IV-409 



The effects of physical destruction of habitat are also easy to 

 assess, at least in terms of the immediate damage caused. The more 

 subtle related effects of damage to organisms dependent indirectly 

 on the habitat for food supply are more difficult, sometimes 

 impossible, to determine. 



Many studies of different aspects of estuarine biology have been 

 made, but there are only a very few cases in which comprehensive 

 ecological studies have been made of pollutional effects. The 

 available information on the extent of ecological damage is 

 summarized in Table IV. 5. 12. The information base for this table is 

 exceedingly sparse; most studies were done when there was apparently 

 some damage or other kind of ecological problem. Therefore, it is 

 not possible to say whether 38 percent of the Nation's estuarine 

 systems are undamaged or merely present no identifiable problems at 

 this time (IV-5 TO). 



The estuarine systems of the Middle Atlantic biophysical region 

 have suffered the most damage; 83 percent exhibit some ecological 

 damage, but only in a few cases is the extent known in any quanti- 

 fiable sense. The Chesapeake Bay and Gulf of Mexico regions have 

 the largest numbers of heavily damaged systems, probably because of 

 the intensity of use of the estuarine systems in these regions. 

 Forty percent of the estuaries of the Pacific Southwest region are 

 heavily damaged; this reflects the intensive development of the 

 relatively few estuarine systems of this region. 



