Influence of environment factors on bacterial ingestion rate of the deposit-feeder Hydrobia ulvae and comparison with meiofauna

Deposit feeders are able to process a considerable volume of sediment, containing large quantities of associated bacteria. However, conclusions concerning the trophic role played by benthic bacteria in marine sediments are still not fully elucidated. This study deals with bacterivory by the gastropod Hydrobia ulvae, one of the most abundant deposit-feeding species in intertidal mudflats in Western Europe. Ingestion rates of bacteria were determined during grazing experiments using N-15 pre-enriched bacteria. Grazing experiments were performed in order to measure effects of abiotic (temperature, salinity and luminosity) and biotic (bacterial and algal abundances) factors on ingestion rates of bacteria by H. ulvae of an intertidal mudflat (Brouage, Marennes-Oleron, France). The mean ingestion rate of bacteria by H. ulvae was 1149 ng C ind(-1) h(-1). The general trend showed a temperature effect with an optimum around 30 degrees C, and the assimilation rate was significantly lower at 5 degrees C. Bacterial assimilation did not significantly differ between salinity 18 and salinity 31. Ingestion was the same in light and in dark conditions. Results were compared with those of other grazing experiments conducted simultaneously in similar conditions with two other grazers with different size and feeding modes: the foraminifera Ammonia tepida and a nematode community from the superficial sediment of the Brouage mudflat H. ulvae and nematodes presented a feeding behavior less influenced by environmental changes than A. tepida. H. ulvae ingested bacteria at a higher rate than smaller meiofaunal grazers and seemed to have a lower ability to selectively ingest diatoms than meiofaunal grazers. (C) 2008 Elsevier B.V. All rights reserved.