PHYTOPLANKTON 39 



PART II. THE PHYTOPLANKTON 

 By A. C. Hardy, m.a. 

 INTRODUCTION 



Our knowledge of the phytoplankton of the Antarctic began with the publication of 

 the report by Castracane (1886) on the diatoms collected by the Challenger Expedition. 

 The 'Challenger' had penetrated as far as 6o° 40' S in the Kerguelen sector in 1874. 

 This knowledge was greatly extended by the reports of Karsten (1905), Van Heurck 

 (1909) and Mangin (1915 and 1922) upon the collections made by the Valdivia, 

 Belgica, Pourquoi Pas ? and Scotia Expeditions respectively. These monographs have been 

 extensively used in the examination and identification of the Discovery material. 

 Laying the foundations of our knowledge, these works have been largely systematic in 

 character; the present report, building on these foundations, aims at examining the 

 phytoplankton from the ecological standpoint, and as far as possible linking its pro- 

 duction with the hydrological data, and later, in Part V, with the distribution of the 

 zooplankton and the whale fisheries. 1 



The routine method of collecting samples of the phytoplankton was that of hauling 

 the N 50 V net 2 from a depth of 100 m. to the surface at a standard uniform speed of 

 1 m. per second. This net has 200 meshes to the linear inch. With the exception of some 

 references to the N 70 V net samples, taken at some of the earlier stations where the 

 N 50 V net was not used, all the results described in this section, except additional 

 data regarding Coscinodiscus, have been obtained from the analysis of the N 50 V 

 samples. The N 70 V net catches only a few of the larger species of diatoms, and 

 only in the case of the large Coscinodiscus bouvet are the results of the two nets at all 

 comparable. 



As many species as possible have been identified in the time available, but since the 

 object of the present survey is to provide a general picture of the plankton community 

 and to show which species are important in its economy, all the rarer forms have not 

 been specifically determined. This is particularly so in dealing with the species of 

 Peridinium, which have at no time in the present survey been really important and which 

 are difficult to identify on the squared slide during the process of analysis. 



Mangin (19 15) has already drawn attention to the small number of Peridinales in the 

 Antarctic. "Peridinales", he writes, "in striking contrast with what has been found in 

 the Arctic regions are very rare in the Antarctic. ... It is the diatoms above all which 

 contribute to and give the Antarctic flora its special character." 



1 Since this Part II on the phytoplankton was written, Mr T. J. Hart (1934) of the Discovery staff has 

 completed a much more extensive survey of the phytoplankton of these regions embracing later surveys at 

 South Georgia and the wider regions of the Weddell Sea, Bellingshausen Sea, and Bransfield Strait areas. 

 The present report (Part II), the publication of which was delayed whilst work on Part V, correlating the 

 phytoplankton with the zooplankton and whale fisheries, was completed, forms an introduction to this 

 excellent and more extensive monograph by Hart. 



2 For a description of this net see p. 17. 



