Ocean acidification robs reef fish of their fear of predators

This finding from a collaboration among scientists from the Australian Institute of Marine Science (AIMS), James Cook University, the National Geographic Society and the Georgia Institute of Technology is particularly concerning not just for conservationists but for fisheries around the world and other industries dependent on the survival of fish species.

"We found that living in an acidic environment makes small reef fish become attracted to the smell of their potential predators. Their sense of smell was acutely affected in CO₂-rich waters in ways that gravely threaten their survival," said AIMS scientist, Alistair Cheal.

The team is studying coral reefs next to natural seeps where carbon dioxide bubbles are made by volcanic activity under the seabed. When CO₂ from the atmosphere dissolves in water, it causes ocean acidification, slightly lowering the pH of the water and changing its carbonate chemistry. This in turn makes it harder for a range of marine animals to survive, for example, crustaceans find it difficult to form their shells and skeletons.

"What we have now also found in our study of fish behavior in this environment is that the fish become bolder and they venture further away from safe shelter, making them more vulnerable to predators," added Mr Cheal.

The scientists also found that fish cannot adjust to rising carbon dioxide levels over time, causing concern for their ability to adapt as more CO₂ dissolves in the oceans over the next few decades.

Over the past five years AIMS researchers have been studying the area, which is the only known CO₂ seep site in coral reef ecosystems in the world. The scientists are, in effect, studying a snapshot of our coral reefs in decades to come if CO₂ levels in the atmosphere continue to rise.