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Bioindication, evaluating biological responses to environmental disturbances, is crucial for assessing the ecological status of an ecosystem. While historical bioindication relied on macroscopic organisms, the introduction of environmental DNA (eDNA) techniques allows the application of protists without the necessity of morphological identification. In this study, we propose a novel bioindication methodology utilizing Arcellinida, a group of top predators among protists, as bioindicators of freshwater ecosystems. For that purpose, we first characterized the Arcellinida diversity over 1 year at three different points of Lake Sanabria, an ancient glacier lake known to be subjected to anthropogenic disturbances. We compared this diversity with an undisturbed control site. Second, we characterized the Arcellinida diversity in other ecosystems to generate the ecological background to test the connectivity between them. Results indicate limited connectivity between the different ecosystems and an edge effect between terrestrial and aquatic ecosystems. Disturbed freshwater ecosystems exhibited reduced Arcellinida diversity at both specific and infraspecific levels, providing valuable insight into recent disturbances. Arcellinida‐based bioindication provides a sensitive, accurate and easy‐to‐interpret protocol for monitoring disturbances in freshwater ecosystems. It represents a valuable tool for environmental assessments and conservation strategies. [ABSTRACT FROM AUTHOR]

Arcella is a genus of testate amoebae with a radially symmetrical shell composed of secreted material arranged in hexagonal units. Within the genus, species are distinguished by the morphology and dimensions of the shell. We describe a new species, Arcella prismatica sp. nov., discovered in a brown-water lake in the Mer Bleue Bog Conservation Area, a protected wetland in the city of Ottawa, Ontario, Canada. Specimens of the same morphotype have also been found in a subarctic peatland on the James Bay coast, near the village of Chisasibi, Quebec, Canada. The species has a polyhedral shell with a relatively flat dorsal surface and an irregularly crenulated aperture, a combination of characters not found in other members of the genus. The discovery of a novel and evidently widely distributed Arcella within the limits of a populous North American city is a reminder that the diversity of microbial eukaryotes is still poorly understood. Further exploration of undersampled peatland habitats can be expected to reveal new organisms and new relationships among known species. [ABSTRACT FROM AUTHOR]

Protists in caves are scarcely researched. Most cave studies address the diversity of protists, but very little is known about their habitats and spatio-temporal dynamics. The aim of this study was to investigate the diversity and abundance of protists in the Veternica cave in the Medvednica mountain in Croatia on hygropetric and sinter and clay pools during six months. During this study, 47 protists taxa were distinguished belonging to the groups of heterotrophic flagellates, ciliates, heliozoans, stramenopiles and testate and naked amoebae. The highest taxon richness was found at the sinter pool site richest in bats guano (36 taxa). Most diverse were testate amoebae and ciliates. The number of taxa and their abundance differed significantly between the sampling sites. The prospected habitats supported different protist assemblages, proved by ordination analysis. The most distinctive habitat was the hygropetric. Habitat heterogeneity could be attributed to the presence of inorganic and organic sediments at the sites and habitat microhydrology (lotic or lentic system). Kendall's concordance coefficient showed a good synchronicity between the habitats in the Veternica cave, based on taxon richness and abundance of protists indicating similar seasonal trends. Seasonality in the studied habitats is attributed to the hydro-meteorological conditions in the Veternica cave drainage area. This study is one of the few studies of spatio-temporal diversity and abundance of protists in caves. Despite the similar appearance of small transitional and aquatic habitats in caves, an example of this study showed specific habitat diversification. [ABSTRACT FROM AUTHOR]