Does my ear bone look asymmetrical in this? A
microscopic view of damselfish eggs just before
hatching.
Image courtesy of the Australian Institute of Marine
Science

A study co-authored by WA fish ecologist Dr Martial Depczynski of the Australian Institute of Marine Science (AIMS) found that environmental stresses, including increased ocean temperatures and acidity, may be affecting the development of ear bones in fish which is in turn affecting the fishes’ ability to navigate to feeding and breeding grounds.

However, Dr Depczynski was quick to warn again being too fast to link the results of the study to global warming.

“There was actually no causal evidence in the scientific paper to make the link,’’ he said.

“It talked about stresses in the environment, which may be caused by global warming, but the next part is to prove that link.’’

By examining the ear bones of reef fish immediately after they hatched and then again as they headed back to the reef after some 20 days in the open water, the study found that fish with asymmetrical ear bones struggled to return to the reef to settle and breed.

“We found that at the hatchling stage 41 per cent had symmetrical otoliths and 59 per cent asymmetrical,” Dr Depczynski said.

“But a few weeks later, when they were due to settle in a habitat and breed, far fewer asymmetrical fish were found to have made their way back to the reef, or were much slower at reaching the reef which increases mortality,’’ Dr Depczynski said.

Dr Depczynski said that while asymmetry was fairly common in nature there was a theory that environmental stresses caused an increase in the level of asymmetry.

He said that at least part of the problem was likely to be linked to ocean acidification, although much more research needed to be done to examine the link.

“Fish ear bones, like their skeletons and many other kinds of structures such as reef-building corals, are made from calcium carbonate, when seawater becomes more acidic, there is less calcium carbonate available for building any calcium-based structure, including ear bones,” he said.

Dr Depczynski highlighted the danger of being too quick to associate any changes in nature with global warming, saying that science was risking its credibility by jumping to such conclusions too quickly.

Dr Depczynski’s co-authors were Dr Monica Gagliano (AIMS and James Cook University), Dr Stephen Simpson (University of Edinburgh) and James Moore (James Cook University) and the research was published in March in the UK scientific journal Proceedings of the Royal Society.