PRIMARY PRODUCTION 



525 



The smooth curves in Fig. 1 represent the ideaUzed sequence 

 of events in the euphotic zone for temperate waters on the con- 

 tinental shelf ^^'here there is moderate vertical mixing. If the points 

 on these graphs are considered as sets of data, collected perhaps on 

 a cruise over the area, then using the usual methods of presenta- 

 tion, I have in Fig. 2 graphed plants against phosphate and animals 

 against plants, with the arrows showing the direction of change 

 with time. For the former it is obvious that the curve does not 

 follow any simple relation. For the latter, however, the relation- 

 ship is more subtle since a correlation exists, as suggested by the 

 dotted line. With a sufficient scatter of values, the roughly ellipti- 

 cal form would not be obvious. The rather poor correlation would 

 not be due to the inadequacy of the data but it is inherent in the 

 relations invoked in the time lag between plant and animal 

 growth. This example has been deri\'ed from time changes, but 



PtiosphoTui 



Phytopbnklon 



20 30 40 SO 60 70 



Zoo plonk ton 



lO 20 30 40 50 60 70 



Days 



Fig. 1. Theoretically computed changes during a spring plankton outburst. 



