Phytoplankton Structure in the White Sea after Summer Bloom: Spatial Heterogeneity in Relation to Hydrophysical Conditions
L. S. ZHITINA1, L. V. ILYASH1, T. A. BELEVICH1, A. A. KLYUVITKIN1, M. D. KRAVCHISHINA2, A. V. TOLSTIKOV3, A. L. TCHULTSOVA4
1Lomonosov Moscow State University, 119991, Moscow, Leninskiye Gory, 1-12
2P. P. Shirshov Institute of Oceanology, RAS, 117997, Moscow, Nakhimovskii ave., 36
3Northern Water Problems Institute of the Karelian Research Centre, RAS, 185030, Petrozavodsk, Alekxander Nevsky str., 50
4P. P. Shirshov Institute of Oceanology, RAS, 163061, Arkhangelsk, North Dvinа emb., 112
Keywords: фитопланктон, Белое море, пространственное распределение, структура фитопланктона, phytoplankton, the White Sea, spatial distribution, phytoplankton structure
Abstract
Species composition and phytoplankton biomass, concentrations of chlorophyll a (Chl) and nutrients, as well as concurrent hydrophysical conditions were studied in the southern part of the White Sea in July 10-15, 2012 during chlorophyll a decrease after summer peak. The water column stability varied, the concentration of dissolved silicon in the upper mixed layer was closed to the range favorable for diatoms with the exception of areas of intensive tide mixing and areas influenced by waters of the Severnaya Dvina River. In the surface layer the dinoflagellates dominated except for areas with intensive tide mixing where diatoms prevailed. Diatoms provided major contribution to biomass in different stations above, in and under pycnocline and in deep waters out of the photic zone. The structural analysis revealed three phytoplankton communities that corresponded to different depths: communities of the photic zone, intermediate and deep layers. Extension of layers inhabited by different communities depended on water column stability and on genesis of water masses. Integrated values of phytoplankton biomass and Chl varied from 250 to 1188 mg С/m2, and from 22 to 51 mg/m2, respectively.
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