Separate and combined effects of boat noise and a live crab predator on mussel valve gape behavior

We exposed mussels to different types of predator cues from shore crabs and playback of boat noise or ambient control. Mussels reduced their valve opening in response to boat noise and a free-ranging predator. Valve opening is an indicator of food intake and comparative impacts of predators and noise yields insight into fitness consequences on mussels. Noisy human activities at sea are changing the acoustic environment, which has been shown to affect marine mammals and fishes. Invertebrates, such as bivalves, have so far received limited attention despite their important role in the marine ecosystem. Several studies have examined the impact of sound on anti-predator behavior using simulated predators, but studies using live predators are scarce. In the current study, we examined the separate and combined effects of boat sound playback and predator cues of shore crabs (Carcinus maenas) on the behavior of mussels (Mytilus spp.). We examined the behavior of the mussels using a valve gape monitor and scored the behavior from the crabs in one of two types of predator test conditions from video footage to control for effects from potential, sound-induced variation in crab behavior. We found that mussels closed their valve gape during boat noise and with a crab in their tank, but also that the stimulus combination did not add up to an even smaller valve gape. The sound treatment did not affect the stimulus crabs, but the behavior of the crabs did affect the valve gape of the mussels. Future research is needed to examine whether these results stand in situ and whether valve closure due to sound has fitness consequences for mussels. The effects on the well-being of individual mussels from anthropogenic noise may be relevant for population dynamics in the context of pressure from other stressors, their role as an ecosystem engineer, and in the context of aquaculture.

Automated summary

This study investigated the effects of boat noise and shore crabs' predator cues on mussel behavior. Mussels responded to boat noise and free-ranging predators by reducing their valve opening. Valve opening serves as an indicator of food intake, and the impacts of predators and noise provide insights into mussel fitness consequences. Despite the important role of invertebrates, such as bivalves, in the marine ecosystem, they have received limited attention compared to marine mammals and fishes affected by human activities.