Influence of adult density on recruitment into soft sediments: a short-term in situ sublittoral experiment

Abstract

Effects of different densities of the ophiuroid Amphiura filiformis and of the bivalve Abra nitida (both species separately) on initial recruitment were studied in situ in a soft-sediment environment at 25 m depth in the Gullmar Fjord (Sweden). Containers with known densities of residents in natural sedlrnent, and some defaunated controls, were exposed for 9 d on the bottom. With both species there was a clear effect on both density and horizontal spatial distribution of recruits in the experimental containers. At high densities (2400 per m'), A. filiformis inhibited recruitment of most taxa, whereas the effect of A. nitida at medium densities (1400 per m2) was facllitation. Both residents caused a less aggregated distribution of recruits compared with controls. The bioturbation disturbance caused by A. nitida seemed to have little negative effect on recruitment. It is suggested that A. filiformis may inhibit recruitment by ingesting settlers or newly settled juveniles.