Evaluating Invertebrate Planktivory in Lake Ontario: a Bioenergetics Approach

Zooplankton biomass has decreased an order of magnitude in the offshore epilimnion of Lake Ontario during the last decade, with the largest decreases in smaller zooplankton (Bosmina and Diacyclops).  These decreases cannot be attributed to alewife planktivory, because alewife has declined during this time period.  However, the invasive predatory cladoceran Bythotrephes has increased since 2005 which may be a result of decreased alewife planktivory.  Other invertebrate predators include the cladocerans Cercopagis, Leptodora and Polyphemus, several copepods (e.g. Limnocalanus), and the mysid Mysis diluviana (relicta).  We analyze the time trends in zooplanktivory from these invertebrates from 2000 to 2010 using bioenergetics models.   Zooplanktivory by invertebrates increased due to the increase in Bythotrephes although Mysis continues to be important.  The role of omnivores like Limnocalanus is increasing.  Understanding recent changes in zooplankton abundance and community composition in Lake Ontario requires attention to invertebrate predators including their energetics, distribution, diet, and abundance.