Patterns of abundance and seasonality of polychaetes sheltering in southwestern Atlantic estuarine epibenthic shell beds

The purpose of this study was to investigate the spatial and temporal distr ibution of the polychaete species that inhabit shell cavities in beds of th e stout razor clam Tagelus plebeius. Samples were taken bimonthly between J uly 1996 and September 1997, and an additional one was taken in February 19 98. The assemblage was dominated by the amphipod Corophium insidiosum and t hree polychaete species (Laeonereis acuta, Heteromastus similis and Neanthe s succinea). The abundance oft, acuta was higher in summer, simultaneously with the occurrence of juveniles. Ln contrast, C. insidiosum and H. similis were more abundant in winter together with the occurrence of juveniles of the latter species. The predator N. succinea occurred at the end of the sam pling period, concurrently with a decrease in all other macroinfaunal taxa. An estimation based on polychaete predation rates indicated that these dec reases in macroinfaunal densities may be the result of consumption by N. su ccinea. Polychaete distribution along the intertidal slope did not vary alo ng the sampling period. Higher density of polychaetes was found in the inte rnal shell sediment than in the sediment outside them. All the evidence sug gests that variability in the intensity of species recruitment and direct o r indirect biotic interactions may determine the spatial and temporal distr ibution of macroinfaunal species in these beds.