227 



MICROPLANKTON 



From Fig. 58 it can be seen that, on the Mowe Point line, the quantities of all main groups excepting 

 Protozoa were highest inshore, with a pronounced falling off at the third station seawards, some slight 

 secondary increase farther out and then a general decrease, most marked among the diatoms, to the 

 low oceanic values at the seaward end of the line. ' Other plants ' were observed in very small numbers 

 some distance offshore, but not at the two outermost stations. The proportion of Dinophyceae to 

 diatoms was above the average for the whole survey area, and Seston was not noted at the dilutions 

 necessary to obtain counts. The relative abundance of Protozoa here was due mainly to large Radio- 

 laria and especially tintinnids. The total estimated numbers of microplankton were relatively small 



throughout. 



It should be noted that the stations have been plotted so that the distance scale from the land sea- 

 wards reads from the left of the page, regardless of chronological sequence. This has been done so 

 as to secure uniformity of treatment throughout the series of diagrams (Figs. 58-64, 66-72). 



o 

 d 



HC? 



a 



Yd 



WS963 WS984 W5985 



"'On 



70 "M^; 



VOLUME 



IIOO 



Yd 



OINOPHYCEAf' 



NO OTHER PLANTS 

 RECORDED 



OO 

 SEA MILES FROM LAND 



SO 60 



SEA MILES FROM LAND 



Fig. 60. Distribution of the main groups of microplankton, 

 estimated totals per net haul, survey I, Walvis Bay line, 

 6-8 March 1950. 



Fig. 61. Distribution of the main groups of micro- 

 plankton, estimated totals per net haul, survey I, 

 Middle-Intermediate line, 9-10 March 1950. 



On the northern intermediate line the quantities of microplankton were still small and rather 

 uniform, greatest at a moderate distance out towards the shelf-edge and least, owing mainly to the 

 usual drop in diatom numbers, at the station farthest offshore. The proportion of Dinophyceae to 

 diatoms was unusually high, and it will be shown later that local abundance of Gonianlax spinifera 

 was mainly responsible for this. Neither ' other plants ' nor Seston were observed on this line. 



Conditions more typical of the Benguela current proper were first encountered on the Walvis Bay 

 line (Fig. 60). Here the vastly greater quantities of diatoms in the inshore waters and their abrupt 

 decrease seawards are even reflected in the settlement volumes. (The latter are rarely a reliable guide 

 to plankton quantities, being frequently distorted by differential packing among organisms of diverse 

 shapes, the presence of small numbers of extra large organisms, and the necessity of settling out large 

 samples in relatively wide cylinders, so that the volumes cannot be read with the same accuracy as the 

 small ones.) They are included only for their value as a basis for crude comparison with earlier 

 collections in other areas, from some of which numerical estimates are not yet available. 



14 



