Microbial Biomass In the Euphotic Zone of the North Pacific Subarctic Water

Microbiological investigations were made in the No rth Pacific subarctic water during spring of 1969. Total bacteria, heterotrophic bacteria, yeasts, and glucose uptake by microorganisms were measured in the euphotic zone. There was no heterogeneity in the distribution of microbial biomasses between Alaskan Gyre, mid-Pacific transitional water, and Western Gyre. Another statistical analysis showed that there was microzonation in the microbial distribution but no specific vertical distribution of total bacteria, heterotrophic bacteria, and glucose uptake. The microbial biomass in the euphotic zone of the North Pacific subarctic water in spring was estimated to be (3 .0 ± 1.4) X 103 clumps of total bacteria per ml, 2.1 -t1.9 clumps of heterotrophic bacteria per 10 ml, and a glucose-carbon uptake of 89 ± 32 flg per m3 per day. THE STUDY reported here of bacterial activity over 10,000 miles of the subarctic North Pacific Ocean was carried out in conjunction with studies by other personnel on the primary, secondary, and tertiary production of the area. In this respect the particular purpose of the bacterial sampling was to determine the extent of changes with geographic area in the standing stock of bacteria and the rate of their production throughout the area. Using data available up until 1946, ZoBell (19 46) concluded that bacteria are not sufficiently abundant in seawaters to constitute an appre ciable item in the diet of marine animals . However, he also stated that cumulativel y bacteria must play an important role in food cycles by synthesizing cell substances and by converting waste or dissolved organic matter into particulate form which can be utilized as food by animals. In the early literature it was generally accepted that" only the living organisms were important as food for particulate feeders in the ocean. Using the data obtained at Station "P" in the Pacific Ocean, McAllister, Parsons, and Strickland (1960) and Parsons and Strickland (1962) reported that detritus accounts for the largest fraction of particulate matter in the sea, and 1 Manuscript received Jul y 2, 1969 . 2 Fisheries Research Board of Canada, Pacific Oceanographic Gr oup, Biological Station, N anaimo, B. C , Canada. Present address: Ocean Research Institute, University of Tokyo, N akano, Tokyo, Japan. they stressed the importance of detritus in . marine ecology. This finding was extremely important in considering the role of bacteria as food for marine animals, because on such detritus bacteria and allied microorganisms can exist and grow. With the theory of the function of solid surfaces as adsorbants of dissolved organic matter (ZoBell, 1946), the finding strongly supported the belief that bacteria and other heterotrophs are important in the food chain of the sea. As part of a series of biological, physical, and chemical investigations of the Strait of Georgia, Seki and Kennedy (1969) studied the role of bacteria and concluded that bacteria and allied microorganisms are important as food for copepods, and that they have nearly the same quantitative importance as phytoplankton, especially in the euphotic zone during winter when primary productivity is low. The present work is part of an oceanographic investigation to study the food chain in the subarctic Pacific Ocean carried out on board the research vessel CNAV "Endeavour" during a trans-Pacific crossing from March to May 1969 (Parsons, 1969). MATERIALS AND METHODS The trans-Pacific crossing followed an approximate great circle route from Esquimalt, British Columbia, to Tokyo, and back from