Chapter 22 



Density of Flagellates and Myxophyceae 



in the Heterotrophic Layers Related 



to Environment 



Francis Bernard 

 INTRODUCTION AND HISTORY 



Xlie paucity of accounts on the density of unicellular organ- 

 isms in the aphotic zone is surprising in the present state of 

 oceanography. More than 30 important cruises have prospected 

 great depths, from the Challenger (1873) to 1960. Between 1903 

 and 1913, H. Lohmann (10) discovered the nannoplankton, 

 showing the importance of Coccolithophorids in warm seas, but, 

 even today, nannoplankton specialists are scarce, and determi- 

 nations are often limited to the photic zone. Many cruises have 

 not caught single samples of deep phytoplankton. 



In the study of deep plankton, German workers are in the 

 lead. In the central and southern Atlantic (Deutschlancl cruise, 

 1921) deep samples were studied by Lohmann (10), and 

 {Meteor cruise, 1933-34) by Hentschel (7), but their samples 

 were centrifuged, and the quantitative results are uncertain. 

 Steemann-Nielsen (1933-38), using Utermohl's method of slow 

 sedimentation, has shown that centrifugation causes at least a 

 loss of one-third of total cells, several species being entirely lost. 



Ercegovic ( 1936 ) followed Steemann-Nielsen in using the 

 inverted microscope, and made interesting studies in the Adriatic 

 Sea off Split, but chiefly in the cuphotic zone. 



Hulburt, Rytlier and Guillard (8) have prospected the 

 Sargasso Sea which is rather poor, finding quantities of Cocco- 

 lithiis huxlei/i at great depths, a species rarely so common at 

 such levels in other wami seas. 



The aim of the present paper is to give recent data on deep 



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