13 



UPLAND PALUSTRINE UPLAND 



PALUSTRINE 



UPLAND 



PALUSTRINE 



UPLAND 



Seepage Zone 



a TEMPORARILY FLOODED 



b SEASONALLY FLOODED 



c SEMIPERMANENTLY FLOODED 



d INTERMITTENTLY EXPOSED 



e PERMANENTLY FLOODED 



( SATURATED 



■^HIGH WATER 

 AVERAGE WATER 

 LOW WATER 



Fig. 6. Distinguishing features and examples of habitats in the Palustrine System. 



sedentary or sessile macroinvertebrate species, without 

 regard for life form. In the Marine and Estuarine Systems, 

 sponges, alcyonarians, mollusks, crustaceans, worms, asci- 

 dians, and echinoderms may all be part of the community 

 represented by the Macoma balthica Dominance Type. 

 Sometimes it is necessary to designate two or more co- 

 dominant species as a Dominance Type. Thorson (1957) 

 recommended guidelines and suggested definitions for 

 establishing community types and dominants on level 

 bottoms. 



Rock Bottom 



Definition. The Class Rock Bottom includes all wetlands 

 and deepwater habitats with substrates having an areal 

 cover of stones, boulders, or bedrock 75% or greater and 

 vegetative cover of less than 30%. Water regimes are 

 restricted to subtidal, permanently flooded, intermittently 

 exposed, and semipermanently flooded. 



Description. The rock substrate of the rocky benthic or 

 bottom zone is one of the most important factors in deter- 

 mining the abundance, variety, and distribution of organ- 

 isms. The stability of the bottom allows a rich assemblage 



of plants and animals to develop. Rock Bottoms are usually 

 high-energy habitats with well-aerated waters. Tempera- 

 ture, salinity, current, and light penetration are also im- 

 portant factors in determining the composition of the ben- 

 thic community. Animals that live on the rocky surface 

 are generally firmly attached by hooking or sucking 

 devices, although they may occasionally move about over 

 the substrate. Some may be permanently attached by 

 cement. A few animals hide in rocky crevices and under 

 rocks, some move rapidly enough to avoid being swept 

 away, and others burrow into the finer substrates between 

 boulders. Plants are also firmly attached (e.g., by hold- 

 fasts), and in the Riverine System both plants and animals 

 are commonly streamlined or flattened in response to high 

 water velocities. 



Subclasses and Dominance Types. 

 Bedrock.— Bottoms in which bedrock covers 75% or 

 more of the surface. 



Rubble.— Bottoms with less than 75% areal cover of 

 bedrock, but stones and boulders alone, or in combination 

 with bedrock, cover 75% or more of the surface. 



Examples of Dominance Types for these two Subclasses 

 in the Marine and Estuarine Systems are the encrusting 



