TEMPERATURE REQUIREMENTS FOR GROWTH AND SURVIVAL OF MACROALGAE FROM DISKO ISLAND (GREENLAND)

The temperature requirements for growth and upper temperature toleranc e were determined in 16 macroalgal species collected on Disko Island ( Greenland). The upper survival temperatures were examined in 1-degrees -C steps, and growth measured at 5-degrees-C intervals between 0 and 2 0-degrees-C using a refined method, where the fresh weight was determi ned weekly or fortnightly over a period of 5 or 6 weeks. To express te mperature-growth responses, growth rates of temperature-acclimated pla nts were taken. Two groups with different temperature requirements wer e identified: (1) A stenothermal group including Acrosiphonia arcta, A crosiphonia sonderi, Urospora penicilliformis, Devaleraea ramentacea, Desmarestia aculeata, Pilayella littoralis, growing between 0 and (10 to) 15 (or 20)-degrees-C with optima between 0 and 10-degrees-C. The u pper survival temperatures in these species and in Chromastrum secunda tum, Chromastrum virgatulum, Chordaria flagelliformis were between 17 and 23-degrees-C (duration of experiment: 2 weeks). (2) A eurythermal group including Enteromorpha clathrata, Enteromorpha intestinalis and Polysiphonia urceolata growing between 0 and 20-degrees-C with growth optima at 10 or 15-degrees-C. The upper survival temperatures in these species and in Chaetomorpha tortuosa, Bangia atropurpurea and Eudesme virescens were between 24 and 31-degrees-C. These algal species showe d little adaptation to the Arctic temperatures. In contrast, algae fro m the first group exhibited a relatively high adaptation to low temper atures - approaching the low temperature requirements of Antarctic alg ae. The results are discussed in relation to the geographic distributi on of individual species.