Marine food web at risk from rising CO2 levels in water – ‘Fish become bolder, and they venture further away from safe shelter, making them more vulnerable to predators’

By Oliver Milman
13 April 2014
(theguardian.com) – A study by the Australian Institute of Marine Science, James Cook University and the Georgia Institute of Technology found the behavior of fish would be “seriously affected” by greater exposure to CO2. Researchers studied the behavior of coral reef fish at naturally occurring CO2 vents in Milne Bay, in eastern Papua New Guinea. They found that fish living near the vents, where bubbles of CO2 seeped into the water, “were attracted to predator odour, did not distinguish between odours of different habitats, and exhibited bolder behaviour than fish from control reefs”. The gung-ho nature of CO2-affected fish means that more of them are picked off by predators than is normally the case, raising potentially worrying possibilities in a scenario of rising carbon emissions. More than 90% of the excess CO2 in the atmosphere is soaked up by the oceans. When CO2 is dissolved in water, it causes ocean acidification, which slightly lowers the pH of the water and changes its chemistry. Crustaceans can find it hard to form shells in highly acidic water, while corals risk episodes of bleaching. The AIMS study found the diversity of fish at the CO2 vents was not influenced by the extra carbon, but that fish’s nerve stimulation mechanisms were altered, meaning the smell of predators became alluring. “What we have now also found in our study of fish behaviour in this environment is that the fish become bolder and they venture further away from safe shelter, making them more vulnerable to predators,” said Alistair Cheal, co-author of the research. [more]