Abstract
Polychaetous annelids are the most dominant macrobenthos in an estuary, Hiroura lagoon, Miyagi Prefecture, Japan. The most abundant species in a polychaete assemblage of Hiroura consists of Notomastus sp. Okuda,Neanthes japonica(Izuka), and Prionospio japonicaOkuda. A dense population of polychaete worms provides large food resollrces for fish inhabiting Hiroura. However, field studies revealed that the abundance of the various species showed spatial and temporal fluctuations. Combined biological and environmental factors affect the seasonal changes in abundance of polychaetes. Polychaete life history traits including reproductive patterns are main factors influencing species' population dynamics.
