Crabs are losing their sense of smell and vanishing due to ocean acidification

Important new research from the University of Toronto Scarborough has revealed that climate change is having a profound impact on the Dungeness crab, a commercially important marine species. The research indicates that ocean acidification, a direct result of increased carbon dioxide levels in the atmosphere, is causing these crabs to lose their sense of smell. 

This discovery may provide partial insight into the dwindling populations of this economically significant species, which generated over $250 million in revenue from fisheries in 2019.

The research, led by Cosima Porteus, an assistant professor in the Department of Biological Sciences at U of T Scarborough, and postdoc Andrea Durant, is the first of its kind to investigate the physiological effects of ocean acidification on the olfactory senses of crabs. 

Ocean acidification and its impact on crabs

With their limited vision, Dungeness crabs rely heavily on their sense of smell to detect food, mates, and suitable habitats, as well as to avoid predators. They accomplish this through a process known as “flicking,” in which they move their antennules (small antenna) through the water to pick up scents.

According to Porteus, the study found that ocean acidification led to a marked decrease in the crabs’ physical sniffing, impaired their ability to detect food odors, and even reduced activity in the sensory nerves responsible for smell. 

These tiny neurons, located inside the antennules, send electrical signals to the crab’s brain, which helps them navigate their environment and make crucial decisions for their survival.

Ocean acidification is caused by the Earth’s oceans absorbing increased amounts of carbon dioxide from the atmosphere, a direct consequence of burning fossil fuels and carbon pollution. 

Numerous studies have demonstrated its impact on the behavior of marine wildlife, but this new research highlights the extent to which it can affect a species’ physiology and, consequently, its survival.

Dungeness crabs are a significant economic resource along the Pacific coast, spanning from California to Alaska. They are among the most sought-after crabs for consumption, which makes the consequences of their declining populations all the more concerning. 

What the researchers learned

The researchers have discovered that when exposed to ocean acidification, the crabs were found to flick less, and their sensory neurons were 50 percent less responsive to odors.

“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,” explained study co-author Cosima Porteus.

There are several potential reasons for this impact on the crabs’ sense of smell. Porteus points to previous research conducted at the University of Hull, which suggested that ocean acidification disrupts odor molecules, affecting how they bind to smell receptors in marine animals such as crabs.

In the study, published in the journal Global Change Biology, Porteus and her colleague Andrea Durant tested the electrical activity in the crabs’ sensory neurons to determine their responsiveness to odors. 

The researchers found not only that the neurons were less responsive but also that the crabs had fewer receptors, and their sensory neurons were physically shrinking by as much as 25 percent 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,” said Porteus.

Far reaching implications

The implications of these findings extend beyond the Dungeness crab to other economically important species such as Alaskan king and snow crabs, whose sense of smell functions in the same way. 

Porteus notes that losing their sense of smell seems to be climate-related, which could partially account for 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.”

These findings emphasize the need for further research on the physiological effects of climate change on marine species and the importance of addressing the root causes of ocean acidification to protect the delicate balance of marine ecosystems and the economies that rely on them.

More about Dungeness crab

The Dungeness crab (Cancer magister or Metacarcinus magister) is a popular marine crustacean species found along the Pacific coast of North America, ranging from Alaska down to California. Known for their sweet and tender meat, Dungeness crabs are a sought-after delicacy and play a significant role in the seafood industry. Here’s what you need to know about them:

Appearance

Dungeness crabs have a broad, oval-shaped body with a smooth shell, which is typically brownish-purple or dark red in color. They have a pair of robust claws, five pairs of legs, and two large black-tipped antennae. Adult crabs can reach up to 10 inches (25 cm) in shell width and weigh around 2-4 pounds (0.9-1.8 kg).

Habitat

These crabs prefer sandy or muddy bottoms in estuaries, bays, and coastal waters. They can be found at varying depths, ranging from the intertidal zone down to about 750 feet (230 meters).

Diet

Dungeness crabs are omnivorous, feeding on a variety of organisms, including mollusks, small fish, crustaceans, detritus, and marine vegetation.

Reproduction

Mating usually takes place during the fall and early winter months when female crabs molt, making it easier for the male to transfer sperm. After mating, females can store the sperm for several months before fertilizing their eggs. The fertilized eggs are carried by the female crab under her abdomen until they hatch into larvae, a process that can take several months.

Life cycle

Dungeness crabs go through several larval stages before metamorphosing into juvenile crabs, which resemble small adults. Juvenile crabs molt several times as they grow, with each molt increasing their size. It typically takes about 2-3 years for them to reach sexual maturity.

Commercial fishing

Dungeness crabs are an economically important species, with their fishery valued at over $250 million in 2019. They are typically harvested using baited traps or pots. The fishing season for Dungeness crabs varies by region, but it generally begins in the fall or early winter and lasts until the summer.

Conservation

Climate change and ocean acidification have been found to affect the Dungeness crab’s sense of smell, potentially impacting their ability to locate food and mates. This may partially explain the decline in their populations. Conservation efforts include regulations on the size and sex of harvested crabs, as well as seasonal closures to protect the breeding stock.

Culinary use

Dungeness crab meat is prized for its sweet, delicate flavor and is often used in a variety of dishes, such as crab cakes, bisques, salads, and seafood boils. The crabs can be cooked by steaming, boiling, or baking, and are often served with melted butter or dipping sauces.

In summary, the Dungeness crab is a valuable marine species found along the Pacific coast of North America. They play a crucial role in both marine ecosystems and the seafood industry, but their populations are facing challenges due to climate change and ocean acidification. 

Conservation efforts are essential to protect this important species and its contributions to coastal economies.

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