Simultaneous,
long-term monitoring of valve and cardiac activity in the
blue mussel Mytilus edulis exposed to copper
T. M. Curtis , R. Williamson , M. H.
Depledge A2
A1 Marine Biological Association of the UK
Laboratory, Citadel Hill, Plymouth PL1 2PB, Devon,
England
A2 Plymouth Environmental Research
Centre, University of Plymouth, Plymouth PL4 8AA, Devon,
England
Abstract:
Abstract 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 (S0.8 M) progressively
reduced the correlation between valve activity and heart rates
(r = 0 for individuals dosed with S6.3 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.
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