Elevated carbon dioxide makes the ear bones unusually large

Increasing the amount of carbon dioxide in the ocean adversely affects shells and corals; New research by Scripps Institution of Oceanography at the University of California at San Diego for the first time has demonstrated that CO2 can affect the basic structure of the fish body.

A brief article published in Science on May 26 describes experiments in which fish bodies exposed to high levels of carbon dioxide develop large ear stones (also called ear bones). unusual way. These ear stones perform an important function for fish, helping them feel the direction and acceleration of swimming.

Previous researchers have hypothesized that ear stones in white seabass growing in the ocean have high carbon dioxide concentrations that will grow more slowly than those in CO2 tanks. often. However, they were surprised to find the opposite of the research results, that fish that grow in high CO2 environments will have particularly large ear stones.

Live fish in a lot of CO2 does not increase the entire body size, but only increases in size in only ear stones.

Images of observed ear stones from one side were taken with an electron microscope. The upper part is smooth and the lower part is covered with small niches. These cavities are about 1-2 micrometers in diameter. (Photo: Scripps Institution of Oceanography, University of California at San Diego)

'No one has known at this point of time whether the big ear stones have any negative effects on the activity or survival of the fish,' said David Checkley, research leader and professor at Scripps Oceanography Institute. know. 'The hypothesis is that anything that is vastly different from ordinary things is unusual, and the anomaly is at least potentially negative.'

With an increasing amount of carbon dioxide due to human activities, especially fossil fuel burning, causing seawater to increase both CO2 and acid levels, scientists plan to expand the study to test specific areas, for example, to find out if this abnormal ear stone development exists in any other fish than cod; identify physical mechanisms capable of enhancing the development of ear stones; assess whether larger otoliths have an effect on fish survival and activity.

'The third issue is the most important,' says Checkley. 'If the fish can function and survive normally, or better when there is a big ear stone, there is nothing to care about. But the fish have evolved through a long journey to reach the body structure as it is today. We think that if it impacts them in some way, it will change the mechanism that ear stones help fish balance, orient and survive. '

In addition to orientation and acceleration functions, ear stones also reveal fish body characteristics. Because ear stones grow in layers of onion-like rings, scientists can use it to determine the age of the fish, similar to how wood is determined by wood in the trees.

The authors of the study include: Andrew Dickson, John Radich and Rebecca Asch both from Scripps Institute, Motomitsu Takahashi of the Seikai National Fisheries Research Institute in Nagasaki, Japan; and Nadine Eisenkolb of the University of Southern California.

The research was funded by the University of California Academy of San Diego.