L9 



omus; in the Estuarine System the ghost shrimp 

 Callianassa is a common dominance type. 



Mud. — In this subclass, the particles smaller than 

 stones are chiefly silt or clay. Mud Streambeds are 

 common in arid areas where intermittent flow is 

 characteristic of streams of low gradient. Such species 

 as tamarisk {Tamarix gallica) may occur, but are not 

 dense enough to qualify the area for classification as 

 Scrub-Shrub Wetland. Mud Streambeds are also 

 common in the Estuarine System and the Tidal Sub- 

 system of the Riverine System. Examples of domi- 

 nance types for Mud Streambeds include the crayfish 

 Proeambarus, the pouch snail Aplexa, the fly Tabanus, 

 the snail Lymnaea, the fingernail clam Sphaeri um, and 

 (in the Estuarine System) the mud snail Nassarius. 



Organic— This subclass is characterized by 

 channels formed in peat or muck. Organic Streambeds 

 are common in the small creeks draining Estuarine 

 Emergent Wetlands with organic soils. Examples of 

 dominance types are the mussel Modiolus in the 

 Estuarine System and the oligochaete worm Limno- 

 drilus in the Riverine System. 



Vegetated Streambeds.— These streambeds are 

 exposed long enough to be colonized by herbaceous 

 annuals or seedling herbaceous perennials (pioneer 

 plants). This vegetation, unlike that of Emergent 

 Wetlands, is usually killed by rising water levels or 

 sudden flooding. A typical dominance type is Panicum 

 capillare. 



Dominance types for streambeds in the Estuarine 

 System were taken primarily from Smith (1964), 

 Abbott (1968), and Ricketts and Calvin (1968) and 

 those for streambeds in the Riverine System from 

 Krecker and Lancaster (1933), Stehr and Branson 

 (1938), van der Schalie (1948), Kenk (1949), Cummins 

 et al. (1964), Clarke (1973), and Ward (1975). 



Rocky Shore 



Definition. The class Rocky Shore includes wetland 

 environments characterized by bedrock, stones, or 

 boulders which singly or in combination have an areal 

 cover of 75% or more and an areal coverage by vege- 

 tation of less than 30%. Water regimes are restricted 

 to irregularly exposed, regularly flooded, irregularly 

 flooded, seasonally flooded, temporarily flooded, and 

 intermittently flooded. 



Description. In Marine and Estuarine systems, 

 Rocky Shores are generally high-energy habitats 

 which lie exposed as a result of continuous erosion by 

 wind-driven waves or strong currents. The substrate is 

 stable enough to permit the attachment and growth of 

 sessile or sedentary invertebrates and attached algae 

 or lichens. Rocky Shores usually display a vertical 

 zonation that is a function of tidal range, wave action, 

 and degree of exposure to the sun. In the Lacustrine 

 and Riverine systems, Rocky Shores support sparse 

 plant and animal communities. 



Subclasses and Dominance Types. 

 Bedrock.— These wetlands have bedrock covering 

 75% or more of the surface and less than 30% areal 

 coverage of macrophytes. 



Rubble. —These wetlands have less than 75% areal 

 cover of bedrock, but stones and boulders alone or in 

 combination with bedrock cover 75% or more of the 

 area. The areal coverage of macrophytes is less than 

 30%. 



Communities or zones of Marine and Estuarine 

 Rocky Shores have been widely studied (Lewis 1964; 

 Ricketts and Calvin 1968; Stephenson and Stephenson 

 1972). Each zone supports a rich assemblage of inver- 

 tebrates, and algae or lichens or both. Dominance 

 types of the Rocky Shores often can be characterized 

 by one or two dominant genera from these zones. 



The uppermost zone (here termed the lit- 

 torine-lichen zone) is dominated by periwinkles (Lit- 

 torina and Nerita) and lichens. This zone frequently 

 takes on a dark, or even black appearance, although 

 abundant lichens may lend a colorful tone. These 

 organisms are rarely submerged, but are kept moist by 

 sea spray. Frequently this habitat is invaded from the 

 landward side by semimarine genera such as the slater 

 Ligia. 



The next lower zone (the balanoid zone) is commonly 

 dominanted by mollusks, green algae, and barnacles of 

 the balanoid group. The zone appears white. Domi- 

 nance types such as the barnacles Balanus, Chtha- 

 malus, and Tetraclita may form an almost pure sheet, 

 or these animals may be interspersed with mollusks, 

 tube worms, and algae such as Pelvetia, enteromorpha, 



and Ulva. 

 The transition between the littorine-lichen and 



balanoid zones is frequently marked by the replace- 

 ment of the periwinkles with limpets such as Acmaea 

 and Siphonaria. The limpet band approximates the 

 upper limit of the regularly flooded intertidal zone. 



In the middle and lower intertidal areas, which are 

 flooded and exposed by tides at least once daily, lie a 

 number of other communities which can be charac- 

 terized by dominant genera. Mytilus and gooseneck 

 barnacles (Pollicipes) form communities exposed to 

 strong wave action. Aquatic Beds dominated by Fucus 

 and Laminaria lie slightly lower, just above those 

 dominated by coralline algae (Lithothamnion). The 

 Laminaria dominance type approximates the lower 

 end of the Intertidal Subsystem; it is generally ex- 

 posed at least once daily. The Lithothamnion domi- 

 nance type forms the transition to the Subtidal Sub- 

 system and is exposed only irregularly. 



In the Palustrine, Riverine, and Lacustrine systems 

 various species of lichens such as Verrucaria spp. and 

 Dermatocarpon fluviatile, as well as blue-green algae, 

 frequently form characteristic zones on Rocky Shores. 

 The distribution of these species depends on the dura- 

 tion of flooding or wetting by spray and is similar to 

 the zonation of species in the Marine and Estuarine 



