OutLook for the Bay
Acid Waters: A New Threat to the Bay?
By Henry S. Parker, PhD
It seems that we’re constantly learning about new threats to Chesapeake Bay. And now there is yet another one, and it’s insidious: ocean acidification.
Simply put, ocean acidification is a rise in the acid content of sea water because of an increase in the concentration of carbon dioxide. It is well known that human activities, including burning fossil fuels, have resulted in the release of large quantities of greenhouse gases into the atmosphere, and that carbon dioxide is the major component of these gases. What is less well known is that the oceans absorb about one-third of the released carbon dioxide. In general, this is a good thing. Without the oceans’ absorptive capacity, more CO2 would accumulate in the atmosphere, exacerbating the “greenhouse effect” and potentially affecting global climate.
But there’s a dark side to this carbon dioxide absorption by the seas: it alters the chemistry of the oceans. To grossly simplify a complex process, the higher the CO2 concentration, the higher the acid content of the water (or, conversely, the lower the pH). This is not to say that the seas are turning to vinegar. The changes are relatively subtle and slow. But since the advent of the Industrial Revolution, the acid content in the oceans of the world have increased 30 percent. And there is concern that ocean acidity could at least double by the end of this century.
You don’t have to be a scientist to realize that such a rapid (in geological terms) increase in acidity cannot be good for living creatures. And that brings us to Chesapeake Bay—and especially the Bay’s emblematic oysters. Oysters and other shellfish, as well as coral, need carbonate to build their shells. The process is called calcification. Increasing acidity strips carbonate ions from the water. Even a small rise in acidity means oysters have to use more energy for shell building. Larval stages could be particularly vulnerable. And a large increase in seawater acid concentrations might mean that existing oyster shells start dissolving.
Oysters are not the only Bay creatures that could be affected. Blue crabs might also suffer. But since they build their shells more quickly than oysters, they could have an advantage. That in turn could upset the evolutionary balance between the two species.
Bay-area scientists have recognized the acidification threat and are working hard to address it. But they know that Chesapeake Bay is a complicated system that might not respond the same way as the open ocean. For example, there is some indication that increased acidity of parts of the Bay may be due to sewage and agricultural runoff, and not CO2 emissions. And research on the topic of ocean acidification is still in its infancy. This makes it difficult to predict the ultimate outcomes of this evolving risk.
Research will be critical to understanding and mitigating ocean acidification. But research takes time and money. Significantly reducing greenhouse gas emissions, while highly important, is also not a short-term—or inexpensive—solution. Fortunately, there are some things that can be done in the nearer term to offset the potential consequences for oysters. For example:
• Seed the Bay with discarded oyster shells. Not only will the added shells help to buffer the water against increased CO2 concentrations, but they will also provide good settling and grow-out surfaces for oyster larvae.
• Aquaculture. Farmed oysters are initially raised in hatcheries, where water quality and other factors can be controlled. Some hatcheries even buffer their water with “antacids.” Then, when it’s time to transplant them to the open waters, the oysters will be larger and hardier. In addition, there is the potential for researchers to develop improved varieties of the bivalve—including, perhaps, strains that are less sensitive to increased acidity.
The bottom line? Rising ocean acidification could do significant harm to the world’s oceans and to Chesapeake Bay. The more we know about this recently acknowledged threat, the better able we are to address it and mitigate its effects. And that involves all of us.
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Henry S. (“Hank”) Parker, PhD is an adjunct associate professor at Georgetown University. He previously directed research programs at the U.S. Department of Agriculture and taught marine sciences at the University of Massachusetts Dartmouth. He can be reached at [email protected]
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