MeGaH: a novel system for concurrent measurement of metabolic rate, valve gape and heart rate in aquatic bivalves, and its application in assessing mussel responses to environmental change

Aquatic bivalves provide valuable ecosystem services and include blue mussels (Mytilus spp.), which are used as a model system for exploring speciation, hybridisation, range expansion and physiology. Here, we present a novel system (MeGaH) for the concurrent monitoring of metabolic rate, valve gape and heart rate in aquatic bivalves. We demonstrate the utility of the system using the response of Mediterranean blue mussels (Mytilus galloprovincialis) to changes in temperature. Stark differences in mussel responses to increased temperature were observed, depending on whether analysis was designed to include all data generated during temperature exposures, or if data pertaining to periods when mussels were open or closed were analysed separately. Our results highlight the importance of measuring valve gape alongside metabolic rate and/or heart rate, to provide context regarding the physiological status of the mussel, and discover responses that are not observable by independent measurement of individual parameters.