Acid oceans threaten jumping snail

A humpback conch snail (L) leaps backwards away from the predatory marbled cone (R)
Image: Courtesy of Sue-Ann Watson

FOR IMMEDIATE RELEASE Carbon emitted into the atmosphere is helping to make the oceans more acid, and that’s not good news for some of the species that live there. LONDON, 9 January – A submarine snail with an unexpected talent for the high jump could be one of the great losers in a warmer, carbon dioxide-rich world. The conch snail Gibberulus gibberulus gibbosus is a gastropod that is notoriously nimble on its single foot. When it scents danger from its biggest predator, the marbled cone shell, it takes what is (for a snail) a great leap backward and slightly sideways out of danger from the attacker’s poisoned dart. In July last year it demonstrated an unexpected ability to stay cool and leap out of harm’s way even when the seawater had warmed to near lethal levels. But, according to new research published in the Proceedings of the Royal Society B, the great challenge for the spring-loaded conch snail is not likely to be a warmer ocean, but a more acidic one. As carbon dioxide levels rise, the seas have become more acidic. Surface sea water’s pH – a measure of acidity – is lower and 30% more acidic than it was 200 years ago, at the start of the Industrial Revolution. The rate of change in this acidity is about 100 times faster than at any period in the last 650,000 years. This is almost certain to create problems for reef corals, and for molluscs that exploit the water’s chemistry to build their primary defence, the shell. But according to Sue-Ann Watson of Australia’s Centre of Excellence for Coral Reef Studies, this increasing acidity is also likely to play havoc with the conch snail’s nervous system. She and colleagues tested Gibberulus in laboratory tanks that held water at the pH levels expected in the decades to come and found that the chemistry of the water had a serious effect on snail behaviour.

Delayed response

The number of snails that jumped to escape a predator fell by half, those that did jump were slower to leap out of danger, and when they did, they used a different escape trajectory. It wasn’t a question of physical ability: what had happened was that the snail’s decision-making capacity had become impaired. In the unforgiving world of predator and prey, a slow-to-respond conch snail is likely to become a soft target; in hunter’s parlance, a sitting duck. That the nervous systems of the little laboratory snails were impaired became much clearer when researchers treated the test tank water with gabazine, a natural chemical that helps the functioning of the neurotransmitter receptors in the creature’s response machinery. Once this had been applied, Gibberulus started behaving more normally. This research echoes earlier studies in California and in Sweden of the effects of changed pH levels on the learning behaviour of juvenile rockfish, and the digestive systems of sea urchins. There too, experiments showed that some kind of nervous system interference was at work. “This neurotransmitter receptor is common in many animals and evolved quite early in the animal kingdom”, said Göran Nilsson of the University of Oslo, one of the authors. “So what this study suggests is that human carbon emissions directly alter the behaviour of many marine animals, including much of the seafood that is part of human diet.” – Climate News Network