The role of sediment particle size in the nutritional energetics of a surface deposit-feeder. I. Ingestion and absorption of sedimentary microalgae by Hydrobia truncata (Vanatta)

The effect of sediment particle size on carbon intake by the deposit-feeding gastropod Hydrobia truncata was investigated. Radiotracer techniques were employed to estimate ingestion rate and absorption efficiency of microalgal carbon and sediment processing rate on two size fractions of natural sediment (silt-clay), < 63 μm; medium sand, 300-600 μm). In two of three experiments, ingestion and absorption rates of microalgal carbon were higher on sand, even though microalgal concentrations were 5 and 17 times lower than on silt-clay. Within each sediment type, ingestion and absorption rates were positively related to microalgal abundance, whereas sediment processing rate and absorption efficiency varied little over a 3-4 fold range in microalgal concentration. Examination of the effect of sediment particle size on carbon intake suggests that the inverse relationship between body size and density of hydrobiid populations and sediment grade in nature is not due to a lack of food associated with coarse-grained sediments.