Light-x^ , 



9 ^'^t^ ^^s=4>^^ 



/ 



Uutrierics 



f 



?/ Phytoplankton 



a 



Zooplankto" 



B 



t > :s'C 



i'i" ^ '«?"- -^ 



Dissolved Y^ prntn^o 



organic 



matter 



Zooplankton 



■lutr lerit'^ 



Fig. 1 Paths of arrival of organic matter (energy) into the food chain 

 of communities. A, "pasture" food chain; B. "detrital" food chain. 



predators. It is more difficult to evaluate the food chains of the smaller 

 animals at the lower levels--those which suck out only the contents of 

 the bodies of their prey, or which feed on small organisms without skeletons 

 (e.g., protozoa) or bacteria. Analysis of the food's remains in their food 

 lump is not sufficient to indicate the spectrum of their nutrition. In 

 this case, other methods must be used for the investigation--study of the 

 morphologic-functional peculiarities of the feeding apparatus, experimental 

 feeding using various food labeled with C^'^, direct observation under 

 experimental conditions of the nature and intensity of feeding. 



sh a number of trophic 

 phytoplankton); phytophagous 

 crustaceans, nnollusks, some 

 us animal s--first-order 

 aths, amphipods, etc.); larger, 

 ophagous fish, baleen whales); 

 d cephalopods, marine birds 

 edators--medium-sized 

 sharks and the toothed whales, 

 even in extreme cases, the 

 n (Parin, 1968, 1970). Upon 

 igher level, an average of 



Within the food network, we can distingui 

 levels: primary producers of organic matter ( 

 pelagic animals: many copepos and euphausiid 

 (few) fish; predators which feed on phytophago 

 predators (many copepods crustaceans, chaetogn 

 second-order predators (decapods, small plankt 

 third-order predators--basical ly small fish an 

 and reptiles; fourth-order and higher-order pr 

 and large bony fish (tuna, alepisauri, etc.). 

 The total number of trophic levels may reach s 

 four upper levels consisting entirely of nekto 

 transition from each lower level to the next h 

 about 90% of the energy is lost. 



Since the food connections in a community are quite complex and 

 variable, the distinction of trophic levels is quite arbitrary. Actually, 

 the diet of many predaceous forms at the lower levels may include phyto- 

 plankton; second and third-order predators eat both predaceous and phyto- 

 phagous animals; some squids and predaceous fish, occupying the upper 

 levels of the trophic network (particularly the bugeye and yellowfin tuna) 

 act as euryphages, eating anything of the appropriate size--from euphausiids 

 to squid and fish. Depending on the presence or abundance of any of these 

 items, their significance as a part of the diet may change significantly. 



In spite of the instability of the separation of individual trophic 

 levels in a community, their number, i.e., the length of the food chain, 

 may differ significantly from community to community. This is determined, 



38 



