MEPS 371:191-198 (2008)  -  doi:10.3354/meps07698

Simultaneous defense against shell entry and shell crushing in a snail faced with the predatory shorecrab Carcinus maenas

Timothy C. Edgell1,4,*, Christian Brazeau2, John W. Grahame3, Rémy Rochette1

1Department of Biology, University of New Brunswick, Saint John, New Brunswick E2L 4L5, Canada
2Department of Biology, McGill University, Montréal, Québec H3A 1B1, Canada
3Institute of Integrative & Comparative Biology, University of Leeds, Leeds LS2 9JT, UK
4Bamfield Marine Sciences Centre, Bamfield, British Columbia V0R 1B0, Canada

ABSTRACT: Prey with versatile predators need diverse defenses. Such an example of a versatile predator is the voracious European green crab Carcinus maenas. Green crabs prey on snails by either crushing shells or, when shells are too tough to break, by extracting flesh through the shell opening (aperture). Among populations in the northwest Atlantic, the claw size of green crabs (an indicator of crushing strength) co-varies with shell mass of the intertidal snail Littorina obtusata (mass is an indicator of a shell’s crushing resistance); thus shell-crushing predation appears to be an important part of the predator–prey interaction. We report that aperture occlusion and soft tissue withdrawal depth (two shell-entry defenses) of L. obtusata snails co-vary with their shell mass (an anti-crushing trait) among populations. When snails were fed directly to green crabs in the laboratory, populations with smaller shell openings and deeper withdrawal depths were less frequently killed by shell-entry attacks, and these same populations, with more massive shells, were also better at resisting shell-crushing attacks. Results provide compelling evidence that greater shell mass, a smaller shell opening, and deeper withdrawal depth are adaptive traits for snails faced with green crab predators. Furthermore, results suggest that American L. obtusata responded to the introduction of green crabs by escalating both anti-crushing and anti-entry defenses.

KEY WORDS: Predator–prey · Invasive species · Biogeography · Functional morphology · Adaptation · Rocky intertidal

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Cite this article as: Edgell TC, Brazeau C, Grahame JW, Rochette R (2008) Simultaneous defense against shell entry and shell crushing in a snail faced with the predatory shorecrab Carcinus maenas. Mar Ecol Prog Ser 371:191-198

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