284 



DISCOVERY REPORTS 



Thalassiothrix antarctica was encountered, and subsequently, by using the continuous 

 Plankton Recorder towards South Georgia, we recorded a dense belt of this diatom for 

 80 miles or so. The instrument, owing to the presence of ice, was unfortunately not run 

 right into the area examined in March, but was hauled up some 60 miles short of it. 



5I°57S 

 3Z°3l'W 



I THALASSIOTHRIX ANTARCTICA 



ON ROLL 



MILLA6E | ^ 



HOUR 2310 



SECTl0re | T p T .-, l 4 | 5 | 6 | 7 | B | 9 | |a | l||li; | l' lh4ll5ll6ll7|lBII9l?0|gllP;i23l24l25l?6l27l?8|a9 | 30|3l|3Z 13 3 ; 

 10 20 30 40 50 , 60 , 70 



34|3S|36|37 138139 14014) I42I43144I45I46I4/155I 

 R0 90 100 110 



03 



04 05 



06 



13 oto 



IS DO 



20 



Fig. 144. Graphical representation of record obtained by the Continuous Plankton Recorder on 

 approaching South Georgia from the north-east in February 1926. 



Whilst the record, which is reproduced in Fig. 144, shows that the dense zone was coming 

 to an end, the fact that Thalassiothrix antarctica was taken in moderate numbers at one 

 of the stations in the March-April survey (St. 41) shows that in March it was still in 

 the area and not far from the island. Whilst there is little relevant evidence here except 

 that there was no dense phytoplankton in the region of the Euphausian concentration, 

 the possibility, in the light of what follows, that in March the zone of Thalassiothrix may 

 have extended farther in towards the concentration of Euphausians against the coast 

 may perhaps be kept in mind. The inverse correlation between the dense patch of 

 Euphausian larvae and the gap in the Thalassiothrix on the record in Fig. 144 is of interest. 

 We have seen in the 1926-7 South Georgia survey how closely the phosphate content 

 of the water corresponded with the production of the phytoplankton. Their corre- 

 spondence is shown in Figs. 38 and 39 and discussed in detail on pp. 79-84. In 

 Fig. 145 the phytoplankton production in this survey is shown in a graph plotted against 

 a scale of phosphate values, the phytoplankton values being averaged for the stations 

 falling within each division of the phosphate scale. We have further seen how closely 

 the whale distribution appears to be bound up with its food Euphausia superba. If there 

 is an inverse correlationship between the distribution of the phytoplankton and 

 Euphausia superba brought about either by the grazing or the exclusion of the latter, 

 then, provided whales and Euphausians are present in the area, it should be possible 

 from a knowledge of the distribution of the phosphate content of the area to deduce to 

 some extent the distribution of the whales whenever the phosphate content is a fair 



