A new study shows evidence that ocean acidification in the Bering Sea has been significantly contributing to the decline of Bristol Bay red king crab. The study, led by Mike Litzow at NOAA’s Kodiak Lab, looked at whether increased acidity or warming could explain the decline in southeast Bering Sea red king crab.

Results showed that ocean acidification appears to be a driver. Increasing acidity explained ∼21% of the population decline over 1980–2023, and ∼45% since 2000. Ocean warming had a negligible effect in the analysis. This outcome matches ocean models which show that pH in the Bering Sea is approaching threshold levels that reduce juvenile survival.

“These findings mark a shift in messaging from the research community,” said Darcy Dugan, the director of the Alaska Ocean Acidification Network. “Prior to the study, researchers believed species in Alaska were likely being impacted but we didn’t have the data or analysis to back it up. Red king crab is the first species where we can see a correlation between acidity and the decline of a wild stock”.

Litzow and his co-authors note that the study shows a correlation, and that it’s very difficult to prove direct causation because ecosystems are complex. Next steps to further substantiate the findings include: (1) Improving validation of the Bering Sea ocean acidification model, 2) Identifying where in Bristol Bay the juveniles are, and see if the pH is dropping down below threshold levels in the areas they are occupying, and 3) Better quantifying the response of juveniles to pH.

Current monitoring and experiments by NOAA Alaska Fisheries Science Center researchers in Kodiak are aimed to address these gaps.