The Heat Is Online

Ocean Acidity Up 30 Percent

Sea life at risk as acid levels rise in oceans


The Seattle Times, April 24, 2007

 

Global warming has increased acidity levels of the oceans by 30 percent and in the decades ahead will create new risks for coral, zooplankton and other creatures that help support the North Pacific fisheries, according to researchers who gathered Monday at the University of Washington.

 

In a two-day workshop that ends today, these scientists are reviewing what is known about this grim corner of climate change and brainstorming ways to measure and assess the threats to a marine ecosystem that yields North America's largest seafood harvests.

 

The acidification is caused by the ocean's absorption of carbon dioxide produced by fossil-fuel combustion. Currently, this is about 2 billion tons of the gas each year. As this gas dissolves, it sets off a chemical reaction that produces carbonic acid, which in high-enough concentrations can erode protective shells and other structures of some sea creatures.

 

"We have significant changes in chemistry," said Richard Feely, a Seattle-based National Oceanic and Atmospheric Administration oceanographer who helped to organize the conference. "And if we project over time ... we are talking about massive changes that will take place."

 

Some of the most acidic waters are found in the North Pacific, which has absorbed more carbon dioxide than tropical oceans. The North Pacific appears to be more acidic because it is colder than tropical oceans, which enables it to absorb more carbon, and because it has older, more carbon-rich water than the North Atlantic.

 

In some areas of the North Pacific  at depths ranging from about 300 to more than 1,000 feet  researchers already have detected a kind of saturation point where acidity causes shells to disintegrate faster than they can grow. This contrasts to the North Atlantic, where the saturation point typically is at depths that exceed 7,500 feet, according to Feely.

 

By the end of the century, these North Pacific saturation zones are expected to expand and extend into much shallower waters. Last year, Feely helped measure the acidity in these zones, and in the years ahead he will start to check the acidity levels of the most productive fishing zone: the Bering Sea.

 

Researchers also are starting to understand the expanding saturation zones' possible effects on sea life.

 

For example, there are some 200 species of coccolithophores, phytoplankton that play an important role in the food chain, according to Victoria Fabry, an oceanographer at California State University at San Marcos. So far, only six of those species have been exposed to the higher acid levels of the saturation zone. They showed markedly different responses that ranged from no effect to a 66 percent decline in the calcification process that builds shells.

 

Fabry also has studied pteropods, tiny mollusks less than an inch long that are an important food source for pink salmon and are susceptible to increased acidity. These pteropods migrate between shallower and deeper waters. So, in some areas they may already swim  at least briefly  in carbon-dioxide-saturated waters.

 

"The bottom line is we really don't know" the long-term effects on the pteropods and how that might affect the salmon, Fabry said.

Another big question mark is the fate of corals.

 

In tropical areas, researchers expect major reefs to reach a kind of tipping point around 2060. By then, coral organisms may not be able to adapt fast enough, and reef systems will crash or be seriously degraded, according to Chris Langdon, a University of Miami researcher who spoke at the conference.

 

Much less is known about the deep-sea corals of the North Pacific, which are vital habitat for rockfish, cod and many other commercially important fish species.

 

These are soft corals, found at much shallower depths than the coldwater hard corals of the North Atlantic that form vast reefs. Some researchers theorize that the differences may reflect the greater natural acidity of the older North Pacific waters, which limited the kinds of coral that could evolve.

 

But at what point would these soft corals suffer from ocean acidity?

"There is no research that anyone is doing on this, and we need this," said John Guinotte, a researcher with the Marine Conservation Biology Institute.