Alaska’s snow crab show resilience to ocean acidification, which is underway in the Bering Sea

Study findings show a possible bright spot for a commercially important population hammered by a warmth-triggered crash

Bering Sea snow crab, with two specimens seen in this undated photo, support an iconic Alaska seafood harvest, but a crash in population since 2018 triggered the first ever closure of the fishery in 2022. That closure was extended for the 2023-24 season. A newly published study shows that snow crab have some resilience to ocean acidification, with eggs and embryos that fare better in acidified conditions than do those of other Alaska crab species. (Photo provided by National Oceanic and Atmospheric Administration)

By Yereth Rosen/Alaska Beacon

The beleaguered snow crab of the Bering Sea may have one strength that could help their population endure rapidly changing marine conditions: an apparent resilience to ocean acidification.

Research by National Oceanic and Atmospheric Administration scientists in Kodiak has found that juvenile snow crabs are not harmed when reared in more acidic waters. That is a contrast with other types of crab found in Alaska waters and even with bairdi crab, commonly referred to as tanner crab, which are closely related to snow crab.

The results come from an experiment that held females for two years and observed development of embryos and larvae from eggs hatched in each of the years.

“The embryos did just fine. They hatched out just fine both years. We didn’t see any indications of negative effects on embryo development,” said Chris Long, the study’s leader and a scientist at NOAA’s Alaska Fisheries Science Center laboratory in Kodiak.

The study found some minor effects on larvae in the first year but not in the second year, he said.

The experiment’s structure duplicated the structure for an earlier tanner crab project, Long said. That project found that negative effects from acidification in tanner crab emerged in the second year, and they were profound, with 70 percent of the eggs failing to hatch, he said.

The new findings also parallel those from other research that found that snow crab shells are more resilient to acidified waters than are tanner crab shells. In that experiment, Long said, snow crab shells remained intact after two years’ exposure to acidified waters while tanner crab shells deteriorated.

Resilience to ocean acidification could be important for snow crab and other Bering Sea species. The Bering Sea is, by its nature, conducive to acidification because of its cold waters, high carbon content, wide seasonal swings and a particular combination of ocean mixing characteristics. Previous research has found that the world’s most acidic ocean waters are found in the northern Bering Sea during the winter, when sunlight is scarce and carbon-absorbing plankton cannot bloom. And Bering Sea acidification is expected to increase into the future as the oceans continue to absorb the carbon being pumped into the atmosphere.

The findings about snow crab embryos and larvae provide a bit of good news in an otherwise bleak picture for the species in Alaska that has supported a lucrative fishery in the past.

The eastern Bering Sea’s snow crab population crashed by 80% from 2018 to 2022, prompting the first-ever harvest closure last year – a shutdown extended in October by the Alaska Department of Fish and Game for another year. During those years, about 10 billion snow crabs were lost, according to NOAA. Any population rebuilding is expected to take several years, fisheries biologists have said.

An egg-containing female snow crab, used for a study about ocean acidification effects, is seen in this undated photo. (Photo provided by Chris Long/NOAA Alask a Fisheries Science Center)

In 2021, the last full year prior to the fishery closure, the Alaska snow crab harvest was worth $219 million, according to NOAA.

The crash is now definitively linked to the extreme marine heatwaves that gripped the Bering Sea in the years just prior. NOAA Alaska Fishery Science Center research found that the heated conditions in the habitat triggered a dramatic speed-up of metabolism. The crab population ate more and, essentially, ran out of food.

The study considered a variety of possible causes, including predation, cannibalism, fishery effects, disease, population density and temperature, said Cody Szuwalski of NOAA’s Alaska Fisheries Science Center, the lead author of the study.

“There were many hypotheses swirling around and our recent paper is the first effort at using data to discriminate among them.  Based on our paper, the marine heatwave appears to have triggered the collapse of snow crab in the eastern Bering Sea,” Szuwalski said by email.

Globally, marine heatwaves have become more frequent and more long-lasting in recent years and are driven by overall climate warming, according to the Intergovernmental Panel on Climate Change. That holds for the Bering Sea as well, where shorter-term warming cycles have exacerbated long-term warming, according to recent research. Recent heatwaves had dramatic impacts on Alaska fish stocks other than crab, such as Pacific cod, and long-term climate change is expected to make future impacts even stronger, scientists have warned.

Alaska’s snow crab population is linked to icy habitat, which makes it vulnerable to warming conditions.

Sea ice serves as a platform for algae that grows on its underside; upon spring melt, that algae drops to the bottom of the sea, where it is food for the brittle stars, clams and other small creatures that are, in turn, eaten by snow crab, Long said.

Additionally, snow crab “really like it cold,” so the presence of ice is a good sign, he said. “If it’s cold enough for snow crab, it’s cold enough for ice. And vice versa.”

The association with sea ice might help explain the snow crab resilience to ocean acidification, Long said. One theory is that the species has become adapted to deepwater conditions below sea ice, where more acidic waters are less likely to be mixed with less acidic waters from above, he said.

The snow crab dependence on cold conditions and sea ice could be put to the test this winter. A strong El Nino weather pattern has already started, and some experts worry that it could help trigger more marine heatwaves. El Nino systems typically push more warmth north into the Gulf of Alaska and Bering Sea.

Surface water temperatures in the Bering Sea and other ocean areas off Alaska have been warmer than normal this fall, though not as much so as other parts of the world, according to NOAA monitoring.

For Alaska, strong El Nino patterns generally mean warmer and less-snowy winters, with weather systems sweeping up from the southwest rather than down from the north, said Brian Brettschneider, a climate scientist with the National Weather Service. While that outcome is more probable, there is no way to be sure how the current El Nino will play out in Alaska, he said.

“It puts a thumb on the scale,” he said. “It makes certain scenarios more likely. But it’s not deterministic.”

Likewise, the future of snow crab is uncertain, Szuwalski said.

“If conditions stay cold, the population might see a short-term rebound. Long term though, I think the expectation is that if the ice goes, the snow crab will follow,” he said.

Tanner crab embryos, used in a study of ocean acidification effects, are seen in this undate photo. (Photo provided by Chris Long/NOAA Alaska Fisheries Science Center)