The effects of Najas marina on the zooplankton species composition and water chemistry in a small, shallow lake (Fehér-tó, Fertő-Hanság National Park, Hungary)

Abstract

Horizontal distribution and diurnal migration of zooplankton as well as a few water chemistry parameters were investigated in the clear-water and the turbid state of the extremely shallow Lake Fehér (Hungary) between 1998-2001. Significant horizontal and diel differences were recorded in the density and composition of zooplankton assemblages as well as a few water chemical parameters between the turbid and clear-water state of lake. In the turbid state copepods dominanted zooplankton assemblages developed with low density and species richness and the cladoceran zooplankton consisted of mainly pelagic species with low abundance values. During the presence of Najas marina the zooplankton community was dominated by cladocerans and the ratio of the macrophyta-associated species was high. In case of few cladoceran species significant diel density differences developed between the macrophyte bed and the above macrophyte-free water column however macrophyta-associated species did not show diel vertical migration. Based on the result of diurnal monitoring the importance of DHM (diel horizontal migration) was irrelevant in the uniform and dense Najas beds and zooplankton appear to migrate vertically rather than horizontally.

Keywords

• Zooplankton
• Najas marina
• horizontal distribution
• Fertő-Hanság National Park
• Hungary