Acid Ocean Impacts on Marine Life Expected to Worsen

by Laurie Schreiber

ROCKPORT—There might be some mite of scientific disagreement about whether increasing atmospheric carbon dioxide is causing global warming. But the scientific community is unanimous in its finding that increased CO2 is resulting in acidic oceans, Joseph Salisbury, a research assistant at the University of New Hampshire’s School of Marine Science and Ocean Engineering, said at a session on the topic at the recent Maine Fishermen’s Forum.

“The ocean is becoming more and more acidified,” Salisbury said.

Increased acidity makes it hard for juvenile shellfish to build their shells, he said.

“They might be okay later in life, but it’s that critical early period,” he said.

The Gulf of Maine may be particularly sensitive to acidification, he said. That might be because it receives plenty of fresh water from the polar region, and fresh water is typically easier to acidify.

Other pathways to ocean acidification include land-based nutrients, such as lawn fertilizer runoff, he said. Fertilizer stimulates phytoplankton blooms, when the bloom rots, it produces carbon dioxide.

Ocean acidity continues to climb, he said.

“We don’t know if organisms will adapt,” he said.

Daniel Small, a post-doctoral fellow at St. Francis Xavier University in Antigonish, Nova Scotia, said little is known about the impact of ocean acidification (OA) on lobster.

“One reason we don’t know much about this, is because crustaceans are tolerant of changes in chemistry. Our focus switched more to sensitive species, such as oysters. And we left more tolerant species to the side,” Small said.

However, Small predicted, “Lobsters are going to be affected by OA in 10 to 20 years time.”

Increase of OA means lobsters are also experiencing an increase in internal acidity, he said.

“Shell species need to keep pH constant in order for them to function,” he said. “Crustaceans are particularly good at this. They can maintain their pH inside despite changes in seawater. However, this maintenance of pH costs energy in order to build their shells and reproduce. That’s where we see more subtle costs and indirect effects on lobsters. They might not be dying outright, but there may be subtle changes that could impact populations in the future.”

If a lobster’s energy goes down, its feeding rate and growth will likely also decrease, he said.

“So you get a downward spiral,” he said.

Lobster larvae already experience various types of stress as they navigate different environments.

“If you add on the stresses of ocean acidification and warming, you can get a bottleneck in terms of their ability to survive,” he said.

Juvenile lobsters, transitioning from larvae to adults, likewise face challenges.

“They’re still developing their ability to regulate themselves in relation to the environment. They still have high energy demands that are invested in growth. Because of this, you see increased mortality due to OA.”

Bill Mook, owner of the oyster-producing Mook Sea Farm in Walpole, said he’s seen several impacts from OA on his business.

“Shellfish hatcheries are canaries in the coal mine here,” Mook said.

Problems include inconsistent larval production in the hatchery, cessation of larval feeding, poor growth, and a protracted larval phase, he said.

Mook mitigated the problems by employing a sophisticated monitoring system and buffering his water.

“Hatcheries in other areas are seeing larval production problems,” Mook said. “The window of conditions sufficient for natural bivalve larvae will continue to close: Recruitment will become less and less predictable. It’s time to turn on the headlights. We need to demand the government spend more money in establishing monitoring systems and doing the thoughtful research that’s going to provide businesses like mine with enough information so we can do the planning and strategy for coping with this. We can’t avert crises unless we know about them. We need to invest in monitoring infrastructure. It’s a highly complex coastline, a big coastline, and that will determine what we might be able to do to mitigate the problems. We also need to understand that some of these changes are going to blindside us….There needs to be more ecosystem-wide research to address the issues.”