PHYTOPLANKTON OF THE BELLINGSHAUSEN SEA 149 



SUMMARY 



Summing up the conditions observed in the Bellingshausen Sea during this survey, 

 it will be seen that several distinct associations were encountered. In the far south-west 

 the rich Nitzschia — Fragilaria — Thalassiothrix association held sway, and evidently 

 persisted to some extent as the water drifted away to the north-east, as the catches at 

 the more northerly stations farther east (e.g. Sts. 566, 567 and 592) bear witness. This 

 association provided catches rich in both species and individuals (owing to the pre- 

 dominance of small forms). Farther east along the ice-edge a poor phytoplankton was 

 encountered, development having evidently only just begun in earnest with the break 

 up of the ice. Here the dominant species were Corethron valdiviae and Chaetoceros 

 neglectiis. To the north-east, off Adelaide Island and the Biscoe Islands, a similar associa- 

 tion was encountered at the earlier stations worked among the ice, but was evidently 

 passing over into the Corethron — Rhizosolenia gracillima association as seen farther off- 

 shore on the return voyage. At a few of the later stations worked close inshore off 

 Adelaide Island and farther north, an additional neritic association similar to that ob- 

 served at the Palmer Archipelago was met with. If due allowance is made for this 

 localization of the abundance of some of the more prominent species, the following list, 

 together with Figs. 75 and 76, which show the total estimated numbers of organisms, 

 and the dominant species at each station, should enable a fairly clear picture of the con- 

 ditions over the whole area to be obtained. The list gives the twelve most numerous 

 species in order of their total abundance at all forty-seven stations, together with the 

 number of stations at which each occurred and their percentage of the estimated total 

 of phytoplankton organisms. This estimate naturally leaves out of account the occasional 

 presence of minute forms in uncountable colonies, but this was fortunately a rare 

 occurrence in the Bellingshausen Sea. 



Corethron valdiviae (46) 

 Nitzschia seriata (32) 

 Chaetoceros neglectus (40) 

 ^Thalassiothrix atitarctica (23) 

 Fragilaria antarctica f. boiwet (16) 

 F. antarctica (37) 



Rhizosolenia alata L gracillima (33) 

 Chaetoceros tortissimus (8) 

 Ch. dichaeta (31) 

 Thalassiosira antarctica (41) 

 Chaetoceros atlanticus (16) 

 Rhizosolenia truncata (30) 

 Other forms 



Total estimated phytoplankton 277,193,350. 



