American Oceans

Alaskan Snow Crabs Are Becoming Acid-Resistant

a person holding a snow crab on a boat

The snow crab population in the Bering Sea has been facing significant challenges due to rapidly changing marine conditions. However, recent research by National Oceanic and Atmospheric Administration (NOAA) scientists in Kodiak has found that juvenile snow crabs may have a strength that could help their population endure ocean acidification, which is a significant threat to marine life. The research revealed that the juvenile snow crabs are not harmed when reared in more acidic waters, unlike other types of crabs found in Alaska waters, including tanner crabs, which are closely related to snow crabs.

The research was conducted through an experiment that held females for two years and observed the development of embryos and larvae from eggs hatched in each of the years. The embryos did not show any negative effects on their development, and they hatched out just fine both years. Although some minor effects were observed on larvae in the first year, no such effects were seen in the second year.

The experiment’s structure duplicated the structure for an earlier tanner crab project, which 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. 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, snow crab shells remained intact after two years’ exposure to acidified waters, while tanner crab shells deteriorated.

The Bering Sea is 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. 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.

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. The heated conditions in the habitat triggered a dramatic speed-up of metabolism, causing the crab population to eat more and, essentially, run out of food.

Globally, marine heatwaves have become more frequent and more long-lasting in recent years and are driven by overall climate warming. 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.

The 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. Additionally, snow crab “really like it cold,” so the presence of ice is a good sign. The association with sea ice might help explain the snow crab resilience to ocean acidification. 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.

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. While that outcome is more probable, there is no way to be sure how the current El Nino will play out in Alaska. Likewise, the future of snow crab is uncertain. If conditions stay cold, the population might see a short-term rebound. Long term though, the expectation

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