PREY CONSUMPTION AND PREDATORY EFFECTS OF AN INVERTEBRATE PREDATOR (BYTHOTREPHES, CLADOCERA, CERCOPAGIDAE) BASED ON PHOSPHORUS BUDGETS

Phosphorus excretion rates, ingestion efficiency, and P content of Byt hotrephes at different developmental stages are used to estimate preda tion rates indirectly from metabolic needs. A growth model is develope d to predict P content and weight of this invertebrate planktivore thr oughout its life. P consumption required to complete one parthenogenic life cycle of the predator is estimated from metabolic rates and weig ht measurements of individual instars. Based on P requirements and pre y stoichiometry, empirical ingestion efficiency of 59%, and assimilati on efficiency of 85%, each Bythotrephes consumes the equivalent of 14 Daphnia per day on average and can inflict mortality equal or greater in magnitude to Daphnia recruitment rates during midsummer in offshore waters of Lake Michigan, particularly when predator population abunda nce exceeds 400 individuals m-2.