Comparing the Past and the Present: Ostracod Associations from a Recent and an Early Holocene Tufa Stream in Thuringia, Central Europe

We compare ostracod communities from two tufa-bearing freshwater environments near Jena (Thuringia, Central Germany): a modern spring-fed stream in the Pennickental and an early Holocene tufa sequence in the Plinz valley. Both sites represent low-order fluvial systems influenced by carbonate-rich groundwater, but they differ in their underlying lithologies, with dominating Muschelkalk at Pennickental and Buntsandstein at Plinz. In total, 19 ostracod species were recorded in the modern stream, whereas the fossil association consists of 11 species.

The early Holocene Plinz profile reveals a succession of three faunal zones reflecting changing aquatic habitats: (1) a plant-rich, fast-flowing brook with cold, oligotrophic water; (2) a shallow pond behind a tufa barrier with stable, nutrient-richer conditions; and (3) a spring-proximal shallow stream. Dominant species include Candona weltneri and Cavernocypris subterranea, indicating cold climate and changing habitat conditions after the Pleistocene-Holocene transition.

The modern Pennickental assemblages are structured by habitat type: spring ponds, waterfalls, ponded zones, and cascading streams. Flow-adapted and eurythermal species such as Eucypris pigra and Ilyocypris inermis dominate. Cluster and PCA analyses suggest temperature, current velocity, groundwater chemistry (especially alkalinity and sulfate), and vegetation cover are key environmental drivers. Species-environment relationships are consistent between fossil and modern datasets, supporting the ecological stability of many non-marine ostracods over millennial timescales. Nevertheless, different recent and fossil ostracod associations point to changing environments by climatic and anthropogenic factors. Our results demonstrate how modern analogues can refine paleoecological interpretations and provide insights into freshwater responses to past climate transitions.