Organic coatings and ontogenetic particle selection in Streblospio benedicti Webster (Spionidae: Polychaeta)

Surface deposit feeders select food particles based upon characteristics including size, texture, specific gravity, and organic coatings. Spionid polychaetes feed at the sediment-water interface using a pair of ciliated palps and switch between surface deposit feeding and suspension feeding primarily as a function of water flow. Juveniles and adults of some spionid species have different stable isotopic carbon signals, indicating the ingestion of different food sources and potentially the ability to differentiate organic cues ontogenetically. In the present study, the feeding responses of juvenile and adult Streblospio benedicti Webster to seven organic coatings bound to glass microbeads were tested using five amino acids and two carbohydrates. Coated versus uncoated particles were presented in equal proportions based upon surface area. Juveniles and adults were highly selective for all seven types of organically coated beads-87.1% of all beads ingested were organically coated beads. For two of the organic coatings, there were ontogenetic differences; juveniles were more selective of threonine and adults were more selective of proline. These differences may result in ontogenetic diet shifts that allow maximization of energy and/or essential nutrients during critical early life-history stages. Particle selection in tentaculate surface deposit feeders is generally thought to occur primarily during particle contact and transport to the mouth, and is typically characterized as a passive process. Active particle selection at the site of the everted pharynx was observed and quantified for S. benedicti. Organically coated particles represented 50% of the ambient experimental treatment, 64.4% of the particles transported along the palp after contact, and 81.8% of the particles ingested after pharyngeal rejection behavior. Of the beads reaching the pharynx, 26.9% were rejected by ciliary sorting on the pharynx before ingestion, and 81.8% of the rejected beads at the site of the pharynx were uncoated. Our study demonstrates that microphagous feeders that generally handle food particles in bulk are capable of significant levels of active selection for organically coated particles.