Undersea vents are providing researchers with a possible view of the future as seawater becomes more acidic due to carbon dioxide emissions.

Researchers at the Hopkins Marine Station at Stanford University looked at near-shore volcanic vents on the seafloor off the coast of Italy as a microcosm of how oceans may react to carbon dioxide, investigating how life changed in these localized environments.

"The most important outcome from this research is documenting how whole communities will respond to ocean acidification," said Fiorenza Micheli, one of the researchers on this project and a professor at the Hopkins Marine Station. Though marine organisms respond differently to acidification, the team found that on the whole, ecosystems lose biodiversity in highly acidified environments.

The ocean vents in this study release large quantities of carbon dioxide, which changes the water's chemistry in the nearby environment through a process called ocean acidification. These underwater soda fountains are particularly unusual because they mostly emit carbon dioxide without the sulfur compounds found commonly in other volcanic vents.

When carbon dioxide is absorbed in the water, whether from the air or from vents on the ocean floor, it forms compounds that cause the water's pH to lower, making the ocean more acidic. Carbon dioxide can also alter the water's calcium ion concentration. Many marine organisms depend on calcium compounds to build their shells.

Recent studies have shown how ocean acidification can affect shellfish, like clams and oysters (ClimateWire, Aug. 4). However, in looking at a whole ecosystem instead of just studying individual organisms, the Stanford researchers found that ocean acidification is not an equal-opportunity phenomenon.

Lower pH makes more losers than winners
"There are winners and losers," said Micheli. She observed that some organisms, like isopods and polychaetes, can thrive at a lower pH, but these organisms tend to be smaller and play different ecological roles, making these underwater habitats less resilient to other environmental problems, like pollution.

"Overall, the diversity and function of communities will be impaired," said Micheli. "Even at an ecosystem level, ocean acidification is a significant factor."

Micheli and her student Kristy Kroeker, a doctoral candidate in biological sciences at Stanford, recently published their findings in the Proceedings of the National Academy of Sciences. "Unlike climate change or global warming, there is a lot less uncertainty around acidification," said Kroeker. "We can predict how much the ocean is going to acidify by looking at the carbon dioxide in the atmosphere."

Acidification can have impacts for those on land, as well. "People are closely linked to near-shore ecosystems," said Micheli, who noted that these regions become less productive in acidic conditions, reducing the amount of food people can harvest. This, in turn, can have strong economic consequences for communities that are dependent on fisheries.

Even ocean aesthetics are affected by acidification: "We'll see less beautiful [marine] ecosystems in the future," said Micheli.

Both Micheli and Kroeker agreed that halting or reversing acidification will be challenging. "To a certain extent, we're committed to some acidification," said Kroeker. Though reducing carbon dioxide emissions will slow the shift, "there are not any quick fixes that we know of," she said.

"Acidification, because of its global nature, needs to be addressed at global and regional scales," said Micheli. "At local scales, ameliorating local impacts will help mitigate impacts of ocean acidification over time." Local environmental impacts from issues like chemical runoff, ocean development and overfishing can be controlled more readily, decreasing the cumulative stress on ecosystems.