DISTRIBUTION OF PHYTOPLANKTON 45 



An examination of the N 70 V net results has in addition shown what appears to be 

 a marked vertical migration of this species. By taking the percentage in which it occurs 

 at different stations, and then taking the average percentages for those stations taken in 

 daylight and those taken in hours of darkness in two series of shallow-water stations 

 and deep-water stations, we see a marked difference between the distribution in the 



SHALLOW-WATER STATIONS 

 DAYLIGHT DARKNESS 



SCALE OF PROPORTIONS 

 10 20 30 40 50 



L_J I I I I 



% PER 50 METRES DEPTH 

 (in DEEP WATER STATIONS 

 FOR TOP 250m — LOWER 

 DEPTHS IN PROPORTION) 



DEEP-WATER STATIONS 

 DAYLIGHT DARKNESS 



■250 



•500 



750 



-*- 1000 



Fig. 17. Showing the average vertical distribution of Coscinodiscus bouvet at shallow- and deep-water stations 

 taken in daylight and darkness and indicating an apparent diurnal vertical migration. 



upper 250 m. in daylight and darkness. This is shown in Fig. 17. The figures are inter- 

 esting. In the shallow-water stations (seven in daylight and four in darkness) we have 

 the following proportions at different depths: 



