Some corals can adapt to ocean acidification

Some corals can adapt to ocean acidification

mongabay.com

July 6, 2006

But the research provides further evidence that corals are extremely sensitive to rapid environmental change and will be negatively affected by increased carbon dioxide levels in the short-term

While scientists warn that increasing ocean acidity will doom marine animals that build skeletons and structural elements out of calcium carbonate, new research has found that corals can change their skeletons, building them out of different minerals depending on the chemical composition of the seawater around them.

The finding could have significant implications for the global marine biodiversity when concentrations of carbon dioxide are growing in the world’s oceans.

Justin Ries, a marine geologist at Johns Hopkins University, and his collaborators note “this is the first known case of an animal altering the composition of its skeleton in response to change in its physical environment.”

“Reefs are large underwater structures of coral skeletons, made from calcium carbonate secreted by generation after generation of tiny coral polyps over sometimes millions of years of coral growth in the same location,” explains a release from Johns Hopkins University. “The team showed that corals can switch from using aragonite to another mineral, calcite, in making the calcium carbonate. They make that switch in response to decreases in the ratio of magnesium to calcium in seawater… That ratio has changed dramatically over geologic time.”

“This is intriguing because, until now, it was generally believed that the skeletal composition of corals was fixed,” Ries said.

Johns Hopkins University post-doc Justin Ries and collaborators demonstrated that corals can build their skeletons out of different minerals depending on the chemical composition of the seawater around them. Photo Credit: Will Kirk/JHU

The researchers found that calcite-producing corals grown under conditions that mimicked water chemistry of ancient times grew significantly slower than did the aragonite-producing corals grown under modern water conditions.

“The reduction in the corals’ rate of growth that accompanied their exposure to the chemically modified seawaters is further evidence of corals’ extreme sensitivity to environmental change,” Ries said.

“This is particularly significant given recently observed and predicted future changes in the temperature and acidity of our oceans — via global warming and rising atmospheric CO2 , respectively — that will presumably have a significant impact on corals’ ability to build their skeletons and construct their magnificent reefs,” he added.

Corals are tiny animals that live in colonies and derive nourishment and energy from a symbiotic relationship with zooxanthellae algae known as dinoflagellates. Coral reefs are formed over the course of thousands of years as limestone skeletons constructed by corals accumulate and form a structural base for living corals. Previous studies indicate that is takes roughly thousand years for a reef to add a meter of height. Individual corals are capable of faster growth — about one meter every hundred years — but wave action and other forms of disturbance moderates overall reef growth.

Coral reefs are crucial ecosystems because they are inhabited by a diversity of fish species and serve important economic roles for humans. Ove Hoegh-Guldberg, head of the University of Queensland’s Center for Marine Studies, says that more than 500 million people live within 100 kilometers of coral reefs, many of whom rely on reefs and the services they provide for daily subsistence. Further, reefs generate billions of dollars worldwide through recreation and tourism. For example, revenue from tourism-related activities on Australia’s Great Barrier Reef dwarf earnings from commercial and recreational fishing industries. Finally, reefs play an important role in buffering adjacent shorelines from wave action, erosion, and the impact of storms.

“Ironically, the same factor that is likely causing such storms to increase in intensity — global warming — is also causing the corals to bleach (lose their symbiotic algae) and die, ultimately leading to the destruction of the coral reefs, which protect the coasts from these storms,” Ries said. “All that being said, it is also important to note that the magnesium-calcium ratio of seawater changes only over millions of years and has no direct relationship to recent global warming and ocean acidification, which are believed to be at least partly human caused.”

Nevertheless, Ries notes that his team’s research “does have significance with respect to global warming and ocean acidification.” Their experiments show that “although corals can adapt mineralogically to altered seawater chemistry, doing so slowed the corals’ rate of growth by nearly 65 percent.”

“This provides us with further evidence that corals are extremely sensitive to rapid environmental change, such as global warming,” he said.

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This article used quotes and information from a release from Johns Hopkins University. It also extensively used information from past mongabay.com news articles.