How Dungeness crabs’ complex lifecycle will be affected by climate change

Dungeness crab
A Dungeness crab, or Cancer magister, sits on kelp.Jerry Kirkhart/Flickr

New research on the Pacific Northwest portion of the Dungeness crab fishery, which spans the West Coast of the U.S. and Canada, projects how this crustacean will fare under climate change.

Results show that by the end of this century, lower-oxygen water will pose the biggest threat. And while these crabs start as tiny, free-floating larvae, it’s the sharp-clawed adults that will be most vulnerable, specifically to lower-oxygen coastal waters in summer.

The open-access study from researchers at the University of Washington, the University of Connecticut and the National Oceanic and Atmospheric Administration will be in the December issue of AGU Advances, a journal of the American Geophysical Union.

The researchers used a detailed computer model of ocean conditions to simulate the shifting properties of the water the crabs inhabit. Using a scenario of high carbon emissions through 2100, the model looks at how heat-trapping gases in the atmosphere will make the ocean warmer, carbon dioxide transferred from the air will make the surface waters more acidic, and warmer water will hold less dissolved oxygen.

Previous research has shown that the Dungeness crab is vulnerable to climate change. Those studies focused on changes in ocean pH, while the new paper includes multiple ocean properties and uses a model that is more detailed in space and time.

Time and place are both important. Crabs mate in spring and females produce eggs in late fall. Eggs begin to hatch in January and release larvae, which float in the offshore currents while growing, shedding and regrowing their shells five times. In summer the fully developed larvae come back closer to shore and molt, becoming juvenile crabs that scamper on the ocean floor.

The authors used an ocean model to study the consequences of climate stressors at different times throughout the Dungeness crab’s life stages — from eggs, to larvae, to juveniles, to adults.

“We found that for all three stressors there will be increased population-level vulnerability, and the most severe is to low oxygen levels,” said first author Halle Berger, a doctoral student at the University of Connecticut. “Low-oxygen events happen during the coastal upwelling season in spring and summer, which impacts the adults, whereas ocean acidification manifests more year-round in the future, impacting all life stages but less severely.”

Lab studies of Dungeness crab combined with model results suggest that the most severe effects will be lower dissolved oxygen along the coastal seafloor in summer, harming the adults. This is unlike other species, such as shellfish, which are thought to be most vulnerable in the larval stage.

Like other animals, crabs breathe oxygen. Warmer water holds less gas, so even if marine life can handle the higher temperature and acidity, the drop in oxygen may lower the chance for survival.

“The value of this down-scaled model is that it can help tribes and state agencies to focus their efforts in both space and time,” said co-author Jan Newton, an oceanographer at the UW Applied Physics Laboratory and co-director of the Washington Ocean Acidification Center. “This information is very pertinent to resource managers.”

The researchers say these results could be incorporated into decision-making as ocean conditions change.

University of Washington, 28 October 2021. Press release.

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