Distribution of planktonic crustaceans and its diurnal changes in a hypertrophic shallow lake: does the switch from turbid-water state to clear-water state matters?

Abstract

The paper presents results of post hoc analysis of diurnal changes in the crustacean distribution along the horizontal transect in the shallow hypertrophic lake, which undergone a switch from turbid-water, phytoplankton-dominated state (chl-a : 257.8 ± 100.2 µg dm−3 , Secchi depth: 0.17 ± 0.02 m) to clear-water plant-dominated state (chl-a : 26.8 ± 4.8 µg dm−3 , Secchi depth: 1.03 ± 0.29 m). Changes in crustacean biomass were observed in two consecutive years during two July days (every sixth hour, starting with the noon) in three sampling sites (emergent macrophytes, submerged macrophytes and center), situated along the horizontal transect between the lake shore and the center of the lake. Analysis revealed that: (a) in turbid-water conditions crustaceans aggregated at night-time near the water surface, both in the littoral zone and the lake center; (b) in clear-water state a nocturnal increase in crustacean biomass was noted only in submerged macrophyte site, but concerned only cladocerans. In conclusion, we hypothesized that switch from phytoplankton-dominated to plant-dominated state effects in change of predator-avoidance strategy showed by planktonic crustaceans.