Acidic oceans make reef fish stupid

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Stupid reef fish would be another effect of ocean acidification, according to a study published in a recent issue of the online journal PLoS ONE.

Maud Ferrari and coauthors found that young Ambon damselfish (Pomacentrus amboinensis) exposed to elevated carbon dioxide levels failed to learn to respond appropriately to a common predator, the Brown dottyback (Pseudochromis fuscus) regardless of the learning methods employed to teach the fish.

In three sets of experiments, the authors compared the learning behaviour of Ambon damselfishes exposed to 440 µatm CO2 (current day levels) and 850 µatm CO2, a concentration predicted to occur in the ocean before the end of this century.

In the first set of experiments, the fish were conditioned with odours from an injured conspecific paired with dottyback odour before being tested for their responses to only dottyback odour.

In the second set of experiments, the fish were trained to visually associate predators with danger (by pairing predator-naive fish with predator-experienced fish and allowing the former to learn the appropriate response on seeing a predator from the latter). The predator-naive fish was then isolated and its response on sighting a predator was assessed.

In the third set of experiments, the fish at 440 µatm CO2 and 700 µatm CO2 were both conditioned as in the first set of experiments before being tested on their responses to dottyback odour after the effects of elevated CO2 were allowed to wear off.

In all three sets of experiments, the authors found that juvenile damselfishes exposed to elevated CO2 levels were cognitively impaired and unable to respond to either visual or chemical cues from the predator, even after the effects of elevated CO2 levels were removed (the fish in the third set of experiments responded to odours from injured congeners but not from predators).

This learning impairment may have far-reaching ecological consequences and may impinge on any conservation efforts to mitigate the ecological effects of ocean acidification, according to the authors.

For more information, se the paper: Ferrari MCO, RP Manassa, DL Dixson, PL Munday, MI McCormick, MG Meekan, A Sih and DP Chivers (2012) Effects of ocean acidification on learning in coral reef fishes. PLoS ONE 7(2): e31478. doi:10.1371/journal.pone.0031478

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