Fish may lose sense of smell if ocean pH drops


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Nemo is in real danger of getting lost due to ocean acidification, according to research published in a recent issue of the Proceedings of the National Academy of Sciences by scientists from Australia, Norway and Russia.

Philip Munday and coauthors tested the hypothesis that reduced seawater pH consistent with ocean acidification predictions could affect the ability of Percula or Orange clownfish (Amphiprion percula) larvae to respond to olfactory cues that are used to locate reef habitat and distinguish preferred settlement sites.

The authors measured the responses of larval clownfish to olfactory cues from a range of tropical vegetation types when reared in seawater simulating two future CO2-induced acidification scenarios (pH 7.8 and 7.6) compared with current-day controls (pH 8.15).

They did so by placing clownfish larvae in a two-channel choice flume, where individuals were allowed to choose between a stream of seawater containing the olfactory cue to be tested and a stream of water without that cue.

The olfactory cues tested were: secretions from a tree to which clownfish are usually attracted (Xanthostemon chrysanthus), oil from a swamp tree they usually avoid (Melaleuca nervosa), secretions of anemones (a favorite clownfish habitat) and secretions from their own parents (which the fish usually avoid).

The authors found that when reared at pH levels of 7.8 (which is the acidity projected for the world's oceans in 2100 at current levels of CO2 emissions), the clownfish larvae retained the same responses to Xanthostemon and anemone secretions, but at a decreased sensitivity, while instead of being repelled by secretions from Melaleuca and their own parents, they became attracted to them.

Larvae reared at a pH level of 7.6 failed to show any response to olfactory cues, indicating that extended exposure to low pH water affected the olfactory system.

The authors conclude loss of larval olfactory capacity in marine organisms through acidification could have significant consequences for marine biodiversity.

Larvae of many marine species appear to navigate and orient toward suitable adult habitat and settlement substrata using a complex range of olfactory stimuli.

If the olfactory system is impaired at high CO2 and low pH, this important life history transition will be disrupted and populations will not be properly replenished.

For more information, see the paper: Munday, PL, DL. Dixson, JM Donelson, GP Jones, MS Pratchett, GV Devitsina and KB Dving (2009) Ocean acidification impairs olfactory discrimination and homing ability of a marine fish. Proceedings of the National Academy of Sciences 106, pp. 1848"1852.