Spatio-Temporal Segregation of Cladocerans within a Chara hispida Bed

ABSTRACT

I examined the diel abundance of cladocerans in the vertical and horizontal profiles through a Chara hispida stand and adjacent open water areas in Lake Wielkowiejskie. The total abundance of cladocerans differed significantly between the stations with the middle part of the stonewort bed having the lowest densities (irrespective of time). Single species differences were recorded for Bosmina longirostris, Ceriodaphnia quadrangula, and Diaphanosoma brachyurum. Total cladoceran abundance at night differed significantly from that observed during the day (irrespective of sampling site); in the central part of the stonewort stand, the highest densities occurred in the early morning, while all other zones had highest densities at night. Single species (Alona costata, Alonella exigua, Bosmina coregoni, B. longirostris, Ceriodaphnia pulchella, C. quadrangula, Chydorus sphaericus, and D. brachyurum) differed mostly with regard to dusk vs. morning or night. Even though the distances between the sampling stations were less than 0.5 m, a classical zooplankton abundance distribution for lakes with fish pressure was observed on a microscale, in terms of both vertical and horizontal profiles within the stonewort bed and the adjacent zones of open water. Chlorophyll a, conductivity, pH, and dissolved oxygen were correlated with diel cladoceran distribution.