PHYTO- AND ZOOPLANKTON INTERRELATIONS 



MILLIONS 

 OF CELLS 



150 



100- 



50- 

 40" 



30 

 20 



10-j 







PHYTOPLANKTON EXPRESSED 

 IN NUMBER OF CELLS 

 AND IN VOLUME 



NUMBER OF STATIONS AVERAGED 



VOLUME 

 IN C.C. 



30 



measure of phytoplankton production. We should not expect to find whale concentra- 

 tions in those parts of an area which had a markedly lower phosphate content than the 

 rest. It is important to observe that the records of phosphate values give an indication 

 of the production of phytoplankton over a little time in the past, a period of time, which 

 would allow either the phytoplankton to be reduced by the Euphausians or allow the 

 distribution of Enphausia to be adjusted according to the hypothesis of exclusion, 

 and also that of the whales. We 

 have demonstrated on p. 68 that 

 measurement of phytoplankton 

 either by the number of cells or by 

 volume is not really satisfactory, 

 so that an estimation by reduction 

 in phosphate content for this and 

 the reason just given may often be 

 a better guide than actual phyto- 

 plankton measurements at the 

 time. This will not invariably be 

 so, because if phytoplankton pro- 

 duction ceases and the crop dies 

 down, then as time elapses phos- 

 phate measurements will lose their 

 value as a guide. 



Since the survey with which we 

 are concerned was carried out the 

 results of the phosphate determi- 

 nations of later surveys have been 



20 



10 



>I05 101-105 96-100 91-95 66-90 



PgOs IN MGM PER M- 



<BG 



Fig. 145. Correlations of phytoplankton production with 

 phosphate values averaged for the top 50 m. 



published in the Station Lists in the Discovery Reports ; x there are whale distribution 

 figures published by Kemp and Bennett which correspond in time to three surveys 

 at South Georgia and one at the South Shetlands. Supposing for a moment that the 

 inverse correlationship between the phytoplankton and the Euphausians is correct, 

 we will attempt to deduce the state of the whale fishery at each of these times from the 

 corresponding phosphate distribution, and then compare the results of our deductions 

 with the actual state of the fishery as reported by the industry. Fig. 146 shows the 

 distribution of phosphate content off the northern, eastern and southern coasts of South 

 Georgia in the December-January survey of 1928-9 expressed as an average for the 

 top 50 m. It is seen that the greater part of the area has a relatively high phosphate 

 content, the area shaded in the figure having a content of over 100 mg. per m. 3 ; to the 

 south of the island, however, there is a region of somewhat lower content. From this 

 we should expect that the greater part of the area was free of dense phytoplankton, but 

 that there was more phytoplankton concentrated towards the south. That this phosphate 



1 Station List 1927-9, Discovery Reports, Vol. in, pp. 1-134, and Station List 1929-31, ibid. Vol. IV, 

 pp. 1-232. 



D xi 37 



