Effects of Particle Surface Properties on Feeding Selectivity in Suspension-Feeding Bivalve Molluscs

The mechanisms by which bivalve molluscs differentiate particles are not clearly understood, and the surface properties of a particle have been proposed as factors that contribute to particle selection. The effects of surface properties upon selection by suspension-feeding bivalves were examined. The charge and wettability of several different types of 10-µm spheres were determined. Microspheres with different surface characteristics were fed to oysters (C. viriginica) and mussels (M. edulis). Microsphere proportions rejected as pseudofeces and egested as feces were determined using flow cytometry. Results suggest that, when given a choice, both mussels and oysters reject some types of microspheres (e.g., aluminum oxide), over other types (e.g. polystyrene). When bivalves were fed different microspheres with similar properties, no selection occurred. Both bivalve species had the same pattern of selectivity, suggesting a generalized mechanism of selection. Both wettable and non-wettable microspheres were rejected in some assays, indicating that wettability is not a sole qualifier for selection. Microspheres within a mid-range of charges were ingested preferentially, and positive or highly-negative particles often were rejected. The discrimination between microspheres based upon surface properties indicates that surface properties may play a role in the mechanism(s) underlying selection