202 DISCOVERY REPORTS 



Dinoflagellates were present occasionally, but in such small numbers as to be altogether 

 negligible when the phytoplankton as a whole is considered, and they have not been 

 included in the tables. 



The diatoms fall very readily into three groups, neritic forms, immigrants and occa- 

 sional stragglers. Of the three neritic forms, FragUaria sp., Coscinodiscus stellaris and 

 Lycmophora lyngbyei, the first two are by far the most important, Lycmophora being 

 typically a bottom form growing very plentifully on the kelp. FragUaria sp. occurred 

 on kelp also, growing in very long chains, but it was the chief and most constant 

 constituent of the phytoplankton, where it occurred in relatively short chains averaging 

 sixteen frustules each. Coscinodiscus stellaris was of fairly constant occurrence also, but 

 its maximum development was reached at a time when the bay was invaded by a mass 

 of high salinity water of extraneous origin, and in considering the phytoplankton m 

 relation to hydrological and other changes, FragUaria sp. has alone been taken as the 

 typical inshore form. 



Fig. 8 1 gives the total diatoms as histograms, FragUaria sp. being shown in black; 

 above are plotted curves for the various meteorological and other features that appear 

 to exert an influence on the phytoplankton. Broadly speaking it will at once be seen 

 that the heaviest catches of diatoms were obtained during the first half of the season, 

 with a very marked falling off after mid-January. Three maximum periods are clearly 

 definable with a sharp decline between each. The first, covered by Sts. MS 84, 85 and 

 86 (November 12-25), consisted of a fair proportion of FragUaria sp. with an in- 

 creasingly large number of immigrants, notably Chaetoceros criophilum and Corethron 

 valdiviae. The next, at Sts. MS 89 and 90, consisted almost entirely of FragUaria sp., 

 and the last (St. MS 95) of Coscinodiscus stellaris of extraneous origin. At the end of the 

 season there were slight indications of what might have become a small secondary 

 autumnal maximum, but conditions at that time had become generally unfavourable 

 for phytoplankton growth. 



From the consideration which follows, of the meteorological and hydrological factors 

 that appear to exert the most influence in determining this seasonal distribution of the 

 phytoplankton, it seems that the principal reasons for its great scarcity in Cumberland 

 Bay are two in number : firstly, the constant and often rapid movements of the surface 

 layers consequent upon the high variable winds, and secondly, the amount of fine in- 

 organic material, largely morainic in origin, in suspension. The wind has the effect of 

 carrying the diatoms out of the area investigated too quickly to permit of extensive 

 proliferation, while the suspended matter greatly decreases penetration of light, and 

 may also interfere directly with the gaseous interchange of the organisms. 



In early attempts to investigate the phytoplankton by means of the centrifuge, which 

 failed in their main object by reason of the small numbers of organisms present, the 

 great amount of inorganic material was at once apparent. A rough indication of the 

 opacity of the water was obtained by noting the depth at which the polished metal top 

 of the Nansen-Pettersen bottle disappeared from view. Unfortunately Secchi-disc 

 readings were not taken, as the importance of this factor was not at first realized. 



