Aquaculture in a time of climate change

Alan Dep — Marin Independent Journal file

The unexpected consequences of climate change are often, well, unexpected. Researchers at the Moss Landing Marine Labs Aquaculture Facility are working with the shellfish industry to make sure that “out of stock” signs at our favorite oyster bars won’t be one of those consequences.

Excess carbon dioxide in the atmosphere leads to changes in our weather patterns but also lead to increases in the carbon dioxide within our oceans. The excess carbon dioxide in the atmosphere dissolves into sea water, increasing the oceans acidity (lowering its pH) which then poses problems for marine life that lives within a naturally narrow range of ocean acidity. Decreases in the local ocean pH have already been causing real impacts, including impacts to shellfish industries.

Already, oyster farms are struggling to raise oyster spat (young recently settled oyster larvae) because the more acidic coastal waters make it difficult for the young oysters to mineralize shell material. Dr. Luke Gardner, Sea Grant Aquaculture Specialist at Moss Landing Marine Labs notes that Hog Island Oysters must now raise the pH of their Humboldt Bay hatchery waters in order for their oyster seed to settle and grow. To support the industry, aquaculture center researchers are studying ways to buffer ocean acidity through integrated techniques where algae and shellfish grown together in multi-chamber recirculating tank networks. This research is critical, notes Gardner, because we are “rapidly approaching a time when shellfish growth will be impacted by ocean acidification.”

These “multi-trophic” systems benefit from the environmental changes each species makes on the environment. In the current experimental framework, red algae are grown in one tank and small, young abalones are grown in an adjacent tank. The water circulates between the tanks with abalone releasing nutrients (poop) to the water before flowing to the red algae tank which absorbs both the nutrients and specifically for this experiment, excess carbon dioxide from the water, increasing the pH and thus helping abalone grow quicker, spending less energy on shell formation. The red algae also become a food source for the abalone. As the abalone grow, they become more resilient to pH fluctuations and are ready for placement in pens under the Monterey Wharf for grow out and harvest.

While similar multi-species aquaculture systems have been in use for millennia in China and Japan, integrating algae to buffer ocean acidification is unfortunately a new need and area of research. Dr. Gardner notes that this type of land based system would likely not be cost-effective for lower priced aquaculture species such as oysters except perhaps for hatchery purposes. Such integrated aquaculture may also help manage water quality within the tanks for inland operated farms where land is less expensive. Of course costs are always a major factor in aquaculture success so having algae buffer and clean the water, and provide food for the animals is a promising opportunity.

Future research may look to offshore algal farms that surround oyster beds and thus buffer the local ocean pH levels to enhance oyster growth. Studies have documented the natural pH changes of water flowing through eelgrass and kelp beds and these local effects may become a necessary association for offshore shellfish aquaculture. Dr. Mike Graham, one of the Aquaculture Facility science coordinators notes that the intention of the facility is to address 21st century seafood challenges and work closely with researchers and industry from around the world to provide healthy and sustainable seafood options.

To learn more about central coast and global water chemistry and ocean acidification check out http://www.cencoos.org and to keep up on local aquaculture research, visit http://www.mlml.calstate.edu/aquaculture.

Ross Clark, Santa Cruz Sentinel, 31 January 2019. Article.

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