Microscopic food webs under vanishing winters

Climate warming is affecting winter conditions in temperate regions, causing rapid changes in the formation and maintenance of snow and ice cover. However, little is known about planktonic and epixylon communities in dynamic river-floodplain systems in winter, as previous research has focused on the spring and summer „growing seasons“. Therefore, changes in the diversity, abundance, and functional groups of phytoplankton, zooplankton, and epixylon in the Danube floodplain (Kopački Rit Nature Park) were studied. In winter (January - March), water surfaces were covered only by a thin and patchy ice cover. Plankton and epixylon were diverse and abundant, and the changes in functional groups described the conditions prevailing in the studied waters well. The relatively stable conditions at the beginning of the study favoured the development of phytoplankton (diatoms, cryptophytes, ochrophytes), and epixylic taxa (diatoms, cyanobacteria) both belong to functional groups characteristic of shallow, turbid waters. Intense flooding and high grazing pressure reduced phytoplankton and epixylon abundance. The zooplankton community changed mainly due to the flood regime, subsequent nutrient loading, and food sources. Microfilter-feeding rotifers depended on phytoplankton, whereas microphytes that developed on epixylon were more important to the community for larger rotifers. The results suggest that further studies of floodplain winter communities are needed to understand better and predict floodplain ecology in future years.