THE OPEN SEA 71 



flea, second link; mackerel, third link; man, 

 fourth link; and so the world goes round. 



This nutritive chain is interesting in theory, 

 but it is also very important practically, for 

 on the abundance of the floating sea-meadows, 

 and the population of small animals which 

 these support, there depends, in large meas- 

 ure, the success of the fishing industry in 

 northern seas. 



In addition to the microscopic plants there 

 are in some places great masses of drifting 

 seaweeds of a higher order. They sometimes 

 occur in such enormous dense patches that 

 they impede the progress of ships passing 

 through them. These seaweeds do not grow 

 at the surface but on the sea-floor in the shal- 

 low water region, and when they are torn off 

 by the waves they are carried by currents far 

 out to sea. They live for a considerable time 

 floating at the surface with the aid of their 

 numerous little bladders, but gradually they 

 lose their vitality and finally sink slowly to the 

 bottom. New clumps are continually being 

 brought by the same currents, so that in some 

 parts of the ocean seaweed is always present. 

 The best known of these areas is the Sargasso 

 Sea in the Atlantic, and the weed there har- 



