Production in the Sea of Okhotsk

Primary production, microbial production and the density of planktonic micr oheterotrophs were estimated at 40 stations in the Okhotsk Sea in July-Augu st 1992 during the seasonal phytoplankton minimum. The primary production b y phytoplankton remained rather high even during this minimum. At most stat ions it was >0.6-0.8 g m(-2) day(-1), and in leftover patches of spring dia tom 'bloom' it reached >5 g C m(-2) day(-1). The deep maxima of phytoplankt on at the upper boundary of the seasonal thermocline were an ordinary pheno menon. The depth of the euphotic zone was normally 30-50 m in the open sea and 12-25 m at the shelf stations. Any correlations between the phosphate c ontents in the upper mixed layer and primary production were absent at the stations. There was no adaptation of the phytoplankton to the light deficie ncy in deep maxima layers. The total numbers of bacterioplankton were 1-1.5 x 10(6) 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 wat ers, the bacterio-plankton biomass decreased to 10-40 mg m(-3). The microbi al production in the upper layer was high, at 50-100 mg m(-3), decreasing 5 0-100 times in the deep waters. The numbers of ciliates in the upper water layer varied from 3 to 6 x 10(3) 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 la yer, and per square metre varied to 1.5-2.5 g. The dominant ciliate taxa be longed to the naked oligotrichid genera Strombidium and Tontonia. Tentative calculations were made of the basin's annual primary production and for th e analysis of energy balance in the ecosystem.