PHYTOPLANKTON OF BRANSFIELD STRAIT 119 



from Fig. 57 in which the estimated phytoplankton totals have been plotted. Com- 

 parison of this chart with Fig. 50 brings out one of the most interesting features of this 

 survey, namely that the centre of the richest phytoplankton production appears to lie 

 farther to the east than on the previous autumn survey. This is also well shown by the 

 distribution of the dominant species, Corethron valdiviae (Fig. 58). 



Summing up the other more noteworthy features it will be seen that while C. valdiviae 

 was still strongly dominant, the proportion of other species was considerably greater 

 than on the autumn survey, especially at the eastern end of the strait. The hauls were on 

 the average much richer, as would be expected in the spring, and the influence of the 

 eddy of Weddell Sea water round Joinville Island was more clearly marked. The fol- 

 lowing is a list of the species recorded with the number of occurrences and estimated 

 total abundance. It will be seen that the number of species was still small, despite the 

 more favourable time of year, a fact which serves to illustrate the local character of the 

 phytoplankton of Bransfield Strait. 



Corethron valdiviae (1%) 124,987,200 Thalassiothrix anfarctica (6) 47.4°° 



Fragilaria antarctica (6) 5,692,200 Melosira sol (i) 42,000 



Tha/assiosira antarctica (12) 5,032,200 Peridiiiium spp. {2) 33,6oo 



R/iisosolenia alata i'. gracillima {i}) 1,248,000 Rhisosolenia alata {i) 21,000 



Eucampia antarctica {■]) 852,600 Peridinium antarcticum {i) 18,000 



Biddulphia striata (13) 619,800 Chaetoceros atlanticus (i) 16,800 



Nitzschia seriata {"]) 581,400 Ch. dic/iaeta (i) 12,600 



Chaetoceros criophilum {%) 272,400 Ch . ? didymum {i) 7,200 



Coscinodiscus bouvef {^) 184,200 Lycmophora lyngbyei {i) 4,800 



Ch. neg/ectus {^) 129,600 Cocconeis ? costata [i) 4,800 



Rhizosolcnia truncata (2) 85,800 Chaetoceros schimperianus (i) 3,600 



Fragilaria antarctica f. bouvet (i) 81,600 Biddulphia {Triceratium) arcticum (i) 1,200 



Coscinodiscus spp. {4) 65,400 Rhisosolenia styliformis (i) 600 



Estimated total phytoplankton 140,045,800. 



Comparing this with the previous survey it will be seen that here Corethron formed 

 89 per cent of the total phytoplankton, as against gS per cent ; but when the distribution 

 of the other more important species is considered, it is seen that the increase in their 

 number was chiefly confined to the eastern end of the strait. 



The most widely distributed, though not the most numerous, species after Corethron 

 was Rhizosolenia gracillima. From Fig. 59 it will be seen that it reached its maximum 

 at the north-eastern end of the strait, that it was absent from the more northerly stations 

 on the middle line, but was encountered fairly constantly in more moderate numbers to 

 the west. In considering the distribution of this species during the survey here de- 

 scribed it is necessary to enquire how far the associations met with in different areas 

 may be attributed to transportation by currents. The great planktologist Cleve carried 

 this concept to such lengths that there has been a tendency to ignore it in recent work ; 

 but the surface currents over the greater part of the area here treated are so strong and 

 persistent (except perhaps in winter) that they must certainly play a great part in de- 

 termining the character of the phytoplankton. As will be seen, this view has permeated 

 the accounts of the diff'erent associations described in this report. The observed dis- 

 tribution of R. gracillima in Bransfield Strait during this spring survey, however, brings 



