PLANKTON 27 



115 days later at Samoa, 6000 miles away. Preliminary reports indicate 

 that he, too, sustained himself to a fair extent on plankton. 



B. PHYTOPLAN KTON 

 (MICROSCOPIC ALGAE) 



1. General Nature 



Phytoplankton or "plant plankton" conists chiefly of microscopic 

 algae, which, with few exceptions, are aquatic organisms. These micro- 

 scopic growths comprise mainly the Divisions Chlorophyta, Euglenophyta, 

 Chrysophyta, Pyrrophyta, and Cyanophyta. Though thousands of species 

 are represented, the diatoms and unicellular flagellates are predominant. 

 They thrive in both fresh and salt water; however, a given species is 

 specific for the one or the other. 



Algae are the only plants that can flourish in the sea. They make 

 available the vast amounts of dissolved minerals and other nutrients ; thus 

 neritic plankton (near the coasts) is richer because of the higher con- 

 centrations of salts. As previously indicated, phytoplankton provides — 

 directly or indirectly — the basic food for all the ascending hierarchy of 

 marine animals. Freshwater algae play a somewhat similar role in their 

 own habitat. The total quantity of phytoplankton perforce exceeds that 

 of zooplankton. However, effective collection of phytoplankton is very 

 difficult because the individual organisms are so small. As Burlew 41 has 

 so strikingly put it, one quart of moderately thin suspension of Chlorella 

 pyrenoidosa contains twenty billion cells, a number equivalent to eight 

 times the world's human population! 



The color of the sea directly -reflects the particulate matter therein. 174 

 When there is little marine growth, the water is deep blue, since the light 

 penetrates to deep levels, and the yellow and red rays are absorbed. When 

 planktonic growth is abundant, the water assumes the yellow, green, or 

 brown shades of the microscopic algae. Seasonal abundance of certain 

 reddish algal growths may produce the "red water" described since an- 

 cient times; to this may also be credited the coloration of the Red Sea 

 and the Vermilion Sea. The nocturnal glow of some seas is attributable 

 to the phosphorescence of certain planktonic organisms. 



Reference is made in the literature to microscopic algal studies as 

 early as 1779; Priestly 175 and Ingen-Housz 176 described experiments on 



