Baby Fish Confused by Sound in High CO2 Conditions

Baby fish could find it harder to reach secure shelters in future acidified oceans – putting fish populations at risk, new research from the University of Adelaide has concluded.

The researchers described how barramundi larvae in high CO2 conditions, predicted for the turn of the century, turn away from the ocean noises they would normally be attracted to. 

Professor Ivan Nagelkerken, said: “Oceanic larvae (hatchlings or baby fish) from quite a few species of fishes and invertebrates listen to sounds of coastal ecosystems. They use these sounds to guide them from the open ocean, where they hatch, to a sheltered home in shallow waters, where they can spend their juvenile and adult lives.”

The research, carried out by then PhD candidate Tullio Rossi, compared the activity of barramundi larvae in marine tanks with levels of CO2 that are predicted for the turn of the century against the responses of barramundi larvae in current day CO2 levels.

While larvae of barramundi were attracted to the sounds of tropical estuaries, larvae raised under future ocean conditions with elevated CO2 were deterred by these natural sounds. Moreover, under elevated CO2, larval barramundi were attracted to the wrong sounds - sounds found on cold water reefs (which are not the correct habitat for barramundi) and artificial sounds.

This could lead to the larvae ending up in the wrong habitat or in places where they cannot survive. This could in turn have a significant impact on fisheries and coastal ecosystems.

While some larvae depend on other factors, including odor plumes, as well as sounds to orient themselves, earlier research has also shown that ocean acidification also alters behavioral responses to these physical and chemical cues.

The research raises questions about future fish populations in areas with unnatural sounds. Will some species be more attracted, for example, to areas where there are a lot of human structures and sounds, such as harbors and oil platforms, in the future?