STUDIES ON THE RECENTLY INTRODUCED BROWN ALGA SARGASSUM-MUTICUM (YENDO) FENSHOLT .5. RECEPTACLE INITIATION AND GROWTH, AND GAMETE RELEASE IN LABORATORY CULTURE

Laboratory culture studies were undertaken on aspects of the reproduction of the large, introduced, brown alga Sargassum muticum (Yendo) Fensholt. Particular attention was given to the individual effects of temperature, irradiance and salinity on receptacle growth, and the combined effects of daylength and temperature on receptacle initiation and growth, as well as the periodicity of gamete release. Receptacle growth occurred over a temperature range of 10–30 °C (optimum, 25), an irradiance range of 9 to 175 μEm-2s-1 (optimum, 175) and a salinity range of 8.5 to 34%0 (optimum, 23.8%o). A similar broad tolerance to temperature and irradiance was demonstrated for gamete release and zygote development, but the latter process was less tolerant to reduced salinity and was not possible below between 13.6 and 18.7%o. Maximum receptacle growth occurred at 25 °C under long day (16 h light: 8 h dark) conditions but temperature alone appeared to influence the frequency of gamete release, this being greater at higher than at lower temperatures in the 15 to 25 °C range. Receptacle initiation was enhanced over the 10 to 25 °C temperature range under long day conditions but only occurred at 20 °C under short day conditions (8 h light: 16 h dark). The results are discussed in relation to previous studies and aspects of the present and probable future ecology and geographical distribution of S. muticum in the North Atlantic. Copyright © 1990 Walter de Gruyter