A new study from the U of T Scarborough finds that climate change is causing a commercially important marine crab to lose its sense of smell, which could partly explain why its populations are declining.
The research was done with Dungeness crabs and found that ocean acidification makes them physically sniff less, affects their ability to detect food odors, and even decreases activity in the sensory nerves responsible for smell.
“This is the first study to look at the physiological effects of ocean acidification on crabs’ sense of smell,” says Cosima Porteus, an assistant professor in the department of biological sciences at U of T Scarborough and co-author of the study with with postdoc Andrea Durant.
Ocean acidification is the result of Earth’s oceans becoming more acidic due to the absorption of increasing amounts of carbon dioxide into the atmosphere. It is a direct consequence of the burning of fossil fuels and carbon pollution, and several studies have shown that it has an impact on the behavior of marine wildlife.
Dungeness crabs are an economically important species found along the Pacific coast, stretching from California to Alaska. They are one of the most popular crabs to eat and their catch was valued at over $250 million in 2019.
Like most crabs, they have poor vision, so their sense of smell is crucial for finding food, mates, suitable habitats, and avoiding predators, Porteus explains. They sniff through a process known as blinking, in which they move their antenulae (small antennae) through the water to detect scents. Tiny neurons responsible for smell are found within these antennae, which send electrical signals to the brain.
The researchers found two things when the crabs were exposed to ocean acidification: They blinked less and their sensory neurons responded 50 percent less to odors.
“Crabs increase their rate of blinking when they detect a scent they are interested in, but in crabs that were exposed to ocean acidification, the scent had to be 10 times more concentrated before we noticed an increase in blinking,” he says. Porteus.
There are a few potential reasons why ocean acidification appears to be affecting the sense of smell in crabs. Porteus points to other research conducted at the University of Hull that showed that 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 Biology of global change, Porteus and Durant were able to test electrical activity in the crabs’ sensory neurons to determine that they were less responsive to odors. They also found that they had fewer receptors and that their sensory neurons were physically shrinking by up to 25 percent in volume.
“These are active cells and if they don’t detect odors as much, they may shrink to conserve energy. It’s like a muscle that will shrink if you don’t use it,” he says.
Porteus says that reduced food detection could have implications for other economically important species, such as Alaskan king and snow crabs, because their sense of smell works in the same way.
“The loss of the sense of smell seems to be related to the weather, so this could partly explain the decline in their numbers,” says Porteus.
“If the crabs have trouble finding food, it stands to reason that the females don’t have as much energy to produce eggs.”
This research was supported by the Natural Sciences and Engineering Research Council of Canada. Part of the analysis was done at U of T’s Stress Neurobiology Center.
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