Low site diversity but high diversity across sites of depauperate Crustacea and Annelida communities in groundwater of urban wells in Kraków, Poland

Crustaceans and annelids are key components of groundwater communities, influenced by both abiotic conditions and biotic interactions. This study assessed their diversity in urban groundwaters accessed via 91 dug/drilled wells in Kraków, southern Poland, subject to chronic anthropogenic disturbance. Invertebrates were recorded in 47 wells, with 19 species-group taxa identified from 28 wells, including eight annelid and 11 crustacean taxa (Ostracoda: 3; Copepoda: 6; Bathynellacea: 1; Amphipoda: 1). Six stygobitic taxa were detected in 10 wells: Trichodrilus cernosvitovi, Trichodrilus sp., Typhlocypris cf. eremita, Diacyclops gr. languidoides, Bathynella natans, and Niphargus cf. tatrensis. Due to some taxonomic uncertainties, open nomenclature was used where necessary. Species accumulation did not reach saturation, but extrapolation suggested the sampling was exhaustive. Alpha diversity was low (1–3 species per well, mean =1.4), while beta diversity was high (Whittaker index =12.3), indicating substantial species turnover, a typical feature of groundwater ecosystems. No clear seasonal trends were observed, consistent with previous studies in Kraków. Four main community types were identified. One, dominated by Enchytraeus gr. buchholzi, may indicate degraded conditions, another, with Bathynella natans and Aeolosoma spp., suggests transitional states; a third, dominated by Trichodrilus spp., likely reflects relatively undisturbed groundwater; and a fourth, more heterogeneous type dominated by surface copepods, was ecologically ambiguous. Despite generally low richness and dominance by surface taxa, the presence of six stygobitic species suggests that at least 20 % of the surveyed wells retain relatively good ecological conditions.