ECONOMIC IMPORTANCE ii 



Among the meteorological factors which may affect the phytoplankton, the prevalence 

 of fogs, especially in the region of the Antarctic convergence, and farther south in 

 summer when the ice is melting, should not be overlooked. The islands in the Southern 

 Ocean are so few and far between, and mostly uninhabited, that our meteorological 

 information is necessarily of the scantiest. A useful idea of the conditions experienced 

 in certain localities may, however, be gathered from the tables in Appendix II of the 

 first edition of The Antarctic Pilot (1930). The most valuable of these deal with the 

 observations of the Argentine Government Meteorological Stations at South Georgia 

 and the South Orkneys. 



THE ECONOMIC IMPORTANCE OF THE PHYTOPLANKTON 



The economic significance of the phytoplankton in Antarctic waters may be judged 

 from the following considerations. It has long been known that the southward migration 

 of the southern rorquals in summer is a feeding migration, and that within the zone of 

 Antarctic surface water the food of these whales consists almost entirely of Euphausia 

 superba, known to the whalers as "krill". The food of these Euphausians consists very 

 largely, if not entirely, of diatoms and other phytoplankton organisms. Thus we have 

 here one of the simplest food chains possible, the building up of the vast body of the 

 whale being only one stage removed from the organic fixation of the radiant energy of 

 the sun by the diatoms. From this it will be seen that some knowledge of the phyto- 

 plankton is essential to a proper understanding of the economic problems of these 

 regions, and it is largely in the hope of providing a working background for other lines 

 of enquiry that this paper has been written. 



Examination of the stomach contents of aduh and post-larval E. superba has been 

 made on a number of occasions, though this line of investigation has not been followed 

 up systematically as yet. Small diatoms appear to be ingested by some form of filtering 

 mechanism, and the more typically oceanic species are evidently digested rapidly: 

 recognizable fragments are rather rare even in the crop, the contents of which in kriU 

 from waters in which such species are dominant, presenting the appearance of a green 

 porridge. Two forms that occurred constantly and remained clearly recognizable were 

 Fragilaria antarctica and Thalassiosira antarctica. Torn fragments of the large species 

 Chaetoceros criophilum indicated that the adults are capable of triturating and swallowing 

 the larger forms in addition to possessing a filtering mechanism. In post-larval forms 

 entire examples of large Foraminifera {Globerigina sp.) were frequently found. Possibly 

 these are eaten for the sake of the contained calcium. 



In working on the larval stages of Euphausia superba Mr F. C. Eraser made the inter- 

 esting discovery that the distribution in numbers and size groups of the larvae showed 

 a very fair degree of correlation with the distribution of the phytoplankton as described 

 in this paper. The same stages were found to show an increase in size at those stations 

 where a rich development of small diatom species was found (e.g. Thahissiosira ant- 



