MICROPLANKTON 



245 



absence of further serial observations to the southward, we can but speculate as to the reasons for this 

 reversal of a feature that remained clear throughout the eleven other series of both surveys. We have 

 seen from the hydrological sections that active upwelling was very pronounced on this line of stations. 

 The stations on the continental shelf lay within the very recently upwelled water, perhaps too recent 

 for extensive plankton production to have got under weigh. The two rich stations were beyond the 

 edge, and may be comparable with those showing secondary offshore increase in phytoplankton on 

 the more northerly series of observations. 



20- 



25°H 



S 1 



o 

 u 



T _ 

 H 



3d- 



N \ 



<I0 



MO HE POINT c a 

 IO-IO 



o 6 -,o 7 



io 7 -to 8 



>I0° 

 H'ALIIS BAY 



SYLVIA HILL 



ORANGE 

 R. 



SURVEY I 



— 1 1 r 



10° 15° EAST 



Fig. 81. Distribution of Chaetoceros, survey I, March 1950 

 (Station numbers are shown in Fig. 1.) 



20°-J 



25°. 



O 

 U 



T 

 H 



30: 



MO WE POINT 



oo s n 

 io s -io 6 r~i 



io^io 7p 



io^o 8 l 



IVALVIS BAY 



IO° 



OMNGE 



SURVEY: II 



EAST 



Fig. 82. Distribution of Chaetoceros, survey II, September- 

 October 1950. (Station numbers are shown in Fig. 2.) 



Special distributional features 

 It is hoped that the following figures are fairly illustrative of the main distributional trends, sum- 

 marizing the features described in discussing group distributions, and giving examples of the most 

 marked divergences from typical group pattern shown by certain individual species. Most of them 

 are based upon estimated numbers per net haul, contoured logarithmically. Percentage of total 

 diatoms has been used as the criterion for certain categories whose great relative importance in the 

 scanty offshore plankton could not be shown by consideration of their numbers alone. This need 

 arises from their cosmopolitan tendencies permitting them to attain equal or even greater abundance 



16-2 



