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Aug. 25, 2008

Crab and Snail Species in Arms Race off Coast of
New England

Global warming may give the crab an advantage.

NORTHAMPTON, Mass. – A native and a newcomer to New England waters are engaged in a high-stakes arms race, with the ultimate price – survival – on the line, according to a new Smith College study.

Biologists studying the adaptability of the invasive European green crab to its New England food source, a native snail, found the crab’s claw size increased when it was faced with thick-shelled as opposed to thin-shelled snails, improving the crab’s ability to make the snail its meal.

However, this diet-induced response – an example of a phenomenon called phenotypic plasticity – was affected by water temperature, the researchers reported in the most recent issue of Marine Ecology Progress Series.

Comparing crabs from the warmer water in the southern Gulf of Maine with their neighbors to the north, they found that the warm-water residents developed a relatively larger crusher claw after molting than did the cold-water residents.

Water temperature influenced claw size, in part, through its effects on molting rate, according to the researchers. Crabs in colder water should only molt twice in the time span in which crabs in warm water molt three times.

“Cold waters appear to hinder crushing performance in the northern Gulf of Maine, but as ocean temperatures rise, the crab is predicted to feed more effectively on native prey,” said L. David Smith, associate professor of biological sciences, who collaborated with former graduate student Ashley K. Baldridge, who is now in a doctoral program at the University of Notre Dame.

In the 1980s, researchers noticed a significant increase in shell thickness in the native snail when comparing the time before and after the European green crab’s arrival. Geographic differences in shell thickness of the snail reflect the snail's defensive response to the introduced crab. This study suggests that correlated patterns in the crab's claw size can be explained by the variation in snail shell thickness and water temperature - a relationship that can be characterized as an arms race in a battle for survival.

Support for the project was provided by a Smith College Wilens Fellowship and the Smith College Faculty Development Fund.


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