ZONES OF THE SEA-WHERE THEY LIVE 



15 



tooether as a connmmity. It is usually possible to apply the same names to 

 communities as to zones, and so there are, for example, tidal, temperate, and 

 euphotic communities. 



Provinces are divisions of the sea similar to zones but larger in scope. The 

 whole of the deep sea, excepting the very bottom, is spoken of as the oceanic 

 province, for instance. 



The communities and zones of land are separated on the basis of plant 

 associations. In the sea, temperature and the nature of the substrate are used. 

 The zones defined bv hght intensitv have already been described. Temperature 

 zonation is simplest and will be considered first. 



Temperature Zones 



The temperature zones are three in number: tropical, temperate, and arctic. 

 (The temperature zones of North America are given in figure 4.) 



Fig. 4. The tetnperature zones of North America. 



THE TROPICS 



The temperature of truly tropical waters almost never falls below 68° 

 Fahrenheit. Near shore, most tropical waters are 75° to 80° all year long. Some 

 subtropical waters fall to a minimum of 61° but are not as different from the 

 tropics as are the temperate zones. The tropical seas represent the most ideal 



