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The temperature requirements for growth and upper temperature tolerance were determined in 16 macroalgal species collected on Disko Island (Greenland). The upper survival temperatures were examined in 1 ~ steps, and growth measured at 5~ intervals between 0 and 20 ~ using a refined method, where the fresh weight was determined weekly or fOrtnightly over a period of 5 or 6 weeks. To express temperature-growth responses, growth rates of temperatureacclimated plants were taken. Two groups with different temperature requirements were identified: The upper survival temperatures in these species and inChaetomorpha tortuosa, Bangia atropurpurea and Eudesme virescens were between 24 and 31 ~ These algal species showed little adaptation to the Arctic temperatures. In contrast, algae from the first group exhibited a relatively high adaptation to low temperatures -approaching the low temperature requirements of Antarctic algae. The results are discussed in relation to the geographic distribution of individual species.

The temperature requirements for growth and the upper survival temperatures (USTs) of the Antarctic-Arctic disjunct green alga Acrosiphonia arcta and of the Arctic/cold-temperate A. sonderi (Acrosiphoniales) from several localities within their distribution areas were determined. Ecotypic variation with regard to growth optima as well as survival temperatures was demonstrated in both species. While cold-temperate strains had relatively high or optimal growth rates at 15°C, polar isolates had very low rates at this temperature and showed growth optima between 0 and I0°C. The UST of the polar isolates of A. arcta is 22°C, i.e. slightly lower than those of the coldtemperate strains at 23-25°C. The cold-temperate isolate of A. sonderi survived 25°C, whereas Arctic strains had USTs of 22-24°C. The data indicate that changes in growth responses to temperature as well as small changes in UST can be achieved in relatively short time periods of exposure to low temperatures (3 million years) as exemplified in Arctic populations of A. arcta as well as A. sonderi. The UST of A, arcta (22-25°C) indicate the possibility of dispersal across the equator into the other hemisphere during the Pleistocene lowering of seawater temperatures in the tropics. Growth, however, would not have been possible during passage across the tropics due to the narrow temperature-growth window. Possible migration routes, seasonal development and the nature of geographical boundaries are discussed in relation to the data obtained for temperature requirements in the context of the present local temperature regimes.

The β-dimethylsulfoniopropionate (DMSP) contents of 46 macroalgal species from the tropical island of Hainan, People's Republic of China, were determined by gas-liquid phase chromatography. In almost all investigated green, brown and red algal species, DMSP could be detected. The highest concentrations were measured in members of the green algal order Ulvales, and these were similar to those of isolates from polar and temperate regions. The tropical Ulvales from Hainan are comparable in their DMSP contents with temperate species of this order. Polar species, in contrast, exhibit significantly higher DMSP values.

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