Simultaneous, long-term monitoring of valve and cardiac activity in the blue mussel Mytilus edulis exposed to copper
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Valve and cardiac activity were simultaneously measured in the blue mussel (Mytilus edulis) in response to 10 d copper exposure. Valve movements, heart rates and heart-rate variability were obtained non-invasively using a Musselmonitor® (valve activity) and a modified version of the Computer-Aided Physiological Monitoring system (CAPMON; cardiac activity). After 2 d exposure of mussels (4 individuals per treatment group) to a range of dissolved copper concentrations (0 to 12.5 M as CuCl2) median valve positions (% open) and median heart rates (beats per minute) declined as a function of copper concentration. Heart-rate variability (coefficient of variation for interpulse durations) rose in a concentration-dependent manner. The 48 h EC50 values (concentrations of copper causing 50% change) for valve positions, heart rates and heart-rate variability were 2.1, 0.8, and 0.06 M, respectively. Valve activity was weakly correlated with both heart rate (r = 0.48 ± 0.02) and heart-rate variability (r = 0.32 ± 0.06) for control individuals (0 M Cu2+). This resulted from a number of short enclosure events that did not coincide with a change in cardiac activity. Exposure of mussels to increasing copper concentrations (≥0.8 M) progressively reduced the correlation between valve activity and heart rates (r = 0 for individuals dosed with ≥6.3 M Cu2+), while correlations between valve activity and heart-rate variability were unaffected. The poor correlations resulted from periods of valve flapping that were not mimicked by similar fluctuations in heart rate or heart-rate variability. The data suggest that the copper-induced bradycardia observed in mussels is not a consequence of prolonged valve closure.
KeywordsHeart Rate Copper Concentration Cardiac Activity Blue Mussel Valve Closure
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