Ingestion rate of the deposit-feeder Hydrobia ulvae (Gastropoda) on epipelic diatoms: effect of cell size and algal biomass

The effects of cell size of epipelic diatoms and sediment Chl a content (as an index of algal biomass) on the ingestion rate of Hydrobia ulvae adults and juveniles were investigated in experimental microcosms. Results showed that both adults and juveniles ingested small and large diatoms without exhibiting cell size selection behaviour. The functional response of H. ulvae, juveniles (<4 mm) and adults (>4 mm), over a wide range of sediment Chl a content, was characterized by an increase of the ingestion rate according to a power law. Ingestion rate varied from 0.75 to 10 ng Chl a ind⁻¹ h⁻¹ for juveniles and from 1 to 52 ng Chl a ind⁻¹ h⁻¹ for adults, in the range ca. 10-100 μg Chl a (g dry weight sediment)⁻¹. The ingestion rate was about three times higher for adults than for juveniles. Based on these experimental results, we further proposed a mechanistic approach, using an individual based-model, to identify simple feeding mechanisms that might be involved in H. ulvae functional response.