MICROPLANKTON 251 



group totals for the chaetocerids, with their pronounced maximum of development inshore. A degree 

 of overlapping in the horizontal plane seems reasonably accounted for by vertical layering, for which 

 there is some hydrological evidence. The point cannot be established from plankton data alone. 



The presence of the Goniaidax patch just where the intrusive tongues of oceanic water extend farthest 

 inshore seems strongly suggestive of mixing between the two types of surface-water. Some time-lag- 

 general slowing of dispersive agencies— must also be postulated, to permit development of the third 



20° 



25° 



S 

 O 



U 

 T 

 H 



30* 



NIL □ 



SURVEY 

 1 



I0« 



15' 



EAST 



Fig. 93. Distribution of Thalassiothrix longissima, survey II, 

 September-October 1950. Expressed as a percentage of total 

 diatoms. (Station numbers are shown in Fig. 2.) 



20° 



25° 



S 

 O 

 U 



T 

 H 



30° 



EAST 



Fig. 94. Distribution of the Soleniineae expressed as a per- 

 centage of the total diatoms, survey II, September-October 

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



distinctive localized type of flora. Much of our evidence points to the prevalence of the conditions 

 required for this immediately prior to the autumn survey. The relatively high stability of the surface- 

 layers, temperature and salinity distribution, and several features of the plant population combine to 

 show that upwelling activity was then much reduced, and the plant succession at or just beyond its 

 peak. Relatively ' old ' surface-water from inshore, such as these conditions imply, should mix more 

 readily with the offshore water than would that cooled by recent upwelling. 



bloom formation. Goniaulax spp. have been known to cause water-bloom elsewhere, but such discoloured water as we were 

 able to sample during these surveys was caused by other organisms. This does not preclude the probability that it may 

 sometimes form blooms in this area — perhaps at other seasons. 



17 



