Studies released in early March by the Alaska Fisheries Science Center support a growing body of evidence that the future for tanner and blue king crab stocks in Alaska is, at best, uncertain.
“In 2013, we announced findings that lower pH levels could have profound effects on the development of Alaska red king crabs and tanner crabs,” said Bob Foy, who heads the AFSC Kodiak lab. “For the last few years, we’ve been looking at the effects of ocean acidification on different life stages of tanner and blue king crab and the projections don’t look good.”
Chris Long, also with the Kodiak lab, noted in the report released on March 1 that the stage of life that a crab is exposed to more acidic conditions – lower pH levels – than normal has a lot to do with this.
Long said that, for example, the ocean environment that larval tanner crabs live in is highly dynamic, with variable levels of acidity.
“At this age, tanner crabs seem able to tolerate shifts in pH,” Long said. “But if these animals are exposed to more acidic conditions at the embryo stage, they may be less able to tolerate changes in ocean acidification as larvae.”
Another issue is that young crabs exposed to low pH levels do not accumulate calcium as well, so their shells are softer, making them more vulnerable to predation. The combined effects of the lower pH means that fewer crabs will be able to make it to adulthood, providing fewer crabs for harvest.
University of Washington scientist Andre Punt used these projections to evaluate effects on commercial fisheries dependent on these crab species.
Punt said the projections suggest that unless crab adapt to changing pH, there will be lower catches in 40 to 50 years, and the need for more effort to catch what crab are out there.
So the big questions is, if the change in pH over decades is gradual, can crab adapt?
Foy said if there is a bright spot in all this, it is that there is evidence that both tanner and blue king crab species do have the capacity to adapt.