Results are presented from laboratory-based experiments in which we investigated short-term responses of Mytilus edulis L. to experimental changes in the amount and composition of suspended seston. Working with large quantities of cultured algae, we have studied feeding behaviour over ranges of food availability and quality that extend well beyond earlier limits. Findings confirm the ability of mussels to selectively reject inorganic particles as pseudofaeces prior to ingestion, thereby enriching the organic content of ingested matter by 30% more than the organic content of natural filtered seston. Our findings also establish acclimation both of selective and absorptive processes, indicating that the extent to which growth of M. edulis can be stimulated in the short-term will depend upon prior nutritional history. Present maximal growth of 14.8% dry soft tissue d−1 in a standard M. edulis of 1 g dry soft tissue was much higher than has previously been documented for any adult mussel. Maximal growth was achieved when natural seston that had been enriched to more than about 60% organic content with a mixture of algal monocultures was available at concentrations above about 11.5 mg total particulates 1−1. Neither ingestion rate nor net energy balance were improved with further increases in food availability, associated with regulatory reductions in the rate of water filtration (clearance rate) that maintained organic ingestion rate independent of increases in both the amount and organic content of available seston. These findings suggest that digestive processes had become saturated when organic ingestion reached about 6.5 mg organics g−1 dry soft tissue h−1 in a standard M. edulis of 1 g dry soft tissue, representing as much as 20.6% of all soft tissue organic mass mussel−1 d−1. Such saturation of organic ingestion is consistent with
previous conclusions based on comparative allometries showing that limitations to growth in M. edulis and other bivalves are associated with the rate of food processing.