The effect of food availability on byssogenesis by the zebra mussel (Dreissena polymorpha Pallas)

The effect of varying algal availability on byssal thread productionbyre–attaching zebra mussels (Dreissena polymorpha) wasquantified. The byssalapparatus was severed and mussels allowedto re–attach to a hard substratum for a 21 dayperiodduring which they were fed at algal concentrations of 0.0, 0.1,0.5, 1.0 or 2.0 mg C l^-1. Byssal thread production was quantifiedby counting the number of newattachment plaques present eachday. Results showed that starved mussels continued to partitionorganiccarbon towards thread production but the resultant byssal masswas compromised,containing fewer threads than those producedby fed mussels. The daily average byssal threadproduction bymussels fed at 2.0 mg C l^-1 was greater than that of starvedmusselsand the final mean dry soft tissue weight higher. At algal Cconcentrations belowmaintenance requirements byssal threadproduction was elevated compared to starved mussels,but therewas no concurrent increase in soft tissue. This suggests thatbelow maintenance levelsassimilated carbon was solely partitionedtowards byssus production and stored reserves mayhave beenutilized. The ratio of organic carbon contained in the byssusto that in the soft tissuesremained relatively constant acrossall feeding levels. This suggests that the carbon content ofthebyssus is a constant function of that of the soft tissuemass. These results may explain seasonalvariation in attachmentstrength of numerous byssate species and seasonal vertical migrationsby D. polymorpha. Present Address-Queen Mary & Westfield College, Dept of Biology,University of London, Mile End Road, London E1 4NS, UK (Received 16 March 1998; accepted 30 September 1998)