Predator-Prey Interactions in the New England Intertidal Zone: Possible Induced Shell Thickening in the Common Periwinkle Littorina littorea in Respone to the Asian Shore Crab, Hemigrapsus sanguineus

Abstract

Hemigrapsus sanguineus, also known as the Asian shore crab, began to invade the Northwestern Atlantic in the 1980’s and interferes with the existing food web of the rocky intertidal zone. The crabs prey upon primary consumers such as Littorina littorea, the Common periwinkle. The objective of this study is to determine whether H. sanguineus induces changes in shell morphology in L. littorea. Two hypotheses were tested: 1) shell thickness increases and 2) more force will be required to crush the shells in response to the presence of the crab. During the first stage the 43 L. littorea from two locations were separated in three 10-gallon tanks for 187 days. The control had solely L. littorea (n=16), the second tank had L. littorea (n=12) and free-roaming H. sanguineus (n=6), and third tank had L. littorea (n=15) and H. sanguineus in enclosed containers (n=6). For the second stage, the thicknesses of the shells were measured at predetermined points and the shells were crushed using a loading frame. The data show that there are significant differences in the change in shell thickness, peak load of crushing force and modulus between the New Hampshire and Maine snail populations. The average thickness of the shells at one point differed by treatment although most of the observed variation was between locations.