AIMS researchers found that fish near a natural CO2 vent were not as scared of predators as their colleagues from more alkaline water: “Ocean Acidification robs reef fish of their fear of predators”.

They compared populations in reefs with normal pH levels with those near the vent. I note this line in the abstract didn’t make it to the press release:

“Contrary to expectations, fish diversity and community structure differed little between CO₂ seeps and nearby control reefs.”

So the natural laboratory of the vent has biodiversity and a community, despite the “acid” (which is not acidic of course). Milne Bay, I gather, has pH of 7.7.

The abstract points out that there might be a reason why fish are bolder:

“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.”

Less predators, anyone?

So these might be well adapted little fish that suit the natural environment around them? Call the press…

If warming were politically correct, then people might say the fish became more confident. : -)

Indeed shouldn’t we worry that fish in higher pH waters might be too anxious? Apparently, that is not the right question to ask.

Here’s fear inducing press release of the Australian Institute of Marine Science:

Ocean Acidification robs reef fish of their fear of predators

Research on the behaviour of coral reef fish at naturally-occurring carbon dioxide seeps in Milne Bay in eastern Papua New Guinea has shown that continuous exposure to increased levels of carbon dioxide dramatically alters the way fish respond to predators.

Or Jo wonders, does continuous exposure to more predators alter the way the fish respond…

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.

[Science Daily]

More information:

• Ocean acidification happens all the time — naturally
• A little bit less alkalinity could be a good thing for plants and fish
• The chemistry of ocean pH and “acidification” (It’s not acid, but rain is.)

REFERENCE

Philip L. Munday, Alistair J. Cheal, Danielle L. Dixson, Jodie L. Rummer, Katharina E. Fabricius. Behavioural impairment in reef fishes caused by ocean acidification at CO2 seeps. Nature Climate Change, 2014; DOI: 10.1038/NCLIMATE2195