Demography of Pholoe minuta (Polychaeta: Sigalionidae) in Galway Bay, west coast of Ireland, with special reference to settlement and recruitment patterns

Abstract

Pholoe minuta is a numerically dominant member of the Amphiura filiformis subcommunity in Galway Bay. A longterm (5 yr) assessment of its population structure highlighted the shortfall in information regarding juvenile stages in the post-spawning months. Additional remote and in situ sampling programmes (including the use of a Muus sampling device), covering two successive postspawning periods, were undertaken to provide information on the juvenile recruits. Estimates of density levels (130 to 680 m-2), growth rates (doubling in size in 2 mo) and mortalities (80%) were calculated for the newly settled P. minuta. Mean monthly densities, seasonal population structure, recruitment levels (21.1%), growth (1 mm per annum) and survivorship patterns of the adult population were evaluated using the dorsal width of the fifth chaetiger, which is shown to be a suitable parameter of total body size. The success of grab sampling as a method for examining early settlement of P. minuta is critically reviewed, and a recommendation for future benthic population studies is proposed.