272 DISCOVERY REPORTS. 



unlikely that they are ever sufficiently important to invalidate the broad picture pre- 

 sented by our study based mainly upon those larger autotrophic organisms. 



Before leaving the work of the 'Meteor', mention should be made of the work of 

 Peters (1934) on the Ceratia. The agreement between his observations upon Ceratium 

 fusiis (p. 37, fig. 12) and C. penlagomim (pp. 27, 32, fig. 10) and my own (Hart, 1934, 

 pp. 23, 173 etc.; 1937, p. 441) is very close, and I think it may be considered as well 

 established that the latter is the only member of the genus whose normal distribution 

 extends so far south as the Antarctic zone. 



The pioneer work on the study of the phytoplankton undertaken as part of the 

 Discovery investigations was carried out by Professor A. C. Hardy. The results, mostly 

 relating to the complicated region of the South Georgia whaling grounds during the 

 season 1926-7, have been described by him in Part H of the very detailed work on the 

 plankton observed in that region pubhshed in collaboration with Mr E. R. Gunther 

 (1935). As the observations were mainly confined to one protracted survey, they 

 yielded little direct evidence with regard to the seasonal cycle of the phytoplankton, but 

 the first attack on many important related problems was made on the basis of these 

 results. Hardy's most important findings in relation to the present work are as follows: 

 On p. 40 he gives strong evidence of the overwhelming predominance of diatoms and 

 the negligible quantity of the larger dinoflagellates in the Antarctic zone. Halosphaera 

 viridis (Protococcoideae) was the only autotrophic organism, apart from diatoms, 

 observed in large numbers, and this had an extremely limited distribution (p. 64). A 

 detailed picture of phytoplankton conditions in the South Georgia area at mid-season, 

 when the diatom maximum was probably just beginning to wane, is given; which agrees 

 well with subsequent observations (Hart, 1934, pp. 66, 67). Hardy has also shown very 

 clearly that while the phosphate content of the surface water was never reduced to such 

 an extent that it could be considered as a limiting factor for phytoplankton, there was 

 good general agreement between production and phosphate reduction (pp. 76-87, 285). 

 Further, he found some slight evidence of a small secondary autumnal diatom maximum. 

 In Part V of the same work Hardy enters into a prolonged and valuable discussion 

 of the relations between zooplankton and phytoplankton, mainly concerned with the 

 development of the hypothesis of animal exclusion. The most important point in relation 

 to the present work lies in Hardy's acknowledgement that the exclusion hypothesis 

 may not hold good for all species of zooplankton, and that the converse of ' exclusion ', 

 limitation of the phytoplankton by the grazing of herbivores, is also probably important 

 far south (pp. 310-11). The most important of Antarctic 'key-industry' animals, 

 Eiiphaitsia superba, is mentioned as probably being an important grazer. The probable 

 importance of the 'grazing down' factor in limiting populations of marine phyto- 

 plankton was first clearly recognized in Harvey's (19346) work in the English Channel. 

 Hardy records Harvey's agreement that the two effects are not necessarily incom- 

 patible, each may operate at different times and places. 



My own earlier work (Hart, 1934) was mainly confined to a discussion of the phyto- 

 plankton conditions round South Georgia, in the Scotia and Bellingshausen Seas, and 



