Relation of particle-size spectrum and food abundance to particle selectivity in the mud snail Hydrobia totteni (Prosobranchia: Hydrobiidae)

We studied the relationship between particle-size selectivity and variable particle-size distribution in the American mud snail Hydrobia totteni Morrison (Prosobranchia: Hydrobiidae) collected in the summer of 1979 and 1982, from saltmarsh mudflats at Flax Pond, Old Field, New York, USA. Using individual size fractions of native sediment, snails fed fastest on intermediate-sized particles (41 to 63 m); this pattern was related to diatom abundance, which was similarly greatest on the intermediate particle-size classes. These results conform to another study, which found a quite different relationship between feeding rate and particle size, but a similarly strong correlation between particle size and diatom abundance. Snails were fed a range of particle-size distributions of glass beads. As median particle size increased, preference shifted towards smaller particles. This shift cannot be explained by feeding rates determined from individual particle-size classes. The most reasonable alternative model is a shift towards feeding on fine particles that occur among the coarser particles that are not ingested. Our data suggest that diatom growth on certain particle sizes is as important to particle selectivity as the particle sizes themselves. Particle size preference cannot be extrapolated from studies of feeding rates on individual size classes since selectivity is qualitatively different in mixtures of various size classes.