Strengthening sustainability in an acidified ocean: does the co-culture of seaweeds and shellfish improve shell integrity in farmed red abalone?

Abalone harvesting and consumption have a long history in California, but recreational and commercial fisheries have been forced to close due to overfishing, habitat destruction, harmful algal blooms and unseasonably warm water temperatures. Red abalone aquaculture is now the only means of abalone production on the U.S. Pacific Coast, but as ocean acidification increases, there are widespread concerns that abalone aquaculture will be impacted. Abalone appear to be vulnerable to ocean acidification, exhibiting shell damage and reduced growth in high carbonic acid conditions.

Previous research by the Co-PIs showed that growing abalone together with seaweed could help reduce carbon dioxide input into the water, hence buffering the acidity of the water and improving abalone growth and shell area. This project, in partnership with the Monterey Abalone Company, aimed to determine whether these increases in growth would translate into reduced stress and increased shell strength and integrity, which would together yield a more marketable product.

The Co-PIs conducted a land-based experiment that compared red abalone grown without seaweed to red abalone that was grown in the same tank as red dulse. The researchers sampled a subset of the abalone to assess shell morphology, mineral content and strength, and collected assays of stress physiology in muscle tissues. The results showed that in normal conditions, with water that hasn’t acidified, abalone grow larger heavier shells, whether or not seaweed is present. Interestingly, in the presence of seaweed, these changes to shell morphology yield significant increases in shell thickness and strength, as well. Together, these results suggest that abalone grow better under normal conditions, regardless of whether seaweed buffering is present. However, seaweed buffering may improve shell thickness and material properties. The co-culture of abalone and seaweed likely translates into increased shell strength and integrity, which will improve the quality of red abalone as a key Californian seafood product.