Shell shape, dysodont tooth morphology, and hinge-ligament thickness in the bay mussel Mytilus trossulus correlate with wave exposure

We examined the shell morphology of the bay mussel Mytilus trossulus (Gould ) at six locations with various levels of wave exposure in Barkley Sound on the west coast of Vancouver Island, British Columbia, Canada. Young adult M. trossulus (29-35 mm shell length) collected from wave-exposed sites disp layed striking differences in shell morphology from M. trossulus from shelt ered sites. Mytilus trossulus from wave-exposed habitats had a lower shell height/shell width ratio and a thicker shell; they also had higher, more ro bust dysodont teeth, as well as a thicker hinge ligament. Examination of ju veniles (12-14 mm shell length) collected from a wave-exposed shore and a s heltered shore separated by only a few hundred metres displayed similar dif ferences in shell morphology and ligament thickness. These observations sug gest that wave exposure is the cause of the observed differences in shell m orphology and ligament thickness in M. trossulus. This is the first report of a correlation between wave exposure and morphology of the dysodont teeth and ligament in a bivalve. We discuss potential selective pressures that m ay favor characteristics of wave-exposed shells, including the probability of dislodgment and misalignment of valves in high wave energy areas.