Journal of Plankton Research, Vol 21, 201-230, Copyright © 1999 by Oxford University Press
Y Sorokin and P Sorokin
Primary production, microbial production and the density of planktonic
microheterotrophs were estimated at 40 stations in the Okhotsk Sea in
July-August 1992 during the seasonal phytoplankton minimum. The primary
production by phytoplankton remained rather high even during this minimum.
At most stations it was >0.6-0.8 g m-2
day-1, and in leftover patches of spring diatom
'bloom' it reached >5 g C m-2
day-1. The deep maxima of phytoplankton at the upper
boundary of the seasonal thermocline were an ordinary phenomenon. The depth
of the euphotic zone was normally 30-50 m in the open sea and 12-25 m at
the shelf station. Any correlations between the phosphate contents in the
upper mixed layer and primary production were absent at the stations. There
was no adaptation of the phytoplankton to the light deficiency in deep
maxima layers. The total numbers of bacterioplankton were 1-1.5 x
106 ml-1 and its biomass was
close to 100 mg m-3 in the open sea. All these
numbers were 2-3 times greater at the shelf stations. In deep waters, the
bacterioplankton biomass decreased to 10-40 mg m-3.
The microbial production in the upper layer was high, at 50-100 mg
m-3, decreasing 50-100 times in the deep waters. The
numbers of ciliates in the upper water layer varied from 3 to 6 x
103 l-1 and were 1.5-2 times
greater than in the shelf areas. Ciliate biomass was 60-100 mg
m-3 in the upper mixed layer, and per square metre
varied to 1.5-2.5 g. The dominant ciliate taxa belonged to the naked
oligotrichid genera Strombidium and
Tontonia. Tentative calculations were made of the
basin's annual primary production and for the analysis of energy balance in
the ecosystem.
ORIGINAL ARTICLES
Production in the Sea of Okhotsk
Institute of Oceanology of Russian Acad. Sci., Southern Branch, Gelendzhik-7-, Krasnodar District, 353470, Russia
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