Climate change has major impact on oceans

BOSTON, Mass. – Climate change is rapidly transforming the world’s oceans by increasing the temperature and acidity of seawater, and altering atmospheric and oceanic circulation, reported a panel of scientists this week at the American Association for the Advancement of Science (AAAS) annual meeting in Boston.

“The vastness of our oceans may have engendered a sense of complacency about potential impacts from global climate change,” said Jane Lubchenco, the Wayne and Gladys Valley Chair of Marine Biology at Oregon State University, who moderated the panel. “The world’s oceans are undergoing profound physical, chemical and biological changes whose impacts are just beginning to be felt.”

Panelist Gretchen Hofmann, a molecular physiologist at the University of California, Santa Barbara, describes the situation as “multiple jeopardy.”

“Ocean ecosystems are facing new stresses and new combinations of stress,” Hofmann said. “The water is warmer, circulation patterns are changing in unpredictable ways, and oceans are becoming acidic.”

Rising greenhouse gas emissions are warming the world’s oceans and providing yet a new threat to coral reefs, which already are among the most threatened of all marine ecosystems, the panelists say. Even modest warming of a degree or two above normal maximum temperatures can cause a breakdown in the relationship between corals and their symbiotic algae, zooxanthellae, said Nancy Knowlton, a marine biologist with the Smithsonian Institution.

Without zooxanthellae corals appear white, or “bleached,” and grow more slowly. They also are more susceptible to disease and may not reproduce. In 1998 there were worldwide mass bleaching events, Knowlton pointed out, affecting 80 percent of the corals in the Indian Ocean, 20 percent of which died. In 2005, severe bleaching occurred over much of the Caribbean as a result of overly warm water temperatures.

“We have already lost some 80 percent of the reef corals in the Caribbean over the last three decades, and losses in the Pacific Ocean also are widespread and severe,” Knowlton said. “Reefs are like cities, with some parts growing and some parts being destroyed, and only when net growth is positive can reefs persist. These reefs already are under threat to overfishing and local pollution and unless drastic action to reduce greenhouse gas emissions is taken soon, these reefs will cease to exist as we know them.”