SEASONAL CHANGES IN ZOOPLANKTON 265 



Table XLVI 



The numbers per 50 m. haul of fourteen different organisms taken by N 70 V nets from a 

 column of water from the bottom to the surface at five different times at St. 41 



SEASONAL CHANGES IN THE ZOOPLANKTON 



As with the phytoplankton, little can be said to advantage regarding the seasonal 

 changes in the zooplankton from the material of the present survey ; it is only when 

 these results are embodied with those of later surveys that a knowledge of these changes 

 will be obtained. At present we have a series of stations taken over the same area, the 

 line running at right angles to the north-east coast of South Georgia, in four different 

 months: November, December, March and May. We must not consider the other 

 stations taken in December over a wider area to the north and south, or those taken in 

 January which were nearly all on the western side of the island, for all these are in areas 

 of different water mixtures. Then again, whilst the observations taken in November, 

 December and May were all in the same Antarctic season of 1926-7, those taken in 

 March were in the previous season 1925-6. It is obviously not satisfactory to include 

 the March of one season with other months of another season in considering the 

 seasonal changes, especially as we shall see in Part V how the conditions of one season 

 may vary from another. 



Bearing in mind these limitations to our material we can make a few observations 

 regarding the commoner forms. These in general, as would be expected, show an in- 

 crease in animal numbers with the advance of the Antarctic spring and a decline at the 

 approach of winter. Tables XLVIII and XLIX show the temperature changes at different 

 times of the year at positions approximately 15 and 45 miles off the north-east coast of 

 South Georgia. The Foraminifera and Radiolaria are well represented in November and 

 December, but very few occur in March and May. Eukrohnia hamata, the only Chaeto- 

 gnath occurring in sufficient numbers to warrant consideration regarding seasonal 

 change, shows a very even numerical strength in these four months November to May. 



