EXTREME 

 HIGH WATER 

 SPRING 



PHYSICAL 



INTERTIDAL. 



ZONE 



EXTREME 

 LOW WATER 

 SPRING 



LlTtOPTAt-^ONH 



(JvJWM NteBllOAf SOBSySTEW) 



;BUBLlTTO,RAL,:ZONe 



i N Wi, .Sl/BTi m S I^.PSVST.EM) 



PROTECTED AREA 



INCREASING EXPOSURE- 



EXPOSED AREA' 



Figure 5-36. Comparison of the boundaries of the physical intertidal zone 

 and the littoral (biological intertidal) zone with increasing 

 exposure to wave action (adapted from Lewis 1964) . 



10,382 acres (4203 ha; 15%), 10,709 acres (4336 ha; 16%), and 6820 acres (2761 

 ha; 10%), respectively. 



The relative physical stability of the subtidal environment allows for the 

 establishment of diverse, highly organized communities. Ecological factors 

 that affect the biota sometimes are quantitatively different in estuaries than 

 in marine systems. Since the biota present in the brackish waters of 

 estuaries are usually of marine origin, in order to survive they must 

 physiologically adapt to estuarine conditions, such as reduced or highly 

 variable salinities and temperatures. Areas that have greatly reduced and/or 

 variable salinities have the fewest species (see "Estuarine Unconsolidated 

 Bottoms" below) . In subtidal subsystems tidal currents that carry suspended 

 sediments and detritus are an important component of the subsystem. Estuarine 

 productivity is dependent largely on attached macroalgae, macrophytes, benthic 

 diatoms, and land-derived detritus, whereas marine systems are dependent 

 largely on phytoplankton productivity. 



In general, pollution loads are greater in estuarine areas than in nearby 

 coastal waters because of their higher human populations. Estuarine organisms 

 generally are more adaptable to a wide range of environmental conditions and 

 are more tolerant of perturbations than their marine relatives. Indeed, some 

 of the species characteristic of upper estuarine areas are also characteristic 

 of polluted water (Boesch 1973). Increased nutrient levels in estuaries due 



5-77 



10-80 



