Influence of predation on shell morphology of Buccinum undatum L. on Atlantic coast of Canada

Abstract

Striking differences were found in the morphology of the boreal neogastropod Buccinum undatum L. among populations in the northern Gulf of Saint Lawrence, in Maces Bay in the Bay of Fundy, and in Kennebecasis Bay in the Saint John River estuary, eastern Canada. The Kennebecasis Bay whelks had the thinnest shells and in the laboratory were rapidly consumed by lobster with no evidence of size selection, whereas the Maces Bay whelks had the most robust shells and were slowly attacked by lobster with smaller individuals being selected first. Similar results were obtained for crabs, except that intermediate-sized Maces Bay whelks were selected. We postulate that the increased shell thickness and elongated apertures of the Maces Bay whelks are adaptations to lobster and crab predation at this site, whereas the thinner shells of Kennebecasis Bay and Gulf whelks reflects decreased crustacean predation. The smaller rounder apertures of the Gulf whelks, compared with the Maces Bay whelks, could be an adaptation to increased seastar predation, but the relative aperture size was even smaller in Kennebecasis Bay where seastars were absent. The very low incidence of the violent escape response in Maces Bay whelks and its absence in Kennebecasis Bay whelks is surprising and may indicate that seastars have little impact on these whelk populations.