COPEPODA 121 



Two of these species, Drepanopus pectinatus 1 and Scolecithricella minor, are of consider- 

 able importance in our region. 



A fraction of every sample of the plankton was passed to Mr Scott, who made the 

 detailed analyses of the Copepoda. In addition he analysed the N 70 H samples for 

 Copepoda. 



The N 70 H results have not been used in studying quantitatively the distribution of 

 the different species. These samples were taken from only three horizontal layers which 

 were intended to be approximately 0-5, 50 and 100 m. in depth ; actually the depths and 

 the speeds of tow sometimes varied considerably with different sea conditions (conditions 

 often not ideal for oceanographical research). This being so, the N 70 H samples cannot 

 give anything like so true a picture of the actual planktonic conditions as the series of 

 vertical nets sampling the whole column of water and fished from the stationary ship 

 in as strictly standard fashion as possible. The N 70 H nets, each being towed for | mile 

 (approximately 463 m.), collected much greater quantities of material than did the 

 N 70 V nets fishing the upper 100 m., for these were hauled vertically for only 50 m. 

 (50-0 and 100-50 m.), and this was the intended function of the N 70 H nets, to collect 

 larger quantities of any species should more material be required for investigation, and 

 to give a greater chance of recording the rarer forms. It is in this latter way that they 

 have been particularly useful, and frequent reference is made to the N 70 H nets in 

 respect to the rarer forms. They have also provided important evidence regarding the 

 vertical migration of the commoner species. 



Whilst the numbers of this and that species might vary very greatly at points quite 

 short distances apart the total number of Copepods at different points throughout the 

 area remained remarkably constant. Fig. 53 shows the average number present per 

 50 m. haul with the N 70 V net in the top 250 m. at all stations in the area. Out of 

 a total of 76 stations only 1 had less than 1000 per 50 m. haul (485), 44 stations had from 

 1000 to 5000, 24 from 5000 to 10,000, 5 from 10,000 to 20,000 and 2 over 30,000 (33,000 

 and 36,000). But this apparent evenness of distribution is largely due to the large 

 number of the small Copepod Oithona frigida . If we eliminate this species we find that 

 out of the 76 stations 32 have less than 1000 Copepoda per 50 m. haul in the top 250 m., 

 34 have from 1000 to 5000, 7 from 5000 to 10,000 and 3 over 10,000 (16,000, 28,000 and 

 35,000). 



The late Mr Andrew Scott drew attention to the increase in the number of species 

 with the increase in depth down to 750 m. This he showed in the form of a curve which 

 is reproduced in Fig. 54 ; this interesting figure should be compared with the curves of 

 temperature and salinity typical for this region, which are shown in Fig. 5. It would 

 appear that only a limited number of species have been able to adapt themselves to the 

 conditions of the cold Antarctic surface layer. Those which have succeeded occur in 

 large numbers. 



1 Mr Scott in a letter of October 1929 wrote regarding this species: "Brady found it in the Challenger 

 plankton off Kerguelen Island very abundantly. One gathering was purely Drepanopus. I cannot trace any 

 (Antarctic) record since Brady's time. It is curious it did not turn up in the Terra Nova collection." 



