ABSTRACT
A population of the fissiparous sea star Stephanasterias albula was studied from May, 1983 to May, 1984. Fission involves a splitting of the disc of the sea star into two approximately equal halves. Each half then regenerates the missing body parts to form a complete individual. S. albula is thus frequently characterized by an asymmetrical body consisting of a set of small and a set of larger arms. Arm number in S. albula is variable, although individuals with 6 arms predominate. Size-frequency analysis has shown that most S. albula range from 4-18 mm in length of longest arm. The complete absence of very small individuals suggests that larval recruitment is absent or minimal. No individuals have yet been found to contain gonads. This population appears, therefore, to be maintained solely by asexual propagation. The incidence of fission is highest in the summer months and may be correlated with seasonal changes in photoperiod and/or water temperature. S. albula can regenerate new arms to 60% of the length of the long arms in roughly 9 months and individuals probably split once a year. It is hoped that further study of this population will provide a better understanding of the evolution and ecological significance of asexual reproduction in echinoderms.
