PHYTO- AND ZOOPLANKTON INTERRELATIONS 



Table LIII 



283 



Important species of macroplankton (N 100 H nets) at stations in the South Georgia survey 



of December-January 1926-7, arranged in order of phytoplankton values and averaged in 



six groups {one of eight stations and five of seven stations) 



Numbers in heavy type are those above the average. 



with in making correlations, particularly factors due to patchiness and to the vertical 

 migration of these organisms into the region of the nets in larger numbers during the 

 night than in the daytime. In Table LII the stations taken during the hours of darkness 

 are marked with an asterisk, 1 and the numbers of the macroplankton organisms which 

 are above the average are shown in heavy type. This table is summarized in Table LIII. 

 In the summary table only one night station is included in the lowest phytoplankton 

 range, but in the other ranges, taking them in ascending order, the night stations are 

 3, 2, 3, 3 and 2. Although the observations are few they suggest that these animals 

 do not occur in large numbers where the phytoplankton concentrations are high. The 

 indication that they do not also occur in large numbers in regions of poor phytoplankton, 

 where perhaps there is insufficient food, is worth little in this series on account of there 

 being only one night station in the lowest phytoplankton range, but later evidence dis- 

 cussed on pp. 301-309 gives some support to this conception. 2 



The question as to how the zooplankton organisms may come to be distributed 

 in this way and the possible causes underlying their apparent exclusion from dense 

 phytoplankton regions will be discussed later ; we must first seek further evidence as to 

 whether the correlation suggested here is a real one or not. 



In March 1926 very few samples were unfortunately taken with the N 50 V net, but 

 at the three stations where it was used, Sts. 23, 31 and 41 in the region of Euphausia 

 concentration, very little phytoplankton was found, with the exception of moderate 

 quantities of Thalassiothrix antarctica at St. 41 (33,000 cells for the N 50 V haul). At 

 St. 12 (taken in February of the same year on approaching South Georgia from the 

 north-east, and approximately 180 miles from the coast) a dense mass of the diatom 



1 Since this section went into proof the deep-water stations, i.e. those in water over 500 m., have 

 been indicated with a dagger and the possible significance of depth of water is considered on pp. 314 

 to 320. 



2 This is discussed further on pp. 350-351. 



