Abstract
Omnivory by the 2 coastal marine copepods Centropages hamatus (Lilljeborg) and Labidocera aestiva Wheeler was examined in laboratory grazing and predation experiments. Cooccurring food items were utilized. C. hamatus ingested more carbon in the form of plant material (x̄ = 2.05 μgC copepod⁻¹ d⁻¹) than did L. aestiva (x̄ = 0.66 μgC copepod ⁻¹ d⁻¹). Conversely, L. aestiva ingested more carbon in the form of animal food (x̄ = 3.35 μgC copepod⁻¹ d⁻¹) than did C. hamatus (x̄ = 0.98 μgC copepod⁻¹ d⁻¹). Rates of ingestion of copepod nauplii and phytoplankton by both C. hamatus and L. aestiva increased significantly with increasing food concentrations and temperatures. Average grazing and predation rates of C. hamatus and L. aestiva upon natural phytoplankton assemblages and nauplii appeared to follow biomass peaks. The maximum field concentration of C. hamatus (722 m⁻³) appeared capable of daily ingesting means of 0.85 % of phytoplankton carbon and 8.23 % of the copepod nauplii present. Maximum field concentration of adult L. aestiva (8 m⁻³) appeared capable of ingesting means of only 0.01 % of phytoplankton carbon and 0.29 % of the copepod nauplii present.