HORIZONTAL DISTRIBUTION, GROWTH AND DYNAMICS OF DISPERSAL 31S 



the island, in the tongue of Weddell water which approaches it from that direction, and our almost 

 total failure to discover there any deep larvae from which they could have sprung, suggest strongly, 

 however, that they could not have been produced in situ but on the contrary got carried there in the 

 surface drift. Some surface Calyptopes now, both in March and April, also appear in the Bransfield 

 Strait, but in view of the pronounced scarcity of Nauplii and Metanauplii in these waters, of which we 

 have ample evidence from November to April (Figs. 69-72), it is doubtful if even they too 

 could have been produced in situ. More likely they drifted into the strait (p. 202) with the Weddell 

 or Bellingshausen Sea water which enters it, the former from the east, the latter from the west. 



MONTH 



STATION 



DATE 



LONG WEST 



FURCIUA 



CALYPTOPIS 



DEEP LARVAE 



2280 

 8 



75° 



383 



14 

 63° 



O 50 100 



o SO lio ^"^^'^ P^"" <:«"' 



t 



MONTH 



STATION 



DATE 



LONG WEST 



FURCILIA 



CALYPTOPIS 



DEEP LARVAE 



Fig. 78. Developmental condition of surface larvae at 

 West Wind Stations 2280 and 383. 



Turning now to the situation in the West Wind drift, it will be noted that in the Bellingshausen 

 Sea-Drake Passage neighbourhood there are two substantial recordings, one in March and one in 

 April, of surface Calyptopis forms. These occurrences at first sight suggest that the larval population 

 of this vast tract of the circumpolar sea is not everywhere so poor as the distributional charts so far 

 presented have suggested it to be. It is distinctly probable, however, that neither is a true West Wind 

 occurrence, much of this West Graham Land region being affected by encroachment from the East 

 Wind drift, a tongue of which, as Deacon (1937, p. 17) has shown, deflected northward near Peter I 

 Island, probably he suggests under the influence of a submarine ridge, penetrates in these parts into 

 the West Wind zone. In both instances, therefore, the larvae very likely sprang from East Wind 

 risings, somewhere possibly on the slope-edge of the extensive region of shallow soundings which 

 between Peter I and Charcot Islands stretches far to the north of the continental land, from such risings 

 later moving to the north and east in the surface drift. As Fig. 78 shows, at both stations the swarms 

 recorded are essentially surface ones, that at Station 383 obviously having been in the surface for some 

 considerable time and almost certainly having come from the west. Moreover, the absence at both 

 stations of deep larvae augmenting them from below and the fact that we have never recorded any 

 deep larvae whatsoever in this particular region considerably strengthen the view that in neither 

 instance could they have been locally derived. 



If it be assumed that these supposed but probably far from hypothetical intruders from the East 

 Wind zone move northwards in more or less the same longitude, and later eastwards in more or less 

 the same latitude, their separation in time and space would give another hint of how long it may 

 possibly take for E. superba to develop from the First to the Third Calyptopis stage. If the observa- 

 tions had been made in the same year they would in fact have suggested an easterly movement of the 

 larvae of about 360 miles in about 37 days, and that during this time they had developed from being 

 First to become dominantly Third Calyptopis forms. The rate of travel, approximately 10 miles a day 

 or a little under 1 knot, seems about right for the West Wind drift and the developmental rate, ahhough 

 rather slower than our previous estimates, is not altogether out of keeping with them. The speed of 



36-2 



