Ecophysiological aspects of cardiac activity in the subtropical mussel Perna viridis (L.) (Bivalvia: Mytilidae)

Cardiac activity in the subtropical mytilid mussel Perna viridis was monitored to assess the influence of various endogenous and exogenous parameters. Temperature had a positive, significant, effect on heart rate; the Q(10) ranged from 2.5 to 2.6. Salinity, over a wide range (15-35parts per thousand), had no significant influence on heart rate reflecting the species' euryhalinity. Reduced oxygen tensions, either induced by emersion or seawater hypoxia, elicited rapid, significant, bradycardia. Positive inotropisms (indicative of greater heart output) were evident during seawater hypoxia and may represent an energetically advantageous mechanism of reducing heart rate while increasing stroke volume to maintain haemolymph circulation to organs associated with digestion and basal metabolism. Malnourishment for 14 days did not affect heart rate. The heart rate of larger mussels was slower than those of smaller individuals. Gender-based differences in R viridis' heart rate were not present. No diurnal (24 h) variation in cardiac activity was evident while mussels were exposed to relatively stable, immersed conditions. Heart rate plasticity often reflected the ambient environmental conditions and such a flexible physiological response may partly explain the species' dominance in transitional, polluted harbours. (C) 2002 Elsevier Science B.V. All rights reserved.