SECT. 2] l'KODUCTIVITY, DEFINITION AND MEASUREMENT 135 



theoretically the relative sizes of the primary production in oceanic areas where 

 the hydrographical conditions are known. It is especially important to know 

 the extent of the intermixing of the euphotic surface layers with nutrient-rich 

 sub-surface water. Present knowledge of primary production in the ocean has 

 shown an exceedingly remarkable correlation with hydrographic conditions. 

 In Fig. 1 the chart shows the outlines of oceanic productivity based on the 

 theoretical considerations exclusively. It was presented by Sverdrup (1955). 

 A chart based on all of the measurements of the rate of primary production 

 made during recent years would not look very different. This statement does 

 not mean, however, that we can now cease to make real measurements of the 

 primary production in the sea and let the physical oceanographers tell us about 

 organic production. On the contrary, the close relationship between primary 

 productivity and hydrography is a stimulus for the biologists to proceed in 



Fig. 1. Theoretical representation of relative productivity of ocean areas. Heavy shading 

 indicates very productive areas, light shading moderately productive regions. (After 

 Sverdrup, 1955.) 



making detailed observations of the rate of organic production. Even a single 

 individual measurement of the rate of organic production in a hydrographically 

 complicated area does not present a random value but is a property charac- 

 teristic of the water-mass in question. The rate of organic production may, to 

 some extent, be treated in the same way as chemical or physical properties 

 such as salinity and temperature (see page 158). 



B. Standing Stock as an Index of the Productivity of the Sea 



All of the pioneer work concerning oceanic productivity was based on the 

 standing stock. In the beginning only catches taken with fine silk nets were 

 used for estimating phytoplankton. In the first decade of the present century, 

 Lohmann (1908), however, showed that usually most of the phytoplankton is 

 not retained by these nets. Silk nets may give quite erroneous results with 

 regard to the amount of plankton found in the sea. In some instances they may 

 catch the main part of the planktonic algae present in the water, in other cases 

 practically nothing. In most cases the diameter of the meshes of the finest silk 



