PHYTOPLANKTON OF BRANSFIELD STRAIT 133 



ADDITIONAL STATIONS TO THE WESTWARD, JANUARY-FEBRUARY 1931 



The full analyses of the phytoplankton hauls from the six stations (Sts. 605-610) 

 worked to the west of Bransfield Strait later in the 1 930-1 season are given in Table XLII. 

 It will be seen that in the table they have been arranged in north to south (i.e. reverse) 

 order, partly for the sake of consistency and partly because by this means the stations 

 bearing more directly upon conditions within the strait are considered first. The dis- 

 tribution of most of the more important species is included in Figs. 66-70. 



It will be seen that at the two stations outside the strait to the north-west of Snow 

 Island, two hauls moderate in quantity and fairly similar in quality were obtained. At 

 the more northerly of the two, St. 610, well out in Drake Passage, the leading forms were 

 Corethron valdiviae, Rhizosolenia gracillima and Chaetoceros neglectus. At the inner 

 station Rhizosolenia gracillima dominated over Corethron, and other important species 

 were Thalassiosira antarctica and Chaetoceros dichaeta. It seems fairly certain from 

 observations in the Bellingshausen Sea described in the next section that this phyto- 

 plankton had drifted to the southern side of Drake Passage from the vicinity of Adelaide 

 Island. 



At two stations worked inside Snow Island, Sts. 608 and 607, two small hauls of 

 pecuHar quality were obtained. The surface salinities at the stations were remarkably 

 high, and the temperatures rather low, for this locality and time of year. These facts 

 point strongly to the probability of vertical mixing, and may well explain the peculiar 

 nature of the phytoplankton observed. An interval of more than a week elapsed between 

 the working of these stations, which is probably in itself sufficient to account for the 

 dissimilarity between them. At the later and more northerly station (St. 608), Thalas- 

 siosira antarctica was strongly dominant, a most unusual feature for this typically spring 

 form during the second half of the season, but showing a possible source of the un- 

 doubted regeneration of this species in the north of the Bransfield Strait in early spring. 

 In the very small catch from St. 607 Corethron valdiviae, Fragilaria antarctica and 

 Nitzschia closterium were the most numerous forms, the presence of the last named, in 

 the absence of ice, being indicative of littoral conditions. 



The conditions at the two stations to the southward, St. 606 in the mouth of de 

 Gerlache Strait and St. 605 in SchoUaert Channel, remain to be discussed. From the 

 analyses in Table XLII it will at once be seen that the phytoplankton at these stations 

 was entirely different from anything encountered in the old BeUingshausen Sea surface 

 water occupying the greater part of the Bransfield Strait, but that it closely resembled 

 the association found earlier in the year in the eddy of Weddell Sea water to the east- 

 ward. Chaetoceros socialis, Ch. neglectus and Ch. tortissimus were the dominant forms in 

 uncountable colonies, and other important species were Thalassiosira antarctica, 

 Biddulphia striata, Eiicampia antarctica, Fragilaria antarctica, Nitzschia seriata and 

 N. closterium. The presence of this last-named species furnished the only notable 

 diff'erence from the Weddell Sea association, apart from the expected occurrence of the 

 Uttoral form Lycmophora in small numbers. At first sight it would seem as if the current 



