Additional link in the food web does not biomagnify a persistent contaminant in Lake Ontario: The case of Cercopagis pengoi

Cercopagis pengoi is a new and abundant non-indigenous predator species in the Lake Ontario food web. We explored the impact of this predator on the levels of a chlorinated hydrocarbon in the pelagic food web through assessments of seasonal abundance and mirex concentrations of Cercopagis pengoi (Ostroumov) and the planktivorous alewife (Alosa pseudoharengus). Abundance, stable isotope, and alewife stomach data indicate that Cercopagis pengoi has become an established portion of the Lake Ontario food web. Cercopagis, a predaceous cladoceran, feeds on the lower portion of the trophic web and is clearly fed upon by the planktivorous alewife. Cercopagis is a link in the Lake Ontario food web, in which energy and materials are being passed from one level of the trophic web to another. However, mirex levels of the planktivorous alewife did not increase during the period of highest Cercopagis abundance. The annual load of mirex (mass of Cercopagis times concentration) transferred from one level of the trophic web to the next is low. In the summer, when Cercopagis is abundant, alewives were not feeding on them.