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Helping shellfish farmers tackle climate change

The Fish Site
by The Fish Site
24 May 2022, at 6:55am

Ensuring the future of California’s shellfish farming sector, despite the threat caused by climate change-linked ocean acidification, is the subject of a new research paper.

California oyster farmers in Tomales Bay © Remy Hale

California has thriving oyster, mussel, abalone and clam farming sectors. However, according to scientists from San Diego State University (SDSU) and Oregon State University, due to rising greenhouse gas emissions, the ocean has become more acidic, threatening shellfish growth.

“There have been calls across the state and across the U.S. to increase aquaculture output because it's so sustainable. But then at the same time, it's a very vulnerable industry,” said Melissa Ward, a post-doctoral fellow at SDSU, in a press release.

In a new study, SDSU and Oregon State University researchers interviewed California shellfish growers to find out how they perceive ocean acidification, and to learn what strategies they think will help their operations adapt to changing environmental conditions.

“This study is fairly unique in that we're getting information directly from the people who are being affected by change and learning directly from their experiences,” said geographer Arielle Levine, director of the sustainability program in SDSU’s College of Arts and Letters.

Ward added: “They're on the front lines of observing climate change and they also are going to be most well-suited to describe what they think they need to adapt to those changes.”

About a third of man-made CO2 is absorbed by the ocean, making it more acidic, and reducing the calcium carbonate shellfish need to form their shells.

“They're basically running out of building blocks to build shell with,” said Ward. “And that can be particularly challenging for a very, very small shellfish that’s just forming.”

Most shellfish used in the US aquaculture industry are spawned in land-based hatcheries. When they’re about the size of a fingernail, they’re moved to floating nurseries in the ocean.

“And at that point, they're just sort of subjected to whatever conditions and whatever food floats by in the water,” said Ward.

If the water is acidic, the juveniles may grow more slowly, or even die, making it harder for aquaculture farms to remain viable.

Pacific oysters are among the shellfish species widely farmed in California
Pacific oysters are among the shellfish species widely farmed in California

Knowledge gaps identified

Interviews with shellfish growers revealed that, while they are concerned about the impact of ocean acidification on their operations, they often lack the scientific instrumentation to know when it’s happening.

Growers also worry about other environmental threats such as warmer water, heavy rainfall and pollution — which all contribute to the spread of marine diseases — as well as toxic algal blooms.

“Sometimes, growers would lose 90, 100 percent of their shellfish in a given area, and they won't really know why,” said Ward. “It's sort of a story of multiple stressors; you can imagine a time when the water is particularly warm or there's a rainfall event, and ultimately you may reach a tipping point that the shellfish in the water just can't remain resilient to.”

Many growers said they need access to scientific resources to pinpoint the environmental factors involved in large die-off events, and to potentially prevent them.

Regulatory concerns

All of the shellfish growers interviewed felt regulatory and permitting requirements for shellfish operations need to be adjusted to respond to the rapidly changing environment. For example, it might be wise to diversify a shellfish operation by growing a new species better adapted to ocean acidification. But obtaining the required permits for that can be onerous.

“California is likely the hardest state to get a permit for shellfish aquaculture, which is seemingly at odds with the messaging that's coming down from the top,” Ward said. While state leaders recognise shellfish aquaculture is sustainable and an opportunity for economic growth, it can take years and hundreds of thousands of dollars for a grower to obtain a permit for a new species. “And they just can't afford that time and money,” she added.

“We need to maintain the environmental protections that we have in California, but if we really want the industry to be resilient to environmental change, we have to kind of allow for flexibility in farm management.”

Another adaptive strategy identified by shellfish growers was a need for more networking opportunities — not only with other growers, but also with managers, scientists and policymakers — to share information and best practices for adapting to environmental change.

The study is published in the journal Ocean & Coastal Management. The researchers hope it will serve as a roadmap for improving the resilience of the aquaculture industry in California.

“This work really draws a connection between environmental change that's happening and will continue to happen, and how that's not just affecting the species in the ocean, but also the people who rely on these species,” said Levine.