January 7, 2014
Carbon Dioxide Emissions Keep Conch Snails From Escaping Predation
Brett Smith for redOrbit.com - Your Universe Online
Conch snails typically use a strong foot-like appendage to leap away from approaching predators. According to the team’s study, published in the Proceedings of the Royal Society B: Biological Sciences, when the snails are exposed to carbon dioxide levels projected for the end of this century they either take longer to jump or they stop jumping altogether.
The study team said higher carbon dioxide concentration and the resulting ocean acidification disrupt a neurotransmitter receptor in the snail’s nervous system, affecting life-and-death decision making. The inability to escape makes the snail more vulnerable to the poisonous dart of the slow-moving marbled cone shell.
“Altered behaviors between predators and prey have the potential to disrupt ocean food webs,” said Sue-Ann Watson, from the ARC Centre of Excellence for Coral Reef Studies (Coral CoE) and James Cook University.
Study author Göran Nilsson, a biologist from the University of Oslo, said this effect of elevated carbon dioxide levels on marine life has also been seen in other animals.
“This neurotransmitter receptor is common in many animals and evolved quite early in the animal kingdom,” Nilsson said. “So what this study suggests is that human carbon dioxide emissions directly alter the behavior of many marine animals, including much of the seafood that is part of the human diet.”
The research team noted that past studies on oceanic carbon dioxide have mostly focused the potential effects to the shells of marine snails and coral exoskeletons. The study revealed that snails may actually face the twin threats of both weaker shells and disrupted survival behaviors.
Study author Philip Munday, a research fellow at Coral CoE, emphasized the importance of studying and and understanding more about the scope of these behavioral disturbances. He also questioned if sea creatures can adapt quick enough to survive rising carbon dioxide levels and ocean acidification.
Another study published by the Proceedings of the Royal Society B: Biological Sciences in December found that rising ocean acidity levels increase anxiety in juvenile rockfish.
Using a camera-based tracking software system, the study researchers compared a control group of rockfish kept in normal seawater to another group in waters with elevated acidity levels matching those projected for the end of the century. They measured each group’s preference to swim in light or dark areas of a testing tank, which is a known test for anxiety in fish.
The researchers found out that normal juvenile rockfish continuously moved between the light and dark areas of the tank. However, experiments have shown that fish administered with an anxiety-inducing drug (anxiogenic) prefer the darker area and seldom venture into the light, an indication that dark-preference is a sign of increased anxiety in juvenile rockfish.
Next, the researchers found that rockfish exposed to acidified ocean conditions for one week also preferred the dark area of the tank, indicating they were significantly more anxious than their normal seawater counterparts.
The study team said the anxiety is traced to the fish’s sensory systems, specifically “GABAA” (neural gamma-aminobutyric acid type A) receptors, which are also involved in human anxiety levels. Exposure to acidified water leads to changes in the concentrations of ions in the blood, which reverses the flux of ions through the GABAA receptors. The end result is a change in neuronal activity that is reflected in the altered behavioral responses described in this study.