Pacific populations of sweet-tasting Dungeness crabs are on the decline, and researchers from the University of Toronto say they’ve found a potential culprit: acidic ocean water related to climate change. The acidic water affects how molecules bind to the crabs’ smell-detecting antennae, which they use to scavenge for food on the sea floor.
For the Dungeness, as with most crabs, its sense of smell is critical to its survival, as it has poor vision and relies on short antennae for finding food, mating and avoiding predators. The antennae “flick” through the water, allowing scent molecules to collide with nerve cells on the appendages, which transmit to the crab’s brain.
“Losing their sense of smell seems to be climate related, so this might partially explain some of the decline in their numbers,” says Cosima Porteus, an assistant professor at the University of Toronto-Scarborough, in a press release.
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The Dungeness Crab Fishery
Because of its sweet, firm flesh, the Dungeness crab stands as one of the most popular types of seafood in the world, with more than 50 million pounds harvested each year. The study values the industry, in 2019, at about $250 million.
Dungeness crabs get their name from a bay found near Dungeness Spit in Washington State, although the commercial fishery stretches across the American and Canadian Pacific Coast.
Like other fisheries, the Dungeness harvest must deal with an increasing amount of carbon dioxide in the atmosphere, which ocean water absorbs, turning it more acidic. While other studies have looked at the effects of climate change on marine wildlife, “This is the first study to look at the physiological effects of ocean acidification on the sense of smell in crabs,” Porteus says.
How Dungeness Lose Their Sense of Smell
For the study, the researchers exposed crabs to acidified water and found that they flicked less, and not only that, their antennae collected 50 percent fewer scents. As a result, they became much less sensitive to crucial environmental cues.
“Crabs increase their flicking rate when they detect an odour they are interested in,” says Porteus, “but in crabs that were exposed to ocean acidification, the odor had to be 10 times more concentrated before we saw an increase in flicking.”
Acidic water, the study found, had caused the scent-detecting neurons to malfunction, making them less responsive. The cells also appeared to have shrunk by as much as 25 percent.
Worn-Out Crabs Don't Lay Eggs
“These are active cells and if they aren’t detecting odors as much, they might be shrinking to conserve energy,” she says. “It’s like a muscle that will shrink if you don’t use it.”
Lack of food means lack of energy, Porteus says, and lack of energy may mean a decline in egg-laying and overall populations, a cycle that may also be affecting snow and Alaskan king crabs.