DISCOVERY REPORTS 



MILLIONS 



paratively rich with a fair variety of diatoms and Coretliroii valdiviae strongly dominant. 

 At the next two stations the phytoplankton was comparatively thin, with C valdiviae 

 still dominant and a fair proportion of the two large 

 dinoflagellates. These last showed a great increase in 

 numbers at the succeeding stations, Sts. 304 and 303 ; 

 but with greatly increased numbers of diatoms — 

 C. valdiviae and Thalassiothrix antarctica dominant 

 and fair numbers of Fragilaria antarctica at St. 304 — 

 they no longer formed such a large percentage of the 

 phytoplankton. At the three outermost stations on 

 this line the dinoflagellates disappeared and the 

 diatoms Thalassiothrix antarctica, Corethron valdiviae, 

 Eiicampia antarctica and Nitzschia seriata predomi- 

 nated in that order of importance. 



The main features of the phytoplankton collected 

 on the Prince Olaf line may thus be summed up as 

 follows : very general dominance of Corethron valdiviae 

 inshore, and of Thalassiothrix antarctica, particularly 

 at those stations worked farthest from the island. The 

 dinoflagellates Peridininm antarcticum and Ceratium 

 pentagonum f. grafidis together formed more than 

 10 per cent of the total phytoplankton at all stations 

 out as far as St. 303, with the single exception of 

 St. 307. 



It will have been noted from the description given 

 above that on the Larsen and Prince Olaf lines the 

 phytoplankton was very scanty inshore, and com- 

 paratively abundant some distance away from the 

 island. Similar conditions were also found on several 

 of the lines still to be described, but on the next to 

 be considered in detail, the Bird Island line, the 

 reverse was the case. The phytoplankton at the three 

 innermost stations on this line was rich in comparison 

 with that found farther offshore, but without achieving 

 such abundance as was found towards the seaward end of the two lines previously 

 dealt with. 



At the three inshore stations on the Bird Island line (Table IV, Figs. 4, 7) Corethron 

 valdiviae was strongly dominant (entirely so at St. 318), and at the first two small pro- 

 portions of Eiicampia antarctica and Melosira sphaerica were also noted (Sts. 316 and 

 317). At St. 3 19 the phytoplankton was almost non-existent, but it became more plentiful 

 though still sparse at the next station seawards, St. 323. Here Corethron valdiviae was 

 still dominant, but the proportion of the two dinoflagellates Peridininm antarcticum and 



Fig. 6. Diagram showing the percen- 

 tages of the principal species in the 

 catches on the Prince Olaf Line, South 

 Georgia survey, January-February 

 1930. 



