# Zooplankton Community Responses to Oxygen Stress
## 3 Results
The first axis of the CCA ordination was the most important, contributing to 70.43% of the inertia, and represented the difference between the zooplankton communities in dystrophic lakes (positively  
Figure 4: The mean biomass of zooplankton in vertical profiles of lakes with different oxygen conditions. Figure 3: The number of Crustacea (**a**) and Rotifera (**b**) species in lakes with different oxygen conditions. related to F1) and harmonic lakes (negatively related to F1). The CCA analysis also distinguished zooplankton communities in the lakes from G1 and G5 (Figure 5). The lakes from G1 were differentiated by the higher share of _Daplinia cristata_, _Daplinia longispina_, _Bosmina crassicornis_, _Polyarthra vulgaris_, and by species that were classified as glacial relicts. The glacial relicts were found in 11 lakes, mostly from G1, and in one lake from G2 (no. 18). The glacial relicts included _Daplinia longiremis_ (no. 9), _Bythotrephs brevimanus_ (no. 1, 3, 4, 5, 9, 10, and 18), _Cyclops lacustris_ (no. 2, 4, and 9), _Eurytemora lacustris_ (no. 1, 2, 3, 9, 11, and 25) and _Heterocope appendicitis_ (no. 1, 3, 4, 8, 9, and 10). In some lakes, these species were a dominant component of zooplankton communities in lower water layers. The lakes from G5 were characterized by _Asplanchua priodonta_ and _Ceriodaphnia quadrangula_ (Figure 5), while zooplankton communities in lakes G2, G3, G4, and G6 were relatively similar (Figure 5). However, G4 and G6 were characterised by a higher relative abundance of Rotifera, while G2 and G3 both had a higher relative abundance of large Cladocera (Figure 5). Comparing the number of species in oxic and anoxic water layers revealed significant differences in Rotifera (F = 18.5; \(p<0.0001\)) and Crustacea (F = 10.7; \(p=0.001\)). Anoxic water had fewer rotifers and crustacean species (Figure 6). However, in the case of Crustacea, these differences were smaller due to the relatively high number of species in anoxic conditions (Figure 6). Figure 5: The canonical correspondence analysis ordination of dominant zooplankton taxa in lakes with different oxygen conditions (black dots). Abbreviations Cladocera (white squares): Dap.c.c.—_Daplinia cucullata_; Dap.cri.—_Daplinia cristata_; Dap.lon.—_Daplinia longispina_; Bos.cra.—_Bosmina crassicornis_; Bos.ber.—_Bosmina berlinensis_; Bos.lon.—_Bosmina longispina_; Bos.the.—_Bosmina thersities_; Dia.bra.—_Diaphanosoma brachyurum_; Cer.qua.—_Ceriodaphnia quadrangula_; Lep.kin.—_Leptodora kinditi_; Byt.bre.—_Bythotrephs brevimanus_. Abbreviations Copepoda (rhombs): Eud.sp.—_Eudiaptomus_ species; Eur.lac.—_Eurytemora lacustris_; Het.app.—_Heterocope appendicitis_; The.oit.—_Thernocyclops oithonoides_; Mes.leu.—_Mesocyclops leukartí_; Cyc.sp.—_Cyclops_ species; cop.Cyc.—copepodites Cyclopoida; cop.Cal.—copepodites Calanoida; nau.Cyc.—nauplii Cyclopoida; nau.Calc.—nauplii Cyclopoida; nau.Calc.—_Caanoida_. Abbreviations Rotifera (cross): Pol.vul.—_Polyarthra vulgaris_; Pol.rem.—_Polyarthra remata_; Con.uni.—_Conochilus unicornis_; Con.dos.—_Conochiloides dossauris_; Col.mut.—_Collotheca mutabilis_; Pom.sul.—_Pompholyax sulcate_; Kel.lon.—_Kellicottia longispina_; Ker.coc.—_Keratella cochlearis_; Ker.qua.—_Kentella quadrata_; Ker.tec.—_Keratella tecta_; Tri.cap.—_Trichocera aapucina_; Tri.sim.—_Trichocera similis_; Asp.pri.—_Asplanchua priodonta_. Oxygen concentrations significantly affected the biomass of large Cladocera (F = 10.3; \(p\) = 0.002), which reached the highest biomass at high oxygen concentrations (>8 mg L\({}^{-1}\)). However, a high biomass of large Cladocera was also noted at low oxygen levels (0.1-1 mg L\({}^{-1}\)). The biomass of Rotifera was not affected by oxygen concentrations (F = 0.7; \(p\) = 0.39), but the highest biomass was observed in low oxygen conditions (Figure 7a). The biomass of Rotifera was similar to large Cladocera and also had two peaks at low and high levels of oxygen (Figure 7a).