OREGON STATE UNIVERSITY

OSU scientist: Increasing acidity affects oysters in Chesapeake Bay – and beyond?

06/10/2010

CORVALLIS, Ore. – A new study of Chesapeake Bay on the East Coast has found that increased acidity in certain parts of the bay is reducing rates of juvenile oyster shell formation, and the Oregon State University oceanographer who led the study says the same thing could happen on the West Coast.

Results of the research, which was funded by the National Science Foundation and St. Mary’s College, have been published in the journal Estuaries and Coasts.

George Waldbusser, a benthic ecologist with OSU’s College of Oceanic and Atmospheric Sciences, said the rate of acidification in parts of Chesapeake Bay is greater than in the open ocean and cannot be attributed solely to atmospheric carbon dioxide. However, in other areas of the bay, acidification was not occurring, or reversed, having little impact on oysters.

The reason, says Waldbusser, may be agricultural runoff and sewage input, both of which promote increased phytoplankton production. As the plants bloom, they absorb large amounts of carbon dioxide from the water column and make those areas less acidic. However, as the phytoplankton is consumed by other marine organisms and respired back into the water column, it increases the acidity.

“These human impacts are tipping the acid balance of the bay,” Waldbusser said. “Though acidity may temporarily be lower in certain parts of the bay because of the phytoplankton blooms, it is at the expense of the water somewhere else. When the plankton die and decompose, the acidity increases, whether the water is washed out to sea or collects in pockets of the bay.”

The key, he says, is to understand the integrative effects of the many processes driving the bay and the relationship between water circulation and biological production – lessons that can also be applied to West Coast bodies of water.

“In Chesapeake Bay we see large daily and seasonal changes in pH that are related to sunlight, photosynthesis and freshwater input,” said Waldbusser, who was lead author on the journal article. He noted that many of these same processes are at work in West Coast estuaries, such as Netarts Bay in Oregon.

However, Waldbusser added, “we should be aware that the baseline may be shifting amongst these larger cycles.”

“Knowing how these systems work is important because these processes are all interacting, and without accounting for all the drivers affecting pH we may be underestimating when we will begin seeing impacts on living resources and marine life that are vital to the health of the environment and economy,” he said.

Waldbusser, who previously worked at the University of Maryland Center for Environmental Science, said oysters build their shells internally by depositing calcium carbonate to the inner shell surface. Meanwhile, corrosive water on the outside is eating away the outer shell.

“From a simple perspective, it becomes something of a race,” he pointed out. “The oysters have to be able to deposit shell faster than the water can corrode it. However, the biology of shell formation is quite a bit more complex.”

Waldbusser and his colleagues, including Roger Newell of the University of Maryland, and Erin Voigt, a recent graduate of St. Mary’s College of Maryland, used 23 years of water quality data to observe trends of acidification and compared these to the response of juvenile oyster shell formation in controlled experiments that also measured temperature and salinity.

They found significantly reduced shell formation or even dissolution in current average conditions that are present today in some parts of Chesapeake Bay that formerly supported robust oyster reefs.

Although there is rising concern about ocean acidification, there is limited formal monitoring of bays and estuaries in the United States, said Waldbusser.

“First, pH is very difficult to measure well in salty water,” he said. “There are problems with calibration and stability in off-the-shelf systems. And there are many different factors that influence it on time scales that we don’t often sample appropriately. But it’s vitally important that we understand the dynamic range of our bays and estuaries so that we may know if we are pushing a particular system beyond its natural ability to adapt, or are subjecting systems to gradual deterioration.”

Waldbusser noted that several colleagues at OSU are “at the forefront of measuring and understanding these acidification dynamics in coastal ecosystems.”

Acidification can affect oyster and clam shells, as well as larval crab development. It also can have an impact on other calcium carbonate shelled animals, including zooplankton and other organisms that are prey for a variety of fish and marine species.