PHYTOPLANKTON OF SOUTH GEORGIA 



31 



80- 



40- 



g O - tU (T) 



tn cn c*) cti rn 

 PHYTOPLANKTON TQTAL5 

 MILLIONS 



mentioned above were more numerous than at any of the other stations worked during 

 the survey. Diatoms were still fairly numerous, particularly Corethron valdiviae (spine- 

 less chains) and to a lesser extent Eucampia antarctica 

 and Nitzschia seriata. The conditions on this line may be 

 summarized as follows: 



At the four inshore stations (Sts. 308-11) an extremely 



scanty phytoplankton with small numbers of dinoflagellates 



dominant, but fair numbers of Corethron valdiviae, alone 



among diatoms, present at Sts. 309 and 310. At the next 



two stations (Sts. 312 and 313) diatoms were completely 



dominant over dinoflagellates, with Thalassiothrix antarctica 



considerably in excess of Corethron valdiviae, and these 



two species far more numerous than all the other forms. 



At these two stations the temperatures were lower than 



those found closer inshore, and lower than at the two 



stations worked farther offshore on this line a fortnight later. 



At St. 358, though the dinoflagellates Peridinium ant- 



arcticuni and Ceratimn pentagomim f. grandis reached their 



highest estimated numbers for the whole survey, it will 



be seen from Fig. 5 that they represented only 7-3 and 



6-0 per cent respectively of the total phytoplankton, the 



diatom Corethron valdiviae in the spineless chain form 



being dominant with 80 per cent. It may be mentioned 



that throughout this survey the C. valdiviae present were 



entirely in the spineless chain form ; the absence of the 



individual frustules, with their double crown of spines so 



characteristic of almost all Antarctic surface waters, was 



most marked, and apparently correlated in some way with 



the abnormal conditions prevailing round South Georgia 



at the time. 



The outermost station on the Larsen line, St. 357, 



showed large numbers of the two dinoflagellates whose 



presence was such a feature of this survey, and with the 



percentage of C. valdiviae falling to 32-9 it will be seen 



that together they accounted for nearly half the total phyto- 

 plankton (Fig. 5). At both the outer stations small pro- 

 portions of the diatoms Eucampia antarctica and Nitzschia 



seriata were found. Thalassiothrix antarctica was absent, 



in strong contrast to the conditions found farther inshore 



a short time earlier 



% 



40 



NITZSCHIA SERIATA 



CERATIUM PENTAGONUM 



F. GRANDIS 



7 



/o 

 40- 



20 

 0-^ 



DINOPHYSIS SR 



I 



Fig. 5. Diagram showing the per- 

 centages of the principal species 

 in the catches on the Larsen Line, 

 South Georgia survey, January- 



February 1930. 



On the Prince Olaf line the phytoplankton at the two inshore stations was almost 

 non-existent (Table III, Figs. 4, 6). Proceeding seawards, that at St. 307 was com- 



