Food patches and a surface deposit feeding spionid polychaete

Abstract

Surface deposit feeders live in an environment in which nutritional states change rapidly due to flux of surface material. This project addressed the question of foraging choice by a common spionid deposit feeder, Streblospio benedicti. Individuals of S. benedicti were offered both organically enriched sediment and unaltered sediment simultaneously as feeding choices. Three organic conditions along with the worms' natural sediment were employed in the choice experiments. The natural sediment had an organic content of 1.5%. Organic enrichments were prepared by adding 0, 2, 4, or 8% by weight of an organically enriched substance to natural sediment, which resulted in final organic contents of 1.5, 4.6, 6.9, and 12.1% organic matter respectively. The worms were videotaped for 30 min each. Feeding was measured as time spent collecting particles on one or the other of the sediment additions. With increasing organic enrichment the worms consistently chose to forage on the enriched sediments and concomitantly reduced their likelihood of major tissue loss by reducing their degree of exposure while foraging. On unenriched sediments worms enlarged their foraging area by increasing their exposure of body segments as well as tentacles, thus also increasing their predation risk. The switches in foraging locale and degree of pre-ingestion sorting with enrichment indicate selectivity on a small spatial scale.