18 



such as the barnacles Balanns, Chthamalus, and Tetra- 

 clita may form an almost pure sheet, or these animals may 

 be interspersed with mollusks, tube worms, and algae such 

 as Pelvetia, Enter omorpha, and Ulva. 



The transition between the littorine-lichen and balanoid 

 zones is frequently marked by the replacement 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 characterized 

 by dominant genera. Mytilus and gooseneck barnacles 

 (Pollicipes) form communities exposed to strong wave 

 action. Aquatic Beds dominated by Fueus 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 exposed at least once daily. The Lithotham- 

 nion Dominance Type forms the transition to the Subtidal 

 Subsystem and is exposed only irregularly. 



In the Palustrine, Riverine, and Lacustrine Systems 

 various species of lichens such as Verrucaria spp. and Der- 

 matocarpon Jluviatile, as well as blue-green algae, fre- 

 quently form characteristic zones on Rocky Shores. The 

 distribution of these species depends on the duration of 

 flooding or wetting by spray and is similar to the zona- 

 tion of species in the Marine and Estuarine Systems (Hut- 

 chinson 1975). Though less abundant than lichens, aquatic 

 liverworts such as Marsupella emarginata var. aquatica 

 or mosses such as Fissidens julianus are found on the 

 Rocky Shores of lakes and rivers. If aquatic liverworts or 

 mosses cover 30% or more of the substrate, they should 

 be placed in the Class Aquatic Bed. Other examples of 

 Rocky Shore Dominance Types are the caddisfly Hydro- 

 psyche and the fingernail clam Pisidium. 



Unconsolidated Shore 



Definition. The Class Unconsolidated Shore includes all 

 wetland habitats having three characteristics: (1) uncon- 

 solidated substrates with less than 75% areal cover of 

 stones, boulders, or bedrock; (2) less than 30% areal cover 

 of vegetation other than pioneering plants; and (3) any 

 of the following water regimes: irregularly exposed, 

 regularly flooded, irregularly flooded, seasonally flooded, 

 temporarily flooded, intermittently flooded, saturated, or 

 artificially flooded. Intermittent or intertidal channels of 

 the Riverine System and intertidal channels of the Estu- 

 arine System are classified as Streambed. 



Description. Unconsolidated Shores are characterized 

 by substrates lacking vegetation except for pioneering 

 plants that become established during brief periods when 

 growing conditions are favorable. Erosion and deposition 

 by waves and currents produce a number of landforms 

 such as beaches, bars, and flats, all of which are included 



in this Class. Unconsolidated Shores are found adjacent 

 to Unconsolidated Bottoms in all Systems; in the Palus- 

 trine and Lacustrine Systems, the Class may occupy the 

 entire basin. As in Unconsolidated Bottoms, the particle 

 size of the substrate and the water regime are the impor- 

 tant factors determining the types of plant and animal 

 communities present. Different substrates usually support 

 characteristic invertebrate fauna. Faunal distribution is 

 controlled by waves, currents, interstitial moisture, salin- 

 ity, and grain size (Hedgpeth 1957; Ranwell 1972; Riedl 

 and McMahan 1974). 



Subclasses and Dominance Types. 



Cobble-Gravel.— The unconsolidated particles smaller 

 than stones are predominantly cobble and gravel. Shell 

 fragments, sand, and silt often fill the spaces between the 

 larger particles. Stones and boulders may be found scat- 

 tered on some Cobble-Gravel Shores. In areas of strong 

 wave and current action these shores take the form of 

 beaches or bars, but occasionally they form extensive flats. 

 Examples of Dominance Types in the Marine and Estu- 

 arine Systems are: the acorn barnacle Balanus, the limpet 

 Patella, the periwinkle Littorina, the rock shell Thais, the 

 mussels Mytilus and Modiolus, and the Venus clam Sax- 

 idomus. In the Lacustrine, Palustrine, and Riverine Sys- 

 tems examples of Dominance Types are the freshwater 

 mollusk Elliptio, the snails Lymnaea and Physa, the toad 

 bug Gelastocoris, the leech Erpodella, and the springtail 

 Agrenia. 



Sand.— The unconsolidated particles smaller than 

 stones are predominantly sand which may be either cal- 

 careous or terrigenous in origin. They are prominent 

 features of the Marine, Estuarine, Riverine, and Lacus- 

 trine Systems where the substrate material is exposed to 

 the sorting and washing action of waves. Examples of 

 Dominance Types in the Marine and Estuarine Systems 

 are the wedge shell Donax, the soft-shell clam Mya, the 

 quahog Mercenaria, the olive shell Oliva, the blood worm 

 Euzonus, the beach hopper Orchestia, the pismo clam 

 Tivela stultorum, the mole crab Emerita, and the lugworm 

 Arenicola. Examples of Dominance Types in the Riverine, 

 Lacustrine, and Palustrine Systems are the copepods 

 Parastenocaris and Phyllognathopus, the oligochaete 

 worm Pristina, the freshwater mollusks Anodonta and 

 Elliptio, and the fingernail clams Pisidium and 

 Sphaerium. 



Mud.— The unconsolidated particles smaller than 

 stones are predominantly silt and clay. Anaerobic condi- 

 tions often exist below the surface. Mud Shores have a 

 higher organic content than Cobble-Gravel or Sand 

 Shores. They are typically found in areas of minor wave 

 action. They tend to have little slope and are frequently 

 called flats. Mud Shores support diverse populations of 

 tube-dwelling and burrowing invertebrates that include 

 worms, clams, and crustaceans (Gray 1974). They are com- 



