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Will climate change disorientate fish?

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Shanta Barley | 13:01 UK time, Monday, 20 July 2009

Humans are regularly lost at sea but what about fish? New research suggests that climate change could disorientate fish by enlarging their ear bones, which they use to navigate.


Previous studies found that seawater rich in carbon dioxide (CO2) shrinks the shells of corals and shellfish by reducing the availability of the bio-mineral aragonite, a form of calcium carbonate and key constituent of shells.

The ear bones (otoliths) of fish are made of aragonite, too. David Checkley at Scripps Institution of Oceanography and his colleagues therefore expected the otoliths of fish reared in CO2-rich seawater to shrink.

To their surprise, the opposite happened. The more carbon dioxide they added to the water, the larger the fishes ear bones grew.

Checkley's team reared the young of white sea bass in seawater containing three levels of CO2: low (380 uatm), medium (993 uatm) and high (2559 utam).

The medium concentration here is approximately 2.5 times the current CO2 concentration, and is likely to occur in the atmosphere by the year 2100, the study notes.

The weight of ear bones rose by 10-14% in fish reared at the medium concentration of CO2, and by as much as 26% at the highest level.

It is hard to overstate the importance of ear bones: when small but perfectly formed, in humans as in fish they help us navigate, stay upright and survive. And studies show that fish with asymmetrical ear bones have difficulty navigating and are less likely to survive than normal fish.

Will fish with larger ear bones suffer a similar fate? It's too soon to tell, but right now there's no conclusive evidence that fish with larger ear bones fare worse than normal fish.


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