Geographical variation in heat coma temperatures in Littorina species (Mollusca : Gastropoda)

Upper critical thermal limits were measured as heat coma temperatures in Li ttorina species (Mollusca: Gastropoda) from sites around the British Isles. Thermal tolerance was found to be stable within a population but extensive variation occurred between populations and species. The majority of specie s examined displayed heat coma values of around 30 degreesC and did mot sho w a positive correlation with shore height. The highest capacity for therma l tolerance was found along the coast of South Wales, while the lowest was found on the south-west coast of Ireland and on the east coast of Scotland.