Evidence of a divergent growth response in the Pacific oyster, Crassostrea gigas, when exposed to native and invasive crab chemical cues

Abstract

Marine invertebrates exhibit a variety of plastic morphological defenses in response to predator chemical cues. Typically, bivalves increase shell mass and strength in order to mitigate predation risk. However, invasive species may give off unfamiliar chemical cues, rendering native prey unable to detect and respond to foreign predators. Nevertheless, some native prey may adapt to recognize foreign predators over relatively short time scales (i.e. decades). The Pacific oyster, Crassostrea gigas, was introduced into Barkley Sound in 1937 and has experienced predation from native predators for nearly 80 years. Little is known about its defence capabilities and how it responds to the invasive European green crab, Carcinus maenas, with which it has coexisted for less than a decade. This offers a unique opportunity to study short-term evolution of defence mechanisms in response to predators over multiple time scales. We conducted a laboratory experiment to test if shell growth of juvenile Crassostrea gigas would be influenced by chemical effluent from native red rock crabs, Cancer productus, and invasive European green crabs, Carcinus maenas. Our results suggest that oysters grown in the presence of Cancer productus produce heavier shells than oysters grown in the presence of Carcinus maenas and controls, although this was not statistically significant. Shell weight increase in response to red rock crabs suggests that Crassostrea gigas may have had time to evolve a response to red rock crabs, but not yet for invasive European green crabs.