Why crab might soon be off the menu

By Alice Clifford via SWNS

The number of crabs in our oceans is dropping as climate change damages their sense of smell, a new study from Canada reveals.

Increased carbon dioxide levels in the atmosphere, mean oceans are forced to absorb more than normal, causing our seas to become more acidic.

This increase in acidity has impacted Dungeness crabs’ sense of smell, preventing them from detecting the smell of food, mates, suitable habitats and avoiding predators.

Dungeness crabs can be found on the Pacific coast, stretching from California to Alaska.

They are one of the most popular crab species to eat. Their fishery was valued at more than $250 million USD, just under £200 million GBP, in 2019.

Like many crabs, they have poor vision, so their sense of smell is crucial.

They sniff through a process known as flicking, where they flick their antennules, which are like small antennas, through the water to detect odors.

Tiny neurons responsible for smell are located inside these antennules, which send electrical signals to the brain.

To reach their results a team from the University of Toronto, Canada, tested the electrical activity in the crabs’ sensory neurons to see if they were less responsive to odors.

When the crabs were exposed to ocean acidification they flicked less and their sensory neurons were 50 percent less responsive to smells.

The study suggests that ocean acidification disrupts odor molecules, which can impact how they bind to smell receptors in marine animals such as crabs.

Co-author Dr. Cosima Porteus, an assistant professor in the Department of Biological Sciences at the University of Toronto, Scarborough, said: “This is the first study to look at the physiological effects of ocean acidification on the sense of smell in crabs.

“Crabs increase their flicking rate when they detect an odor they are interested in, 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.”

They also discovered acidification had left them with fewer receptors and their sensory neurons were physically shrinking by as much as 25 percent in volume.

Dr. Porteus added: “These are active cells and if they aren’t detecting odors as much, they might be shrinking to conserve energy. It’s like a muscle that will shrink if you don’t use it.”

Other economically important species, such as Alaskan king and snow crabs, could also be at risk, as their sense of smell functions the same way.

Dr. Porteus said: “Losing their sense of smell seems to be climate-related, so this might partially explain some of the decline in their numbers.

“If crabs are having trouble finding food, it stands to reason females won’t have as much energy to produce eggs.”

The study was published in the journal Global Change Biology.