Epilimnetic rotifer community responses to Bythotrephes longimanus invasion in Canadian Shield lakes

Hovius, Jonathan T., Beatrix E. Beisner, Kevin S. McCann

Limnol. Oceanogr., 51(2), 2006, 1004-1012 | DOI: 10.4319/lo.2006.51.2.1004

ABSTRACT: We studied whether the effects of Bythotrephes longimanus, a new predatory cladoceran zooplankton species to North America, can extend beyond the macrozooplankton to the rotifer community, which is known to be an important controller of the microbial loop. During summer 2003, 14 Canadian Shield lakes were sampled biweekly to evaluate the effect of Bythotrephes on epilimnetic rotifers. Rotifer densities, particularly those of Conochilus unicornis, significantly increased, with elevated Bythotrephes densities. Conochilus became the dominant rotifer species in the pelagic community of lakes with high B. longimanus populations. Bythotrephes densities were a better estimator of rotifer densities than physical and chemical lake properties. Bythotrephes has indirect effects beyond its preferred prey species, cladocerans. The potential for increased rotifer densities to act as a secondary source of food for Bythotrephes was also investigated. In a 24-h feeding experiment, Bythotrephes did not prey on various common rotifer species, suggesting that Bythotrephes ignores rotifer species as a prey even when they form the sole food source. Rotifer increases are likely either due to competitive release when crustacean zooplankton decline or predatory release when native invertebrate predator populations decline.

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