276 MARINE ANIMALS 



Foodstuffs necessary to the plants accumulate, while animals depend- 

 ent upon plants survive only by reason of stored reserves. Whether 

 the entire year's production of the polar sea is greater than that of the 

 tropical cannot yet be stated with certainty. Hensen is inclined to 

 believe that it is, but his evidence is inconclusive. 



The abundance of the lower forms of animal life in the upper 

 strata of the cold seas attracts a large number of bird and mammal 

 predators; these are lacking in the tropical seas or occur sparingly, 

 or in limited regions with special conditions. The sharks occupy a 

 similar place in the food chain in the warm-water pelagial. The birds, 

 which breed in enormous numbers along the coasts of the polar seas, 

 on islands and cliffs, during the warmer seasons, are entirely dependent 

 upon the sea for their nourishment. Many, especially the diving birds 

 like the eider ducks (Somateria) , feed on the benthic animals; others 

 such as penguins feed on pelagic fishes and on plankton. Some of the 

 mammals of the polar seas live on plankton, such as the whalebone 

 whales or the crab-eating seals {Lobodon carcinophaga) which feed 

 upon Euphausidae, and the Weddel seal; others, like the walrus, 

 depend on the benthic life for food. Still others are predators, and 

 live principally on cuttlefishes and fishes. Better testimony could 

 scarcely be given for the abundance of life in the polar seas during the 

 summers than the immense numbers of these birds and mammals 

 which found their sustenance there before their decimation by man. 

 Thus, according to Heuglin, 700 walruses were killed in a few hours 

 on Bear Island in 1606, and fully 900 the following year, and the 

 former vast abundance of the fur seals on the Arctic islands is one 

 of the most notable of animal phenomena. 



Comparisons of the animal communities of tropical seas with those 

 of polar regions have been made primarily on the basis of the situation 

 in the Atlantic, where relationships are best known. Even here the 

 difference in density of population in warm and cold waters need not 

 be due to temperature alone. Unusually large amounts of plankton 

 from the tropical Indian Ocean are reported. 12, 13 In comparison with 

 the equatorial Atlantic, the Indian and Arctic oceans and also the 

 Antarctic have a greater development of coast line and are relatively 

 more shallow. Similar relations prevail in the East Indian Archipelago 

 and undoubtedly affect the development of related pelagic life. Com- 

 parisons of the animal life of tropical and polar seas demonstrate 

 marked differences, but as is to be expected, the animal communities 

 of the cool and temperate areas, while fairly closely allied to those of 

 higher latitudes, are not sharply differentiated from those of tropical 

 and subtropical waters. The greater temperature variations in the 



