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 Palustrine 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 important 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, salinity, 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 scattered 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 Estuarine 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 Saxidomus. In the Lacustrine, Palustrine, and Riverine Systems 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 calcareous or terrigenous in origin. They are prominent features of the Marine, Estuarine, Riverine, and Lacustrine 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 conditions 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 commonly colonized by algae and diatoms which may form a crust or mat.
  Irregularly flooded Mud Shores in the Estuarine System have been called salt flats, pans, or pannes. They are typically high in salinity and are usually surrounded by, or lie on the landward side of, Emergent Wetland (Martin et al. 1953, Type 15). In many arid areas, Palustrine and Lacustrine Mud Shores are encrusted or saturated with salt. Martin et al. (1953) called these habitats inland saline flats (Type 9); they are also called alkali flats, salt flats, and salt pans. Mud Shores may also result from removal of vegetation by man, animals, or fire, or from the discharge of thermal waters or pollutants. Examples of Dominance Types in the Marine and Estuarine Systems include the fiddler crab Uca, the ghost shrimp Callianassa, the mud snails Nassarius and Macoma, the clam worm Nereis, the sea anemone Cerianthus, and the sea cucumber Thyone. In the Lacustrine, Palustrine, and Riverine Systems, examples of Dominance Types are the fingernail clam Pisidium, the snails Aplexa and Lymaea, the crayfish Procambarus, the harpacticoid copepods Canthocamptus and Bryocamptus, the fingernail clam Sphaerium, the freshwater mollusk Elliptio, the shore bug Saldula, the isopod Asellus, the crayfish Cambarus, and the mayfly Tortopus.

• Organic. -- The unconsolidated material smaller than stones is predominantly organic soils of formerly vegetated wetlands. In the Marine and Estuarine Systems, Organic Shores are often dominated by microinvertebrates such as foraminifera, and by Nassarius, Littorina, Uca, Modiolus, Mya, Nereis, and the false angel wing Petricola pholadiformis. In the Lacustrine, Palustrine, and Riverine Systems, examples of Dominance Types are Canthocamptus, Bryocamptus, Chironomus, and the backswimmer Notonecta.

• Vegetated. -- Some nontidal shores are exposed for a sufficient period 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 and may be gone before the beginning of the next growing season. Many of the pioneer species are not hydrophytes but are weedy mesophytes that cannot tolerate wet soil or flooding. Examples of Dominance Types in the Palustrine, Riverine, and Lacustrine Systems are cocklebur (Xanthium strumarium) and barnyard grass (Echinochloa crusgalli).