PHYTOPLANKTON OF BRANSFIELD STRAIT 127 



full Stations worked on this line are given in Table XL. From this table it will be seen 

 that at the inshore station to the north Tholassiosira antarctica predominated in a small 

 catch. The inshore character of the surface water here was clearly indicated by the 

 presence of a large species of Lycmophora in the phytoplankton. It is thus probable that 

 this catch represents the surviving remnant of the previous association to the north of 

 the strait. It has already been noted, in the account of the February survey, that the 

 typically spring form, Tholassiosira antarctica, appears to persist in small numbers just 

 within the South Shetland Islands. 



At the next station to the southward, St. 543, another very poor catch was obtained, 

 this time with Coretliroii valdiviae dominant, as we have learnt to expect in the more 

 open waters in Bransfield Strait, though the poverty of the catch may have been due in 

 part to inshore influence, as the presence of a Lycmophora sp. shows. In the course of 

 these investigations the phytoplankton of littoral areas occupied by old Antarctic surface 

 water has been frequently found to be much poorer than that present farther offshore. 

 The possible reasons for this, in the case of South Georgia, are discussed in Appendix I. 

 At both of the succeeding stations to the southward on this line Corethron valdiviae 

 was very strongly dominant in hauls of moderate quantity, the phytoplankton thus bemg 

 typical of the old Bellingshausen Sea surface water occupying the bulk of the strait, but 

 still farther south, at Sts. 546 and 547, it was very evident that the surface water was of 

 Weddell Sea origin. Indeed these stations are the best illustration yet obtained of the 

 pronounced effect of the eddy round Joinville Island, for not only was the different 

 character of the surface water clearly shown by the marked rise in salinity and fall m 

 temperature, but the phytoplankton was totally different, being of the same nature as 

 that described from St. 541, the southernmost on the preceding line farther to the east- 

 ward. The phytoplankton at these three stations was moderately rich, and composed of 

 a much greater variety of species than that found at the other stations. The dominant 

 forms in this western Weddell Sea surface water were Chaetoceros socialis, Ch. neglectus 

 and Ch. tortissimus, and other important species were Corethron valdiviae, Fragilana 

 antarctica, Thalassiosira antarctica. At the end of this section, when the phytoplankton 

 collected on this December survey is considered as a whole, it will be seen that the pro- 

 portion of other species to Corethron was considerably higher than in the surveys made 

 in November and February, but it is important that it should be recognized that this 

 was entirely due to the relatively large numbers of other species taken at the three stations 

 in the eddy of Weddell Sea surface water. This applies to all the species other than 

 Corethron totalling over one hundred thousand, with the sole exception of the typically 

 Bellingshausen Sea form Rhizosolenia gracillima. Several species did not occur at any 

 of the other stations on the survey, the more noteworthy of these being the normal 

 form of Rhizosolenia alata, Chaetoceros dichaeta, Ch. flexiiosus, Ch. socialis and Ch. tor- 

 tissimus. It may be noted in passing that this is our only record of the rather rare 

 Ch. flexuosus occurring in surface water of Weddell Sea origin. 



On this survey the line of stations across the middle of the strait was omitted, and the 

 line at the western end was brought slightly to the eastward of its old position. The 



