THE INFLUENCE OF TEMPERATURE, IRRADIANCE AND PHOTOPERIOD ON THE REPRODUCTIVE LIFE-HISTORY OF PORPHYRA-LEUCOSTICTA (BANGIALES, RHODOPHYTA) IN LABORATORY CULTURE

Laboratory culture studies were undertaken on aspects of the reproduction of the red alga Porphyra leucosticta Thuret. The life cycle of Porphyra is characterized by two different phases: 1. a leafy thallus, the haploid gametophyte and 2. a filamentous conchocelis, the diploid sporophyte. Particular attention was given to the individual effects of temperature, light intensity and photoperiod on the vegetative and the reproductive stages. A temperature optimum of 15-degrees-C, an illumination of 9.5 Wm-2 and a daylight of 16: 8BAR h light : dark were optimal for vegetative growth of the conchocelis. Vegetative growth of the thalli was maximal at the same temperature and irradiance as for the conchocelis, however the optimal daylength was 8 : 16BAR h light : dark. A similar broad tolerance to temperature was demonstrated for carpospore and conchospore induction and release, but these processes were favoured by a particular combination of irradiance and photoperiod. In contrast to the thallus, the conchocelis exists for several seasons after releasing conchospores. The complete life history can, under optimal conditions, be observed within two months.