The vertical distribution of zooplankton in brackish meromictic lake with deep-water chlorophyll maximum

Abstract

We examined the dynamics of the vertical stratification of physical, chemical and biological factors in a brackish meromictic lake with a deep-water chlorophyll maximum (Shira Lake, Russia, Khakasia) during the growing season and estimated how the vertical distribution of these factors influences the vertical distribution of the zooplankton community. The vertical distribution of zooplankton was restricted by the anoxic hypolimnion. Nauplii and younger copepodides (C1–C3) of the copepod, Arctodiaptomus salinus, and the rotifer, Brachionus plicatilis, were found in the upper warm waters. During summer stratification the maximum of A. salinus biomass, which consisted mainly of older copepodides (C4–C5) and females, was associated with the deep-water maximum of biomass of green algae, which are the preferred diet for this species. The vertical distribution of the rotifer Hexarthra oxiuris was bimodal with numerical peaks in the epi- and hypolimnion. Reproduction peaks of dominant species were separated in time. The reproduction peak of A. salinus was at the beginning of summer when A. salinus constituted up to 99% of total zooplankton biomass. The development of rotifers was detected after the reproduction peak of A. salinus when the biomass of rotifers reached 50% of total zooplankton biomass.