Title:

Energetic consequences of inducible defenses to invasive green crab (Carcinus maenas) predation in blue mussels (Mytilus edulis)

Blue mussels (Mytilus edulis) exhibit inducible defenses, or phenotypic plasticity in the presence of predators that varies with predator identity and environmental context. In the Western Gulf of Maine, mussels exposed to invasive green crabs (Carcinus maenas) and native sea stars (Asterias spp.) develop distinct defensive traits: sea stars primarily induce changes in abductor muscle morphology, whereas green crabs typically alter shell thickness and shape. Our work shows that mussels from wave-protected sites with abundant green crabs possess thicker shells and larger adductor muscles than mussels from wave-exposed sites with fewer crabs, phenotypes that increase handling time for the sea star A. forbesi. These findings suggest that trait expression does not occur through simple trade-offs, indicating that energetic costs may be allocated from other physiological processes. Building on this foundation, we will test whether predation pressure from C. maenas constrains reproductive investment in M. edulis, a species experiencing significant population declines and recruitment failure. We will combine field sampling across gradients of crab density with controlled laboratory experiments isolating the effects of crab chemical cues on gonad development. This research will determine whether inducible defenses impose hidden reproductive costs and clarify how shifting predator–prey interactions influence marine invertebrate resilience in a rapidly changing Gulf of Maine.

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