High CO2 levels lead to abnormally large fish ear bones

Washington, June 26 (ANI): Rising carbon dioxide (CO2) levels in the ocean can cause abnormally large growth in the otoliths, or ear bones, of fish, say researchers at Scripps Institution of Oceanography at UC San Diego.

Considered a fundamental bodily structure in fish, otoliths serve a vital function in fish by helping them sense orientation and acceleration.

In the study, the researchers have described experiments in which fish that were exposed to high levels of carbon dioxide experienced abnormally large growth in their otoliths.

The researchers had hypothesized that otoliths in young white seabass growing in waters with elevated carbon dioxide would grow more slowly than a comparable group growing in seawater with normal CO2 levels.

But, to their surprise, they discovered the reverse and found "significantly larger" otoliths in fish developing in high-CO2 water.

Although the fish in high-CO2 water were not larger in overall size, it was only the otoliths that grew demonstrably bigger.

"At this point one doesn't know what the effects are in terms of anything damaging to the behavior or the survival of the fish with larger otoliths. The assumption is that anything that departs significantly from normality is an abnormality and abnormalities at least have the potential for having deleterious effects," said David Checkley, a Scripps Oceanography professor and lead author of the new study.

Now, the researchers are poised to determine whether the otolith growth abnormality exists in fish other than white seabass; to locate the physical mechanism that causes the enhanced otolith growth; and to assess whether the larger otoliths have a functional effect on the survival and the behaviour of the fish.

"Number three is the big one. If fish can do just fine or better with larger otoliths then there's no great concern. But fish have evolved to have their bodies the way they are. The assumption is that if you tweak them in a certain way it's going to change the dynamics of how the otolith helps the fish stay upright, navigate and survive," said Checkley.

The study has been published in the journal Science. (ANI)