34 UNDERWATER GUIDE TO MARINE LIFE 



the large species which eat large carnivores themselves (killer whale, white 

 shark). Rarely does an animal have a diet that is restricted to only one food 

 species. The dependency of the sperm whale on giant squid, the blue whales 

 on krill, or the sea slug on seaweed are three of the few examples of such 

 dependency. It is much more common to find that an animal will eat a variety 

 of things depending on its food-getting mechanisms and the availability of 

 food species. Probably the animals with the most catholic tastes are the omnivores 

 which eat just about anything they can catch and swallow (some sharks, many 

 crabs, catfishes, etc.). 



The importance of size on choice of food is easily illustrated. For instance, 

 the killer whale and the blenny are probably equally voracious feeders, but they 

 are forced to eat very dissimilar things because of a vast difference in size. 

 There are exceptions to the size rule that the biggest animals eat the biggest 

 objects. Puffers and killer whales gang up on prey to increase their effective 

 size. Poison, as a food-getting mechanism, increases effective size. On the other 

 hand, the largest of all cartilaginous fishes and mammals (basking sharks, 

 whale sharks, manta rays, and baleen whales) eat tiny planktonic animals. 



One primitive mechanism of food getting is filter-feeding and is extremely 

 widespread in the animals of the sea. It alwavs involves the straining of plankton- 

 bearing water. The larger plankton-eaters feed by a filtering process. Such 

 fishes as whale sharks, mackerels, and herrings, filter with gill rakers, and 

 whales filter with baleen. Many groups of invertebrates also filter-feed. Among 

 these are clams, oysters, sea squirts, sponges, crustaceans, corals, many worms, 

 and salpas. Some of these, such as crustaceans and salpas, are planktonic and 

 form a vital link between small, single-celled planktonic plants or protozoans 

 and the large fish or mammal plankton-feeders. The other groups are sedentary 

 and depend on small plankton brought to them by water currents. 



A food chain may be drawn for any animal in the sea. Examples of food 

 chains follow. (The arrow points from the food or energy source to recipient.) 



Oceanic, plankton-eating, carnivore food chain (whale): 



sun ^planktonic plant >- krill ^baleen whale 



Coral reef, omnivore food chain (angelfish) : 



sun galeae ^anoclfish 



planktonic pla 



Small invertebrates 



— ^ angcU 

 lant / 



Inshore, carnivore food chain (striped bass): 



sun ^.planktonic plant ^planktonic animal 



striped bass -^ small fishes^ 



