Behavioural responses to predators in Mediterranean mussels (Mytilus galloprovincialis) are unaffected by elevated pCO2

Ocean acidification is expected to affect marine organisms in the near future. Furthermore, abrupt short-term fluctuations in seawater pCO(2) characteristic of near-shore coastal regions and high-density aquaculture sites currently have the potential to influence organismal and community functioning by altering animal behaviour. While anti-predator responses in fishes exposed to elevated pCO(2) are well documented, such responses in benthic marine invertebrates are poorly studied. We used high frequency, non-invasive biosensors to test whether or not short term (3-week) exposure to elevated pCO(2) could impact behavioural responses to the threat of predation in adult Mediterranean mussels from Galicia on the northwestern coast of Spain. Predator alarm cues (crushed conspecifics) resulted in a prolonged (1 h) reduction in the degree of valve opening (-20%) but had no clear effect on overall valve movement activity, while elevated pCO(2) did not affect either response. Our results add to the increasing body of evidence suggesting that the effects of end-of-century pCO(2) levels on marine animal behaviour are likely weak. Nonetheless, longer-term exposures spanning multiple generations are needed to better understand how ocean acidification might impact behavioural responses to predation in marine bivalves.