49 



DISTRIBUTION OF PHYTOPLANKTON 

 Stephanosira decussata, Karsten. 



Found only at a single station: WS 50. 



Thalassiosira antarctica, Karsten. 



This species was recorded in small numbers (300) at one of the stations off South 

 Georgia in March 1926: St. 30 in the N 70 V net, 100-50 m. It was most abundant 

 on the C line, taken in November 1926, a month before the main December-January 

 survey ; on the November line the N 50 V net was unfortunately not used, and the 

 following results are taken from the N 70 V net samples. It was found to occur at 

 considerable depths — see Table II. 



Table II 



The numbers of this diatom on the C line in November must have been prodigious, 

 clogging the meshes of the net. Normally this diatom passes through the meshes of 

 the N 70 V net ; for on only one occasion out of the ten on which it was taken by the 

 N 50 V net was it also taken in the N 70 V net, and here only 660 are recorded against 

 19,200 taken in the N 50 V net. We can be certain that had the N 50 V net been used 

 on this November C line the numbers of Thalassiosira recorded would have been very 

 much higher. 



A month later when this line was repeated in the December-January survey it had 

 disappeared from this immediate region, although it occurred in moderate numbers to 

 the south-east. Its distribution during this survey is shown in Appendix I and Fig. 18. 

 It will be seen that it was more abundant in water of Weddell Sea origin. 



Dactyliosolen. 



Two species were recorded : D. laevis, Karsten, the distribution of which is shown 

 in Appendix I, where it is seen to occur irregularly both in Weddell Sea water and in 

 Bellingshausen Sea water; and D. antarcticns, Castr., which was only met with on the 

 C line in late May 1927, in water of Weddell Sea origin, at the following stations: 

 WS no, 2300 (23); WS 112, 1 100 (n); WS 113, 1700 (17) and WS 114, 1000 (10). 



Corethron valdiviae, Karsten. 



Mangin (191 5) describes this diatom as the most important plant of the Antarctic 

 plankton. Whilst it was all but absent in the stations taken in March 1926, being only 

 taken at St. 23, it was taken at every station in the December- January survey of 

 1926-7, and at most of these stations in large numbers. It was particularly abundant 



