CORETHRON VALDIVIAE 



SPINELESS CHAINS 



PHYTOPLANKTON OF SOUTH GEORGIA 35 



Stations on the Cooper Island line, were richer than those obtained on the more westerly 

 lines described above, and this was, in fact, the case. 



At all the first five stations proceeding outwards from the land, the two large dino- 

 flagellates so common on this survey predominated in small 

 hauls taken in water of comparatively high temperature. Out- 

 side these, however, a fairly rich diatom plankton was found, 

 and the dinoflagellates were of no appreciable importance. 

 The three outer stations, 344, 343 and 342, all showed surface 

 temperatures more than 0-5° C. lower than those at the inshore 

 stations where dinoflagellates were dominant. The principal 

 diatoms were Corethron valdiviae and Thalassiothrix antarctica, 

 the proportion of the latter increasing as one proceeded off- 

 shore. 



The January-February 1930 survey of the South Georgia 

 area was concluded by the Vakop line (Table VIII, Figs. 4,11), 

 worked almost due east from the island. The conditions found 

 on this line formed a close parallel to the results obtained on 

 the Cooper Island line described above. At the five inshore 

 stations temperatures were relatively high, and dinoflagellates 

 dominant, except in the small sample obtained at St. 353, 

 where the diatom Th. antarctica predominated. At the two 

 outermost stations, worked at somewhat wider intervals than 

 usual in order that the survey might be completed before 

 weather conditions led to delay, the two diatoms Corethron 

 valdiviae and Thalassiothrix antarctica became completely 

 dominant, the change again being accompanied by a consider- 

 able drop in temperature to 2-01° C, the lowest value recorded 

 in the surface waters examined on this survey. St. 356 pro- 

 vided the richest haul of the survey, over 30 million diatoms 

 being estimated. 



The last two lines worked on this survey thus cut into a 

 comparatively rich zone of fairly homogeneous phytoplankton 

 lying to the south and east of the island, further evidence of 

 which was obtained at the first two stations worked on the way 

 to the South Sandwich Islands a fortnight later (see pp. 88, 89 

 and Table XXIV). 



The general distribution chart (Fig. 12) showing the total 

 diatoms for January-February 1930 indicates clearly where the comparatively rich hauls 

 were obtained, and when this is compared with the separate distribution charts (Figs. 

 13-17) upon which the five leading species are plotted individually, a very fair picture of 

 the phytoplankton conditions prevailing over the whole area can be built up. From the 

 general chart it can readily be seen that except at the northern end of the island, the 



% 



BO 

 40 

 20 



CERATIUM PENTAGONUM 



F. GRANDI5 



u 







Fig. II. Diagram showing 

 the percentages of the prin- 

 cipal species in the catches 

 on the Vakop Line, South 

 Georgia survey, January- 

 February 1930. 



