The mechanism by which elevated carbon dioxide in the world's oceans is affecting fish brains has been explained in a study published in the most recent issue of the journal Nature Climate Change.
Göran Nilsson and colleagues found that high levels of CO2 interfere with neurotransmitter function in the brain of two larval coral reef fish (the clownfish Amphiprion percula and Yellowtail demoiselle Neopomacentrus azysron), causing them to develop behavioural and sensory abnormalities.
It has been known for some time that elevated CO2 levels in seawater cause juvenile fish to behave erratically, including increased boldness and activity, loss of instinctive ability to turn, altered preferences for sound and impaired smelling ability.
The authors found that increasing CO2 levels to concentrations predicted for the end of the century directly stimulates a receptor in the fish brain (GABA-A) that reverses its normal response (causing excitation instead of inhibition).
The authors also found that exposing the fish to a chemical that deactivates the GABA gateway could reverse the impaired behavioural responses of the larval fish caused by high carbon dioxide levels.
According to senior author Philip Munday: "We've now established it isn't simply the acidification of the oceans that is causing disruption – as is the case with shellfish and plankton with chalky skeletons – but the actual dissolved carbon dioxide itself is damaging the fishes’ nervous systems."
For more information, see the paper: Nilsson, GE, DL Dixson, P Domenici, MI McCormick, C Sørensen, S-A Watson and PL Munday (2012) Near-future carbon dioxide levels alter fish behaviour by interfering with neurotransmitter function. Nature Climate Change 2, pp. 201–204.
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