Several recent studies have indicated that deposit feeder nutrition is more complex than depicted in traditional models of detrital food webs. Micro‐organisms may be less important as sources of carbon than as sources of nitrogen, and the microbial contribution to deposit feeder diets appears to vary from site to site. The carbon requirements for respiration of two populations of the gastropodAmphibola crenatawere compared with carbon available from assimilation of sediment bacteria and microalgae. The calculated total microbial contributions were 23.5 and 50.3% of the snails’ estimated carbon requirements for respiration. The contribution of microalgae is probably subject to more local variability than that of sediment bacteria. These results suggest that several living and non‐living food sources collectively contribute to the nutritionof Amphibola crenata, with non‐living sources possibly supplying the major portion of the snail's carbon requirement.