HSP70 levels in physiologically stressed Baltic Sea mussels

Mussels, Mytilus edulis L., from the Baltic Sea were exposed to stressful cadmium and temperature environments. The expression of the 70 000 kD heat shock protein family (HSP70) and of several organismal responses was observed in two phases. Mussels exposed to 20 °C for one day had higher levels of HSP70 than controls at 4 °C, with 20 μg litre−1 cadmium or without cadmium. The higher temperature increased respiration and ammonia excretion and decreased clearance rate and scope for growth. In the second phase, mussels pretreated at 20 °C for 5 days and reacclimated to 4 °C for 5 days still showed significantly elevated HSP70, with 20 μg litre−1 cadmium and without cadmium. The organismal responses in the second phase were much less affected by treatment, although scope for growth declined in pretreated animals exposed to cadmium. HSP70 seems to be a suitable indicator of both present and recent stress. A functional relationship between HSP70 levels and adaptation to heat and cadmium is suggested but not established.