Field. — Sources of Marine Food 181 



the water is not subject to extreme changes. Under 

 such conditions growth is so rapid that it passes beyond 

 our powers of conception. Microscopic examination of 

 water taken from almost any part of the sea shows that 

 in reality it is a living broth. To give us a clear picture 

 of the wonderful productivity of these unicellular organ- 

 isms it requires the expression of the late Professor 

 Brooks who says, "Their vegetative power is wonderful 

 past all expression. Among land plants, corn, which 

 yields seed a hundredfold in a single season, is the 

 emblem of fertility, but it can be shown that a single 

 marine plant, very much smaller than a grain of mus- 

 tard seed, would fill the whole ocean solid in less than 

 a week if all its descendents were to live. This stupen- 

 dous fact is almost incredible, but it is capable of 

 rigorous demonstration and it must be clearly grasped 

 before we can understand the life of the ocean." 



Until recently students of marine biology have looked 

 upon diatoms as constituting the ultimate food basis of 

 marine animals. Practical oyster growers in order to 

 find out the best localities in which to plant their oyster 

 beds have tried to determine the food value of the sur- 

 rounding waters in quantity of diatoms per volume of 

 water. In general it has been found that oysters and 

 mussels thrive best where diatoms are most abundant. 

 On the other hand investigations, made by Dr. H. F. 

 Moore of the U. S. Bureau of Fisheries and others, show 

 that the amount of diatoms consumed by shellfish is not 

 sufficient to account for their increase in growth. The 

 question then arises what is the source of the additional 

 nourishment that they obtain? Some investigators say 

 it is from the soluble organic matter in sea water which 

 is constantly absorbed through the body surface, while 

 others attribute it to the suspended organic particles 

 which are taken in with the diatoms. The truth prob- 

 ably lies in the latter assumption as is shown by several 

 very important researches recently conducted at the 

 Danish Marine Biological Station. 



Petersen, 1890, was the first to express the idea that 

 the abundance of fish on the Danish coasts was due 



