THE OPEN SEA 71 



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 measure, the 

 success of the fishing industry in northern 

 seas. 



In addition to the microscopic plants there 

 are in some places great masses of drifting sea- 

 weeds 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 shallow 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 harbours count- 



