474 Dynamics of the Ecosystem 



from surrounding areas of a different sort will take place. As has 

 been pointed out in earlier chapters, the ocean represents a relatively 

 uncomplicated biotope compared to many others, particularly those 

 in the terrestrial environment. In a volume of sea water it is possible 

 to measure with accuracy the physical and chemical factors with 

 which we are concerned and to enumerate the living components with 

 sufficient precision. 



Producers. In the open sea the planktonic plants are the essential 

 producers since the reduction in light with depth prevents benthic 

 plants from growing in important numbers in deep water. The main 

 bulk of the phytoplankton is represented by diatoms, but green flagel- 

 lates and other types of nannoplankton may also play a significant 

 role because of their great numbers and the rapidity of their repro- 

 duction. The preponderance of unicellular plants in the oceanic com- 

 munity is related to the retardation of sinking rate resulting from small 

 size and to the increased effectiveness with which widely distributed 

 cells can absorb dilute nutrients. The zones of diatom growth are 

 sometimes spoken of as the pastures of the sea, and the phrase current 

 on land, "All flesh is grass," has been paraphrased for the ocean as 

 "All fish is diatoms." 



Since diatoms and other types of phytoplankton represent the pro- 

 ducer component of the oceanic ecosystem, we shall consider briefly 

 their typical cycle of abundance and the factors controlling it. In the 

 temperate ocean a sudden outburst of diatom growth generally occurs 

 in the spring months (Fig. 13.4), and this is often called the "spring 



Surface 

 temperature 



•Diatoms 



Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. 

 Fig. 13.4. Generalized diagram of seasonal cycle of diatom abundance and cer- 

 tain controlling factors in the temperate ocean. 



