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In a shocking revelation, it has come to light that from 2018 to 2021, a staggering 10 billion snow crabs vanished from the eastern Bering Sea off Alaska’s coast. The crab population, which plummeted to record lows in 2021, left researchers puzzled about the mysterious disappearance. However, a study published in the October 20 edition of Science has unveiled a likely culprit behind this mass die-off – a marine heat wave, partly responsible for driving the crabs to starvation.

Cody Szuwalski, a fishery biologist at the U.S. National Oceanic and Atmospheric Administration’s Alaska Fisheries Science Center in Seattle, has aptly described the situation as a “fishery disaster in the truest sense of the word.” Snow crabs typically contribute around $150 million annually to Alaskan fisheries. Yet, in the 2021-2022 crabbing season, revenue plummeted to approximately $24 million. With marine heat waves becoming more frequent due to human-caused climate change, the future of these fisheries, as well as Arctic marine ecosystems, hangs in the balance.

The findings from this research can play a vital role in assisting fishery managers in anticipating and preparing for similar events like the crab collapse in the future. Szuwalski highlights the importance of promptly providing disaster aid to affected fishers.

The ideal habitat for snow crabs, like the Chionoecetes opilio, is typically found in cold, Arctic waters. As winter’s thick sea ice melts, frigid meltwater forms a cold-water pool with temperatures below 2˚ Celsius on the seafloor, offering a sanctuary for crabs to thrive. However, the marine heat wave that hit the region in 2018 and 2019 disrupted the usual sea ice formation. Subsequently, according to yearly temperature and population survey data, the cold pool failed to appear, leading to the collapse of the crab population.

Szuwalski and his colleagues employed computer models to scrutinize temperature data, combined with population surveys, fishing catch numbers, and lab experiments, in their quest to uncover the reasons behind this sudden collapse. Two primary factors emerged – higher water temperatures and an initially dense crab population.

The data indicate that the water temperature itself likely did not kill the crabs directly, as laboratory tests showed snow crabs can survive in waters up to 12°C. Instead, the crabs might have succumbed to starvation. According to Szuwalski, the crowded crabs from 2018 required more food due to the heat wave, but the limited foraging area resulted in fewer resources available to sustain them. When compared to crabs from the previous year, those surveyed in 2018 displayed lower body weights, further supporting the theory that starvation played a pivotal role in the disappearance of the crabs.

Christopher Harley, a marine ecologist at the University of British Columbia in Vancouver, who was not involved in the research, aptly observes, “It’s just yet another example of something we didn’t expect, but now we have to live with.” For fishers in the eastern Bering Sea, it may take at least four years before crabs of a fishable size become abundant once more, leaving them in a precarious situation.

The ramifications of marine heat waves extend beyond snow crabs. Ecosystems in northern latitudes, including Alaska, are experiencing rapid changes due to climate change. Scientists typically rely on historical data to predict and prepare for the future, but events like the snow crab population collapse, which have never occurred before, are becoming increasingly challenging to anticipate. This is compounded by the fact that there hasn’t been sufficient attention on the secondary effects of marine heat waves on cold-blooded creatures, including heightened calorie requirements and the risk of starvation.