Gametophytic development of Laminaria spp. (Laminariales, Phaeophyta) at low temperature

Laminaria saccharina, L. hyperborea and L. digitata (Laminariales, Phaeophyta) were cultivated at 0°C from embryospores. Slow germination of embryospores and temperature-limited growth of primary cells were found. Laminaria saccharina developed most rapidly and produced oogonia 18-20 days after sporulation, and sporophytes after 23-26 days. No differences were found in the rate of development of the primary cells between L. digitata and L. hyperborea; the first oogonia were observed after 20-34 days in L. hyperborea and after 33 days in L. digitata. Sporophytes were observed after 54-59 days in L. hyperborea, whereas the experiment with L. digitata had to be terminated after 42 days. The relatively rapid development of L. saccharina at 0°C suggests good adaptation of the gametophytic stage to Arctic conditions. The slow growth of L. hyperborea and L. digitata at 0°C suggests that this is close to the lowest temperature allowing vegetative development of primary cells of both species. Laminaria hyperborea produces spores during winter and L. digitata during late summer and autumn, and different seasons of gametophytic establishment may possibly explain why L. digitata extends into the Arctic, whereas L. hyperborea does not.