107 



over a limited range of concentration ; solar energy ; water temperature 

 variation; water quality and nutrients favorable to their propagation, 

 growth, and survival; and, for some life forms, bottom conditions 

 suitable to their unique needs. 



Many forms of plant and animal life can tolerate salinity ranging 

 from ocean concentrations (35 parts per thousand) to practically 

 zero. Other life forms must have a much narrower salinity range in 

 which to live and reproduce. There are animals which require differ- 

 ent salinities at different parts of their life cycle and which migrate 

 to find it. Figure IV.1.36 shows the range of salinity tolerance of 

 some characteristic estuarine plants and animals. Most of those with 

 a limited salinity tolerance can also withstand temporary exposure 

 to salinities outside that range. 



Solar radiation governs the photosynthetic process by which plants 

 manufacture the basic food upon which all life ultimately depends. 

 The primary producers of food in the aquatic environment are the 

 microscopic plants upon which the succession of more advanced life 

 forms feed. Planktonic communities exist in all ranges of salinity and 

 temperature, but their composition may vary even with constant tem- 

 perature and salinity. The rate of input of solar radiation is greater 



FIGURE IV.1.36 COMMON SALINITY RANGES OF OCCURENCE FOR SOME 

 ESTUARINE-DEPENDENT PLANTS & ANIMALS 



Salinity Range 

 (parts per thousand) 



Source: Odum, H. T. , op. cit . 



