ANIMAL LIFE OF THE DEEP SEA BOTTOM 



155 



The dinghy has been launched 

 in order to make sure of a good 

 haul. A large branch can be 

 seen in the middle of the trawl. 



thermosphere and the cold, deeper psychrosphere, referred to above by 

 A. Kiilerich, is so rich in pelagic animals. Here the dark-loving pelagic 

 animals of the thermosphere are stopped by the cold of the deep; and 

 here also the animals of the psychrosphere, seeking the richer food levels 

 above, are stopped by the higher temperatures. Lower down come the 

 kilometre-thick layers where there is only a very little food available in 

 the form of bacteria, which can utilize falling organic matter like excre- 

 ment and other dead material. It is not surprising that higher animal life 

 here is sparse. 



Only at the bottom do we get a new accumulation. Everything ends 

 here; and whereas in the deep, free water masses there were only a small 

 number of bacteria to the cubic centimetre, and sometimes none at all, here 

 they are teeming, breaking down all the material which still has a little 

 radiant energy left in it — that is, all the dead organic matter — exactly 

 as on land. Here we understood the link between the rich trawls which 

 we brought up and the large quantities of dead vegetable material from 

 the land (see Figs. p. 154 and p. 172, below) filling the trawl at the same 

 time — • branches, leaves, palm and mangrove fruits, and much else. Dead 

 vegetable material of this kind can hardly be broken down by the gastric 

 juices of animals; but bacteria can cope both with cellulose and with 

 everything else, and they in turn can be consumed by mud-eaters which 

 gorge themselves on the soft oozy bottom, such as bristle-worms, sea- 

 cucumbers, and bivalves. And then a new link can be added to the food 



