40 DISCOVERY REPORTS 



entirely towards the northern extremities of the Larsen and Prince Olaf lines. It seems 

 quite probable that we have here an example of the normal seasonal effect. From 

 subsequent work it appears that Eiicampia antarctica reaches its maximum round South 

 Georgia in the spring and perhaps early summer — it was very abundant to the south of 

 the island in November 1930. Now, the general direction of the surface drift, apart from 

 the circulation set up by the configuration of the land, which seems to be confined to 

 within a comparatively short distance of the coast, is to the north-east. Hence it is quite 

 natural to find the last traces of the Eiicampia maximum away to the north and east of 

 the island during the late summer and autumn. 



SUMMARY 



The main features of the survey as a whole, which will have become apparent from 

 the above description, were the sameness of the phytoplankton throughout and its 

 poverty in both species and individuals when compared with the earlier survey described 

 by Hardy, and with other areas during the same season. There was also no comparison 

 with the very abundant plankton found on a detailed survey over the same area worked 

 early in the following season, when production was at its height. These difl^erences are 

 so great that there is little doubt that they should not be attributed to seasonal variation : 

 the conditions in January-February 1930 should almost certainly be regarded as ab- 

 normal — an instance of one of the major fluctuations of which we know but little as yet 

 beyond the bare fact that they occur. On this survey the conditions were much milder 

 than any experienced in the South Georgia area since the Discovery investigations were 

 begun, and it seems certain that the unusually poor phytoplankton encountered was in 

 some way a resultant of these abnormal conditions. 



Everywhere during the January-February 1930 survey when diatoms were at all 

 numerous Corethron valdiviae and Thalassiothrix antarctica were the dominant forms, 

 with occasionally smaller numbers of Eucampia antarctica and Nitzschia seriata. The 

 very general presence, in comparatively large numbers, of the two large dinoflagellates 

 Peridiniiim antarcticum and Ceratium pentagomim f. grandis was an unusual feature 

 directly traceable to the abnormally mild conditions. Representatives of the genus 

 Chaetoceros, usually abundant in nearly all types of Antarctic surface water, were almost 

 entirely absent from the material collected on this survey. 



The following is a Hst of all the forms recorded during the survey, arranged in order 

 of their total abundance ; the figures in brackets immediately after the specific names 

 represent the number of stations at which each was recorded. In addition, the pro- 

 portions of the more important forms to the total phytoplankton are expressed as per- 

 centages in the right-hand column : 



Total % 



Corethron valdiviae (spineless chains) (43) 

 Thalassiothrix antarctica (i^) 

 Peridiniiim antarcticum (52) 

 Eucampia antarctica (ii) ... 



