A new U of T Scarborough study finds that climate change is causing commercially important sea crabs to lose their sense of smell, which may partly explain why their numbers are dwindling.
The research was done on Dungeness crabs and found that ocean acidification causes them to physically decrease their smell, affects their ability to detect food odors and even reduces the activity of the sensory nerves responsible for smell.
says Cosima Porteus, assistant professor in the Department of Biological Sciences at U of T Scarborough and co-author of the study along with postdoctoral researcher Andrea Durant.
Ocean acidification results from the acidification of the Earth’s oceans due to the absorption of increasing amounts of carbon dioxide into the atmosphere. It is a direct result of fossil fuel burning and carbon pollution, and many studies have shown it to have an impact on the behavior of marine wildlife.
The dung crab is an economically important species found along the Pacific coast, which stretches from California to Alaska. It is one of the most popular types of edible crabs and its fishery was valued at more than $250 million in 2019.
Like most crabs, they have poor vision, so their sense of smell is critical in finding food, mates, and suitable habitat and avoiding predators, Porteous explains. They sniff out through a process known as clicking, in which they flick their antennae (a small antenna) through the water to detect odors. Within these antennae are tiny nerve cells responsible for the sense of smell, which send electrical signals to the brain.
The researchers discovered two things when the crabs were exposed to ocean acidification: They had less movement, and their sensory neurons were 50 percent less responsive to odors.
“Crabs increase their flicking rate when they detect an odor that interests them, but in crabs that have been exposed to ocean acidification, the scent has to be about 10 times more concentrated before we see an increase in flicking,” Porteous says.
There are a few possible reasons why ocean acidity may affect the sense of smell in crabs. Porteous points to other research at the University of Hull that has shown ocean acidification disrupts odor molecules, which may affect how they bind to odor receptors in marine animals such as crabs.
For this study published in the journal The biology of global changePorteous and Durant were able to test the electrical activity in cancer sensory neurons to determine that they are less responsive to odors. They also discovered that they had fewer receptors and their sensory neurons physically shrank by up to 25% in size.
“These are active cells and if they aren’t detecting odors as much, they may contract to conserve energy. It’s like a muscle that will contract if you don’t use it,” she says.
Porteous says that reducing food detection could have implications for other economically important species like Alaskan king and crabs because their sense of smell works in the same way.
“The loss of smell appears to be related to climate, so this may partly explain some of the decline in their numbers,” Porteous says.
“If the crab is having a hard time finding food, it makes sense that the females wouldn’t have as much energy to produce eggs.”
This research was supported by the Natural Sciences and Engineering Research Council of Canada. Some analysis has been done at U of T’s Center for the Neurobiology of Stress.