Effects of the Bythotrephes invasion on native predatory invertebrates

Abstract

We explore the effects of the invasive predatory cladoceran Bythotrephes longimanus on the abundances and seasonal zooplankton consumption by the native predatory invertebrates Leptodora kindtii, Chaoborus spp., and Mysis relicta in inland lakes of Ontario. In lakes with Bythotrephes, the seasonal consumption by all invertebrate predators combined ranged from 2.39 to 13.50 g m−2 and was 300% higher than in lakes without the invader. This was due to Bythotrephes because there was no invasion effect on Chaoborus or Mysis consumption, while it actually decreased Leptodora consumption. Leptodora and Chaoborus abundances were lower in invaded lakes, but only Leptodora abundance was negatively correlated with Bythotrephes abundance. There was no effect of Bythotrephes on Mysis abundance. Bythotrephes consume more zooplankton than most other predatory invertebrates, including copepods, and often consume more zooplankton than planktivorous fish. The large increase in predatory invertebrate abundance and consumption due to Bythotrephes means that substantial portions of zooplankton production are probably being diverted from other consumers, such as juvenile and planktivorous fish, and that the role of predatory invertebrates in the pelagia of inland lakes has been intensified by the arrival of Bythotrephes.