EFFICIENCIES OF INGESTION AND ASSIMILATION BY AN INVERTEBRATE PREDATOR USING C-DUAL AND P-DUAL ISOTOPE LABELING

Daphnia rosea was uniformly labeled with both C-14 and P-33, then offe red as prey to Bythotrephes cederstroemi Schoedler, a nonindigenous pr edatory cladoceran which has become established in the Laurentian Grea t Lakes. Both C and P from the prey were ingested with equal efficienc y (58-59%, SE = 2%) by Bythotrephes and retained with equal efficiency over the next 12 h. Feeding behavior by the predator involves a fasti dious process of shredding and discard of exoskeletal material and sel ective ingestion of soft tissue. Most of the ingested matter is conseq uently digested; assimilation efficiency is 85% (SE = 2%).