Journal of Plankton Research Vol.24 no.5 pp.453-470, 2002
© Oxford University Press 2002
Microplankton and primary production in the Sea of Okhotsk in summer 1994
Shirshov Institute of Oceanology Ras (Southern Branch), Gelendzhik-7, Krasnodar District, 353470, Russia
Corresponding author: YU. I. Sorokin. E-mail: sorokina{at}sclios.coast.ru
Phytoplankton composition, density, vertical distribution and primary production were investigated in the Sea of Okhotsk and in the adjacent northern north Pacific in July–August 1994, together with measurements of density and distribution of planktonic microheterotrophs: bacteria, nanoheterotrophs and ciliates. Different phases of phytoplankton seasonal succession were encountered during the period of investigation in various regions of this sea. Primary production measured at 144 stations was found to be greatest (1.5–4 g C m-2day-1) in areas of spring-phase succession along the Sakhalin shelf and the Kashevarov bank. Periodic relapses of the spring blooms of ‘heavy’ diatoms during the whole growth season were recorded over this bank. The summer phase of the phytoplankton minimum prevailed in the central and eastern parts of the sea, manifested by the dominance of nanoflagellates in terms of phytoplankton biomass. Primary production was 0.5–1 g C m-2 day-1. The early autumn phase of succession was typical of the Kurile strait area and the adjacent north Pacific. Primary production there varied from 0.7 to 2 g C m-2 day-1. The integrated phytoplankton biomass in the water column varied from 9–12 g m-2 in zones supporting the summer minimum assemblage to 15–20 g m-2 in zones of early autumn recovery of phytoplankton growth, and up to 40–70 g m-2 in areas of remnant or relapsed diatom blooms. The numerical density of bacterioplankton was between 1 x 106 and 3 x 106 cells ml-1 and its wet biomass was between 100 and 370 mg m-3. In deep waters it was 8–15 mg m-3. The integrated bacterioplankton biomass in the upper water column varied from 6 to 29 g m-2. The numerical density of zooflagellates varied in the upper layer between 0.8 x 106 and 4 x 106 l-1 and their biomass was between 20 and 50 mg m-3. In deep waters they were still present at a density of 0.05 x 106 to 0.2 x 106 cells l-1. The biomass of planktonic ciliates varied between stations from 20 to 100 mg m-3. The joint biomass of planktonic protozoa in the water column was between 3 and 12 g m-3 at most of the stations.
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