MEASURING 

 THE PRODUCTIVITY OF THE SEA 



By E. Stemann Nielsen 



What a dull word "productivity" is! Yet it explains everything: all 

 life on land and in the sea, politics, even wars. For though wars are 

 ostensibly waged for other reasons, their underlying causes are usually 

 "productivity"; too little of it at home and a tempting amount in other 

 territory owned unfortunately by other people. 



Replace the word "productivity" with "volume of food" and the 

 meaning is clear. 



Man cannot live on inorganic matter but, like other animals, must 

 have organic food; that is to say, carbohydrates, fats, and proteins. Plants 

 are different; they are able to convert inorganic matter into organic, 

 producing both carbohydrates and fats from carbon dioxide and water. 



Conversion of inorganic into organic matter, however, requires a 

 supply of energy. When we burn wood, thereby forming carbon dioxide 

 and water, we release energy which may be applied, let us say, to driving 

 a steam engine. It follows from the law of the conservation of energy that 

 the same amount of energy must be supplied when the tree is originally 

 formed from carbon dioxide and water. In fact, it is supplied by the rays 

 of the sun, which are absorbed by the green pigment of the plant. That 

 is why plants need sunlight. 



All animals, including man, live on vegetable matter. Herbivorous ani- 

 mals obviously do, but so, ultimately, do lions, though they get their 

 vegetable matter through the medium of herbivora like antelopes and 

 gazelles. 



This is the law of all life on land, and the law of life in the sea is 

 exactly the same. Here also plants are the basis of all other life. If there 

 were no plants there would be no fish. In fact, there is an abundance of 

 plants in the sea. This is obvious by the shores, where we find green, 

 brown, and red sea-weed clinging to rocks and stones and marine grasses 

 growing on a sandy bottom, and forming in sheltered places whole 

 "pastures". 



Attached plants, however, are not found in deep waters, since marine 

 plants need light just as much as land plants. In Danish waters, for exam- 

 ple, there are no attached plants living at depths greater than 30 metres, 

 and though in certain parts of the world they are found below 100 metres, 



