II. FERTILITY OF THE OCEANS 



7. PRODUCTIVITY, DEFINITION AND MEASUREMENT 



E. Steemann Nielsen 



1. Introduction 



Quantitative investigations of the marine plankton were initiated early in 

 the history of oceanography. The most important pioneer work was done by 

 the German scientist Victor Hensen towards the end of the 19th century. 

 Attempts to understand the background of oceanic production were also made 

 during this early period, for example by Hensen (1890). 



Production as such was not investigated during this initial period of plankton 

 science. It was the standing stock of organisms- — plants and animals — which 

 was measured. No methods were available at the time for measuring the 

 production directly. We must admit that we still lack methods for measuring 

 the production of animals directly. All estimates of animal production are 

 based on measurements of the standing stock combined with assumptions and 

 theoretical considerations (see, for example, Gushing, 1959). 



The situation is more fortunate in the case of the primary production of 

 organic matter by the photo -autotrophic planktonic algae. As will be shown 

 later, the development of methods for directly measuring primary production 

 began during the twenties of this century. During recent years the measure- 

 ments of primary production have become one of the main tasks in oceano- 

 graphy. 



A real production of organic matter takes place almost exclusively during 

 photosynthesis ; chemosynthesis is of very little importance. Organic matter 

 is synthesized from inorganic matter, and the radiation energy from the sun 

 is transformed into chemically bound energy. "Production" of animal organic 

 matter is only a transfer of organic matter — or energy — from one trophic level 

 to another. Hence we may concentrate here on discussing primary production 

 and outline only a few aspects of "production" at higher levels. 



A necessary condition for a large-scale fishery to be possible in a certain sea 

 area is that a significant part of the primary production is within the area ; but 

 presumably this is not the only necessary condition. Thus the transfer of 

 organic matter between the different trophic levels must be considered to be 

 important also. However, our present knowledge is too incomplete to allow 

 more than a general discussion. 



The next trophic level following the autotrophic plants is made up in the 

 ocean by the herbivores of the zooplankton (secondary production). A con- 

 siderable part of the organic matter — and of the energy — is lost during the 

 transfer from one trophic level to another. Ignoring at first the sinking of the 



[MS received August, 1960] 129 



