DISTRIBUTION OF ANTARCTIC MACROPLANKTON 109 



DISTRIBUTION OF RICH AND POOR PLANKTON 



It is well known that as a general rule the plankton of the surface waters of the tropics 

 is very thin, that in the temperate regions it is richer, and that in the Arctic and Antarctic 

 it is comparatively abundant. Murray and Hjort (1912) mention that " the closing nets 

 of the ' Michael Sars ', when hauled from 200 m. to the surface in the Sargasso Sea, 

 yielded on the average 3 c.c. of plankton, while in the Norwegian Sea from 85 to 225 c.c. 

 were obtained in numerous similar hauls". According to Jespersen (1923) the volume 

 of macroplankton in 50-60 N in the North Atlantic is 10-20 times as great as in 20- 

 30 N. The upwelling in the Antarctic Zone of water rich in nutrient salts results in a 

 luxuriant development of phytoplankton, and this in turn supports an abundant animal 

 plankton. Hart (1934) mentions the richness of the Antarctic phytoplankton, and 

 Hentschel (1928) and Hentschel and Wattenberg (1930) publish charts of the South 

 Atlantic which show the association of areas of rich plankton with the areas of upwelling 

 of cold water. 



The richest plankton of all is found in the Antarctic surface water, but it is by no 

 means uniformly abundant over the whole of the Antarctic Zone. The quantity of 

 macroplankton, for instance, varies very much at different times and in different places, 

 and these variations so far as they can be ascertained from the present material will be 

 described in the following pages. 



A chart showing the distribution of the total number of organisms per haul is roughly 

 representative of the distribution of the richness of plankton, though it does not neces- 

 sarily illustrate the distribution of the majority of species. It represents rather the half- 

 dozen commonest species. But the main difficulty in charting the richness of the plank- 

 ton is, perhaps, that there is no quite satisfactory means of allowing for diurnal variations, 

 since different samples have different proportions of the variable species. However, the 

 few species like Calanus acntus and Rhincalamis gigos, which make up the bulk of the 

 plankton, do not have a very marked diurnal variation and the time of day has a far smaller 

 effect on the amount of plankton in a sample than the actual distribution of quantity. 



GENERAL DISTRIBUTION 

 Fig. 23 shows the numbers of organisms taken at all stations in January, February 

 and March in all four seasons (1927-31), with the exception of the intensive lines of 

 stations taken in the South Georgia and Bransfield Strait surveys. The figures stand for 

 the number of hundreds of organisms in each sample, but the shoaling species, Euphausia 

 superba, Limacina balea, and Salpa fusiformis are omitted. For instance at WS 551, the 

 last station on the line to the eastern Weddell Sea and marked 56, just over 5600 

 organisms were taken. Although the diurnal variations have a minor effect on the total 

 contents of a sample, the figures are shown in italics for hauls made in daytime between 

 the hours of 0600 and 1700. The shading is based purely on the figures shown on the 

 chart, and is intended merely to draw attention to the positions at which large, medium 

 or small hauls were taken. 



