The winged snail Clione limacina, a small mollusc floating in the water, is able to go without food for a whole year. Investigations at the Alfred Wegener Institute for Polar and Marine Research demonstrate that the snail’s ability to survive extended periods without nutrition is based on a combination of an extremely low metabolic rate, the breakdown of body cells and the utilisation of special lipids. The unusual fat molecules are also stored in the outer dermal layers, where they probably have an antibacterial function.
In the oceans, winged snails can occur in high abundances, and they represent an important link in the marine food chain. The wing-like protrusions that have given the snails their name enable them to float in the water column. Together with numerous other animal species drifting in the current they constitute the zooplankton. The winged snail Clione limacina lives in oceans of temperate latitudes and in the Arctic. It feeds exclusively on another species of winged snail, Limacina helicina, which, in turn, consumes microalgae. The extreme degree of diet specialisation and the often uneven distribution of predator and prey in the ocean can lead to extended periods of starvation.
Special lipids to survive
Laboratory investigations at the Alfred Wegener Institute have shown that Clione synthesises substantial amounts of rare so-called ether lipids. “We were able to demonstrate that these ether lipids function as a long-term energy depot. During periods of starvation, they are metabolised much more slowly than triacylglycerols which occur more frequently in nature”, explains Dr Marco Böer. “In addition to that, the Arctic winged snail has by far the lowest metabolic activity of all marine invertebrates.” Not only are the high-energy lipids depleted during extended periods of starvation, but the snails also begin consuming their own body mass, shrinking in the process. As soon as the vegetarian sibling Limacina is available again, Clione takes advantage of the food and restocks its reserves. Up to 80 percent of the food is metabolized. Other marine animals often use only 20 percent.
Chemical defense against predators
Further investigations have revealed that ether lipids are embedded as droplets in the skin of the animals. In this location, these specialised lipids probably function in chemical defence against parasites. Similarly, the snail produces other chemical compounds, rare in the animal kingdom, to protect against predation. Pteroenone represents one of the molecules turning the snail into a distasteful bite for fish and other predators.
Nowadays, however, the survival of Clione limacine is threatened for completely different reasons. With globally increasing carbon dioxide concentrations, the oceans’ acidity is also on the rise. Even in the near future, this may prevent shell formation in Limacina helicina. With the disappearance of its only food source, Clione loses the base of its existence. The extinction of both winged snails would have consequences for the whole food web as both species represent important members of the food chain in the Arctic Ocean.
Bremerhaven, February 14, 2006
Your contact persons in the department 'Chemical Ecology' are: Prof. Gerhard Kattner und Dr. Martin Graeve
