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RHINCALANUS GIGAS (BRADY) 



A COPEPOD OF THE SOUTHERN 



MACROPLANKTON 



By F. D. Ommanney, PH.D.{Lond.), a.r.c.s. 

 (Text-figs. 1-29) 



INTRODUCTION 



DURING the second Antarctic commission (1931-3) of the R.R.S. 'Discovery II' 

 the programme carried out involved two extensive plankton surveys of the waters 

 of the Falkland Sector, one between November 193 1 and January 1932 and a second 

 between October 1932 and March 1933. During each of these surveys the same general 

 plan was adopted. North to south lines of stations were taken across the Sector, extend- 

 ing from sub-Antarctic latitudes as far south as the edge of the pack-ice. These north 

 to south lines were connected by east to west lines along the edge of the ice. A number 

 of routine stations was also taken in particular areas where observations have been made 

 repeatedly by the Discovery Committee's ships during several seasons — such as South 

 Georgia, the Bransfield Strait and the South Atlantic Ocean between South Georgia 

 and the Falkland Islands. During the winter months of 1932 these north to south lines 

 were extended around the Antarctic Continent and a circumnavigation of the southern 

 hemisphere was made, the ship leaving Cape Town in early April 1932 and arriving 

 at the Magellan Straits in early October 1932. 



At nearly every one of the stations taken during these cruises, both in the Falkland 

 Sector and around the Antarctic Continent, oblique towings were made with the i-m. 

 stramin net (see Kemp, Hardy and Mackintosh, 1929, p. 184). From these towings a 

 large collection of macroplankton was obtained and the Copepoda from a selection of 

 the catches have been analysed. The following report is an attempt to give an account 

 of the distribution, and an outline of the general life cycle, of one species of macro- 

 planktonic copepod from among the many species (about fifty in all) which were 

 frequently encountered in the macroplankton during the cruises. 



The species, Rhincalaims gigas (Brady), has been specially selected for investigation 

 for two reasons. Firstly, it is the dominant copepod throughout a very large area of the 

 Falkland Sector of the Antarctic, with which the work of the Discovery Committee is 

 chiefly concerned. In this area it is the dominant organism of the macroplankton, 

 forming in its region of greatest abundance over 75 per cent, and sometimes over 90 per 

 cent, of the total copepod catches. It may be said with some safety, therefore, that the 

 life history of this species will typify that of the Antarctic macroplanktonic Copepoda 

 generally, and for this reason a knowledge of its biology is of the greatest importance. The 



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