Polychaete abundance and dispersion patterns in mussel beds: a non- trivial "infaunal' assemblage on a Pacific South American rocky shore

Abstract

Mussel beds were made up of two zones in the intertidal, the lower, more extensive zone formed by Semimytilus algosus and the upper by Perumytilus purpuratus. Total polychaete density in the Semimytilus habitat was in the range of 18 800 to 36 300 ind. m-2 indicating that mussel bed environments on hard substrata are a major habitat for polychaetes free-ranging. Populations of six taxa (Pseudonereis, Halosydna, Lumbrineris, Scoloplos, Mediomastus and Typosyllis) demonstrated moderate seasonal fluctuations. Numerically, typosyllis was the most abundant taxon, accounting for 52 to 71% of all individuals. All the taxa showed a contagious (aggregated) dispersion, with the deposit feeder Mediomastus demonstrating the strongest aggregation. All taxa were more strongly aggregated in the Perumytilus than in the Semimytilus habitat, probably reflecting the variability and more patchy occurrence of favourable microhabitats and available resources in the former. -from Author