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Fighting Ocean Acidification With Underwater Forests

As the ocean’s pH drops, scientists are studying whether kelp and seagrass can create refuges that could help marine life survive acidifying waters.

Written by Erica Cirino Published on Read time Approx. 4 minutes
A California sea lion in a kelp forest.Reinhard Dirscherl/ullstein bild via Getty Images

As the sun crept above the horizon on a recent April morning, Anna George, an environmental science student at the University of California, Los Angeles, and two peers climbed into an idling zodiac and cruised into Santa Monica Bay off the Southern California coast. Cutting the engine when they reached a patch of kelp, its floating brown-green ribbons visible at the surface, they dipped in an instrument to measure the dissolved carbon dioxide the water contained.

Scientists have already studied how kelp and seagrasses – marine ecosystems that are threatened by the ocean’s rising temperatures – also help slow global warming by storing carbon. What has been less explored, and is now the focus of research by several groups on the West Coast, is these ecosystems’ ability to buffer against the ocean’s other climate change problem: waters turning more acidic as they absorb carbon dioxide from the air.

George’s field research is part of a project called Turning the Tides, a collaboration established in 2017 by Robert Eagle, assistant professor at UCLA’s Institute of the Environment and Sustainability, and the Bay Foundation, a Los Angeles conservation organization.

“We are interested in the fact that kelp draws down carbon dioxide from seawater as it grows, thereby changing ocean chemistry in a localized way,” Eagle said. “When carbon dioxide is drawn out of seawater, it elevates the pH.” In other words, it becomes less acidic.

California has recently made it a priority for scientists like Eagle to research how these sea plants might serve as refuges for marine wildlife as waters acidify. In 2016, the state passed a bill commissioning scientific research on the ability of kelp and sea grasses to reduce ocean acidification locally. Last year, the government-commissioned California Ocean Protection Council working group teamed up with the nonprofit California Ocean Trust to produce a report, published in January, reviewing the current scientific understanding of the issue.

A research scientist monitors a kelp ecosystem off the coast of California. (Allen J. Schaben/Los Angeles Times via Getty Images)

The study found that a major challenge to preserving kelp and seagrass as a wildlife refuge is that these plants themselves appear to be in decline from climate change and human activities. This is especially true in California, where kelp forests have disappeared in some regions, laid bare by a rise in populations of urchins that munch on them. Scientists say it may already be difficult to bring kelp back in areas where urchins have taken over.

There’s also still a lot more that scientists need to investigate about kelp and seagrass’ acidification-fighting capabilities, according to the report. It’s still unknown, for instance, how many plants are needed to have any effect, how wide an area might benefit and whether they would only make a difference during the day, when there is sunlight for photosynthesis. “These are relevant questions when considering the effectiveness and requirements for an intervention, for example when restoring degraded kelp forests,” Eagle said.

Proof that kelps and seagrasses can provide shelter from climate change for marine wildlife would make a more compelling case for planting or restoring these species along California’s coast, Eagle added. Doing so, he said, would have the added benefit of creating more habitat for marine organisms – such as anemones, crabs, jellyfish and sea stars – that call kelp and seagrasses home.

Some days, Eagle’s students can be found flying drones over the kelp and seagrass forests they’re monitoring by boat. The goal is to relate the marine chemistry data to maps of these ecosystems to get a better sense of how kelp influences surrounding waters. Their findings might offer clues as to how large an area of the ocean a cluster of plants might benefit.

Off the coast of Washington, the Puget Sound Restoration Fund is already two years into a $1.5-million kelp replanting and research project in collaboration with the University of Washington and the National Oceanic and Atmospheric Administration. Last year, scientists with the group grew 20 metric tons of kelp in the Puget Sound, and this year are on track to grow even more, according to Betsey Peabody, executive director of the Puget Sound Restoration Fund, co-leader of the project.

Like Turning the Tides, the team’s work involves testing seawater located around kelp forests to better understand their effects on ocean pH. They have a slightly different approach, though – the group is also testing how continuously replanting and removing kelp might remove carbon dioxide from a local marine ecosystem over the long term.

“We know we can grow kelp that sequesters carbon and that can be removed permanently from the marine system at harvest,” said Peabody. Kelp they grew recently, she said, was roughly 20 percent carbon by weight when dry – a significant amount of carbon removal per plant, she said.

Seagrass. (Universal History Archive/UIG via Getty Images)

What effects growing and harvesting kelp would have on marine life is not well understood. However, Peabody said that aquaculture facilities could grow and harvest kelp near shellfish farms and might find practical, near-term applications. Acidic seawater makes it harder for shellfish to build shells and skeletons.

Kelps and seagrasses could also benefit corals reefs, according to coral scientist Ruth Gates, director of the Hawaii Institute of Marine Biology. She said applauds these and other efforts to better understand how sea plants – which also include mangroves – might reduce ocean acidification, particularly near ecologically important temperate coastal reefs.

But she urges scientists not to wait until it’s too late to attempt an intervention by reforesting the world’s coastlines with sea plants, even if they discover that doing so only benefits localized parts of coastal ecosystems. That’s because these habitats are home to many of the world’s marine organisms vulnerable to acidification.

“Ocean warming and acidification are the worst global threats to corals currently,” Gates said. “There is a lot we can do about this if people start acting now.”

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