SUMMARY: SPECIAL AREAS: DISCUSSION 343 



fertility of the more northerly Antarctic surface waters when neritic influences are at 

 work. Though results from different seasons have had to be considered together it 

 seems clear that the essential form of the seasonal cycle is similar to that of the oceanic 

 northern zone. The quantitative values recorded are nearly ten times as great, however, 

 and the whole cycle oriented so that the maximum falls somewhat earlier in the year. 

 The same conditions are reflected in a lesser degree in the larger area of the Scotia 

 Sea. Here of course neritic influences are less pronounced, but the quantitative values 

 are still twice as great as in corresponding oceanic latitudes. 



The qualitative sequence of the phytoplankton in these two areas has not been 

 considered in detail here, for many observations on it have already been published. The 

 main features are predominance of Group III and, to a lesser extent, Group II during 

 the main increase, the latter increasing in importance later in the year. Members of all 

 groups probably reach their maximum ' absolute ' abundance during the main increase 

 of the very rich mixed South Georgia plankton. Under the slightly more oceanic 

 conditions of the Scotia Sea area, predominance of Group III species is much more 

 sporadic, and the relative importance of the small oceanic pennate forms (Group I) is 

 much greater. 



The other special areas have not been worked sufficiently to permit of more than 

 suggestions of the probable implications of the scanty data available. In some these are 

 strengthened by a considerable body of previous evidence. The eastern South Pacific 

 is the best known, and it appears that the time cycle here is roughly intermediate 

 between that of the Northern and Intermediate Regions, and the phytoplankton 

 exceptionally scanty. 



Incidental observations on biological features of special interest are described. The 

 Antarctic phytoplankton exhibits extreme development of the colonial habit which 

 cannot be fully realized unless fresh samples are examined. A possible correlation 

 between change of form with adoption of the chain-forming habit in Corethron with 

 reduction of silicate content of the medium, previously suggested on theoretical grounds, 

 is partly confirmed. Some observations on spore formation are discussed in the light 

 of recent laboratory experiments. Examinations of stomach contents showed that in 

 addition to Euphansia superba, other Antarctic Euphausians, some of the most important 

 Calanoids, and some of the more abundant Pteropods, all feed extensively upon diatoms. 

 Moreover, the Calanoids are capable of triturating and swallowing the large spiny 

 diatom species as well as ingesting smaller ones entire. 



In discussing the implications of the work as a whole it is seen that in the Antarctic 

 zone neritic influences extend farther from the land than elsewhere, but when truly 

 oceanic observations throughout the year are available, it becomes evident that they are 

 just as important as in other parts of the world. This was not readily apparent from 

 earlier work confined to the complicated Falkland sector. As it seems impossible for 

 phosphate and nitrate to be factors limiting phytoplankton production in any part of 

 the Antarctic zone, the observed differences in distribution both in time and space must 

 be explained on other grounds. The importance of the physical factors, light, stability 



