Massive die-offs of Dungeness crab have been documented off the Pacific Northwest Coast. Once dead, the aquatic crabs often wash up on beaches, such as the ones photographed on Kalaloch Beach on June 14, 2022. Photo: Jenny Waddell/NOAA
Dungeness crab is an iconic and valuable fishery resource that is culturally and economically important to West Coast communities. Off the coast of Oregon and Washington, tribal, commercial, and recreational fishers pull up crab pots, expecting a haul of Dungeness crabs. Too often lately, what they find are pots filled with dead crabs, suffocated from a lack of oxygen near the seafloor.
Hypoxia—dangerously low oxygen levels—is killing Dungeness crabs off the Pacific Northwest Coast, predominantly during the summer and early fall. Marine animals don’t breathe air, but they still need oxygen, which they absorb from the water. If sufficient oxygen is missing from the water column, the animals may perish.
In addition, blooms of harmful algae have led to the closure of entire Dungeness crab fisheries on the West Coast in past years. Harmful algal blooms are the rapid growth of algae that can produce toxins dangerous to animals and habitats, with potential risk to humans who eat contaminated shellfish.
Multiple Stressors
Hypoxia and harmful algal blooms are considered stressors to the health of Dungeness crabs. Other stressors include ocean acidification, rising ocean temperatures, and marine heatwaves. Each of these stressors is known to harm marine species and ecosystems independently, but scientists are only beginning to unravel the ways in which environmental stressors may interact, and whether there may be unprecedented consequences.
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Sarah Marquis, National Marine Sanctuaries, November 2022. Full article.
