ABSTRACT: Environmental temperature is a controlling factor in ecology and is influenced by global climate change. Upper/lower thermal limits for 10 species of sessile/sedentary invertebrates were established on a single rocky shore. Two species withdifferent reproductive strategies (Littorina littorea, Nucella lapillus) from 3 Scottish and 3 Irish shores were investigated to test effects of small scale (<10 km) or larger scale (ca. 500 km) distances, and shore height on upper lethaltemperature. At 3 sheltered and 3 exposed shores in Ireland, thermal responses of N. lapillus from the middle of their vertical distribution were compared. Amongst the 10 species from a single shore, thermal niche width rose asymptotically withmaximum height of distribution on the shore and maximum emersion time. Median upper lethal temperature and median lower lethal temperature were closely correlated. For 8 species on the middle and upper shore, there were significant linear relationshipsbetween shore height and the variables upper lethal temperature, lower lethal temperature and thermal niche width. L. littorea upper lethal temperature was found not to vary with shore height, varied little over small geographical distances, butwas significantly higher in Ireland than in Scotland. N. lapillus upper lethal temperature was higher in animals collected from the upper limit of distribution on the shore than in dogwhelks from the lower limit of distribution, was higher inanimals taken from sheltered shores than from exposed shores and showed significant local differences. Upper lethal temperature was higher in Scottish than Irish dogwhelks.