Anosmia, or the loss of sense of smell, can occur as a result of various conditions such as colds, sinus infections, allergies, and COVID-19. Usually, these symptoms are temporary and resolve on their own in a short period of time.
According to a recent study conducted by doctors at Johns Hopkins University in the US, a declining sense of smell may indicate declining health and potential frailty.
But, according to a new study, for this particular species, losing its sense of smell can be a life-ending event.
New research from the University of Toronto Scarborough has revealed that Dungeness crabs, a commercially significant marine crab, are losing their sense of smell due to climate change. This could be a key factor in the thinning of their populations.
The study found that ocean acidification caused the crabs to physically sniff less, impacting their ability to detect food odors and decreasing activity in the sensory nerves responsible for the smell. The study highlights the importance of addressing the impact of climate change on marine ecosystems and their inhabitants.
“This is the first study to look at the physiological effects of ocean acidification on the sense of smell in crabs,” adds co-author Cosima Porteus.
The rise in carbon dioxide levels in the Earth’s atmosphere is causing the oceans to become more acidic, leading to ocean acidification. The burning of fossil fuels and the increase in carbon pollution is directly responsible for this phenomenon. Multiple research studies have indicated that ocean acidification is significantly affecting the behaviour of marine wildlife.
Dungeness crabs, a highly valued species found along the Pacific coast from California to Alaska, are facing a potential crisis due to their reliance on their sense of smell. Their fishery was worth over $250 million in 2019, making them an economically important species.
According to experts, the crabs have poor eyesight and rely heavily on their sense of smell for finding food, suitable habitats, and mates, as well as avoiding predators. They utilize a process called “flicking” where they move their antennules (small antennas) through the water to detect scents. The antennules house tiny neurons responsible for smell, which send signals to the crab’s brain.
They uncovered alarming findings about the impact of ocean acidification on crabs. According to the new study, exposure to ocean acidification resulted in a 50% reduction in the sensory neurons of crabs in response to odors. Additionally, the crabs were observed flicking less when exposed to ocean acidification.
“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,” adds Porteus.
According to the co-author of the study, ocean acidification disrupts odour molecules, which can affect how they bind to smell receptors in marine animals such as crabs. The team tested the electrical activity in the crabs’ sensory neurons and found that they were less responsive to odors. They also discovered that the crabs had fewer receptors and that their sensory neurons were physically shrinking by as much as 25% in volume.
“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,” she adds.
The findings of Porteus and her team regarding the potential implications of reduced food detection in one species could have far-reaching consequences for other economically significant species, such as Alaskan king and snow crabs, as they share similar mechanisms of smell detection.
“Losing their sense of smell seems to be climate related, so this might partially explain some of the decline in their numbers,” adds Porteus.
“If crabs are having trouble finding food, it stands to reason females won’t have as much energy to produce eggs.”
The findings were published in the journal Global Change Biology.
Dr. Porteus had previously conducted a study that revealed that fish were losing their sense of smell due to the rising levels of carbon dioxide (CO2) in the atmosphere, leading to increasingly acidic oceans.
“The sense of smell of sea bass was reduced by up to half in sea water that was acidified with a level of CO2 predicted for the end of the century. Their ability to detect and respond to some odors associated with food and threatening situations was more strongly affected than for other odors.”
“We think this is explained by acidified water affecting how odorant molecules bind to olfactory receptors in the fish’s nose, reducing how well they can distinguish these important stimuli,” she said at that time.
Source: 10.1111/gcb.16738
Image Credit: Getty