Thermal ecotypes of amphi-Atlantic algae. 1. Algae of Arctic to cold-temperate distribution (Chaetomorpha melagonium, Devaleraea ramentacea and Phycodrys rubens )

Three species of Arctic to cold-temperate amphi-Atlantic algae, all occurring also in the North Pacific, were tested for growth and/or survival at temperatures of -20 to 30 degree C. When isolates from both western and eastern Atlantic shores were tested side-by-side, it was found that thermal ecotypes may occur in such Arctic algae. Chaetomorpha melagonium was the most eurythermal of the 3 species. Isolates of this alga were alike in temperature tolerance and growth rate but Icelandic plants were more sensitive to the lethal temperature of 25 degree C than were more southerly isolates from both east and west. With regard to Devaleraea ramentacea , one Canadian isolate grew extraordinarily well at -2 and 0 degree C, and all tolerated temperatures 2-3 degree C higher than the lethal limit (18-20 degree C) of isolates from Europe. Concerning Phycodrys rubens , both eastern and western isolates died at 20 degree C.