IY-7G 



SECTION 5. THE LIFE 

 ENERGY AND LIFE IN THE ESTUARINE ZONE 



It is in the variety and diversity of estuarine life that the input 

 of energy to the estuarine zone finds ultimate expression. Whether 

 energy comes directly, as in the solar radiation stimulating photo- 

 synthesis, or whether it comes indirectly, as with tidal flows or 

 wind and rain pounding on the shoreline, its absorption and conver- 

 sion to other forms of energy (such as food) are essential steps in 

 the continuation of life 1n the water, in the marshes, and on the 

 land. 



Energy input from gravitational forces, as illustrated by tidal 

 action and river flow, depends primarily on local or regional con- 

 ditions, but direct energy input from solar radiation depends largely 

 on the latitude, the tropics receiving more energy per acre than the 

 arctic. The relative amounts of energy entering an estuarine system 

 govern the kinds of life found there, and natural ecosystems show 

 systematic variations related to the sources and amounts of energy 

 received. 



Estuarine zones with strong mechanical energy inputs from waves, 

 currents, tides, or river flows develop similar ecosystems no matter 

 whether in the tropics or the arctic. Exposed ocean beaches at all 

 latitudes have communities of burrowing animals such as snails, worms, 

 clams, and crabs. Rocky sea fronts develop communities of attached 

 algae and mollusks (Figure IV-1 -30) . Channels with strong currents 

 develop firmly attached communities where bottoms are hard, and only 



