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Abstract
Post iron ore mining reservoirs in Łęczyca (Poland) can be considered extreme habitats because they are characterized by high pH, conductivity, and sulfate, sodium and potassium concentrations. We observed high abundances in these water bodies of several centric diatom species that are otherwise known from less extreme environments. These included Thalassiosira duostra, Cyclostephanos dubius, Stephanodiscus binatus, Stephanodiscus invisitatus, Stephanodiscus parvus, Stephanodiscus hantzschii, Lindavia aff. balatonis, Discostella woltereckii, Discostella pseudostelligera, and Cyclotella meneghiniana, revealing the eurytopic nature of these species. Morphological differences between populations from extreme habitats and their counterparts from less extreme environments may indicate phenotypic responses of eurytopic taxa to the differing environmental regimes, or the presence of distinct, more stenotopic taxa. In both cases, this could be relevant for biomonitoring. For this reason, we carefully observed the morphological variability of our target taxa in the Łęczyca reservoir samples compared with literature accounts from less extreme habitats, and in some cases, with type material of the species concerned. Specimens similar to Aulacoseira muzzanensis α-chains were observed. Following comparison with the type material of Melosira muzzanensis Meister (≡A. muzzanensis), we concluded that the Łęczyca populations are sufficiently different to be recognized as a separate species, here described as Aulacoseira pseudomuzzanensis sp. nov. The importance of identifying centric diatoms to species level for water management surveys is emphasized, even for those taxa that are difficult to identify using only LM.