A MODEL FOR GROWTH, DEVELOPMENT, AND DIET SELECTION BY THE INVERTEBRATE PREDATOR BYTHOTREPHES-CEDERSTROEMI

A growth model is developed to predict C content, respiration, and rat es of both embryonic and post-embryonic development by the invertebrat e predator Bythotrephes. The model incorporates temperature dependent rates of embryonic and postembryonic development as well as respiratio n and variations in body mass. Estimated growth efficiencies indicate that this invertebrate predator converts about 25% of its prey biomass into predator mass, thus reducing potential resource availability to planktivorous fish. The physiological economics of Bythotrephes with r espect to both P and C indicate that copepods can be only a minor comp onent of the predator's diet, owing to the high C:P composition of cop epod tissues. Mass balance constraints dictate that field-collected po pulations of Bythotrephes in Lake Michigan consume a prey mixture with bulk tissue stoichiometries less than about 40:1 C:P by mass. The req uisite stoichiometry correponds with the elemental composition of Clad ocera, particularly Daphnia, which are the dominant Cladocera in offsh ore regions. Thus an analysis based on conservative elemental budgets of P and C points to Daphnia as the dominant prey of Bythotrephes in L ake Michigan.