PHYTOPLANKTON OF THE WEDDELL SEA AREA 



97 



very distinctive, as the catch consisted almost entirely of the three large forms whose 

 extensive development has been found to be such a feature of the older surface water 

 of eastern Weddell Sea origin, namely, Ch. criophilutn, Rhizosoleuia styliformis and 

 Corethron valdiviae, in that order of importance. 



The last station dealt with in this table was worked a long way to the westward on the 

 return voyage a fortnight later, after the pack-ice had cleared away. The phytoplankton 

 here was rich, with Chaetoceros criophihim dominant, and Rhizosolenia styliformis and 

 Corethron valdiviae also present in large numbers. Very few species were present in this 

 catch, which closely resembled those in surface water of the same type obtained nearer 

 South Georgia during the plankton survey worked earlier in the year: of the smaller 

 species present, only Chaetoceros neglectiis occurred in large numbers. 



Besides the selected leading forms dealt with in Table i6, certain other species 

 occurred in large numbers in the vast haul at St. WS 535, as may be seen from the full 

 analysis in Table XXVIII. The relative proportions of the more noteworthy of these 

 were Ch. dichaeta, 3 per cent of the total; Thalassiothrix antarctica, 2-5 per cent; and 

 Rhizosolenia alata, 1-3 per cent. 



Continuing this general survey of the stations worked during this southern voyage 

 of the ' William Scoresby ', the next group to be considered includes all those stations 

 between 57 and 60° S, 15 and 25° W. The full analyses of the phytoplankton hauls from 

 these stations are given in Table XXIX. Of the six stations thus included, reference 

 to Fig. 46 shows that the first three in point of time were worked while skirting the 

 pack to the south-east, one (St. WS 559) in the same neighbourhood on the return 

 voyage, and the last two after the pack had been successfully rounded to the eastwards 

 and course altered to approximately due south. As will be seen from the analyses the 

 phytoplankton hauls, while moderately rich in individuals, were poor in species, all 

 being characterized by the pronounced dominance of a single large species as we have 

 learnt to expect in surface water of the eastern Weddell Sea type. The relative propor- 

 tions of the leading forms are shown in Table 17. 



Table 17 



13 



