BIOLOGY OF THE SEA-HOW THEY LIVE 35 



Each of these examples is somewhat simpHfied. The striped bass, for instance, 

 does not eat only small fishes, but may also eat crabs, but in spite of this, food 

 chains are short. The shortest consists of three steps and concerns herbivores 

 as follows: 



sun >• algae or turtlegrass >■ green turtle 



The longest are of the large, voracious carnivores, but these are lengthened 

 only because of a step-by-step increase in the size of the carnivores involved: 



sun ^planktonic plant ►•planktonic animal 



Killer whale -^ seal -< herring 



It is often stated that parasitism and mud-eating are examples of simplified 

 food chains. This is not really so. For instance, the mullet is a mud-eater, but 

 its food chain is not the following: 



mud ^mullet 



Instead this food chain is quite complex as follows: 



sun >planktonic plant ^planktonic animal 



plants (/ ^ plankton-eaters 



debris and mud 

 planktonic plant 1 



X 



small mud-dwellers 



illet 



Therefore, the mullet's diet of mud consists of three separate food chains, 

 all of at least four steps. Similarly, the parasite's food chain is not simple but 

 is exactly like that of a carnivore in that it involves flesh-eating. 



One food chain deserves to be somewhat set apart from the rest. This is the 

 food chain of the deep sea. It is a popular opinion that life decreases from 

 the surface to the bottom, but several scientists, including Beebe, Barton, and 

 Jacques Cousteau (Cousteau, 1954), have remarked that life decreases to the 

 dimly lit or dysphotic zone and then increases downward. Deep plankton 

 forms the DSL (deep scattering layer) which can be detected on echo-sounding 

 devices. Direct observations made from the bathyscaphe, a remarkable undersea 

 boat which uses the principles of an aerial balloon, indicated an increased 

 abundance of life with depth and that the DSL is the top layer of this abundance. 

 This has led Cousteau and others to suspect that some unknown link in the 

 food chain is responsible. 



