A 2018 and 2019 Bering Sea heat wave caused a massive boom in hybrid crabs. A 2025 survey showed their numbers were 13.4 times the historical average. Researchers said, "Our results suggest that predator or competitive release increased postmating hybrid survival, driving the surge in hybrid crab abundance."
Marine heat waves are usually seen as destructive events that can disrupt entire ocean ecosystems and trigger massive environmental damage. In 2018 and 2019, an extreme heat wave hit the Bering Sea, causing spring sea ice levels to plummet.
This loss of ice helped trigger a devastating collapse in the local snow crab population. But the long-term consequences of extreme heat can be far more unpredictable than initial population crashes.
A new study published in the journal Proceedings of the National Academy of Sciences suggests that this particular heat wave led to an unprecedented boom in the number of hybrid crabs.
A surge in crab numbers
Researchers from the National Oceanic and Atmospheric Administration's (NOAA's) Alaska Fisheries Science Center analyzed data from annual seafloor surveys of the eastern Bering Sea that monitored crab populations.
As part of their research, the team compared their 2025 estimates with historical data stretching back to 1988. That revealed that the abundance of these hybrid crabs, a natural cross between snow crabs and Tanner crabs, was 13.4 times greater than the historical average for 1988 to 2024.
But that wasn't the only finding that raised eyebrows.
Previously, hybrids had never accounted for more than 10% of the commercial-sized snow and hybrid male crabs in the area. However, in the 2025 survey, they made up 41.7% of all market-sized snow and hybrid males combined.
What caused the hybrid crab boom?
That got the team wondering what the cause could be. To find out, they used statistical causal models to test three possible scenarios. These were whether heat wave conditions directly boosted hybrid survival, whether changing ocean conditions brought snow crabs and Tanner crabs into closer contact, or whether the collapse of the snow crab population reduced competition or predation, allowing more hybrid crabs to survive.
The study authors used several variables in their models, including crab population estimates, the extent of sea ice (as a measure of heat wave conditions) and how much the areas inhabited by snow crabs and Tanner crabs overlapped.
Their analysis found that the heat wave was an indirect cause, as it led to the collapse of the snow crab population. This appears to have allowed more hybrids to survive because of reduced competition or predation. "Our results suggest that predator or competitive release increased postmating hybrid survival, driving the surge in hybrid crab abundance, rather than a breakdown of premating barriers," said the researchers.
A population surge like the one the research team found creates a challenge for fishery managers. Although hybrids can legally be harvested as snow crabs, managers do not separately account for their numbers when setting harvest quotas. "Our results underscore the importance of greater flexibility in management systems to increase resilience amid the unforeseen ecological consequences of marine heat waves."