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 rates of both embryonic and post-embryonic development by the invertebrate predator Bythotrephes. The model incorporates temperature dependent rates of embryonic and postembryonic development as well as respiration 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 plank-tivorous fish. The physiological economics of Bythotrephes with respect to both P and C indicate that copepods can be only a minor component of the predator's diet, owing to the high C:P composition of copepod tissues. Mass balance constraints dictate that field-collected populations of Bythotrephes in Lake Michigan consume a prey mixture with bulk tissue stoichiometries less than about 40:1 C:P by mass. The requisite stoichiometry correponds with the elemental composition of Cladocera, particularly Daphnia, which are the dominant Cladocera in offshore regions. Thus an analysis based on conservative elemental budgets of P and C points to Daphnia as the dominant prey of Bythotrephes in Lake Michigan.