SPOROPHYTE FORMATION OF LAMINARIA-HYPERBOREA (LAMINARIALES, PHAEOPHYCEAE) RELATED TO PHOTON DOSES OF BLUE-LIGHT IN THE SEA

The sporophyte formation of Laminaria hyperborea (GUNNERUS) FOSLIE in the sea was studied from January till the end of May at a locality on the west coast of Norway. Three series of gametophytes, which had been cultured in red light to prevent sexual reproduction, were transferre d to the sea at depths between 10 and 45 m. After about 30 or 70 days in the sea the frequency of sporophytes in each series was registered. From 14 January to 13 February sporophytes had developed at 10 m. Fro m 14 February to 18 March sporophytes had developed at both 10 and 20 m, while from 20 March to 28 May sporophytes had developed at all exam ined depths. In the period from 20 March to 28 May sporophytes constit uted 82 and 27 % of the examined specimens at 40 and 45 m, respectivel y. In all the other cases where sporophytes were registered, 100 % of the specimens examined had developed into sporophytes. Based on contin uous recordings of photon irradiance (PAR) in air and measurements of blue and integrated irradiance transmittance at the locality, the phot on doses of blue light at the experimental depths were calculated. The depths at which sporophytes developed corresponded with the depths at which the calculated photon dose of blue light exceeded the critical photon dose for reproduction of gametophytes.