BIOLOGIYA MORYA, 2015, Vol. 41, No. 3, pp. 165-173

Changes in the frequency of occurrence and abundance of ostracods (Ostracoda: Halocyprididae) in the epipelagic zone of the North Pacific

© 2015 N. L. Kaplun¹, E. R. Mazdygan¹, V. G. Chavtur^{1, 2}, K. M. Gorbatenko³, A. G. Bashmanov¹

¹A.V. Zhirmunsky Institute of Marine Biology, Far Eastern Branch, Russian Academy of Sciences, Vladivostok 690041;
²Far Eastern Federal University, Vladivostok 690091;
³Pacific Fisheries Research Center, Vladivostok 690950

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The structure of the epipelagic halocypridid ostracod fauna of the boreal northwestern Pacific has changed during the last 50-60 years. As a result, the frequency of occurrence and abundance of traditionally the most mass and cold-water species Discoconchoecia pseudodiscophora (Rudjakov, 1962) significantly decreased, while, in contrast, those of the previously rare, relatively heat-loving Conchoecia sp. A increased to the level of mass species. In 2009 and 2010, the position of the northern boundary of the Subarctic Front in this area in the period of biological spring already corresponded to its position at maximum water warming (biological summer) in the middle of the past century. Based on the ostracod distribution, the northern boundary of the Subarctic Front roughly corresponds to the position of a 10°C surface isotherm, and at the present time in the summer it lies farther north than half a century ago.

Key words: distribution, pelagic ostracods, Halocyprididae, epipelagic zone, northwestern Pacific.