The drop in Metacarcinus (also known as the blue or red rock crab) population on the West Coast correlates with changes in their sense of smell. Researchers from the University of Toronto have noted a potential link between ocean acidity and this decline.
These crabs, common to the shores of western North America, are valued for their meat. Like many crustaceans, they rely more on their chemical sense than sight to locate food, find mates, identify suitable habitats, and steer clear of predators. Olfactory detection occurs through their antennae. Within those structures lie sensory neurons that pick up odors and relay signals to the brain, guiding behavior and foraging decisions.
What scientists found is that rising ocean CO2 levels cause the seawater to become acidic, and this chemical shift alters crab sensory responses. Specifically, crabs showed less frequent and weaker antennal movement, while their sensory neurons became approximately half as responsive to odors when exposed to higher acidity levels that accompany carbon dioxide uptake.
In practical terms, a crab might display agitation or curiosity toward an aroma, but the scent would need to be markedly stronger before it translates into noticeable movement. Researchers describe a tenfold increase in odor concentration required to trigger the same behavioral response observed under normal conditions.
The proposed mechanism involves acidified water interfering with the chemical molecules that normally bind to olfactory receptors. As a result, the olfactory organs may deteriorate, and the sensory neurons can shrink by roughly a quarter when living in more acidic environments. Ocean acidification is a widely discussed consequence of rising atmospheric CO2 and is considered a major threat linked to climate change and greenhouse gas accumulation. These physiological changes in crabs could help explain observed declines in populations over time.
From a long view, paleontologists have discussed ancient crabs and similar marine life, but contemporary science is concentrating on how today’s changing oceans affect living species such as the Metacarcinus on the Pacific coast. The combination of ecological sensitivity and commercial value makes this a critical area for ongoing observation, monitoring, and potential management strategies that could help sustain crab populations while marine ecosystems adjust to changing chemistry in seawater.
University researchers emphasize that further studies are needed to quantify the full impact of acidification on crab behavior, reproduction, and survival. Continued collaboration among marine biologists, ocean chemists, and fisheries managers will be essential to understand the resilience of these crabs and to develop adaptation measures that protect both biodiversity and coastal economies.