364 DISCOVERY REPORTS 



occurring in sufficient numbers are now correlated with phosphate values. All the 

 organisms show, in general, reduced numbers in the regions of low phosphate values 

 except the Copepoda Calanus acutus, Khincalanus gigas and Oithonafrigida, which appear 

 to be unaffected, and certain organisms which appear to prefer these regions: Calanus 

 simillimus, Drepanopus pectiuatus and Antarctomysis maxima (pp. 301-308). These results 

 are confirmed in different series of nets. 



The appearance of exclusion from regions of low phosphate (high phytoplankton) 

 is shown to apply to animals belonging to such widely different groups as Foraminifera, 

 Radiolaria, Polychaeta, Crustacea, Molluscs, and Tunicates. It is considered that 

 if the distribution of the animals is being modified by the phytoplankton, then this 

 modification must be brought about by variations in the vertical migration in conjunc- 

 tion with differing water movements at different levels (p. 311). All the animals which 

 show the exclusion effects are shown to have a marked vertical migration; the three 

 copepods which show no such effects have little or no vertical migration, and are rarely 

 taken in large numbers in the upper phytoplankton zones. Calanus simillimus and 

 Drepanopus pectiuatus, which show a preference for rich phytoplankton in their hori- 

 zontal distribution, are the two species of copepod which are found higher in the water 

 than any other (p. 312). Depth of water in relation to vertical migration is considered 

 as a possible cause of the effects produced, but similar results in general are obtained 

 from shallow and deep-water stations (pp. 314-320). Further considerations suggest 

 that it is possible that Euphausia superba may be a key organism controlling the phyto- 

 plankton by its feeding, and that the other animals may be adjusting their distribution to 

 the resulting phytoplankton densities (p. 319). Vertical migration is considered in relation 

 to phytoplankton, and the hypothesis of a modification of migration by phytoplankton 

 examined. The evidence is suggestive but not conclusive (pp. 322-339). The general 

 significance of vertical migration is considered (p. 340). Theoretical considerations 

 regarding the combined effect of vertical migration and different current systems are 

 described (pp. 343-356). Some of the main differences between the Antarctic and other 

 pelagic areas are considered, and a hypothesis concerning the influence of the phyto- 

 plankton tentatively suggested (pp. 356-360). The distribution of coral reefs is briefly 

 referred to (p. 360). 



Addendum (referring to footnote on p. 279). Since going to press we see that W. E. Allen 

 (1934, p. 176) writes as follows: "It is possible that certain kinds of diatoms may be poisonous to 

 animals (or to certain animals) just as land plants are known to be so, and it is possible that when 

 present in great abundance they may interfere more or less with respiration of some animals by 

 clogging the gills. 1 Direct evidence is not available in Southern California except that commercial 

 fishermen say that fishing is not good where diatoms are so abundant as to discolour the water." 

 He also refers to Torrey (1902) who records that abnormal swarms of Dinoflagellates (Gonyaulax) 

 may cause great destruction of inshore forms of animal life. 



1 See also Hardy (1924, p. 34). 



