Effects of contaminated sediments on particle size selection by the polychaete Capitella sp. I

Capitellid polychaetes are generally considered opportunistic species, characteristic of organically enriched and disturbed habitats. The feeding behavior of capitellids dramatically affects physical properties of sediments by repackaging sediment particles into large fecal pellets that persist for years. Particle size selection by Capitella sp. I was quantified using two approaches. Organic-rich sediments from four locations subjected to varying degrees of anthropogenic disturbance were used in the first approach. Sediment contamination, measured as the concentrations of selected polycyclic aromatic hydrocarbons (PAHs) varied from 0.08 to 31 ppm. The median size of mineral particle ingested was ≃ 4 μm for all sediments. Worms selectively ingested the smallest particles in the most contaminated sediment. Because of potential ambiguity in obtaining accurate measurements of in situ particle sizes of natural sediments, a second experiment used glass beads as tracers added to natural sediment. Treatments consisted of phenanthrene added at six concentrations, from 0.07 to 13 ppm. Worms preferentially fed on small beads (most preferred particle size 17±4 μm) in all treatments, and selection was unaffected by phenanthrene concentrations. Selective feeding on the finest sediment particles and their incorporation into long-lived fecal pellets may affect the persistence of organic contaminants in sediments.