PHYTOPLANKTON OF SOUTH GEORGIA 



33 



7 



/o 



zo 



PHYTOPLANKTON TOTALS 

 MILLIONS 



MELOSIRA SPHAERICA 



Ceratiiim petttagomim f . grandis was much higher than at the inshore stations, and at the 

 two succeeding stations to seaward (Sts. 322 and 321) these two species together pre- 

 dominated over Corethron to a marked extent, these three forms together comprising 

 almost the whole of the catches (Fig. 7). At the last station 

 of all, St. 320, C. valdiviae again predominated over the 

 dinoflagellates. 



The most striking feature of the phytoplankton on the 

 Bird Island line was thus the relatively high proportion 

 of dinoflagellates at the four outermost stations. They 

 were in excess of the diatoms at Sts. 322 and 321, and 

 formed 30 per cent of the total phytoplankton at Sts. 323 

 and 320. C. valdiviae was very generally present, and was 

 the most numerous form at six of the eight stations. It was 

 markedly dominant in the three comparatively rich hauls 

 close in to the land. The other diatom species met with 

 most frequently on this survey, Thalassiothrix antarctica, 

 was entirely absent from the Bird Island line. 



Again, upon the Cape Nunez line (Table V, Figs. 4, 8), 

 the usual order of small samples inshore and richer phyto- 

 plankton off'shore was reversed, but the phytoplankton was 

 very poor throughout. At the innermost station, St. 328, 

 Peridinium antarcticum predominated. Proceeding sea- 

 wards, at St. 327, Corethron valdiviae with an estimated 

 number of 1,200,000 frustules, or 88-9 per cent of the 

 total phytoplankton, was the dominant form in the richest 

 haul of the line. Still farther seaward the two large dino- 

 flagellates, Peridinium antarcticum and Ceratiiim penta- 



20 







7 



40 

 20- 



/o 

 40 



20 







EUCAWPIA ANTARCTICA 



PERIDINIUM ANTARCTICUM 



CERATIUM PENTAGONUM 



E GRANDIS 



Fig. 7. Diagram showing the per- 

 centages of the principal species 

 in the catches on the Bird Island 

 Line, South Georgia survey, 

 Januar}'-February 1930. 



goniim f. grandis, the former usually being the more 

 abundant of the two, predominated over diatoms at all 

 the stations right out to the end of the line. The single 

 exception was the very poor haul at St. 325, in which Corethron was again dominant. 



The chief features of this line, apart from the poverty of the phytoplankton through- 

 out, were the extreme scarcity of diatoms other than C. valdiviae and the general 

 predominance of dinoflagellates. 



On the line worked southwards from Undine South Harbour (Fig. 4) the phyto- 

 plankton hauls were uniformly small and of very much the same character throughout. 

 The same two large dinoflagellates predominated, except at Sts. 338 and 337 (Table VI, 

 Fig. 9). At the first of these a fair proportion of C. valdiviae and Nitzschia seriata led to 

 the diatom total exceeding that of the dinoflagellates, though Peridinium antarcticum was 

 still the most important individual form. At St. 337 Corethron was definitely dominant, 

 and with a considerable proportion of Thalassiothrix antarctica also present, the dino- 

 flagellates were less important at this station than anywhere else on the line. It will be 



