SUMMARY OF OBSERVATIONS 175 



GENERAL CONCLUSIONS 

 SUMMARY OF OBSERVATIONS 



Full summaries of the observations within each area will be found at the ends of the 

 several sections ; the following brief synopsis of the more important features is designed 

 to facilitate the consideration of the section on limiting factors which follows. 



During the survey round South Georgia in the warm summer of 1929-30 a very 

 poor phytoplankton association was encountered with the following species dominant: 

 Corethron valdiviae, entirely in the spineless chain form, Peridinium antarctiaim, 

 Ceratiinn pentagonum f. grandis, and, more numerous than the di.noflagellates but much 

 less widely distributed, Thalassiothrix antarctica. On this occasion the richest hauls 

 were all obtained to the east and south-east of the island at some distance from the land. 



In the following season, an unusually cold one, the survey was made in spring just 

 after the pack-ice had disappeared from the neighbourhood of the island, and an 

 extremely rich phytoplankton was met with. Species as well as individuals were ex- 

 ceedingly numerous, but it was possible to recognize three definite associations. In the 

 tongue of eastern Weddell Sea surface water the large species Chaetoceros criophilum, 

 Corethron valdiviae, and Rhizosolenia styliformis predominated over smaller forms. To 

 the north of the island, and inshore off the north-east coast, older mixed water with an 

 association in which Corethron valdiviae was strongly dominant was evidently in the 

 main derived from this source. 



To the south and south-west of the island the phytoplankton reached its maximum 

 in water mainly of western Weddell Sea origin with a slight admixture from the 

 Bellingshausen Sea. Here there was a vast profusion of small forms, Chaetoceros socialis, 

 Thalassiosira antarctica, Chaetoceros neglecttis, and Fragilaria antarctica being the most 

 important, and Corethron present only in small numbers. To the north-west a few 

 stations with a comparatively poor phytoplankton, with small species dominant, were 

 worked in water of Bellingshausen Sea origin. 



Dinoflagellata were extremely rare round South Georgia on this survey. Other work 

 later in the season indicated a shght increase in their number, but nothing approaching 

 the abundance of the previous abnormally warm summer. Moreover the diatom plankton 

 never deteriorated to anything like the same extent. 



Of the Scotia Sea little can be said for want of observations at mid-season, when the 

 research ships were engaged farther south. South of the convergence in Drake Passage 

 a rich phytoplankton with Nitzschia seriata and small Chaetocerids dominant was 

 found in April (autumn), and a similar association, with in addition a large proportion 

 of Thalassiosira antarctica, was found slightly farther east in November. In March a 

 poor phytoplankton was usually encountered in this area. In the sub-Antarctic water 

 between the Falkland Islands and South Georgia, at the end of February 1930, a highly 

 characteristic Rhizosolenia plankton was found, with R. polydactyla dominant and 

 R. curva very conspicuous. 



