242 DISCOVERY REPORTS 



The results from the northern intermediate line showed essentially the same features as those 

 observed off Mowe Point, most of them even more definitely (Fig. 77). It is true that Fragilaria 

 karsteni was not present among the ' Pennatae ' at the inshore station, but this was 30 miles from the 

 land, and from all our other observations the species seemed to be the most strongly neritic in habit 

 of all the important plankton forms in this area. The solenoid community, with some few of the more 

 oceanic Chaetoceros spp. was even more completely dominant offshore, where the line extended into 

 a region where almost all the microplankton was essentially oceanic in character. At station WS 1088, 

 no less than 94% of the diatoms was made up of the cosmopolitan Rhizosolenia spp. R. styliformis, 

 R. hebetata and R. imbricata. 



WSD96 WSI097 WSI098 WSI099 WSIIOO WSHOI WSII02 



D 



re? 

 rf 



rf 

 rf 

 rf 



rrf 

 rf 

 rf 

 rf 

 rf 



WS 1093 



WS I09I 



WS O90 WS 1089 WS O88 



-• TOTAL DIATOMS 



- CHAETOCERACEAE 

 -' 'PENNATAE" 



>■■ BIDDULPHIINEAE 

 o DISCINEAE 



— SOLENIINEAE 



SO 



160 



SEA MILES FROM LAND 



Fig. 77. Estimated total diatoms and diatom group totals, survey II. A. Mowe Point line, 9-1 1 October 1950. 



B. Northern Intermediate line, 8-9 October 1950. 



The dominance of this solenoid community at offshore stations persisted in very marked degree 

 at the outer end of the Walvis Bay line, where, however, there was a larger proportion of Thalassiothrix 

 longissima, perhaps the most oceanic of the ' Pennatae ', among the small fraction of the total not 

 accounted for by the solenoids. Indeed it would appear that with minor modifications the solenoids 

 predominated in the offshore plankton from about the middle of the area to the northern limit of our 

 serial observations at the time of this second survey (cf. Table 17, Figs. 76-8). 



The inshore stations on both the Walvis Bay and mid-intermediate lines also displayed common 

 features that differed markedly from those observed in autumn. In spring the rich coastal flora of 

 Chaetoceros spp., with Asterionella and Fragilaria karsteni among the 'Pennatae', etc., was confined 

 to the innermost stations, with an abrupt diminution seawards before the shelf-edge was reached. There 

 was thus a pronounced narrowing of the rich coastal belt here in spring, where it had been wide, and 

 fanned out seaward to the shelf-edge on the Walvis Bay line, during the first (autumnal) survey 

 (cf. Fig. 57 and Fig. 65). The spring results resembled more the extreme contrast within a relatively 

 short distance out from the coast, that had been shown on the Sylvia Hill line, immediately to the 

 southward, in autumn. The distributional pattern is consistent with the active upwelling which was 

 demonstrated by the hydrological results from this region. Within the upwelling water, the larger 



