16 



Some of the rooted vascular species are characterized 

 by floating leaves. Typical dominants include water lilies 

 (Nymphaea, Nuphar), floating-leaf pondweed (Potamoge- 

 ton natans), and water shield (Brasenia schreberi). Plants 

 such as yellow water lily (Nuphar luteum) and water 

 smartweed (Polygonum amphibium), which may stand 

 erect above the water surface or substrate, may be con- 

 sidered either emergents or rooted vascular aquatic plants, 

 depending on the life form adopted at a particular site. 



Floating Vascular.— Beds of floating vascular plants 

 occur mainly in the Lacustrine, Palustrine, and Riverine 

 Systems and in the fresher waters of the Estuarine Sys- 

 tem. The plants float freely either in the water or on its 

 surface. Dominant plants that float on the surface include 

 the duckweeds (Lemma, Spirodela), water lettuce (Pistia 

 stratiotes), water hyacinth (Eichhornia crassipes), water 

 nut (Trapa natans), water ferns (Salvinia spp.), and mos- 

 quito ferns (Azolla). These plants are found primarily in 

 protected portions of slow-flowing rivers and in the 

 Lacustrine and Palustrine Systems. They are easily moved 

 about by wind or water currents and cover a large area 

 of water in some parts of the country, particularly the 

 Southeast. Dominance Types for beds floating below the 

 surface include bladderworts (Utricularia), coontails 

 (Ceratophyllum), and watermeals (Wolffia) (Sculthorpe 

 1967; Hutchinson 1975). 



arily their elevation, wave exposure, the age of the Reef, 

 and its exposure to waves. 



Mollusk.— This Subclass occurs in both the Intertidal 

 and Subtidal Subsystems of the Estuarine System. These 

 Reefs are found on the Pacific, Atlantic, and Gulf Coasts 

 and in Hawaii and the Caribbean. Mollusk Reefs may 

 become extensive, affording a substrate for sedentary and 

 boring organisms and a shelter for many others. Reef 

 mollusks are adapted to great variations in water level, 

 salinity, and temperature, and these same factors control 

 their distribution. Examples of Dominance Types for this 

 Subclass are the oysters Ostrea and Crassostrea (Smith 

 1964; Abbott 1968; Ricketts and Calvin 1968). 



Worm.— Worm Reefs are constructed by large col- 

 onies of Sabellariid worms living in individual tubes con- 

 structed from cemented sand grains. Although they do 

 not support as diverse a biota as do Coral and Mollusk 

 Reefs, they provide a distinct habitat which may cover 

 large areas. Worm Reefs are generally confined to tropical 

 waters, and are most common along the coasts of Florida, 

 Puerto Rico, and the Virgin Islands. They occur in both 

 the Intertidal and Subtidal Systems of the Marine and 

 Estuarine Systems where the salinity approximates that 

 of sea water. The reefworm Sabellaria is an example of 

 a Dominance Type for this Subclass (Ricketts and Calvin 

 1968). 



Reef 



Definition. The Class Reef includes ridge-like or mound- 

 like structures formed by the colonization and growth of 

 sedentary invertebrates. Water regimes are restricted to 

 subtidal, irregularly exposed, regularly flooded, and 

 irregularly flooded. 



Description. Reefs are characterized by their elevation 

 above the surrounding substrate and their interference 

 with normal wave flow; they are primarily subtidal, but 

 parts of some reefs may be intertidal as well. Although 

 corals, oysters, and tube worms are the most visible 

 organisms and are mainly responsible for reef formation, 

 other mollusks, foraminifera, coralline algae, and other 

 forms of life also contribute substantially to reef growth. 

 Frequently, reefs contain far more dead skeletal material 

 and shell fragments than living matter. 



Subclasses and Dominance Types. 

 Coral.— Coral Reefs are widely distributed in shallow 

 waters of warm seas, in Hawaii, Puerto Rico, the Virgin 

 Islands, and southern Florida. They were characterized 

 by Odum (1971) as stable, well-adapted, highly diverse, 

 and highly productive ecosystems with a great degree of 

 internal symbiosis. Coral Reefs lie almost entirely within 

 the Subtidal Subsystem of the Marine System, although 

 the upper part of certain Reefs may be exposed. Examples 

 of Dominance Types are the corals Porites, Acropora, and 

 Montipora. The distribution of these types reflects prim- 



Streambed 



Definition. The Class Streambed includes all wetland 

 contained within the Intermittent Subsystem of the River- 

 ine System and all channels of the Estuarine System or 

 of the Tidal Subsystem of the Riverine System that are 

 completely de watered at low tide. Water regimes are 

 restricted to irregularly exposed, regularly flooded, irreg- 

 ularly flooded, seasonally flooded, temporarily flooded, and 

 intermittently flooded. 



Description. Streambeds vary greatly in substrate and 

 form depending on the gradient of the channel, the veloc- 

 ity of the water, and the sediment load. The substrate 

 material frequently changes abruptly between riffles and 

 pools, and complex patterns of bars may form on the con- 

 vex side of single channels or be included as islands within 

 the bed of braided streams (Crickmay 1974). In mountain- 

 ous areas the entire channel may be cut through bedrock. 

 In most cases streambeds are not vegetated because of 

 the scouring effect of moving water, but, like Uncon- 

 solidated Shores, they may be colonized by "pioneering" 

 annuals or perennials during periods of low flow or they 

 may have perennial emergents and shrubs that are too 

 scattered to qualify the area for classification as Emer- 

 gent Wetland or Scrub-Shrub Wetland. 



Subclasses and Dominance Types. 

 Bedrock.— This Subclass is characterized by a bedrock 

 substrate covering 75% or more of the stream channel. 



