Sunday, January 20, 2008

Ocean acidification, carbon dioxide damage Hawaiian reefs

Climate change is happening in the air, but big changes associated with greenhouse gases are also taking place in the ocean.

One of them is acidification. New research shows that increased acidity in the oceans, associated with more carbon dioxide in the air, will have dramatic impacts. Lots of forms of life that depend on a slightly alkaline and stable ocean chemistry will suffer.

In a recent report on the subject, a group of Hawai'i, Florida and Bermuda scientists conducted studies that show that coralline algae will have difficulty in a more acid ocean.

Why is that important? Because in many places it is coralline algae, more than actual coral, that binds our Hawaiian reefs together.

This is the form of life—a crusty, often pink-colored kind of algae—that acts like the resin binding fibers together in a surfboard skin. It grows up and over chunks of rock, broken coral, and other materials, solidifying them and creating a sturdy barrier, protecting the Islands from the rough seas.

The new research was reported in a December issue of Nature Geoscience, in an article entitled, “Decreased abundance of crustose coralline algae due to ocean acidification.” The authors are Ilsa Kuffner, of the U.S. Geological Survey's Florida Integrated Science Center, Paul Jokiel and Ku'ulei Rodgers of the Hawai'i Institute of Marine Biology, Fred Mackenzie of the University of Hawai'i Oceanography Department, and Andreas Andersson of UH Oceanography and the Bermuda Institute of Ocean Sciences.

“These findings suggest that at lower pH, these reef-building algae could be much less competitive on future coral reefs,” Kuffner said.

The chemistry of acidification is pretty simple. If you bubble carbon dioxide through water, it becomes more acidic as carbonic acid is formed. If you increase the amount of carbon dioxide in the atmosphere, the oceans soak up some of it and become more acidic.

The increased acidity of the oceans is already being measured. It's not about models of something that might happen. It's already happening.

The researchers, working at Coconut Island in Kāne'ohe Bay, in a nine-month study ran seawater with with different acidities through six jars. They found that coralline algae settle at lower rates and grow more poorly when the acidity is higher. Also, fleshy (which is to say, soft rather than hard) algae grew more readily.

“The results of our study were visibly obvious and may provide a glimpse into the future,” Kuffner said.

“We saw a 92 percent degrease in the area covered by the crustose coralline algae in the tanks with lower pH compared with tanks at today's ocean pH level. Non-calcifying fleshy algae increased by 52 percent.”

One issue for future research is whether the competition from fleshy algae increases the decline in coralline algae, the authors say. Another issue could be how changes in acidity add to detract from the impacts of increased temperature associated with global warming.

“Predicting changes in community structure resulting from ocean acidification and other stressors (for example high-temperature anomalies) will be important in modelling future rates of carbonate production by coral reefs and associated ecosystems,” the scientists say in their conclusion.

The impact for crustoese coralline algae and for our oceans, they say in a press release associated with the scientific article, is potentially severe.

“They carry out key ecological roles that affect the health and sustainability of coral reef ecosystems.

“Not only do they build reef framework, produce sand, and help cement loose coral fragments into massive reef structures, they also attract reef-building coral larvae by providing a place to settle.

“If these ecosystem services are left undone, coral reefs and associated systems and coastlines could be notably altered as the pH of the oceans slowly declines,” they said.

(We've discussed this before in this blog. See: and and and our initial take on the issue,

© 2007 Jan W. TenBruggencate