Ecol. Mont., 2 (3), 2015, 255-270 ISSN 2336-9744 (online) | ISSN 2337-0173 (print) The journal is available on line at www.ecol-mne.com Deep - water hypoxic meiobenthic Protozoa and Metazoa taxa of the Istanbul Strait’s (Bosporus) outlet area of the Black Sea NELLI G. SERGEEVA 1 * & SOFIA A. MAZLUMYAN 2 1 Institute of Marine Biological Research Russian Academy of Sciences, 2, Nakhimov ave., Sevastopol 299011, Russia. E-mail: nserg05@mail.ru 2 Institute of Natural & Technical Systems Russian Academy of Sciences, 28, Lenin str., Sevastopol, 299011, Russia. E-mail: mazlmeister@gmail.com Received 8 May 2015 │ Accepted 22 May 2015 │ Published online 26 May 2015. Abstract The purpose of these investigations was to understand the response of different meiobenthos taxa on the oxygen depletion in the habitat in the deep-water areas of the Black Sea. The results of first study were published in TrJFAS (Sergeeva et al. 2013) and were devoted to vertical distribution of the deep-sea meiobenthic communities. This article includes a historical overview of research dedicated to meiobenthos and represents first detailed quantitative analysis of taxonomic composition and vertical distribution of main taxa of meiobenthos in the Istanbul Strait’s (Bosporus) outlet area of the Black Sea along the transition from oxic to anoxic conditions, where the sinking water is in contact with the bottom. Nine stations were carried out in the Istanbul Strait’s outlet area of the Black Sea during 9th–21st November 2009 at the R/V ‘Arar’ cruise from the Istanbul University. The abundance and vertical distribution of main taxa of Protozoa (Ciliophora, Gromida and Foraminifera) and Metazoa (Nematoda, Polychaeta and Harpacticoida) on the Black Sea shelf and the upper slope area (75–300 m depth water) were studied. Meiobenthos was present at all investigated depths and included 21 taxa. Gromiids, hard-shell foraminifera and polychaetes were found at depths between 75–250 m, Ciliophora, soft-shelled foraminifera and nematodes were found at depths between 75–300m. Our data suggest that some benthic eukaryotes (protozoa and metazoa) can tolerate anoxic and sulfidic conditions of the Black Sea. Key words: Ciliophora, Gromida, Foraminifera, Nematoda, Polychaeta, Harpacticoida, abundance trends, depth gradient, sediment layers habitat versatility. Introduction This work continues a series of studies on deep-water meiobenthos in the Istanbul Strait’s (Bosporus) outlet area of the Black Sea, conducted within the framework of the EU 7 th FP project HYPOX (In situ monitoring of oxygen depletion in hypoxic ecosystems of coastal and open seas, and land-locked water bodies) EC Grant 226213. The aim of that study was ambiguous. Firstly, to understand the response of the benthic fauna on oxygen depletion and secondly, to analyze the taxonomic composition and distribution of the benthic fauna inhabiting the depth zone where the oxic/anoxic interface zone meets the sea floor. Previous Studies Pioneer studies of benthic fauna in the Bosporus outlet area were done in 1890, where new mollusks species were discovered, previously not described for the Black Sea (Ostroumov 1893, 1894). In subsequent studies the research interests were focused only on the macrobenthic component of bottom fauna (Zernov 1913; Research Article