5.1.1 Certain Characteristics of Phytoplankton 



MIKHAIL V. VENTSEL and NATALIA P. VASJUTINA 



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



Introduction 



This report presents results of the preliminary analysis of 

 phytoplankton samples collected during the Third Joint 

 US-USSR Bering & Chukchi Seas Expedition. The specimens 

 were observed by the "living droplet" method using a light 

 microscope. We determined the species composition of the 

 microalgae, their size, and the number of cells. As a result, we 

 have quantitative estimates of the total number and biomass of 

 phytoplankton per unit volume. In addition, dominant species 

 have been identified, since their development in the plant 

 community strongly influences the value of the quantitative 

 indices mentioned before. These results are shown in Table 1 . 



Distribution of phytoplankton was determined in the 

 following regions: the Chirikov basin (Stations 87-107), the 

 Gulf of Anadyr ( Stations 9^ 1 ). the central Bering Sea region 

 (Stations 1-7), and the southern Bering Sea region (Stations 

 108-113). 



An intensive development of phytoplankton was observed 

 in the Chirikov basin. The number and biomass of microalgae 

 were high at all stations. The total number in the surface layer 

 varied in the range of 500-1,700 x 10' cells/1, and the highest 

 value was observed at Station 86. Total numbers of 

 phytoplankton were dominated by diatoms: Leptocylindrus 

 daniciis, Chaetoceros socialis. Chaetoceros debilis, and 

 Rhizosolenia alata. Biomass at the surface varied in the range 

 of 300-3,000 mg/1. The largest contribution to the total 

 biomass was also due to diatoms: Leptocylindrus danicus, 

 Rhizosolenia alata. and Chaetoceros concavicornis. At all 

 stations in the Chirikov basin, the quantitative indices decreased 

 with the depth. The only exception was Station 1 06. where the 

 number and biomass were high at a depth of 45 m as well. In 

 general at 40—45 m, the numbers varied in the range of 

 80-1,000 X 10' cells/1, and biomass — 120-850 mg/1. 



Thus, in the Chirikov basin an intensive development of 

 phytoplankton was observed, with diatoms occupying a leading 

 position in the plant community. 



In the Gulf of Anadyr, phytoplankton were not as abundant 

 as in the Chirikov basin and their numbers varied in a smaller 

 range, from 100 to 700 x 10' cells/1. At many stations, the 

 number of phytoplankton increased with the depth 

 (Stations 15, 19,32,36). This was probably connected with the 

 presence of the pycnocline at these depths. The most numerous 

 species in the plant community of the Gulf of Anadyr were 

 algae of various classes: 



Class Bacillariophyceae — Fragilaria oceanica, 



Fragilaria striatula, 

 Chaetoceros compressus, 

 Chaetoceros socialis, 

 Leptocylindrus danicus. 



Class Dinophyceae 

 Class Chrysophyceae 



Gymnodinium wulffii, 

 Goniaulax orientalis. 

 Chromulina sp. 



Biomass of phytoplankton in this region varied over a wide 

 range from 6 to 3,600 mg/1. High values of biomass were 

 caused by the presence of large diatoms like Rhizosolenia 

 alata. Amphiprora hyperborea, and Coscinodiscus oculus 

 iridis in the plant community. 



In general, it may be noted that during the period of the 

 expedition, the phytoplankton composition of the Gulf of 

 Anadyr was very diverse. While the number of microalgae was 

 evenly distributed throughout area, there was a wide range in 

 the biomass values. This was connected with the presence of 

 large forms of phytoplankton in the samples. 



There was an uneven distribution of phytoplankton in the 

 central area of the Bering Sea. The phytoplankton numbers in 

 the surface waters varied in the range of 

 100-2,400 X 10' cells/1 and biomass in the range of 

 40-1,800 mg/1. Quantitative indices decreased with depth, 

 which was characteristic for all the central area stations, except 

 for Station 7. At this station, the number and biomass of 

 phytoplankton were roughly uniform with depth. 



Most abundant vegetation in this region consisted of small 

 forms. The taxonomic composition of phytoplankton is 

 characteristically depauperate in diatoms as compared with the 

 northern part of the sea. The following species were numerically 

 dominant: 



Class Chrysophyceae — Chromulina sp. 



Class Haptophyceae — Calyptrosphaera insignis. 



Class Xanthophyceae — Meringosphaeramediterranea. 



Class Cyanophyceae — Synechococcus sp. 



Class Loxophyceae — Pedimonas mikron. 



Class Bacillariophyceae — Fragilaria striatula, 



Chaetoceros debilis, 

 Nitzschia delicatissima. 



In the southern part of the Bering Sea, phytoplankton was 

 characterized by the following: their numbers at the sea 

 surface varying in the range of 700-1, 700 X 10' cells/1. Among 

 numerically dominant species there were no diatoms or 

 peridinians. Instead, representatives of the following classes of 

 algae were most abundant in this region: 

 Class Cyanophyceae — Synechococcus sp. 



Class Loxophyceae — Pedimonas mikron. 



Their biomass ranged from 3 to 1,300 mg/1. 



As for biomass, the following species of microalgae were 

 dominant: 

 Class Bacillariophyceae — Fragilaria striatula. 



Chaetoceros concavicornis. 



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