Growth responses of seven temperate Laminarialean taxa from Japan to high light and UV radiation
摘要
Marine forests continue to decline along the Japanese coast. To restore them, seedlings production of macroalgae, especially Laminarialean taxa, has been initiated using seaweed aquaculture techniques. However, “bleaching” has been reported in young sporophytes cultivated in indoor tanks when moved to outdoor tanks or the open sea. Therefore, we investigated the effects of high light and ultraviolet (UV) radiation on young sporophytes cultured in vitro. These included young sporophytes of Eisenia bicyclis, Ei. nipponica, Ecklonia cava, Ec. cava subsp. kurome, Ec. cava subsp. stolonifera, Undaria pinnatifida and synonym U. undarioides which is a growth form of U. pinnatifida. The sporophytes were exposed to artificial solar light, with an emission spectrum similar to that of sunlight (wavelength, 300 – 800 nm), and light without UV radiation (< 370 nm). A 3 mm thick acrylic plate was used to block UV radiation during the experiment. Young sporophytes of each species were cultivated under light intensities of 60, 600 and 1000 μmol photons m-2 s-1 with/without UV radiation for 4 days. During the experiment, growth and effective quantum yield (YII) were measured every day. All young sporophytes exhibited bleaching at 1000 μmol photons m-2 s-1 with UV radiation, whereas those cultured without UV radiation displayed no bleaching. At 60 μmol photons m-2 s-1, all sporophytes grew regardless of UV exposure. The YII values of all species decreased as the amount of UV energy and light intensity increased. Thus, high-energy UV radiation is a major factor contributing to the bleaching phenomenon observed in young sporophytes.