Zooplankton Diel Vertical Distributions in Lake Crescent, a Deep Oligotrophic Lake in Washington (USA)

We evaluated diel vertical migration (DVM) of major zooplankton populations in Lake Crescent, Washington, a deep oligotrophic lake where this phenomenon has not previously been studied. Duplicate daytime and nighttime samples were collected on June 27 and August 1, 2003 at ten depth intervals spanning 0–140 m. The major zooplankton taxa were the crustaceans Diaptomus tyrrelli, Daphnia rosea, Holopedium gibberum and the rotifers Conochilus spp., Kellicottia longispina, and Polyarthra vulgaris. The diel vertical trends of these taxa were analyzed using a two-sample Kolmogorov-Smironov test and a DVM index. All major taxa demonstrated diel shifts indicative of DVM behavior.