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 (CO(2)) concentrations in the ocean1, 2, 3, 4. However, whether fish can acclimate to elevated CO(2) over the longer term, and the consequences of altered behaviour on the structure of fish communities, are unknown. We used marine CO(2) seeps in Papua New Guinea as a natural laboratory to test these questions. Here we show that juvenile reef fishes at CO(2) seeps exhibit behavioural abnormalities similar to those seen in laboratory experiments. Fish from CO(2) seeps were attracted to predator odour, did not distinguish between odours of different habitats, and exhibited bolder behaviour than fish from control reefs. High CO(2) did not, however, have any effect on metabolic rate or aerobic performance. Contrary to expectations, fish diversity and community structure differed little between CO(2) seeps and nearby control reefs. Differences in abundances of some fishes could be driven by the different coral community at CO(2) seeps rather than by the direct effects of high CO(2). 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 CO(2) within the seeps. However, continuous exposure does not reduce the effect of high CO(2) 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 CO(2) emissions