FEEDING OF PLANKTON ORGANISMS: DISCUSSION 329 



herbivores, but are digested too thoroughly to be identified in the stomach contents. 

 The elucidation of the full dietary of Euphausia superba, therefore, could only be 

 accomplished by special and prolonged study for which there has not yet been sufficient 

 opportunity. 



Large specimens of Sagitta gazellae have been seen with entire post-larval Euphausia 

 superba in their stomachs, and we have been able to add one or two species of birds and 

 fishes to the long list of those already known to prey upon that unhappy key-industry 

 animal. 



With the aid of the numerous records in the literature by naturalists to the earlier 

 expeditions as well as our own, it becomes possible to draw up a tentative food-chain 

 diagram (Fig. 16), illustrating some of the more important links in the Antarctic zone 

 with fair certainty, though future work will no doubt lead to minor modifications and 

 considerable extension of it. 



DISCUSSION 



One of the main results of the investigations described in this paper has been the 

 confirmation of several of the generalizations regarding the phytoplankton cycle made 

 as the result of earlier and more restricted work (Hart, 1934). The fact that the time of 

 the main increase falls later in the year as one proceeds southwards is most clearly seen 



2500 



2000 — 



1500 



1000 



500 



Julu 'August 'September October November December JanuarL| FebruarL| March April Mat] 



June 



Fig. 17. Seasonal variation in plant pigments per m.^, in the three oceanic regions compared, means of 

 50-0 m. hauls at mean dates. For numbers of observations see Figs. 10-12. Thick line: Northern Region. 

 Thin line: Intermediate Region. Pecked line: Southern Region. 



