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Fish ears and ocean chemistry

Seven day old white seabass larva live in seawater. You will note two bright objects in the left side of the fish head, just behind the eye and slightly toward the center. This is a pair of otoliths.
[Image courtesy of David Checkley]

In environments with high carbon dioxide levels, researchers say that the ear bones of young fish actually grow larger than normal rather than smaller, as they had expected. This finding means that ocean chemistry could have unexpected effects on the minerals produced by fish larvae.

Dr. David Checkley and colleagues grew fish eggs and larvae of white sea bass under a range of carbon dioxide concentrations and measured the size of their ear bones, known as otoliths, with scanning electron microscopes in order to reach this conclusion.

Top (dorsal) view of otolith.
[Image courtesy of David Checkley]

The researchers suggest that carbon dioxide is able to move freely through the fishes' skin and around the otoliths, which accelerates their growth. This discovery, however, reveals a very different effect of carbon dioxide on marine bio-minerals than the effects found in previous studies.

Checkley and his colleagues say that their findings highlight the need to understand the unexpected effects of ocean chemistry on a range of other marine organisms during their various stages of development.

The experiment was not designed to test how the over-sized otoliths actually affect the fish, but the authors predict, based on past studies, that the effects would be negative for the fish. They say that more research is needed to understand those effects.


This research appears in the 26 June 2009 issue of Science.