442 



RILEY 



[CHAP. 20 



the seasonal cycle were controlled by a single factor. For example, the onset of 

 the spring flowering was controlled by light and stability, and its termination 

 was brought on by grazing, nutrient depletion and reduction in transparency. 

 The conclusion of Harvey et al. (1935), which has been reiterated by Cushing 

 (1958), that flowerings are controlled by grazing, may be true in British waters 

 but is not applicable to the New England area. There the relative importance 

 of grazing varies from one part of the area to another, suggesting that this is 

 not a subject for broad generalization. 



3000 - 



New England 

 coastal water 



^J'F'M'A'M'J'J'A'S'O'N'D'^J'F'M'A'M'J'J'A'S'O'N'D 

 1932 1933 



Fig. 1. Comparison of observed seasonal cycles of phytoplankton (solid lines) with 

 theoretical cycles (dotted lines) computed according to equations (4) to (9). 



The Volterra equation for predators was applied, with some modifications, 

 to the Georges Bank zooplankton by Rile}^ (1947a). The equation for the 

 herbivore population. H, was 



dH 



= H(A-R-C-D), 



(10) 



where A is a coefficient of assimilation, R is the respiratory coefficient, C is 

 predation by carnivores, and D is natural death. R was determined from 

 laboratory experiments, but other coefficients contained arbitrary elements. 

 A was postulated to equal gP, using the same numerical value for g that was 

 established in the phytoplankton analysis (equation 8). However, it was neces- 



