Primary Production 



JOHN H. STEELE 



Murine Lnhnratory. Aberdeen, Scotland 



ONE difficulty in preparing this paper has been that I feel there 

 is really no subject that can properly be called "primary produc- 

 tion." Rather, the phrase is used as a focus for many diverse in- 

 terests connected with what may be called, rather vaguely, the 

 relation between phytoplankton and their en\^Ironment. The in- 

 terest in this field is not merely to measure production but to 

 try and explain how these values arise, not only from the physio- 

 logy of the plants themselves but also from their interaction with 

 the physical conditions and with the animals that graze on them. 



The basic problem in relating these various trophic levels is 

 the great complexity in the species composition of the plants and 

 animals. The one feature of primary production which perhaps 

 separates it from other branches of marine biology is its attempt 

 to escape from this complexity by considering plants and animals 

 as chemical rather than biological entities. Thus the common unit 

 is quantity of organic carbon and, for example, grazing on the 

 plants is expressed as the rate at which plant carbon is eaten by 

 animal carbon. 



This hypothseis of simplicity is a much blunter instrument than 

 Occam's razor, and it is obvious that too much has been cut away. 

 In using the same example, salps and copepods can hardly be 

 expected to have the same feeding rates for each unit of their 

 carbon content. Beyond this there are the problems raised by 

 Lucas (p. 499), problems of the effects of traces of organic sub- 

 stances on particular species and on the interrelations between 

 species. In ignoring these problems, we are postulating that these 

 "metabolites" may determine which species compose the popula- 

 tion but that the total population is determined by the much 

 simpler large-scale factors we study. Thus this hypothesis of 



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