The effects of genotype, density and irradiance on the growth and mortality of the brown seeweed Fucus serratus germlings

Effects of genotype, settlement density and irradiance on the growth, mortality and population structure of Fucus serratus germlings were examined in the laboratory. The growth of F. serratus germlings was influenced by genotype of parent plants, which is likely to occur by microclimatic differentiation of substrata. The growth of germlings were greater at lower densities than higher densities indicating that intraspecific competition between germlings occurred within three weeks. Also, the growth of F. serratus germlings was better at 120 μmol m‐2 s‐1 than at 60 μmol m‐2 s‐1. However, mortality of germlings was determined by settlement density rather than irradiance. In population structure, skewness was increased at low irradiance and high density indicating that population structure could be changed by intraspecific competition. Thus, it is concluded that genotypic differentiation of F. serratus germlings occurred in a microgeographic scale, and the experimental density and irradiance level affected the growth of germlings.