# Zooplankton Community Responses to Oxygen Stress
## 3 Results  
The full list of species found in the pelagic zones of the 41 lakes consisted of 47 crustacean species (31 Cladocera and 16 Copepoda) and 54 rotifer species (Table S1). Most of the species were typically planktonic, but a few of them were typical for littoral vegetation (e.g., _Sida crystallina_, _Alona_ species, _Pleuroxus_ species, _Eucyclops macurus_). There was a large difference in the species richness between the harmonic and dystrophic lakes. Most of the recorded crustacean and rotifer species were found in harmonic lakes, and only two Cladocera and four Rotifera species were found exclusively in dystrophic lakes. The zooplankton of dystrophic lakes consisted of 20 crustacean species (15 Cladocera and five Copepoda) and 38 species of rotifers (Table S1). In dystrophic lakes, there were three euconstant species (_Ceriodaphnia quadrangula_, _Eudiaptomus gracilis_, and _Conchiloides dossuarius_) and seven constant species (_Bosminu longispina_, _Diaphanosoma brachypartum_, _Mesocyclops leuckariti_, _Asplanchua priodonta_, _Collotheca mutabilis_, _Polyarthra remata_, and _Polyarthra vulgaris_). In harmonic lakes there were two species, which were present in all lakes (_Daphnia cucullata_ and _Diaphanosoma brachyutum_) and 13 other species were classified as euconstants (_Bosmina longispina_, _Daphnia longispina_, _Leptodora kindti_, _Mesocyclops leuckariti_, _Thernocyclops oithonoides_, _Eudiaptomus graciloides_, _Asplanchna priodonta_, _Conochilus unicornis_, _Keratella cochlearis_, _Polyarthra remata_, _Polyarthra vulgaris_, _Pompholyx sulcate_, and _Trichocerca similis_). There were significant differences between the harmonic and dystrophic lakes in both the number of crustacean (F = 81.2; \(p<0.0001\)) and rotifer species (F = 19.4; \(p<0.0001\)). The number of crustacean and rotifer species in harmonic lakes was 11-15 and 13-16, respectively, while in dystrophic lakes there were 5-6 and 8-10 species, respectively (Figure 3). However, there was one outlier in the dystrophic lakes (Lake Wadolek, no 38) where 23 Rotifera species were found, and this was the highest number of rotifer species observed in any of the lakes (Figure 3b). The highest diversity of crustacean zooplankton (21 species) was found in oligotrophic Lake Serwy (no. 3). A relatively high number of crustacean species (19) was found in two other oligotrophic lakes (no. 2 and 4). The average biomass of zooplankton in harmonic lakes was 2.3 \(\pm\) 2.1 mg L\({}^{-1}\). The lakes from groups G2-G4 were characterized by a high biomass of zooplankton in the epilimnion and metalimnion, but a low biomass in the hypolimnion. The lakes from G1 were characterized by similar levels of zooplankton biomass in all three layers (Figure 4). The average biomass of zooplankton in dystrophic lakes was 2.7 \(\pm\) 7.7 mg L\({}^{-1}\). The high variability in zooplankton biomass in dystrophic lakes was due to _Asplanchua pridonta_ in two lakes, with biomass reaching 40 mg L\({}^{-1}\) (lake no. 31, metalimnion). The low biomass of zooplankton in humic lakes was observed in the hypolimnion of G5 and metalimnion of G6 (Figure 4). The dominant group of zooplankton in harmonic lakes was large Cladocera, except the hypolimnion of G4 lakes, where large Cladocera were almost absent (Figure 4). The large Cladocera in the epilimnion of lakes from G1, G2, and G3 were strongly dominated by _Daphnia cucullata_ and _Diaphanosoma brachyum_, but _Daphnia cristata_ and _Daphnia longispina_ increased in the lower layers. The lakes from G2 and G4 were distinguished by a higher relative abundance of Rotifera, and the G4 lakes had an increased share of small Cladocera with a declining share of large Cladocera. The dystrophic lakes were characterized by Rotifera and small Cladocera, and by the low relative abundance of large Cladocera (Figure 4). The most common species with the highest biomass in dystrophic lakes were _Asplanchua pridonta_, _Ceriodaphnia quadrangular_, and _Eudiaptomus gracilis_.