Local recruitment differences in Platynereis dumerilii (Polychaeta, Nereididae) and their consequences for population structure

Abstract

The population structure of Platynereis dumerilii (Annelida. Polychaeta, Nereididae) was investigated for 18 months (February 1997-August 1998) in two sites (Gargano and Otranto), located 400 km from each other along the Adriatic coast of Apulia (Italy). Samples were collected in three replicates by scraping off 100-cm2 quadrats in a fringe of the brown alga Cystoseira amentacea. At the beginning of the study period, a recruitment event was observed in both sites. Despite the great difference in recruitment rates, at the end of the study period, local population density was similar in the two sites, suggesting the importance of post-recruitment factors in controlling population density. Intra- and interspecific competition, predation, and physical stress are discussed in the light of the different ecological conditions of the two sites. Recruit distribution appeared relatively homogeneous in space with recruitment rates not being different among quadrat replicates. Variability in size class distribution among quadrat replicates was lower during the recruitment period, suggesting that the observed patchy patterns of adult distribution were a product of post-recruitment events.