Temperature requirements for growth and survival of macroalgae from Antarctica and southern Chile

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Abstract
Optimum and limiting temperature demands for growth and survival were determined in 14 species from the Antarctic/cold-temperate region and in 7 cold-temperate species from southern Chile. The growth response was tested in steps of 5.degree. C from 0 to 25.degree. C. In Antarctic/cold-temperate macroalgae 4 groups with different temperature-growth-ranges could be distinguished. The highest possible growth temperature was 5.degree. C in Iridaea cordata (Group 1), 10.degree. C in Geminocarpus geminatus, Ulothrix subflaccia and the female gametophyte of Desmarestia menziesii (Group 2), 15.degree. C in Adenocystis utricularis, Scytothamnus fasciculatus, Urospora penicilliformis and Acrosiphonia arcta (Group 3) and 20.degree. C in Prasiola crispa ssp. antarctica f. antarctica, Ulothrix implexa and Enteromorpha bulbosa (Group 4). Maximum survival temperatures of 14 to 19 (up to 25).degree. C were found in those species growing up to 10 or 15.degree. C. Species growing up to 20.degree. C tolerated 24 to 28.degree. C. Maximum survival temperature in Gigartina skottsbergii was 15.degree. C, and in Leptonematella falklandica (nov. comb., formerly Leptonema falklandicum) and Pilayella littoralis 22 to 24.degree. C (growth no determined in these 3 species). Species with exclusively temperate distribution can be divided into 2 groups: The more stenotherm species Iridaea laminorioides, I. undulosa and a ligulate Desmarestia sp. grew between (0 or) 5 and 15 ( or 20).degree. C (Group 1). The more eurytherm species Chordaria magellanica, Ectocarpus siliculosus, Enteromorpha clathrata and Scytosiphon lomentaria (Group 2) had an extended growth range from 0.degree. C up to 20 (or 25).degree. C. Growth at 0.degree. C was very reduced or not possible in all cold-temperate species except for C. magellanica and E. siliculosus. The maximum survival temperatures of these species were 17 to 24.degree. C. The evolution of cold water macroalgae in Antarctica from cold-temperate species probably started after opening of the Drake Passage and the concomitant temperature lowering in Antarctica some 25 to 30 million yr ago. It is still in process today as indicated in A. utricularis. In macrothalli of this species from Antarctica and southern Chile ecotypes were demonstrated exhibiting different temperature optima for growth (at 10 and 15.degree. C) and different upper survival temperatures (at 18 and 19.degree. C).