The Impact of Environmental Factors on Diversity of Ostracoda in Freshwater Habitats of Subarctic and Temperate Europe

Spatio-temporal distribution of ostracod species in saline inland lakes (Mansfeld lake area; Central Germany)

Ostracods are a diverse group of microcrustaceans with a ubiquitous distribution in a wide array of aquatic habitats and are common constituents of lake sediments. Inferences on the temporal-spatial distribution of ostracod species is a prerequisite for reconstructions of palaeoenvironmental conditions. This requires a precise knowledge not only about ecological preferences and specific life histories, but also the understanding how (local) ecological parameters affect ostracod species assemblages (abundance and composition). Generally, these studies are rare and often characterized by an insufficient differentiation of living specimens from the total amount of valves of the modern population leading to uncertainties in species occurrences and diversity data. Modern ostracod populations were sampled from 12 water bodies within a relatively small study area (Mansfeld lake area, Central Germany). Physico-chemical parameters (temperature, oxygen content, conductivity, pH) were measured in situ and the uppermost 2 cm of sediment were collected in different seasons (April, June, September). Relative abundances of ostracods (living and dead), differentiated for adults and juveniles, were used for statistical analyses (Spearman's rank correlation, Canonical correspondence analysis, Cluster analyses, Fisher's α), to investigate relationships between species distribution and environmental factors as well as to identify habitat similarities and ostracod species assemblages. In total, 27 ostracod species (20 living species) were identified. Majority of them are considered as very common (cosmopolitan) freshwater species. Only two species are usually known from brackish water (Cytheromorpha fuscata and Cyprideis torosa). This is the first confirmation of living C. torosa in German inland waters. The relative abundances of ostracods show strong fluctuations during the study period and differences in composition of the ostracod species assemblages between and within the water bodies. There are also strong differences between bio- and taphocoenoses. The measured physico-chemical parameters which are usually considered as most important drivers on ostracod species distribution do not contribute to explain the observed temporal-spatial distribution of the ostracod species. Differences in taphocoenoses show, that taphonomic processes can be very local and the sampling site, as well as the sampling time, is crucial. Biodiversity of ostracods is biased by sampling time, the variability of the ostracod assemblages between sampling month and the relationship between abundance of valves and living ostracods is not straightforward. Therefore, without precise knowledge of the ecological requirements of a species at a local scale, uncertainties may exist for the palaeoecological indication of a species.

Comparison of Ostracoda (Crustacea) species composition between lakes and streams at high elevations in Turkey

Ostracods are one of the most suitable organisms because of their ecological and morphological preferences for habitat types to study the diversity between streams and lakes. Here, 24 streams and 16 lakes were sampled in 2019 to evaluate the species compositions between streams and lakes. Environmental heterogeneity in the sense of the physico-chemical variables was found among the habitats. 24 of the 29 species with 923 individuals were found in the lakes when 13 species with 898 individuals were found in the streams. Eight species were common in both habitat types. Species contributing about 70.81% to the significant differences in the species composition between the habitats showed cosmopolitan characteristics. Species variation among the replicates of lakes were higher than streams. Results indicated that the species composition was probably associated to dissolved oxygen in lakes, while electrical conductivity in streams. Relationship amid elevational range and ostracod species richness was negative in lakes when there was no clear relationship in the streams. Overall, results suggested that determination of influential regional factors in different aquatic bodies can provide important contributions to the estimation of which habitat types can be chosen by species, and the using of species as bioindicators.