UC Davis study shows effects of climate change on oyster farming

Jose Quezada — For the Times-Standard

A four-year academic study funded by California Sea Grant and conducted by lead researcher Ted Grosholz of UC Davis found that oyster habitats in bays and estuaries along the California coast can be impacted by climate change.

The study, conducted from 2014-17, was performed in Tomales Bay and the research found that the greatest impact on oysters occurred in the earliest stages of development, particularly when the oyster was ready to start forming its shell.

Increased ocean temperatures, increased runoff from rivers and the inflow of upwelled ocean waters all combine to affect the growth of oysters, according to the study.

“To my current knowledge, the CO2 accumulation in the water and the atmosphere lower the pH and increase the acidity, and in that higher acidic water it’s difficult for larval shellfish to form a shell,” said Todd Van Herpe of Humboldt Bay Oyster Company, which operates oyster beds on the bay.

Grosholz, in his study, said a variety of factors were at play.

“In an estuary, you have freshwater coming down from rivers, and there are plants, macroalgae, and phytoplankton that are much more abundant and greatly influence pH,” said Grosholz in his paper. “This leads to a daily cycle of changes in pH (the measure of acidity) that can far exceed pH changes in the ocean. Estuarine organisms have evolved with this variable pH regime, which could make them more resilient to ocean acidification. But other factors important to oyster health, such as temperature, salinity and dissolved oxygen, are also projected to change with climate change.”

Van Herpe said that oyster hatcheries are the most directly affected because they must get the oysters past the larval stage and to the point where they grow the shell in order to grow large enough to be harvested.

“The hatcheries have gotten a handle on a lot of the impacts — 10 years ago we nearly lost the industry and the whole industry relies on those hatcheries for seed oysters,” Van Herpe said. “The oysters need the calcium carbonate to make their shells and a lower pH makes that more difficult to sequester carbon from the water. The hatcheries put a lot of effort into their water quality and the larvae need a very tight pH range to develop.”

There is a delicate balance involved in the development of the oyster and the breeding grounds are impacted not just by ocean and bay conditions by river runoff as well.

“The studies pointing out the challenges in the restoration of Olympia oysters show they are not just being challenged by land-use practices and their impacts, but also by the impacts of climate change, and that makes it very difficult for the native species and for aquaculture” said Terry Sawyer, vice president of Hog Island Oyster Co., which operates hatcheries on the Samoa peninsula and is looking to establish its own oyster beds on the bay.

“To go back to your basics in Chemistry 101, change one variable of an experiment and it completely changes the results,” Sawyer said. “It’s not all doom and gloom and I would like to point out on the private sector side we’re having to move forward on this from a business perspective and trying to adjust to changes and work on strategies to develop more resistant brood stocks. We are looking at that in relation to other species as well. You need to be quick on your feet in the private sector and the absolute parallel for all of us is to get the government, the regulatory bodies on the same page. We cannot wait it must be addressed now.”

For Humboldt Bay Oyster Company, the future of its business relies on a steady stream of quality oyster seedlings to succeed, and that means the hatcheries, where the impacts on the development of juvenile oysters are more immediate, need protection.

“The hatchery collect the oyster larva and set it on a mother shell to grow and if those conditions aren’t just right you can lose the entire harvest,” Van Herpe said. “It’s (prime growing conditions) critical for the hatcheries because we rely upon them for seed stock. If they don’t have the seed stock we’re out of work.”

The study is just one of the numerous efforts aimed at understanding the impacts of a changing climate and for a $25 million industry like oysters, greater understanding means a sustainable future.

If nothing else, the latest study on climate impacts on oyster development can now be used by others in the industry and provide information and insight for restoration projects and aquaculture endeavors for commercial oyster farmers, including the best sites for oyster beds and what species has the best chance for success.

“Oysters settle to rocks so they cannot move and track changing water conditions like some other organisms,” said UC Davis graduate student Jordan Hollarsmith, who is first author of the study. “The goldilocks zones within California estuaries, where conditions are just right for maximum growth and survival, are incredibly important for the economic success of farmed oysters and the ecological success of native oysters. Our findings help us to understand the environmental factors that make these zones so favorable, which will aid in restoration and aquaculture efforts.”

Dan Squier, Eureka Times-Standard, 9 August 2019. Press release.

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