DISTRIBUTION OF PHYTOPLAN KTON 



69 



volumes were nearly all considerably smaller and their relative proportions were con- 

 siderably altered. The following examples will show how great can be the differences 

 in the relative reductions in volume ; such are largely due to species of different sizes 

 and shapes predominating in the different samples. 



For comparison with Fig. 38 the phytoplankton production as measured by these 

 revised volumes is shown in Fig. 40. The two methods of measuring show, when 

 charted, patterns of general similarity, and a true idea of production probably lies be- 

 tween the two. A discussion of this production in relation to hydrology is reserved for 

 the following section ; here we will consider the grouping of the species in relation to the 

 two currents of Bellingshausen Sea and Weddell Sea origin and their mixture. 



We shall anticipate what will be discussed in the next section by noting that the two 

 main areas of intense production lie in the areas of mixture of the two currents over the 

 continental shelf on each side of the island. The charts of phytoplankton production 

 should be compared with the water-movement chart in Fig. 6. Immediately inside the 

 coast there is a belt of very poor phytoplankton production ; this is in the area of poorly 

 saline coastal water. 



It is found that the results of phytoplankton analysis place the stations in certain 

 groups defined by the principal contents of their samples. This grouping is shown in 

 Fig. 35 where the water movements, slightly modified, are also shown (see later). We can 

 recognize five distinct groups and then there are three stations, 151, WS 30 and WS 61, 

 which do not fit with any particular group. The results of analysis have been tabulated in 

 Appendix I in this arrangement of grouping, the stations being arranged topographically 

 within each group. These tables should be referred to as the different groups are 

 discussed. 



Phytoplankton Group 1. This group is in water of definitely Bellingshausen Sea 

 origin. It is represented in the December-January survey by only one station, WS63, 

 but with it may be grouped three stations to the west of South Georgia, 160, 161 and 

 WS 67, which are also in Bellingshausen Sea water. In this group Rhizosolenia styli- 

 formis, Chaetoceros atlanticiis, Ch. criophilum, Fragilaria antarctica and Nitzschia seriata 

 may be abundant; Corethron valdiviae is present in moderate numbers, Chaetoceros 

 socialis is present in very small numbers, and the following are absent: Coscinodisats 

 bouvet, Thalassiosira antarctica, Biddulphia striata and Thalassiothrix antarctica. These 

 remarks refer only to the water sampled at this time and locality; we know that 

 Thalassiothrix antarctica can occur in Bellingshausen Sea water, for it was taken in 

 dense masses outside the South Shetland Islands in April 1927 (see Hardy (1928)). 



