Ocean acidification makes killer cone snails hyperactive and too impatient to hunt

Snails moved around three times faster when exposed to the carbon-dioxide levels we are expected to reach by the year 2100. Predatory cone snails live in coral reefs and use a venomous harpoon in order to catch their prey. Although the snails became much faster when their environment became more acidic, they didn't get better at catching prey – in fact, they actually got a lot worse.

Increased atmospheric carbon dioxide means that more carbon dissolves in the seas, where it causes acidification. The effect of rising carbon-dioxide levels in the atmosphere on species such as the cone snail has so far been largely unknown.

Speedier, but much less efficient

Researchers at James Cook University in Australia exposed cone snails to realistic projected future levels of carbon in seawater, with the results featured in the journal Biology Letters. The cone snails sped up from an average speed of 4 millimetres a minute to 12 mm a minute. This species of cone snail, Gibberulus gibberulus gibbosus, measures between about 30mm and 70mm.

Cone snails in the equivalent of today's seas caught their prey around 60% of the time in the experiment. The hyperactive snails in the more acidic water only caught their prey around 10% of the time.

"Although an increase in distance covered might be expected to increase foraging success, predators were no closer to their prey at the end of the 15-minute trial," the authors wrote in the paper.

Too impatient to hunt

The cone snails in the more acidic water spent less than a third of the time buried in sandy compared with the control snails. Snails tend to catch their prey by submerging themselves in a coral reef's sandy floor, and then shooting out their venomous harpoons. Too much time racing around and not enough lying in wait for prey is thought to be the reason for the snails' lack of hunting success in acidic waters.

This is clearly bad news for predatory cone snails, but it could also have a disruptive effect on their marine ecosystem.

"Combined evidence that the behaviours of both species in this predator-prey relationship are altered by elevated carbon-dioxide suggests food-web interactions and ecosystem structure would become increasingly difficult to predict as ocean acidification advances over coming decades," the authors wrote.