Why sea crabs starve despite food
California crabs sniff out their food in the sea as scavengers. Carbon dioxide makes the water more acidic. Researchers have therefore carried out experiments on the animals’ sense of smell – and present disturbing results.
DAccording to a study, increasing ocean acidification is affecting the sense of smell of California crabs. This could be a reason for the declining numbers of these sea crabs, write three researchers the University of Toronto. Accordingly, in acidic water, the animals can recognize bad smells that emanate from their food. The activity of the nerves responsible for the sense of smell also decreases, writes Cosima Porteus’ team in the journal “Global Change Biology”.
California edible crabs (Metacarcinus magister) are found along the Pacific coast from California to Alaska and are a favorite food of many people. They usually grow to a size of 20 centimeters and are also known as Dungeness crabs or Pacific crabs.
The oceans are becoming more acidic because they absorb much of the carbon dioxide (CO2) that man produces. As a result, the oceans reduce the warming effect of the greenhouse gas produced on the climate. But in seawater, CO reacts2 to carbonic acid and thus makes it more acidic. Very acidic water can damage coral reefs and Shellfish as well as, for example, also damage cod larvae. “This is the first study to look at the physiological effects of ocean acidification on the olfactory sense of crabs deals”, said Porteus.
According to Porteus, most edible crabs have poor eyesight. Therefore, they rely on their sense of smell to find food, mates and suitable habitats or to flee from predators. The tiny nerve cells of the sense of smell sit on the antennae of the animals. By moving the antennae, the crayfish Substances and thus chemical signals in the surrounding seawater – the researchers compare this with the sniffing of other animals. As scavengers, this is particularly important for the crabs, for example in order to recognize the substance cadaverine emitted by carrion.
The team released 17 edible crabs into ordinary ocean water the current acidity (pH 8.08) and 18 in water enriched in CO₂ and therefore more acidic (pH 7.74). According to the Intergovernmental Panel on Climate Change, seawater has already become significantly more acidic (from around pH 8.2 to around pH 8.1) due to man-made CO₂. In the worst-case scenario, by the end of the century, the world’s oceans could reach roughly the level of acidity tested in the study.
In the experiment, edible crabs in ordinary ocean water reacted to even low concentrations of cadaverine by increasingly wagging their antennae. Those in the acidic water needed a concentration ten times higher to react. The researchers have not yet been able to determine whether the acidic seawater changes cadaverine, making it less effective, or whether the crabs’ sensors are damaged. In any case, the CO₂ dissolved in the water has a negative impact on the important perception of cadaverine.
In another test with a dose of cadaverine, the nerves in the animals’ antennae fired far fewer signals than usual in the acidic water. They also had fewer nerve cells and their sensory neurons shrank by up to 25 percent of their volume. “These are active cells, and if they’re not very good at sensing smells, they may shrink to conserve energy. It’s like a muscle that shrinks if you don’t use it,” Porteus said.
The loss of the sense of smell may explain part of the decline in California edible crabs, Porteus said. “If the crabs are having trouble finding food, it stands to reason that the females don’t have as much energy to produce eggs.”
The study provides further evidence of the impact of ocean acidification crustaceans, write the authors. It remains to be seen how rising sea temperatures and the expected decrease in oxygen content will affect this. In any case, the scientists assume that other crustaceans will also be affected by the increasing acidity in the future.
According to Porteus, reduced food recognition could also have an impact on other economically important species such as the king crab (Paralithodes camtschaticus) and the snow crab (Chionoecetes opilio). Your sense of smell works the same way.