engleski

Spatial and seasonal oscillation in zooplankton taxonomical and functional groups under distinct environmental scenarios

In freshwater environments, zooplankton influences the functioning of an ecosystem through its species composition and biomass which affects the structure of other food web components. By using a zooplankton functional groups viewpoint, species can be arranged into classes with distinct ecological roles. The aim of the study was to evaluate the change in zooplankton taxonomical and functional feeding groups among different habitat types, following season and hydro regime replacement. Six sampling sites were chosen: two river stations (Danube, Site 1 ; Drava, Site 2), one floodplain lake (Lake Sakadaš, Site 3), and three channels placed close to the farm areas (Sites 4-6). Samples were collected on two occasions in 2016: in June during flood and September in low water period. A total of 73 zooplankton species were recorded (53 Rotifera, 14 Cladocera and 6 Copepoda). Among measured environmental variables, water depth and conductivity values varied significantly among sites, while transparency values and concentrations of total nitrogen and total phosphorous oscillated between seasons. All zooplankton taxonomical groups differed significantly among sites, while functional classification revealed spatial oscillation in microphagous species. During low water period cladocerans and copepods strongly correlated with dinophytes and cryptophytes, with the dominance of small-bodied microcrustaceans (Ceriodaphnia sp., Thermocyclops sp.) known to prefer these algae in their diets. Following flooding condition, rotifers correlated with several phytoplankton groups, especially chrysophytes, chlorophytes and xanthophytes. At sites 3 and 5 significant proportion of cyanobacteria during September influenced the development of bacteria‐detritus suspension and minute algae feeding zooplankton species (Anuraeopsis fissa, Brachionus angularis) with occasional occurrence of raptorials. Algivorous zooplankton species, especially those feeding on algae ranging in size from 20-50 µm, like Synchaeta genera, prevailed at sites where chlorophytes, diatoms and cryptophytes were abundant. The raptorial way of feeding characterised high-flow environments, especially during low water period, while microfilter-feeders marked channel environments. The results of our study point to the significant spatial oscillation of zooplankton functional groups and indicate proper diagnostics of the applied approach in describing the lower trophic levels, in all types of studied environments.

Rotifera, Cladocera, Copepoda, phytoplankton, river, channel

nije evidentirano