Influence of Pretreatment with Constant and Changing Temperatures on Heat and Freezing Resistance in Gill-Epithelium of the Mussel Mytilus edulis

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Abstract
The influence of constant and changing temperatures (CT) and of different salinities on heat and cold resistance of the ciliary epithelium of the common mussel M. edulis from different biotopes were investigated. Reasonable heat adaptation can only be obtained with mussels of the North and Baltic Seas in low salinity, not in high salinity. Re-adaptation to high and to low adaptation temperatures (AT) requires the same period of time; it is completed after 3 d [days]. Mussels were placed abruptly into water of different temperatures; initially this resulted in high standard deviations. The same response was obtained in CT in high salinities, but no heat adaptation was demonstrable. Periodic changes in temperature (12 h 8.degree. C, 12 h 20.degree. C) result in increased heat resistance; a new level is reached after 3 d; its value correlates with high AT. Standard deviations do not decrease. This was the same with 6-h periodic changes. Resistance to freezing correlates with constant AT. Abrupt single changes in a 12-h rhythm present a particular load, which initially leads to increased heat resistance and sensitivity to cold, and which shortens the life span of unfed individuals.