Streblospio shrubsolii(Polychaeta:Spionidae)temporal fluctuations in size and reproductive activity

Temporal fluctuations in size and reproductive activity of a Streblospio shrubsolii population were studied in a small brackish basin, to evaluate how these features influenced population dynamics and determine the persistence of this species in such an unstable environment. In the three study years, S. shrubsolii exhibited continuous reproduction from March to November but with two seasonal peaks in late spring and autumn. Larvae were lecithotrophic and developed between the female body and the tube wall. Individual fecundity showed significant differences between seasons, with trends coinciding with variations in mean female size. Changes in population size structure gave evidence that density fluctuations resulted mainly from recruitment during spring-early summer, or autumn. Potential larval production patterns peaked 1 or 2 months prior to periods of maximal abundance, and exhibited a progressive increase especially during the autumn of the study periods. Different life-history traits and different levels in reproductive activity were observed both on the temporal (study population) and spatial scale (other populations described) in S. shrubsolii. It is suggested that S. shrubsolii life- history flexibility may represent a successful way to maximize fitness in a fluctuating environment