Habitat of Polycelis felina (= cornuta) and Crenobia alpina in the British Isles

Abstract

THE few text-books on freshwater biology which refer particularly to the British Isles regard Polycelis felina and Crenobia alpina as stenothermous, stream-dwelling species. Beauchamp1, however, showed that C. alpina inhabited suitable shores of some Cumberland lakes during the winter; but he considered that summer temperatures were too high for their occurrence in lakes at this season. The generally accepted view is that in the British Isles these two species cannot establish themselves where the temperature exceeds 13°–15° C. in the case of C. alpina2,3 and 16°–17° C. for P. felina3. On the Continent, Theinemann4 considered that the widest range of C. alpina and P. felina was 0.7°–15° C. and 0.5°–15.75° C. respectively. It has been reported several times from the Continent that Crenobia alpina is a permanent member of the fauna of Alpine and other mountain lakes where a suitable substratum occurs (for references see Beauchamp1).