Ann. Zool. Fennici 49: 193–218 ISSN 0003-455X (print), ISSN 1797-2450 (online) Helsinki 31 August 2012 © Finnish Zoological and Botanical Publishing Board 2012 The impact of environmental factors on diversity of Ostracoda in freshwater habitats of subarctic and temperate Europe Anna Iglikowska 1,2 & Tadeusz Namiotko 2 1) Institute of Oceanology, Polish Academy of Sciences, Department of Marine Ecology, ul. Powstańców Warszawy 55, PL-81-712 Sopot, Poland (corresponding author’s e-mail: iglikowska@ iopan.gda.pl) 2) Laboratory of Limnozoology, Department of Genetics, University of Gdańsk, ul. Kładki 24, PL-80-822 Gdańsk, Poland Received 3 Aug. 2011, final version received 15 Feb. 2012, accepted 22 Mar. 2012 Iglikowska, A. & Namiotko, T. 2012: The impact of environmental factors on diversity of Ostracoda in freshwater habitats of subarctic and temperate Europe. — Ann. Zool. Fennici 49: 193–218. In this study, we compared the ostracod species diversity in selected inland-water habi- tats of Lapland and Poland, and assessed the relationships between ostracod occur- rence and abiotic environmental variables. In total, 41 species were collected, of which only 15 species were found in Lapland, as compared with 35 in Poland. Almost all spe- cies collected from the Lapland sites were eurybiontic and no clear differences were found between ostracod assemblages inhabiting different habitat types. We hypoth- esize that this homogeneity might be a consequence of the raised water level during the springtime snow melt, temporarily connecting various waterbodies. The main factors limiting distribution of ostracod species in Lapland appeared to be low pH and low ionic content of water. In Poland, predominantly stenobiontic species were observed. In temporary waters and peat-bogs of this area useful indicator species were identified. Introduction Ostracods are tiny ubiquitous arthropods, occur- ring in all marine and non-marine aquatic habi- tats, and are even found in some terrestrial habitats such as humid forest soils (Horne et al. 2002). Nowadays, there are about 8000 ostra- cod species globally, of which slightly more than 2000 are freshwater species belonging to three superfamilies: Darwinuloidea, Cypridoidea and Cytheroidea (Martens et al. 2008). In the whole Palaearctic, the region with the highest ostracod specific diversity, there are 87 known genera with about 700 freshwater species (Mar- tens et al. 2008), but even within Europe there are areas where the ostracod fauna has been less well explored, as e.g. northern Fennoscan- dia (Iglikowska & Namiotko 2010). The Polish ostracod fauna is faunistically better known, but our knowledge of ecology and relationships with environment is still inadequate, with only a single paper published on this topic to date (by Martins et al. 2009). Ostracods are used as indicators of particular characteristics of aquatic habitats: many species have different, specific tolerance ranges and pref- erences within the full spectrum of environmen- tal factors (see e.g. reviews in Holmes & Chivas