BALANCE BETWEEN LIVING AND DEAD MATTER 541 



Zooplankton 



The second actor, the zooplankton, has held the attention of so 

 many zoologists and zoological specialists engaged in general 

 marine research that the systematics seem fairly well known. In 

 addition, we are somewhat familiar with its distribution in space 

 and time and with its physiology. Between the pioneer work of 

 Lohman (1908), who determined the annual cycle of individual 

 species and the zooplankton volumes, and the excellent work of 

 Vinogradov and Bogorov, who investigated the quantitative 

 distribution of the zooplankton biomass, the methods have 

 markedly improved, and valuable results have now been obtained 

 at many localities in the deep sea. We may cite Bogorov's (1957) 

 figures for the biomass of living zooplankton, namely an average 

 at the surface (0-50 m) of almost 50 mg/m^ and between 6000 m 

 and 8500 m of only 1.7 mg/m^ Very little is known, on the other 

 hand, about the physiological responses of the zooplankton, and 

 not enough about its metabolism and its nutrient requirements. 

 Therefore the work of Conover (1959) on the respiration rate of 

 copepods is of greatest importance. 



In connection with these unanswered questions, I draw your 

 attention to an important problem, the base of reference to be 

 used in all metabolic measurements. We cannot refer to the length 

 of the body or the wet w^eight of an organism because these units 

 contain many inert materials, such as the skeleton, reserve ma- 

 terial, and differences in water content. In this connection, we 

 may cite AlacFadyan's (1957) Animal Ecology, which has an 

 excellent discussion based on terrestrial organisms. C. Barker 

 j0rgensen (1955) has added to this by summarizing what is known 

 of the food intake of marine filter-feeding animals and based some 

 of his computations on nitrogen. With modern methods, we can 

 make basic analysis for proteins and thus improve our knowledge 

 in this area. 



Limiting Nutrients 



The quantity of limiting nutrients in ionic solution is the third 

 actor. Everybody engaged in marine research knows the role of 



