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Behavioural impairment in reef fishes caused by ocean acidification at CO2 seeps


Experiments have shown that the behaviour of reef fishes can be seriously affected by projected future carbon dioxide (CO2) concentrations in the ocean1,2,3,4. However, whether fish can acclimate to elevated CO2 over the longer term, and the consequences of altered behaviour on the structure of fish communities, are unknown. We used marine CO2 seeps in Papua New Guinea as a natural laboratory to test these questions. Here we show that juvenile reef fishes at CO2 seeps exhibit behavioural abnormalities similar to those seen in laboratory experiments. Fish from CO2 seeps were attracted to predator odour, did not distinguish between odours of different habitats, and exhibited bolder behaviour than fish from control reefs. High CO2 did not, however, have any effect on metabolic rate or aerobic performance. Contrary to expectations, fish diversity and community structure differed little between CO2 seeps and nearby control reefs. Differences in abundances of some fishes could be driven by the different coral community at CO2 seeps rather than by the direct effects of high CO2. Our results suggest that recruitment of juvenile fish from outside the seeps, along with fewer predators within the seeps, is currently sufficient to offset any negative effects of high CO2 within the seeps. However, continuous exposure does not reduce the effect of high CO2 on behaviour in natural reef habitat, and this could be a serious problem for fish communities in the future when ocean acidification becomes widespread as a result of continued uptake of anthropogenic CO2 emissions.

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Figure 1: Preference of juvenile fish for water streams containing different chemical cues presented in a two-channel flume chamber.
Figure 2: Activity level and boldness of fish from CO2 seep and control reefs.
Figure 3: Comparisons of fish community structure at CO2 seep and control locations.

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We thank the people at Upa Upasina (Illi Illi Bwa Bwa), Dobu and Esa’Ala reefs for allowing us to visit their reefs, and Rob van der Loos and the crew of MV Chertan for logistical support. Special thanks to S. Noonan for logistic support and assistance with experiments. The study was funded by the Australian Institute of Marine Science, a Grant for Research and Exploration by the National Geographic Society, and the ARC Centre of Excellence for Coral Reef Studies.

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All authors contributed to the designs of the study, collection and analysis of data, and writing the article.

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Correspondence to Philip L. Munday.

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Munday, P., Cheal, A., Dixson, D. et al. Behavioural impairment in reef fishes caused by ocean acidification at CO2 seeps. Nature Clim Change 4, 487–492 (2014).

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