MANIPULATION OF DIETARY CONDITIONS FOR MAXIMAL GROWTH IN MUSSELS, MYTILUS-EDULIS, FROM THE MARENNES-OLERON BAY, FRANCE

Results are presented from laboratory-based experiments in which we in vestigated short-term responses of Mytilus edulis L. to experimental c hanges 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, thereb y enriching the organic content of ingested matter by 30% more than th e organic content of natural filtered seston. Our findings also establ ish 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 maxima l 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 f or any adult mussel. Maximal growth was achieved when natural seston t hat had been enriched to more than about 60% organic content with a mi xture of algal monocultures was available at concentrations above abou t 11.5 mg total particulates l(-1). Neither ingestion rate nor net ene rgy 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 o f 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 t issue h(-1) in a standard M. edulis of Ig dry soft tissue, representin g as much as 20.6% of all soft tissue organic mass mussel(-1) d(-1). S uch saturation of organic ingestion is consistent with previous conclu sions based on comparative allometries showing that limitations to gro wth in M. edulis and other bivalves are associated with the rate of fo od processing.