Figure 4: Co-occurence plot of the most common merolimnic species that occur at least in 10 % of the samples. Diptera are excluded because species numbers were too high to visualize clearly.
The indicator species analysis identified most species indicative for a certain season or seasons when either winter or spring samples were included in the combinations: autumn + spring + winter: 35 indicator species; spring + winter: 30; winter: 24; spring: 20. Groups including the summer samples showed the lowest number of indicator species: autumn + summer: 2 indicator species; summer: 1; autumn + summer + winter: 1; spring + summer + winter: 1, indicating the presence of few species characteristic only for summer. Some species were exclusively found in one season, like the Plecoptera Protonemura nitida in autumn and the Trichoptera Chaetopteryx major in winter (see also Figure 5 & S18). Species not found in summer, but quite frequently in all other seasons, were Trichoptera Silo piceus, Potamophylax latipennis,Plecoptera Nemoura flexuosa, Diptera Tipula paludosa, Rheocricotopus atripes, Coleoptera Platambus maculatus and Annelida Tubifex tubifex . Species that were almost exclusively (high A value) and often (high B value) found in spring and winter included Trichoptera Glyphotaelius pellucidus, Limnephilus flavicornis, Halesus radiatus and Plecoptera Nemurella pictetii, Isoperla grammatica . Here, results were congruent with the NMDS and co-occurrence plots showing a clear distinction between summer and winter samples. In some cases, more than one OTU was assigned to the same species. Here, most OTUs showed similar association values. However, for Baetis vernus the different OTUs showed different associations even though it had no significant association to any season(s) when all OTUs were combined. One OTU was significantly associated with autumn, one with autumn + spring and two with autumn + spring + summer.