Chironomid-climate continentality conundrum

PLOS One | https://doi.org/10.1371/journal.pone.0327780 August 5, 2025 8 / 18 ANOSIM revealed that the chironomid assemblages can be significantly divided by KOI (p = 0.007) with an R-value of 0.24 indicative of some overlap in taxonomic composition between continental, transitional, and continental sites. Redundancy analysis For the two tested continentality indices, KOI explained more variation in the chironomid assemblages than ATR (18.4% and 15% respectively; Table 2) with a λ1:λ2 ratio greater than 1. GDD5 and July mean air temperature explained the same amount of chironomid assemblage variation (17.2% and 17.4%, respectively; Table 2) and both have a λ1:λ2 ratio >1 and a stronger explanatory power compared to April (4%), January (8%) and October (14.2%) mean air temperatures. April and January mean air temperatures are the only variables aligned with the second RDA axis. The number of ice-cover days shows a sig- nificant influence on the chironomid assemblages (Table 2) with 15.5% of the variation explained and a λ1:λ2 ratio >1. Bedrock explained 16.8% of the chironomid-assemblage variation (Table 2; Fig 4). Lake-water pH accounted for 12.3%, and lake-water depth explained 8.3% of the variation in the chironomid assemblages. LOI did not reveal any significant influence on chironomid assemblages (Russian and Latvian parts). Chironomid – Kerner Oceanity Index relationships INDVAL revealed significant indicator morphotypes for the continental, oceanic, and transitional (continental-transitional

and oceanic-transitional) groups (Fig 5; S3 File). Continental sites are indicated by the presence of Glyptotendipes Fig 3. Chironomid morphotypes with abundances in the dataset of at least 2% in one sample. Species are arranged in abundance according to the longitudinal gradient. Continental sites (orange) are KOI −10–0, transitional (green) are KOI = 0–10, and oceanic (blue) are KOI 10–20. https://doi.org/10.1371/journal.pone.0327780.g003