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 offered as prey to Bythotrephes cederstroemi Schoedler, a nonindigenous predatory cladoceran which has become established in the Laurentian Great Lakes. Both C and P from the prey were ingested with equal efficiency (58-59%, SE = 2%) by Bythotrephes and retained with equal efficiency over the next 12 h. Feeding behavior by the predator involves a fastidious process of shredding and discard of exoskeletal material and selective ingestion of soft tissue. Most of the ingested matter is consequently digested; assimilation efficiency is 85% (SE = 2%).