Vertical distribution of zooplankton under the ice in lake Hibara-ko [Fukushima, Japan]

The vertical distribution of zooplankton under the ice in Lake Hibara-ko was studied in February 1989 and 1990. The cyclopid copepod Cyclops vicinus was the most predominant species in both times. The population of this species was mostly composed of nauplius and copepodite stages. In the daytime, C. vicinus seemed to have aggregated at the surface near the ice with a density of 9.7 x 10 super(3) ind./m super(3) in 1989 and 6.7 x 10 super(3) ind./m super(3) in 1990. Cladocerans and rotifers have different vertical mode of maximum abundance. Cladocerans tended to distribute in the metalimnion and rotifers were different among the species. Adult and copepodite stages of C. vicinus exhibited reverse vertical migration, but nauplii did not. Other species migrated with small amplitude, or did not show such distinct vertical movements.