PHYTOPLANKTON OF BRANSFIELD STRAIT 



125 



Bellingshausen Sea, whereas the more westerly parts of the Bellingshausen Sea have 

 been found to support a more varied association in which Nitzschia seriata was pro- 

 minent (see pp. 148, 177). The drift from the more westerly parts of the Bellingshausen 

 Sea will in the normal course of events pass to the north of the South Shetlands, 

 scarcely influencing the Bransfield Strait at all. This was the probable source of the rich 

 flora of Chaetocerids, Nitzschia seriata, etc., observed in the southern half of Drake 

 Passage in April 1930, in old surface water of Bellingshausen Sea origin, a flora which 

 was evidently the outcome of a secondary autumnal diatom increase (see p. 76, 

 Table XX). On this occasion we were unfortunately able to work only one station m 



Fig. 64. The distribution of Fragilaria antarctica in Bransfield Strait, November 1929. 



I = one thousand. 



Bransfield Strait owing to ice conditions. This station showed, however, a similar flora 

 to that found outside Livingston Island, though not so rich. It seems, therefore, that if 

 N. seriata ever reaches great abundance in Bransfield Strait, it does so in late autumn. 

 The only other species of much importance in the phytoplankton community of the 

 strait on this November survey was Fragilaria antarctica. As can be seen from Fig. 64, 

 this species was fairly abundant to the north-east and also in the eddy of Weddell Sea 

 water. It was absent from the middle line and present at two stations only to the west- 

 ward (at St. WS 490 as f. bouvet). The distribution of this species is thus obviously to 

 be explained on the same lines as that of Thalassiosira antarctica and Biddulphia striata, 

 namely regeneration from the remnant that had survived the winter within the strait, 

 or from their spores. 



