Recent studies substantiate the importance of the unsaturated zone in groundwater biodiversity of karst areas. Few investigations, however, have addressed the temporal changes in community composition in relation to water physico-chemical features. We provide information on the distribution pattern of the fauna in dripping water at spatial and temporal scales. This is related to variation in water chemistry and other environmental features in five caves within two hydrographic basins of the Pa˘durea Craiului Mountains (northwestern Romania). The analysis revealed no major pollution in the dripping water. The physicochemical parameters varied within and between caves over one year. The dripping water fauna is heterogeneously distributed within and between the caves, containing a mixture of epigean and hypogean species. This emphasizes high microhabitat partition and also underlines the influence of physico-chemical parameters. The species composition among the two hydrographic basins was different. Crustaceans are the best represented in terms of both abundance and species richness. Six out of 15 crustacean species are endemic to the Pa˘durea Craiului Mountains and four are new to science. All these point to the importance of unsaturated karstic habitats as biodiversity hot spots in groundwater ecosystems.

Eukaryotes may influence pollutant degradation processes in groundwater ecosystems by activities such as predation on bacteria and recycling of nutrients. Culture-independent community profiling and phylogenetic analysis of 18S rRNA gene fragments, as well as culturing, were employed to obtain insight into the sedimentassociated eukaryotic community composition in an anaerobic sandy aquifer polluted with landfill leachate (Banisveld, The Netherlands). The microeukaryotic community at a depth of 1 to 5 m below the surface along a transect downgradient (21 to 68 m) from the landfill and at a clean reference location was diverse. Fungal sequences dominated most clone libraries. The fungal diversity was high, and most sequences were sequences of yeasts of the Basidiomycota. Sequences of green algae (Chlorophyta) were detected in parts of the aquifer close (<30 m) to the landfill. The bacterium-predating nanoflagellate Heteromita globosa (Cercozoa) was retrieved in enrichments, and its sequences dominated the clone library derived from the polluted aquifer at a depth of 5 m at a location 21 m downgradient from the landfill. The number of culturable eukaryotes ranged from 10 2 to 10 3 cells/g sediment. Culture-independent quantification revealed slightly higher numbers. Groundwater mesofauna was not detected. We concluded that the food chain in this polluted aquifer is short and consists of prokaryotes and fungi as decomposers of organic matter and protists as primary consumers of the prokaryotes.Food webs in aquifers may comprise eukaryotes in addition to bacteria and archaea. Groundwater eukaryotes range from singlecelled heterotrophic nanoflagellates and fungi to amphipod crustaceans, each of which has important roles in the functioning of the groundwater ecosystem (8). The occurrence of fungi in low numbers has been described for a few pristine and polluted aquifers, but to our knowledge the identities and activities of these organisms have hardly been investigated (26,27,42). Protozoans, especially nanoflagellates, selectively graze on the biomass of the bacterial community (35) and recycle nutrients (36).The abundance of protists, such as ciliates and flagellates, generally increases when there is pollution (27, 35). Biodegradation of organic pollutants often results in the development of anaerobic conditions. Under anoxic conditions, protists can survive and affect the abundance and diversity of bacteria (20). Protists can indirectly affect contaminant biodegradation. By feeding on bacteria, protists can reduce degrader populations, negatively influencing the process of biodegradation (21, 49). However, protists can also positively contribute to organic contaminant degradation by recycling limiting nutrients and making them available to pollutant-degrading bacteria (36), stimulating the activity of each bacterium (29, 30), or sustaining bioremediation by maintaining hydraulic conductivity of the aquifer as a result of reduced bacterial clogging (31, 43).Landfill leachate is an important source of groundwater po...

Niphargus is a speciose amphipod genus found in groundwater habitats across Europe. Three Niphargus species living in the sulphidic Frasassi caves in Italy harbour sulphur-oxidizing Thiothrix bacterial ectosymbionts. These three species are distantly related, implying that the ability to form ectosymbioses with Thiothrix may be common among Niphargus. Therefore, Niphargus–Thiothrix associations may also be found in sulphidic aquifers other than Frasassi. In this study, we examined this possibility by analysing niphargids of the genera Niphargus and Pontoniphargus collected from the partly sulphidic aquifers of the Southern Dobrogea region of Romania, which are accessible through springs, wells and Movile Cave. Molecular and morphological analyses revealed seven niphargid species in this region. Five of these species occurred occasionally or exclusively in sulphidic locations, whereas the remaining two were restricted to nonsulphidic areas. Thiothrix were detected by PCR on all seven Dobrogean niphargid species and observed using microscopy to be predominantly attached to their hosts' appendages. 16S rRNA gene sequences of the Thiothrix epibionts fell into two main clades, one of which (herein named T4) occurred solely on niphargids collected in sulphidic locations. The other Thiothrix clade was present on niphargids from both sulphidic and nonsulphidic areas and indistinguishable from the T3 ectosymbiont clade previously identified on Frasassi-dwelling Niphargus. Although niphargids from Frasassi and Southern Dobrogea are not closely related, the patterns of their association with Thiothrix are remarkably alike. The finding of similar Niphargus–Thiothrix associations in aquifers located 1200 km apart suggests that they may be widespread in European groundwater ecosystems.

Movile Cave hosts one of the world’s most diverse subsurface invertebrate communities. In the absence of matter and energy input from the surface, this ecosystem relies entirely on in situ primary productivity by chemoautotrophic microorganisms. The energy source for these microorganisms is the oxidation of hydrogen sulfide provided continuously from the deep thermomineral aquifer, alongside methane, and ammonium. The microbial biofilms that cover the water surface, the cave walls, and the sediments, along with the free-swimming microorganisms, represent the food that protists, rotifers, nematodes, gastropods, and crustacean rely on. Voracious water-scorpions, leeches, and planarians form the peak of the aquatic food web in Movile Cave. The terrestrial community is even more diverse. It is composed of various species of worms, isopods, pseudoscorpions, spiders, centipedes, millipedes, springtails, diplurans, and beetles. An updated list of invertebrate species thriving in Movile Cave is provided herein. With 53 invertebrate species (21 aquatic and 32 terrestrial), of which 38 are endemic for this unusual, but fascinating environment, Movile Cave is the first known chemosynthesis-based groundwater ecosystem. Therefore, Movile Cave deserves stringent attention and protection.