DISTRIBUTION OF ANTARCTIC M ACROPLANKTON m 



It may be mentioned that Hart (1934) finds that the Bransfield Strait is on the average 

 also poorer in phytoplankton than other areas, but the contrast is not so great as it is 

 with the macroplankton. 



The reason for the scarcity of plankton around the South Shetlands and South 

 Orkneys cannot at present be stated with certainty, but this is an area in which there is 

 a considerable upwelling of water from the deeper layers, and these deeper layers are 

 of course comparatively poor in plankton. I am informed by our hydrologists that the 

 region of thin plankton shown in Fig. 23 coincides roughly with an area in which the 

 surface water has been found to have a low oxygen content. This suggests that the water 

 has recently risen from a deeper level where the consumption of oxygen has not been 

 balanced by exposure to air. It is curious that some species, such as Euphausia superba and 

 Salpa fusiformis, are nevertheless sometimes found in large numbers in parts of this area. 



VARIATIONS IN ABUNDANCE 

 There is evidence to show that in the course of the year certain changes take place in 

 the distribution of the amount of plankton, and although these changes cannot be 

 followed with certainty at the present stage it is worth while to consider the material 

 in some detail. It has not been found practicable to make a series of repeated observa- 

 tions in one place throughout a year or part of a year, and it will be necessary to compare 

 the conditions in, for instance, December in one season with April in another season, 

 and so on. Conclusions drawn in this way must of course be formed with caution. 



South Georgia 



Figs. 24-30 represent the results of successive surveys of the South Georgia whaling 

 grounds in the four seasons 1927-31, and they are constructed on exactly the same lines 

 as Fig. 23. 



The essential facts shown by these charts are as follows. 



In the 1927-8 survey (February-March, Fig. 24), the plankton was very thin to the 

 north, east and west, but abundant on the south-west side. The increase here was not 

 due to a special development of one species but to a general increase of all the im- 

 portant species. 



In the first 1928-9 survey (August-September, Fig. 25), there was a very thin 

 plankton to the west, north, east and south-east. The south and south-west sides were 

 not examined. 



In the second 1928-9 survey (December-January, Fig. 26), the plankton was in most 

 places moderate or rather poor, but there was a patch of rich plankton to the south-east. 

 In general it might be called " patchy". Two extra lines (WS 417-26) worked in April 

 of the same season (Fig. 27) produced fairly heavy catches near the south end of the 

 island, but indicated a rather scarce plankton to the south-west. 



In the 1929-30 survey (January-February, Fig. 28), the plankton was patchy in 

 places but in general very abundant. In the same season South Georgia was revisited 

 in May. Although the routine N 100 B was not used again, closing N 100 B's were 



