Increased CO2 levels make fish unafraid of predators

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Fish on a remote coral reef in the South Pacific have altered their behavior, as acidification of the ocean changes their natural habits, making them attracted to the smell of their predators and unafraid of approaching them.

The research, carried out at an isolated "natural laboratory" off the coast of Papua New Guinea, where coral reef waters are made acidic by the natural carbon dioxide seeping from the ocean bed, found small fish were attracted to their predators, instead of avoiding them.

"They are more active and display riskier behaviors, venturing further away from shelter, which makes them even more vulnerable to predators," Professor Philip Munday, from the ARC Center of Excellence (CoE) for Coral Reef Studies at James Cook University, told Reuters on Monday.

The report found the location ideal for studying how fish and other coral reef species may respond to the extent of ocean acidification forecast for the next 50-80 years.

"We've found fish living in those conditions similar to what we predict in the second half of the century. Their behavior is fundamentally altered and impaired such that we see they've become attracted to odors they'd normally avoid," Munday said.

Close to the seeping carbon dioxide, there is no coral growth, but further away lies a unique coral reef zone with carbon dioxide levels similar to risig levels predicted to be ocean-wide by the end of the century.

Munday said an important part of the study was that the fish take their time adjusting within a lifetime to higher CO2 levels.

The findings of the study and the likely changes to the food chain will be of concern to millions in the tropics who depend on coral reefs for food security and livelihoods.

The collaboration involving the Coral CoE, Australian Institute of Marine Science, Georgia Institute of Technology and the National Geographic Society is the first to shift out of the science laboratory and into the natural environment to study the effects of ocean acidification on fish.

REUTERS