OPTIMAL-GROWTH AND MAXIMAL SURVIVAL TEMPERATURES OF ATLANTIC LAMINARIA SPECIES (PHAEOPHYTA) IN CULTURE

The effects of temperature on growth rate of rapidly-growing cultured macrosporophytes of 9 isolates of Atlantic Laminaria comprising 4 spp. [L. saccharina, L. longicruris, L. digitata and L. hyperborea] were investigated. No significant population variation occurred within species despite wide variations in temperature between the original collecting sites. L. saccharina had a broad temperature optimum in the 10.degree.-15.degree. C range, whereas L. longicruris had a sharp optimum at 10.degree. C. L. digitata and L. hyperborea grew more slowly with only slightly sub-optimal growth over a wide temperature range, but with peaks at 10.degree. C (L. digitata) and 15.degree. C (L. hyperborea). The maximum survival temperature of individual male and female vegetatively-growing gametophytes were ascertained for these species plus the Arctic L. solidungula and were as follows: L. saccharina and L. longicruris, 23.degree. C; L. digitata (male), 23.degree. C; L. digitata (female), 22.degree. C; L. hyperborea, 21.degree. C; and L. solidungula, 18.degree. C. The lack of within-species differences demonstrates that the success of the genus in areas with different temperature regimes is brought about by phenotypic plasticity of individuals rather than the selection of temperature races or ecotypes.