HORIZONTAL DISTRIBUTION, GROWTH AND DYNAMICS OF DISPERSAL 355 



The principal East Wind risings (Fig. 106) tend to be concentrated in the more southerly 

 parts of the East Wind zone in a relatively narrow coastal or near coastal belt either inside the 

 I coo-fathom line or at no great distance outside it. Beyond this belt, risings are conspicuously few 

 and such as have been recorded are of Calyptopes in small or negligible numbers. In this coastal 

 zone, which is generally much encumbered by ice, the surface temperatures are almost permanently 

 below zero C and the phytoplankton values (Fig. 104), by Weddell standards, even at the height 

 of summer, exceedingly low. It is perhaps not surprising, therefore, that the larvae, beginning their 



2864 W267 W285 W302 



ADOLESCENT 



FURCILIA 6 



i/i " 5 



a 



g „ 4 



n 52 

 o 



48 



1 44 



■« 40 



Z 36 



ul 32 



i 28 



2 24 

 I 20 

 5 16 

 ^ 12 

 -> 6 



4 



Tl @^ ^^ 



RS9 

 537 



815 813 2547 2561 2562 2560 2004 2606 2603 260O 1154 1297 1361 



W540W540 S W540 W538 643 2594 24 23 368 38 1781 I360 



MAY 

 JUNE 



^ WEDDELL ZONE 

 ■ EAST WIND ZONE 



ADOLESCENT 

 6 FURCILIA 

 5 " o) 



EAST WIND SWARMS 

 DEVELOPING BELOW THE ICE 



STATION 



52 

 48 

 44 

 40 

 36 

 32 

 28 

 24 

 20 

 16 

 12 

 8 

 4 



Fig. 107. Developmental condition of the young first- and second-year swarms in the Weddell and East Wind zones, showing 

 the backward state of the southern swarms following their prolonged 'wintering' below the polar pack. Note on vertical 

 scale : specimens were measured to the nearest millimetre, the diagram showing the percentage length frequencies in 4-mm. 

 groups, the figure in the vertical scale being the fourth in the group. Thus the block opposite ' 8 ' in the scale shows the 

 proportion of specimens measuring 5-8 mm. inclusive (In later text-figures with 2-mm. groups the scale figure is the second 

 of the group, e.g. 14 refers to 13 and 14 mm.). 



surface existence under such conditions, should from the outset (p. 321, Fig. 83) develop slowly 

 or that II and even 13 months later, in January and March of the following year, the Sixth Furcilia 

 (p. 372, Fig. 120) should still be surviving in these high latitudes, if only in rapidly declining numbers. 

 Under the winter ice-sheet that envelops them from May to December the far southern larvae, it 

 seems, continue to develop slowly, evidently not completing their surface life-cycle until long after 

 this phase has been accomplished and passed in the less rigorous conditions of the northern zone, the 

 backward state we have repeatedly recorded in high latitude 11-15 month old East Wind swarms in 

 January, March and May^ (Fig. 107) providing the clearest evidence of how slow the winter 

 growth-rate must be.^ Fig. 107 shows the developmental condition of typical young Weddell 

 and East Wind swarms, over a period covering the winter and spring of the first year of their growth 

 and extending into autumn of their second, the length frequency being shown in the lower part of the 



^ We have no high latitude East Wind data for February and April. 



^ As Thomas (1959) remarks, the vast ice-sheet that invests so much of the larval population throughout winter and spring 

 can best be described as 'frozen solid', and where such conditions exist he adds it would appear that production of a basic 

 holophytic food supply cannot take place because ' solar radiation cannot penetrate the solidified media in sufficient quantities 

 per unit time'. Below the ice off Mawson in 64° E Bunt (1959) reports a virtual absence of phytoplankton all through the 

 winter months. It would not, therefore, be at all surprising if it should prove that, in the East Wind zone as a whole, winter 

 growth among the larvae came virtually to a standstill. It is difficult in fact to understand how the young krill, especially 

 the East Wind krill, survive the polar night at all. Are they, as Marshall and Orr suggest (19536), carnivorous then? That 

 they are is at least a possibility, Hart it will be recalled (p. 44) having recorded the frequent occurrence of large Foraminifera 

 (Globigerina sp.) in the stomachs of post-larval specimens. The occasional presence of Foraminifera, Radiolaria and Tintinnids 

 in the stomachs (p. 173) is also reported by Barkley. 



41-2 



