Non-native crustacean predators conditionally trigger inducible defense behaviors in blue mussel

Climate change is driving the poleward expansion of many species, including the Atlantic blue crab (Callinectes sapidus), whose northern range now extends into the Gulf of Maine. As a recently arrived predator, the blue crab may pose a threat to native prey communities already impacted by the earlier introduction of the European green crab (Carcinus maenas). This study investigates the defensive capacity of native blue mussels (Mytilus edulis) in response to 45 h of exposure to chemical cues of blue versus green crabs. Mussels were hypothesized to invest more energy in defensive behaviors in response to green crab cues, owing to a longer shared ecological history in the Gulf of Maine. The results support this hypothesis: female blue mussels exposed to green crab cues spawned, and small mussels exhibited increased relocation behavior. In contrast, exposure to blue crab cues did not alter mussel reproductive, movement, or attachment behaviors. Notably, neither treatment significantly affected mussel attachment as measured by byssal thread quantity and tenacity, suggesting that this behavior may not be a primary defense mechanism against crab predators in this context, contrary to previous findings. These findings underscore the importance of understanding species- and size-specific interactions as expanding ranges and species introductions continue to reshape predator-prey dynamics across coastal ecosystems.