Ecology and demography of a population of Anseropoda placenta (Echinodermata: Asteroidea) in the Bay of Brest, Brittany

Abstract

The starfish Anseropoda placenta (Pennant) is abundant in the gravelly sands of the Bay of Brest (Finistere, France). The size, distribution and density of this animal were evaluated along a transect perpendicular to the River Aulne in the southern part of the Bay. The spawning phases, the recruitment and growth processes were defined. When the entire population was considered, three plurimodal year classes were visible from the length frequency histograms. Year-class segregations were observed. Their density varied in space and time in a manner which suggests a pattern of migration from the southern part of the transect towards the northern part. Juveniles were recruited mainly during the autumn on the gravelly bottom of the southern shallow part. By late winter, they had migrated to the deeper parts of the channel. Feeding preferences do not seem to be the main factor controlling these migrations which are discussed in relation to environmental factors and the intra- and inter-specific competition.