Microbiological Studies of Tokyo Bay Us~o SIMU)U
Ocean Research Institute, University of Tokyo, Minamidai, Nakano-ku, Tokyo, Japan EMIKO KANEKO
Research Institute for Chemo-Biodynamics, Chiba University AND NOBUO TAGA
Ocean Research Institute, University of Tokyo, Minamidai, Nakano-ku, Tokyo, Japan
Abstract. The generic compositionof the heterotrophic bacterial populationof Tokyo Bay, which is now highly polluted and eutrophic, was compared with that of the adjacent, less polluted regions of Sagami Bay and Suruga Bay. Membersof Vibrionaceaepredominatedin the bacterialflora of seawater and zooplanktonsamples from Sagami Bay, Suruga Bay, and the mouth of Tokyo Bay. However, Fibrio spp. formed only a small proportion of the bacterial populationof the water and sedimentsamplesfrom the innerTokyo Bay; there the Gram-negative,nonmotile,nonpigmentedbacteria, which were tentatively identifiedas Acinetobacter, were predominant. The result of experiments, in which seawater samplesfrom Tokyo Bay were incubatedundervariousexperimentalconditions, indicatedthat two significantfactors apparentlycontrol the growth of Vibrio spp. in seawater; (1) a direct antagonismbetween Vibrios and phytoplanktonundergoingrapid growth, and (2) a limiting organic nutrient for vibrios.
Introduction The most serious environmental problems of Tokyo Bay derive from the pollution and eutrophication caused by the pollutants entering the Bay. Pollution has brought about profound changes in the floral and faunal populations inhabiting the Bay. Although few quantitative data are available concerning the plankton populations, a substantial increase in plankton biomass and changes Microbial Ecology 3, 173-191 (1977) 9 1977 by Springer-VerlagNew York Inc.
U. Simidu et al.
in the plankton community structure have been reported by several investigators. For example, Marumo and Murano  have concluded that the number of species of diatoms occurring in the inner region of Tokyo Bay decreased from 35 in 1947 to 23 in 1972-73. Twelve oceanic species were present in 1947; whereas none were found in 1972-73. Funakoshi  reported that the composition of the plankton populations causing red tides clearly altered after the 1940's. Although diatoms were not observed in red tides before the 1940's, thereafter several species of diatoms, along with dinoflagellates such as Exuviaella, were often found to be dominant. There is little information concerning the microbial flora of seawater and marine sediment affected by pollution. However, it is logical to assume that the composition of the microbial flora will be altered by pollution and subsequent eutrophication. This would occur not only as a direct result of the increase in nutrients, such as phosphate and nitrogenous compounds from terrigenous effluents, but also to alteration of the environmental conditions by massive outgrowths of phyto- and zooplankton. In the investigations reported here, the bacterial flora of Tokyo Bay has been compared with that of adjacent regions. Environmental factors contributing to the differences observed in the floras have also been considered in reaching the conclusions presented here. Materials and Methods Water samples were collected in 1971-72 using a glass bottle sampler (Hyroth water sampler) at a depth of 5 m below the surface at stations A and B. The location of the stations is given in Fig. I. Samples were kept cold by storing in ice prior to plating out in the laboratory. The bacteriological analyses were performed within 8 hr of sample collection. A cruise aboard R/V TANSEI-MARU in 1973-74 permitted the collection of additional seawater, plankton, and sediment samples in Tokyo Bay at stations 1 to 10, indicated on the map in Fig. 1. Sagami Bay and Suruga Bay at stations A-l, A-2, U-1, and U-2 were also sampled (Fig. 2). Water samples were collected at several depths using the ORIT water sampler ; sediment samples were collected using a core sampler. All samples were stored on board ship at 5~ and were plated within 4 hr after collection. Total bacterial counts were determined by the direct microscopic method . Viable counts, i.e., colony-forming units (cfu), were made by surface spreading of aliquots of the samples on 2216E medium  and on PPES-II medium . Selected chemical and biochemical parameters of the seawater were also measured, the results of which will be given elsewhere. In the case of samples collected during 1971 72, the concentrations of NH4-N, NOz-N, NO2-N, total and inorganic phosphate, and Si were also determined following standard methods . The water samples were also analyzed for total organic carbon using a total carbon analyzer (Beckmann Model 915). Relatively high concentrations of organic carbon in the seawater samples of Tokyo Bay allowed for the direct determination of the carbon content with this apparatus. At each sampling station, 30 to 60 strains of bacteria were picked from within circles drawn on the center of the count plates and purified by streaking twice on agar plates. The purified cultures
Bacterial Flora of Tokyo Bay
Sampling,Station at Tokyo Bay
T-2E 30' Yokoham;