DISTRIBUTION OF YOUNG STAGES OF EUPHAUSIA SUPERBA 129 



The number was reduced to twenty-nine at St. WS 201, with the same stages represented as 

 before and the same principal stage. 



At St. WS 202, to the north-east of Elephant Island, twelve larvae were taken in which Calyptopis 

 2 and Furcilia i and 2 were present with Furcilia 2 the principal stage. 



(g) South Shetlands to the Burdwood Bank, April 1928 (Sts. WS 203-209). 

 This line was made immediately after that just described, and no larvae were taken. 



The observations in the Scotia Sea emphasize the general and widespread distribution 

 of E. superba larvae within that part which is south of the Antarctic convergence. The 

 occurrence of the different developmental stages is broadly what would have been an- 

 ticipated from the foregoing observations. In February, in three different seasons, 

 Calyptopis 2 is the predominant stage, showing that spawning must have commenced 

 at about the same time as was indicated in the South Georgia region. But although in 

 February 193 1 Calyptopis 2 predominated there is a reversion of predominance to the 

 previous stage in a line to the westwards made in March 193 1. In March-April 1930 

 Furcilia 2-5 are most prominent; in April 1928 there is a reversion of predominance to 

 earlier stages. It is thus obvious that in the same season, but in different localities of the 

 same area, there is quite considerable variation in the degree of development at com- 

 parable times. It also demonstrates that different stages may predominate at the same 

 time of year in different years. 



The series of stations 618-639 requires particular attention. At each of the vertical 

 stations along the ice-edge, larvae were taken in considerable quantity, which diminished 

 in amount from west to east. From St. 625 onwards no larvae were taken. Compare 

 these results with those described by Mackintosh (1934, p. 128, fig. 45) for this hne of 

 stations. He states: 



In February the ' Discovery II ' returned to the South Sandwich region working stations along the 

 ice-edge between the South Orkney Islands and the Sandwich Group. These stations (618-629) ^re 

 shown in Fig. 45. The ice line had retreated very little since December but the plankton had changed 



to a much warmer type None of the very "cold" group was present but such warm water species 



as Pareuchaeta, Pleuromamma and Euphaiisia frigida were included in the catches. As the ship ap- 

 proached the South Sandwich Islands, however, signs of a "colder" plankton appeared. Vanadis 

 occurred at St. 624 and Diphyes antarctica at Sts. 625, 626, 628 and 629. 



That is to say that the young krill, though admittedly taken at the ice-edge, were ob- 

 tained exclusively in the region of Mackintosh's "warmer " plankton. Mackintosh states 

 that the presence of ice does not necessarily entail the presence of cold-water plankton. 

 This is a point to be emphasized, that the presence of the larval krill at the pack-ice edge 

 does not mean that it is a "cold" species. This is borne out by the line from South 

 Sandwich to the Burdwood Bank in March- April, 1930. The whole of this line was in a 

 region where conditions for the occurrence of " warmer " plankton were prominent, and 

 at each of the stations excepting St. WS 528, young larvae were present in an abundance 

 which was conspicuous at St. WS 527 and WS 529, where the water was even warmer 

 than at the preceding stations. 



D XIV 17 



