support generalizations about energy transfer efficiencies there. Retaining 

 the 10% assumption, 10 pounds of smaller fish are required as prey to produce 

 1 pound of commercially utilizable fish. The support of 10 pounds of small 

 fish requires 100 pounds of zooplankton, which in turn requires 1000 pounds of 

 phytoplankton (figure 5-26). In other words, even a simple food chain must 

 contain a large amount of energy at the lowest level to support the higher 

 trophic levels, to which energy is progressively less available. 



A sample series of food chains organized into a Maine estuarine food web is 

 shown in figure 5-27. The species shown, which are representative of a larger 

 number of species, are arranged in the illustration to show their approximate 

 trophic level. Energy fixed by estuarine diatoms (primary producers) is 

 transferred via feeding to zooplankton (primary consumers), Atlantic herring 

 (secondary consumers), and terns (tertiary consumers). The detrital-based 

 food web is the dominant avenue of energy transfer in Maine estuarine system. 



1 LB 

 FISHES 



10 LB 

 SMALL FISHES 



100 LB 

 ZOOPLANKTON 



1000 LB 

 PHYTOPLANKTON 



Figure 5-26. 



Simple representation of the energetic relationships between 

 trophic levels. 



5-48 



