Morphology of the foolish mussel(Mytilus trossulus) : variation and defense

Mussels (Mytilus spp.) are dominant members of the rocky intertidal ecosystem, where interactions with predators and competitors are well documented. However, little is known about how variation in defensive morphological traits of mussels affects the outcome of interactions, or how predation affects the variation observed. In this thesis, I show that morphological diversity in foolish mussels (M trossulus) in Howe Sound, British Columbia, is potentially important to interactions with mussel predators of the rocky intertidal community. Byssal attachment strength is positively related to the presence of crab and seaduck predators, but variation in several other morphological features is not easily attributable to predators. In addition, I experimentally demonstrate that seastars preferentially consume mussels with uneven shell margins and small crabs preferentially consume thinner-shelled mussels. However, large crabs either have no preference, or consume more thick-shelled mussels. Finally, I review the concepts of keystone species and trait-mediated indirect interactions, and make the case that traitmediated interactions impact the structure and dynamics of the Howe Sound rocky intertidal community.