OCEAN SEASONS 245 



now become abundant. All these are bom in time to 



partake of the rich pasturage drifting in the sea. The 

 most minute of the animals will feed directly upon the 

 diatoms, and in their turn will fall a prey to their own 

 larger enemies. 



By May or June the great crop of drifting plants is 

 considerably diminished ; much of it has been eaten, but 

 a large quantity also has sunk to the sea floor where it 

 forms food for the large population of minute animals 

 living in the muddy layers just above the bottom. This 

 plant community, or phytoplankton as it is called, gives 

 place in the summer months to a community of animals, 

 the zooplankton, forms which are now growing up and 

 feeding one upon another. Throughout the summer the 

 appearance of this population is always changing, new 

 forms being set free into the water by their parents and 

 others disappearing to take up their abode on the sea 

 bottom. 



So the succession of life passes on until in the autumn, 

 about October, there is another somewhat surprising 

 outburst of plant life, yet never so great as that of the 

 spring. Soon after this the plankton rapidly dies down, 

 until in the winter it is at its poorest, only a small number 

 of animals surviving to tide over the lean months and give 

 rise once more to their numberless progeny in the following 

 spring when the sea wakes up from its winter sleep. 



One of the most interesting problems in marine research 

 has been the search for the causes of this succession of 

 life in the sea, and it is only in quite recent years that the 

 underlying principle has been brought to light. It is 

 evident that on the quantity of plant life present depends 

 the number of animals that can exist, and that therefore 

 the great changes in wealth of animal life can be traced to 

 the increase or decrease of plants. The countless animals 



