Effects of environment and population density on the sea anemone Actinia tenebrosa

Within each of four Western Australian colonies of A. tenebrosa, adults developed gonads and brooded asexually produced juveniles during the summer months. The brooded juveniles were released throughout the year but most settlement occurred in autumn and winter. Dispersal of brooded juveniles was highly localized and they typically settled within 2 m of adults. Adults were sedentary and long- lived and recruitment rates were extremely low (about 1% per annum during the study period). Adult size and asexual fecundity differed markedly between colonies over three breeding seasons, but between-colony comparisons revealed no simple relationship between those characteristics. The mean number of juveniles per adult varied up to ninefold between colonies. Sex ratios deviated significantly from a ratio of 1 : 1 in samples from three colonies, and males predominated in two of these. Density-manipulation experiments revealed that intraspecific competition affected adult size, sexual maturity, asexual fecundity and rates of settlement and recruitment.