HORIZONTAL DISTRIBUTION, GROWTH AND DYNAMICS OF DISPERSAL 351 



grounds the Fifth Furcilia has remained dominant in the surface swarms until far into the winter 

 months. It might be concluded then, that while there is rapid and continuous growth from January 

 to about the middle of March, the winter slowing up of the larval development, culminating in the 

 long drawn out existence of the Sixth Furcilia in the plankton, happens quite suddenly in the latter 

 part of March, and begins it seems with the Fifth Furcilia stage. 



3000 



2500 



?; 2000- 



I500- 



1000 



O 

 U 



500- 



-WEDDELL DRIFT 

 -E. WIND DRIFT 



I 1 1 1 1 — 



Jon Feb Man Mar: Apr May Jun 



Fig. 104. Phytoplankton values (plant pigments per cubic metre) in the Weddell drift and the corresponding values 

 in the coastal region of larval abundance in the East Wind zone (after Hart, 1942). 



The second objection is perhaps of greater concern. It has already been shown (p. 313, Fig. 76) 

 that the populating of the far eastern reaches of the Weddell stream, at the outset at least, is 

 brought about partly through the eastward spreading in the surface drift of larvae that spring from 

 March risings (Fig. 76, Stations 1994, 1142 and 1144) in Weddell Middle and partly, though less 

 commonly, through risings that take place (Fig. 76, Station 2346) locally. If the March risings, 

 then, be taken as the starting-point, the life-cycle of the larvae in the surface would appear to take 

 roughly about 4 months to complete, the later April rising at Station 2346 suggesting it could con- 

 ceivably be accomplished in three. Both estimates seem more reasonable than the original one, both 

 being more in keeping with the speed with which the larvae earlier on pass from the First Calyptopis 

 to the Fifth Furcilia stage and both still allowing for a period of dormancy in the latter which it seems 

 might result from the early onset in March of winter or semi-winter phytoplankton conditions. 

 Similarly, the July concentrations of Sixth Furcilias in Weddell West and Weddell Middle (p. 339, 

 Fig. 95) would have their origin in March and April risings in Weddell West (p. 321, Fig. 82 

 and p. 331, Fig. 90), suggesting again that the surface life-cycle might be accomplished in from 

 3 to 4 months. Many of the larvae rising in Weddell West from January to April, all, that is to say, 

 that do not get diverted to the South Georgia whaling grounds, but pass onwards in the main east- 

 flowing surface stream, must eventually, of course, turn up in Weddell East, but in view of the distance 

 they have to travel and the relatively short time it seems to take for the majority to reach the last larval 

 stage, they probably do so as Sixth Furcilias of some considerable standing or mainly as young 

 adolescents. 



The backward development of the young swarms that has repeatedly been recorded in Weddell 

 East (p. 340) must clearly be aggravated by the fact that by the time the Calyptopes reach 0° in 

 mid-April (p. 313, Fig. 76) the phytoplankton values (Fig. 104) have for all practical purposes 

 already reached their winter minimum. In other words, as compared with the successive batches of 

 Calyptopes that come to the surface in Weddell West from January to early March, when the phyto- 

 plankton is at its summer maximum, the larvae in Weddell East, in so far as feeding goes, begin their 



