DENSITY AND DISTRIBUTION OF BACTERIOPLANKTON AND PLANKTONIC CILIATES IN THE BERING-SEA AND NORTH PACIFIC

The total number of planktonic bacteria in the upper mixed layer of th e Bering Sea during the late spring-early summer period ranged between 1 and similar to 4 x 10(6) ml(-1) (biomass 10-40 mg C m(-3)). In the northern Pacific, along 47-52 degrees N, the corresponding characteris tics of the bacterioplankton density in the upper mixed water layer we re: total number 1-2 x 10(6) cells ml(-1) and biomass 15-46 mg C m(-3) . Below the thermocline at 50-100 m, the density of bacterioplankton r apidly decreased. At 300 m depth, it stabilized at 0.1-0.2 x 10(6) cel ls ml(-1). The integrated biomass of bacterioplankton in the open Beri ng Sea ranged between 1.2 and 3.6 g C m(-2) (wet biomass 6-18 g m(-2)) . Its production per day varied from 2 to 23 mg C m(-3) days(-1) in th e upper 0-100 m. The numerical abundance of planktonic ciliates in thi s layer was estimated to be from 3 to 10 x 10(3) cells l(-1), and in t he northern Pacific from 0.4 to 4.5 x 10(3) l(-1). Their populations w ere dominated by naked forms of Strombidium, Strombilidium and Tontoni a. Ln some shelf areas, up to 40% of the total ciliate population was represented by the symbiotic ciliate Mesodinium rubrum. The data on th e integrated biomass of basic groups of planktonic microheterotrophs a re also presented, and their importance in the trophic relationships i n pelagic communities of subarctic seas is discussed.