Field and culture observations on Coelocladia arctica (Fucophyceae): growth and reproduction in relation to temperature

Abstract

Coelocladia arctica (Fucophyceae) is most often reported from arctic and subarctic environments with few records from temperate areas. Young vegetative macrothalli of C. arctica are indistinguishable from similar stages in the type species of Stictyosiphon, S. adriaticus. Later stages of C. arctica, with divisions in the cortical cells formed prior to formation of sporangial filaments, are indistinguishable from initial plurilocular sporangia development in Stictyosiphon, for example in S. soriferus. These morphological similarities may explain the very rare reports of this species outside the arctic and subarctic environments. Temperature gradient experiments with one strain from Baffin Island (arctic) and one from Greenland (subarctic) show that their upper survival temperature, their ability to form macrothalli, and the characteristic sporangial filaments are almost identical. The Baffin Island strain, however, seems to adjust its reproduction to the hostile arctic environment in being able to liberate and germinate swarmers only at temperatures from c. 4 to 13°C. In both cases the optima for growth and reproduction, as determined by laboratory experiments, lie far above the temperature conditions experienced by this species in nature.