THE FOOD CHAIN 



in this food chain as the main food of the demersal fish and so in the economy 

 of the sea. There are even heterotrophic diatoms, flagellates, bacteria and 

 protozoa on the sea floor which use what is leit by the coarser tflter feeders. 



Food originally produced at the surface is used over and over again as 

 one animal feeds on another, or on its waste products. Creatures living 

 below the surface are thus not starved, though they tend to get scarcer in 

 deeper water until quite near the bottom. Here, there is a further supply of 

 food available as the bottom acts as a physical barrier to further sinking, 

 and so concentrates what is left to be used by detritus feeders and those that 

 prey on them. 



All the organisms in the sea, alive, dead or disintegrated, form the food 

 of something else, and any organic material not re-absorbed by animals 

 is regenerated by bacteria into the basic inorganic nutrients which will 

 eventually nourish new plants. Nothing is useless in this great cycle of con- 

 tinuously interdependent events. The only losses from the sea are those 

 deliberately removed as fish etc by man or by birds. These losses in actual 

 protein add up each year to an enormous figure (Chapter lo), but are 

 compensated by the return to the sea of sewage, detritus and nutrients, and 

 the drainage of fertilizers from of the land. Most the droppings of the sea 

 birds, and their bodies after death, fall back into the sea. The sea is, in 

 fact, probably becoming rather richer than poorer every year in its total 

 productive capacity, helped also by the increase in atmospheric carbon 

 dioxide due to man's use of fuel in industry. 



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