17 



It occurs most commonly in the Riverine System in high 

 mountain areas or in glaciated areas where bedrock is ex- 

 posed. Examples of Dominance Types are the molluskAn- 

 cylus, the oligochaete worm Limnodrilus, the snail Physa, 

 the fingernail clam Pisidium, and the mayflies Caenis and 

 Ephemerella. 



Rubble.— This Subclass is characterized by stones, 

 boulders, and bedrock that in combination cover more than 

 75% of the channel. Like Bedrock Streambeds, Rubble 

 Streambeds are most common in mountainous areas and 

 the dominant organisms are similar to those of Bedrock 

 and are often forms capable of attachment to rocks in flow- 

 ing water. 



Cobble-Gravel— In this Subclass at least 25% of the 

 substrate is covered by unconsolidated particles smaller 

 than stones; cobbles or gravel predominate. The Subclass 

 occurs in riffle areas or in the channels of braided streams. 

 Examples of Dominance Types in the Intermittent Subsys- 

 tem of the Riverine System are the snail Physa, the oligo- 

 chaete worm Limnodrilus, the mayfly Caenis, the midge 

 Chironomus, and the mosquito Anopheles. Examples of 

 Dominance Types in the Estuarine System or Tidal Sub- 

 system of the Riverine System are the mussels Modiolus 

 and Mytilus. 



Sand.— In this Subclass, sand-sized particles predom- 

 inate among the particles smaller than stones. Sand 

 Streambed often contains bars and beaches interspersed 

 with Mud Streambed or it may be interspersed with 

 Cobble-Gravel Streambed in areas of fast flow or heavy 

 sediment load. Examples of Dominance Types in the 

 Riverine System are the scud Gammarus, the snails Physa 

 and Lymnaea, and the midge Chironomus; in the 

 Estuarine System the ghost shrimp Callianassa is a com- 

 mon Dominance Type. 



Mud.— In this Subclass, the particles smaller than 

 stones are chiefly silt or clay. Mud Streambeds are com- 

 mon in arid areas where intermittent flow is character- 

 istic 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 Estu- 

 arine System and the Tidal Subsystem of the Riverine 

 System. Examples of Dominance Types for Mud Stream- 

 beds include the crayfish Procambarus, the pouch snail 

 Aplexa, the fly Tabanus, the snail Lymnaea, the finger- 

 nail clam Sphaerium, 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 Wet- 

 lands with organic soils. Examples of Dominance Types 

 are the mussel Modiolus in the Estuarine System and the 

 oligochaete worm Limnodrilus in the Riverine System. 



Vegetated.— 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 Domi- 

 nance Type is Panicum capillare. 



Dominance Types for Streambeds in the Estuarine Sys- 

 tem were taken primarily from Smith (1964), Abbott 

 (1968), and Ricketts and Calvin (1968) and those for 

 streambeds in the Riverine System from Krecker and Lan- 

 caster (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 en- 

 vironments characterized by bedrock, stones, or boulders 

 which singly or in combination have an areal cover of 75% 

 or more and an areal coverage by vegetation 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 ex- 

 posed 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 seden- 

 tary invertebrates and attached algae or lichens. Rocky 

 Shores usually display a vertical zonation that is a func- 

 tion 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 com- 

 bination 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 invertebrates 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 littorine-lichen 

 zone) is dominated by periwinkles (Littorina 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 

 dominated by mollusks, green algae, and barnacles of the 

 balanoid group. The zone appears white. Dominance Types 



