Conservation & Science

Field studies of ocean acidification

Sometimes, research has to venture out of the lab and into the wild. That’s the basis for a long-term Monterey Bay Aquarium Research Institute (MBARI) project to study how the ocean’s changing chemistry will affect marine life.

A shallow-water Free Ocean CO2 Enrichment (FOCE) system in place near Hopkins Marine Station. Photo courtesy MBARI.

Ocean acidification is a change in seawater pH (and other elements of the ocean carbonate system) as the ocean absorbs excess carbon dioxide from the atmosphere. This change will become more pronounced as people continue to burn fossil fuels.

“It’s important to try to get a better understanding of what impact that will have,” says George Matsumoto, senior education and research specialist at MBARI.

In a more acidic ocean, the minerals used to form calcium carbonate are less abundant, making it more difficult for marine species—from tiny sea snails to oysters and crabs—to build shells or skeletons. MBARI marine ecologist Jim Barry says researchers are working to understand the impact not just on individual animals, but also on broader ecosystems.

Prey and predators both affected

Jim points to an earlier lab experiment as an example

Researchers put predators and prey—including snails, crabs and abalone—in tanks together. The question was how warmer, more acidic waters would affect their growth and survival when their interactions were taken into account.

In the lab, MBARI scientists could add carbon dioxide to seawater, and measure its impact on ocean animals like abalone.

As expected, more acidic waters made survival harder for the abalone. They grew thinner shells; they weren’t as robust. But the crabs, which prey on abalone, also proved vulnerable. Many died, and they had a harder time feeding themselves.

And here’s the unexpected part: With the crabs weakened, the situation for abalone seemed to improve.

“Even though ocean acidification was harmful for the abalone, it affected their predator even more,” Jim says. “The net effect was that abalone were able to do better—because they were basically released from predation by those crabs.”

The findings from that multi-factor experiment provided a deeper understanding than researchers could have gained in studies of acidification impacts on crabs and abalone in isolation.

“But a lot of ocean researchers are saying, well, that’s all laboratory work,” George says. “What happens in the field, where the data are really messy?”

Taking the lab to the field

Research in many terrestrial habitats called FACE (Free Air CO2 Enrichment) experiments were performed over decades to explore how an increase carbon dioxide will affect plants on land, from forests to deserts to grasslands. These FACE studies have been a key approach in understanding the likely consequences of global change on terrestrial plant communities.

This diagram shows some of the key components of the deep-water FOCE system created at MBARI. Image: © 2012 MBARI

George and his colleagues were inspired to try a similar experiment in the ocean, creating a Free Ocean CO2 Enrichment (FOCE) system to look at the effects of increased carbon dioxide concentrations on marine animals. They put a clear plastic box in the ocean—sort of an underwater flume—pumped in carbon dioxide to raise the seawater’s acidity, and observed the animals inside.

“The idea of the chamber in the ocean is to open up the whole system to as many potential variables as possible,” George says.

As on land, the approach has been tried in a variety of ocean locations and habitats, from off the coast of France to the Great Barrier Reef, and from waters more than half a mile deep to just underneath Antarctic ice.

“MBARI has had a hand in pretty much every one of these efforts,” Jim says.

Local challenges

One area that’s been difficult to study is visible from the Aquarium’s back deck, looking out toward neighboring Hopkins Marine Station. It’s about 20 meters below the surface, in a sandy spot near a kelp bed.

The challenges at this site include relentless wave action, sand that’s constantly moving and poor visibility. There are also animals “curious and nimble enough that we’ve had to put locks on the [flume] opening,” George says. Crabs left in a clear box are evidently enticing to predators, although the researchers aren’t sure whether seals, sea lions or octopuses are taking advantage.

Resarchers and engineers are fine-tuning the design of the FOCE system, to keep unwanted animals out of the flume. Photo courtesy MBARI

Then there’s an apparent leak in the hose—roughly 1,000 feet long—that pumps treated seawater from the Aquarium out to the chamber. The team has been waiting for calm conditions so divers can find and patch the leak. George and Jim expect to get the system online by summer.

George hopes to study the impact of changing ocean chemistry on sanddabs, a type of small flounder that’s abundant—and an important commercial seafood species—in Monterey Bay.

The resulting data may help the public and policymakers better understand what a more acidic ocean will look like, and what we can do about it.

“Coral reefs around the world are disappearing, due mostly to global warming,” Jim says. “In addition to their importance as sources for fisheries, biodiversity and ecotourism, the loss of coral reefs will remove the shoreline protection afforded by offshore reefs, leading to increased storm damage to coastlines.”

Acidification could also inhibit the reproduction of commercially raised shellfish, affecting a source of seafood needed to help feed a growing human population.

— Daniel Potter

Learn more about MBARI’S ocean acification research.

Featured photo: MBARI researchers retrieve a FOCE ocean acidification flume from waters in Monterey Bay, at Hopkins Marine Station adjacent to Monterey Bay Aquarium. Photo courtesy MBARI.

 

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