74 ECOLOGY Part II 



Types of Environment. The Land. Terrestrial animals of various groups 

 are described briefly in Part 5. 



The Sea. The greatest numbers of living organisms in the world are the 

 plankton that live in the surface waters of the sea. They are small, mainly 

 minute and microscopic plants and animals that drift with the currents. No 

 plants are so completely open to the energy of the sun. No mixed population 

 of animals is more uniformly short-lived and prolific. In no other place are 

 there, in season, such multitudes of floating eggs and swimming young (Figs. 

 5.7, 5.8). 



The richest population in numbers and kinds of animals visible to the naked 

 eye lives between the tides and near the bottom out to depths of about 400 

 feet. Hosts of them are attached to rocks and seaweeds; or crawl and burrow 

 on the bottom (Fig. 5.9 and 5.10). Farther from shore are the larger free- 

 swimmers (nekton), the fishes; coastal waters are the main fishing grounds. 



The deep water of the open sea from the surface well into its depths is the 

 home of the largest fishes, the giant squids, sea turtles, and the mammals, 

 porpoises, dolphins, and great whales. Except for the whalebone whales all 



M^:: 



Fig. 5.8. Photograph of marine diatoms. Their beauty and variety are due to 

 their silicious shells. Diatoms of fresh waters are less various but equally beautiful 

 and important in the economy of their environments. (Courtesy, Paul B. Conger, 

 United States Museum, Washington, D.C.) 



