CHAPTER 1 



INTRODUCTORY 



The sea, therefore, we may safely infer, has its offices and duties to 

 perform; so, may we infer, have its currents, and so, too, its inhabi- 

 tants; consequently, he who undertakes to study its phenomena must 

 cease to regard it as a waste of waters. He must look upon it as a part of 

 that exquisite machinery by which the harmonies of nature are pre- 

 served, and then he will begin to perceive the developments of order 

 and the evidences of design; these make it a most beautiful and interest- 

 ing subject for contemplation. 



Lieut. F. M. Maury, 1883 



THE REALM OF MARINE LIFE 



The oceans in their vast expanses cover seven-tenths of the earth's surface 

 and in their deepest reaches extend downwards into the earth's crust to 

 some 10,000 metres below sea level. The mean depth of the ocean has been 

 estimated at about 4,000 metres, which is considerably greater than the 

 mean height of land above sea level, namely some 850 metres. All this 

 tremendous expanse and depth are inhabited by living things; animals 

 have been secured from beneath the polar ice sheets, and from the ocean 

 deeps more than 10 kilometres beneath the surface. These abyssal forms are 

 normal inhabitants of that world and know no other, and similarly at 

 intermediate depths there are other animals which tend to remain at defi- 

 nite levels. 



The ocean is not evenly populated throughout its extent. The density 

 and total volume of living organisms are greatest in coastal waters and at 

 the surface, and decrease rapidly with depth in the waters of the open 

 ocean. The food of all animals in the sea is ultimately derived from marine 

 plants, phytoplankton and, to a small extent, seaweeds. Since the energy 

 for their synthetic activities is provided by sunlight, plants can thrive only 

 in shallow or surface waters within the range of adequate light penetration. 

 In these regions the herbivores graze upon the plants, but at deeper levels, 

 extending down to the deepest waters of the abyss, the animals are depen- 

 dent upon the remains of dead or dying surface organisms which slowly 

 shower upon them from above, and to some extent upon the spatial 

 organization of food chains in vertical series. 



VARIETY OF MARINE ANIMALS 



Of the nineteen or so phyla recognized by zoologists all except one or two 

 are found in the sea. Of these, four are exclusively and four are predomi- 

 nantly marine in habit, while many of the remaining phyla are well 

 represented. The entirely marine phyla are the Brachiopoda, Chaetognatha, 



M.A. — 1 1 



