164 DISCOVERY REPORTS 



ACKNOWLEDGEMENTS 



I would like to take this opportunity of thanking Dr N. A. Mackintosh, C.B.E., for permitting me to 

 work on Discovery collections and for advice during the preparation of this report. My thanks are 

 due also to Dr G. R. Deacon, F.R.S. and my colleague, Mr N. B. Marshall for helpful criticism. In 

 addition Miss A. C. Edwards has been very helpful in many ways, particularly in the preparation of 

 charts and hydrological sections. 



MATERIAL AND METHODS 



The plankton samples examined for this report are a selection from material collected by the Royal 

 Research ships 'Discovery', 'Discovery II' and 'William Scoresby', between the years 1925 and 

 1939, on cruises in the Atlantic Ocean from the Ice Edge in 70 S. to just north of the Equator. 

 Selection was necessary because there is a greater concentration, particularly during the summer 

 months, of Discovery stations in the Antarctic region than elsewhere in the Atlantic. It was accor- 

 dingly decided (1) to examine material from as wide an area as possible, and (2) to use certain lines 

 of stations for this purpose. The positions of the stations from which samples were used are shown 

 in Text-figs. 1-5; the approximate positions of the major surface hydrological boundaries are 

 indicated in Text-figs. 1, \a and b. These boundaries fluctuate and are therefore shown nearest to 

 their actual location when the stations were worked. 



Station data are given in the text, in tables, charts, hydrological sections and the appendices, but 

 should further information be required the reader is referred to the Discovery Station Lists {Discovery 

 Reports, vols. 1, m, iv, xxi, xxn, xxiv). Full descriptions of the plankton nets and hydrological 

 methods are given in Kemp, Hardy and Mackintosh (1929) and in the respective Station Lists; the 

 nets used are briefly given below: 



(1) N 50: hauled vertically (V) only. With its very fine mesh this net is primarily designed to 

 capture phytoplankton ; the NC 50 net (attached to larger nets) was used to a small extent. 



(2) N70: hauled vertically (V), towed obliquely (B) or horizontally (H); designed to capture 

 medium and smaller size macroplankton. 



(3) N 100: hauled vertically (V) and towed obliquely (B) or horizontally (H); designed to collect 

 the larger macroplankton. 



(4) TYF: hauled vertically (V), towed obliquely (B) or horizontally (H); designed to catch macro- 

 plankton. 



(5) N 450: for macroplankton. 



The N 50 and N 70 nets when used vertically were hauled at a constant speed through a known 

 depth range, but the speed and depth of the towed nets were subject to some variation depending on 

 weather conditions and regulation of the speed of the ship. The vertical nets are therefore of greater 

 value for quantitative analysis. 



Unless otherwise stated, all station numbers used in this report refer to those made by the Dis- 

 covery Investigations. When made by 'Discovery' (Sts. 1-299) or 'Discovery II' (Sts. 300-2648), 

 these are not prefixed, but when made by ' William Scoresby ', the letters WS precede each ; for the 

 South Sandwich Survey the letters SS are used, and for the Marine Biological Station on South 

 Georgia, the letters MS. 



Details of areas from which samples have been examined are given here: these are considered 

 either as ' Surveys ', where a comparatively small area was made the object of intensive collecting, or 

 as ' Lines ' when the ships made collections in set directions. 



