252 



DISCOVERY REPORTS 



IO EA5T 



IO EAST 



Fig. 95. Distribution of (A) Planktoniella, (B) Goniaulax, and (C) Chaetoceros between Mowe Point and Sylvia Hill, survey I, 

 March 1950. Where there is no shading none was recorded. The lightest shading represents estimates of < io 4 per net 

 haul, the next io 4 ~ 5 , and so on. 



Observations on discoloured water 



Large areas of the sea near Walvis Bay were discoloured ' blackish ' by diatoms during our first survey, 

 the general appearance being dark green to black, and opaque, very similar to that described in arctic 

 regions by Brown (1868) and found by him to be due to diatoms also. In the Benguela current we 

 found the inshore chaetocerids, especially Chaetoceros didymum and Aster ionella japonica, to be the 

 species chiefly responsible. Within this same region, however, were many more localized brownish or 

 khaki-coloured discolorations, forming irregular bands and streaks roughly parallel with the coast, 

 sometimes associated with foam streaks and lanes of dead and dying macroplankton — mainly 

 ctenophores and salps — at the surface. A minor fish mortality had occurred near Walvis Bay just 

 before we got there. 



Three samples from some of these more strikingly discoloured waters were obtained off Sandwich 

 Harbour (about 22 30' S. and 10 sea-miles offshore). Subsequent detailed microscopic examination 

 of these yielded the results shown in Tables 18, 19 and 20. 



