showed coral growth "can be slowed pretty dramatically" by decreasing carbonate ions, said Marlin Atkinson, UH oceanographer and specialist on coral reef biogeochemistry.

Chris Langdon, associate director of the National Center for Caribbean Coral Reef Research, said the carbon dioxide being absorbed by the ocean is "causing measurable changes in seawater chemistry."

The chemical composition of the world's oceans has been moving toward more carbon dioxide and less calcium carbonate, an important mineral for coral growth, said Atkinson, principal investigator on the project.

Ten years ago, scientists were most concerned about nutrients from runoff ruining coral reefs. Now interest has shifted to carbon dioxide because of global warming and coral bleaching, he said.

"Those (runoff) are very small, local impacts," he said. "The kind we're talking about are truly global. This is happening worldwide."

In July, Ralph Cicerone, the new head of the National Academy of Sciences, told a Senate Commerce subcommittee on global climate change that the level of carbon dioxide in the atmosphere is at its highest level in 400,000 years.

Nearly all climate scientists believe that much of the Earth's current warming can be blamed on increases of greenhouse gases, such as carbon dioxide, he said.

Those gases accumulate in the atmosphere as a result of industrial and other processes and are believed to trap solar heat, similar to a greenhouse.

The Hawai'i study reported in the September issue of the Journal of Geophysical Research-Oceans found that increases in carbon dioxide decreased skeletal growth of coral by 50 percent. At the same time, photosynthesis of algae within the coral increased.

The results point to a possible breakdown in the normally beneficial relationship between coral and algae, which bond corals together with calcium compounds, the researchers said.