Succession of Phyto plankton 271 



There are other examples of an interaction between growth 

 factors. Sverdrup's (53) "critical depth" theory demonstrates that 

 light intensity coupled witli water mass stability is a critical 

 factor governing the inception of growtli in natural populations 

 after the winter minimum. Significantly, Riley's (38, 39, 40) 

 statistical assessment of the factors influencing the dynamics 

 of natural populations has been more successful when these 

 variables have been treated collectively rather than singly. 



This diverse but consistent body of evidence indicates that 

 many factors are simultaneously operative in determining phyto- 

 plankton growth. The manifold environmental interactions of 

 growth variables reveal the ocean to be a holocoenotic environ- 

 ment, that is, an environment in which the observed phytoplank- 

 ton dynamics aie the resultants of the collective, simultaneous and 

 interdependent action of many parameters. The combined action 

 of these variables is expressed in the recurrent succession and 

 cyclic abundance of marine phytoplankton. 



This conclusion is not new, although its significance appears 

 to have been frequently overlooked in the design of field and 

 experimental studies. Yet a scientific approach based on the 

 holocoenotic concept has merit in being more representative 

 of natural conditions, which enhances its prospects of contribut- 

 ing significantly to the development of a quantitative theory of 

 phytoplankton dynamics. 



REFERENCES 



1. Braarud, T.: a quantitati\e method for the experimental study of 

 plankton diatoms. /. Cons. int. Explor. Mer. i2:321-332, 1937. 



2. : A phytoplankton survey of the poHuted waters of the 



inner Oslofjord. Nor.ske Vidensk. Akod. Uvahaad Skr., No. 28:1-142, 

 1945a. 



3. : Experimental studies on marine plankton diatoms. 



Norske Vidensk. Akad., Oslo. I Mat.-Naturv. Klasse, 1944, No. 10: 

 1-16, 1945b. 

 4. , G.\ARDER, K. R. and Gr0ntved, J.: The phytoplank- 

 ton of the North Sea and adjacent waters in May 1948. Rapp. Cons. 

 Explor. Mer, 133:1-87, 1953. 



5. Br.\xdt, K.: Uber den Stoffwechsel im Meere. Wiss. Meeresuntersuch, 

 N.F. Aht. Kiel, 4:215-230, 1899. 



