317 



THE SOUTH GEORGIA AREA 



This is the area that saw the first development of modern whahng on a large scale. 

 This was due in part to the fact that in the earlier days good harbours and shore bases 

 were essential, but also to the exceptional richness of the plankton. The production of 

 phytoplankton during the main increase is indeed probably as great as that to be found 

 anywhere else in the world. 



The earlier observations of Hardy (Hardy and Gunther, 1935) and Hart (1934) 

 give a good idea of the qualitative sequence here. The great difference from the 

 oceanic Northern Region lies, of course, in the immense quantities of neritic species 

 present during the main increase, particularly Chaetoceros sociale, Ch. neglectum, 

 Thalassiosira spp., Biddulphia striata and Eticampia balaustium. Members of the 

 oceanic groups were also more abundant by far than in more truly oceanic areas, though 

 less important in their proportion of the total phytoplankton. During the post- 

 maximal decrease Group H, the larger oceanic diatom species, became predominant, 

 with Corethron criopJiilum in spineless chains and Thalassiothrix antarctica together 

 forming some 80% of the phytoplankton during January- February 1930. The very 

 detailed description of the qualitative aspect of the South Georgia phytoplankton given 

 in previous work (Hart, 1934, pp. 29-69; Hardy, Hardy and Gunther, 1935, pp. 39-87) 

 has been fully borne out by our subsequent surveys. These have been less extensive, but 

 far more numerous, so that some attempt at a picture of the seasonal variation m 

 quantity can now be drawn. Also observations have been obtained at intervals suffi- 

 ciently close to permit of theoretical calculations of the crop in terms of the consumption 

 of nutrient salts, which it had been thought would be impossible. Of course, such 

 calculations can only give very approximate minimal values, but they are of great help 

 in comparing conditions with better known ones in the northern hemisphere. 



From the observations made subsequently to 1931 the seasonal variation in quantity 

 can be pictured as being reflected in Fig. 13. It will be seen that results from different 

 seasons have had to be considered together in order to get this, but when all our previous 

 work quoted above is taken into account, there is little doubt that the figure represents 

 the main trends in a normal year quite fairly. The observations upon which this figure 

 is based are given in Table 8, with data on nutrient salt content which permits of the 

 somewhat speculative calculations mentioned above. It is important to bear in mind 

 that owing to the quantities of phytoplankton present off South Georgia during the 

 main increase being from five to ten times greater than in the oceanic Northern Region, 

 for instance, it has been necessary to plot these results on a much smaller scale than that 

 uniformly adopted for the three oceanic regions. 



It will be seen that the main increase begins suddenly late in October and rises to a 

 high peak about the end of November. There is then a marked post-maximal decrease 

 to a late summer minimum in February, and a secondary autumnal maximum in March 

 before the final descent towards minimal winter values. No doubt the height and precise 

 time of the peak period fluctuate somewhat from year to year, and the secondary 



