3.1 A Description of Bacterioplankton 



VASSILIY M. KUDRYATSEV, VLADIMIR O. MAMAEV. and NADEZHDA V. SUKHANOVA 



Institute of Global Climate and Ecology, State Committee for Hydrometeorology and Academy of Sciences, Moscow, USSR 



Introduction 



An assessment of the role played by bacteria in 

 biodegradation processes occurring in the World Ocean requires 

 data concerning bacterial population counts, bacterial population 

 distributions, and a number of other functional characteristics. 



Studies carried out in the course of the First Joint 

 US-USSR Central Pacific Expedition in the equatorial Pacific 

 and the South China Sea produced new findings characterizing 

 the present state of microbiocoenoses in this part of the World 

 Ocean. 



Materials and Methods 



The microbiological studies described below were 

 conducted using methods set out in several handbooks 

 (Romanenko& Kuznetsov, 1974;Tsyban, 1 980; Tsyban etal.. 

 1988). Analyses of total counts, biomass, bacterioplankton 

 production, indicator group distribution, and degradation 

 process rates were performed at 1 8 stations. The samples were 

 taken from 6 to 19 depths using 5-1 Niskin bottles. To allow for 

 overall bacterial counts, samples of 20-50 ml were passed 

 through "Synpor 8" membrane filters with pore size 0.23 urn. 

 The filters were desalinated onto filter paper moistened with 

 distilled water, dried, and dyed with a 5% carbolic erythrosine 

 solution. The bacteria deposited on the filters were counted by 

 direct oil-immersion microscopy (xl350 magnification. 20 

 visual fields). 



The average bacteria volume was assessed by measuring 

 bacterial cell size with the aid of an ocular ruler. The mean 

 bacterial cell volume was found to be 0.3 urn'. 



The daily bacterial biomass production rate was calculated 

 on the basis of CO : assimilation in darkness. The latter was 

 ascertained using a radiocarbon technique (Romanenko. 1964; 

 Sorokin. 1971a). The determinations were made in 

 1 00- 1 20-ml jars. The radioactivity of the working solution of 

 carbon-labeled sodium carbonate introduced into the sample- 

 containing jars was 18 x 10 6 counts/min. The samples were 

 incubated in darkness for 24 h at the temperature of the water 

 where the sample was taken. Once the incubation was 

 completed, the samples were fixed with a 40% formaldehyde 

 solution, then passed through "Synpor-7" filters (pore size 

 0.35 (tm). The radioactivity of the bacteria deposited on the 

 filters was measured using an '•Intertechnique'" liquid 

 scintillation counter. The scintillation cocktail was ZhS-8. 

 The CO, assimilation rate in darkness (T ass ) for the bacterial 

 plankton was calculated by means of the formula 



T — '* x Qart 



± ass ' 



R xt 



where r the radioactivity of the bacterial cells on 



the filter (counts/min); 

 the hydrocarbonate content of seawater 

 (mg/1 ) determined by direct titration of 

 0. IN HC1 in the presence of methyl 

 red; 

 — the radioactivity of the isotope Na l4 CO, 

 used in the experiment (counts/min); 

 t the incubation time (h). 



The bacterial biomass production was obtained by 

 calculation, setting P h = T MS x 16.6. Bacterial plankton 

 respiration was determined by applying the formula 



C„ 



k 



D = 1J1, 



where D 



— the amount of oxygen expended on decom- 

 position (mg 1 ' d '); 

 T ass — rate ofCO : assimilation in darkness (|ig of 



C perl" 1 d '); and 



the coefficient of 7 is the ratio of oxygen uptake to 



CO, assimilation. 



The studies were carried out in the tropical and equatorial 



portions of the Pacific Ocean, as well as in the South China Sea. 



The locations of the stations are indicated on the Frontispiece. 



Results 



The equatorial Pacific is characterized by upwelling. The 

 latter occurs mostly along the boundaries of west-to-east zonal 

 flows and alternates with surface-water downwelling zones. 

 The intrusion of deep waters rich in biogenic elements into the 

 euphotic layer determines the way in which biocoenoses develop 

 (i.e., their spatial and trophic structures, productivity, and other 

 functional characteristics) (Vinogradov, 1978). 



Some temperature stratification was evident during the 

 period of our studies in the 0-8°N, 1 60- 1 80° E rectangle of the 

 equatorial Pacific. The water temperature and dissolved oxygen 

 content remained virtually constant down to a depth of 150 m. 

 The parameters in question declined rapidly below this level. 

 however, which necessarily affected the formation and 

 distribution of microbiocoenoses. Results of analyses 

 (Figs. 1-3) indicate that bacterioplankton counts and biomass 

 in the 0-100-m layer varied within fairly broad limits. The 

 highest bacterial population density was noted at Station 1 16, 

 where the average total count and biomass were 

 591 x 10 3 cells/ml ' and 13.29 ug C V d' 1 , respectively. The 

 lowest bacterioplankton concentration was noted at 

 Station 118, where the average total bacteria count was 

 199 x 10 3 cells/ml 1 and the biomass 4.48 ug C V d '. The 

 average values of the total bacteria count and biomass in 



207 



