15 



Organic— The unconsolidated material smaller than 

 stones is predominantly organic. The number of species 

 is limited and faunal productivity is very low (Welch 1952). 

 Examples of Dominance Types for Estuarine and Marine 

 Systems are the soft-shell clam Mya, the false angel wing 

 Petricola pholadiformis, the clam worm Nereis, and the 

 mud snail Nassarius. Examples for the Lacustrine, Palus- 

 trine, and Riverine Systems are the sewage worm Tubifex, 

 the snail Physa, the harpacticoid copepod Canthocamptus, 

 and the oligochaete worm Limnodrilus. 



Dominance Types for Unconsolidated Bottoms in the 

 Marine and Estuarine Systems were taken predominant- 

 ly from Miner (1950), Smith (1964), Abbott (1968), and 

 Ricketts and Calvin (1968). Dominance Types for Uncon- 

 solidated Bottoms in the Lacustrine, Riverine, and Palus- 

 trine Systems were taken predominantly from Krecker 

 and Lancaster (1933), Stehr and Branson (1938), Johnson 

 (1970), Brinkhurst and Jamieson (1972), Clarke (1973), 

 Hart and Fuller (1974), Ward (1975), and Pennak (1978). 



Aquatic Bed 



Definition. The Class Aquatic Bed includes wetlands 

 and deepwater habitats dominated by plants that grow 

 principally on or below the surface of the water for most 

 of the growing season in most years. Water regimes in- 

 clude subtidal, irregularly exposed, regularly flooded, 

 permanently flooded, intermittently exposed, semiperm- 

 anently flooded, and seasonally flooded. 



Description. Aquatic Beds represent a diverse group of 

 plant communities that requires surface water for opti- 

 mum growth and reproduction. They are best developed 

 in relatively permanent water or under conditions of re- 

 peated flooding. The plants are either attached to the 

 substrate or float freely in the water above the bottom 

 or on the surface. 



Subclasses and Dominance Types. 

 Algal.— Algal Beds are widespread and diverse in the 

 Marine and Estuarine Systems, where they occupy sub- 

 strates characterized by a wide range of sediment depths 

 and textures. They occur in both the Subtidal and Inter- 

 tidal Subsystems and may grow to depths of 30 m (98 feet). 

 Coastal Algal Beds are most luxuriant along the rocky 

 shores of the Northeast and West. Kelp {Macrocystis) beds 

 are especially well developed on the rocky substrates of 

 the Pacific Coast. Dominance Types such as the rockweeds 

 Fucus and Ascophyllum and the kelp Laminaria are com- 

 mon along both coasts. In tropical regions, green algae, 

 including forms containing calcareous particles, are more 

 characteristic; Halimeda and Penicillus are common ex- 

 amples. The red alga Laurencia, and the green algae 

 Caulerpa, Enteromorpha, and Ulva are also common 

 Estuarine and Marine dominance types; Enteromorpha 

 and Ulva are tolerant of fresh water and flourish near the 

 upper end of some estuaries. The stonewort Chara is also 

 found in estuaries. 



Inland, the stoneworts Chara, Nit.ella, and Tolypella are 

 examples of algae that look much like vascular plants and 

 may grow in similar situations. However, meadows of 

 Chara may be found in Lacustrine water as deep as 40 m 

 (131 feet) (Zhadin and Gerd 1963), where hydrostatic 

 pressure limits the survival of vascular submergents 

 (phanaerogams) (Welch 1952). Other algae bearing less 

 resemblance to vascular plants are also common. Mats of 

 filamentous algae may cover the bottom in dense blankets, 

 may rise to the surface under certain conditions, or may 

 become stranded on Unconsolidated or Rocky Shores. 



Aquatic Moss. —Aquatic mosses are far less abundant 

 than algae or vascular plants. They occur primarily in the 

 Riverine System and in permanently flooded and inter- 

 mittently exposed parts of some Lacustrine systems. The 

 most important Dominance Types include genera such as 

 Fissidens, Drepanocladus, and Fontinalis. Fontinalis may 

 grow to depths as great as 120 m (394 feet) (Hutchinson 

 1975). For simplicity, aquatic liverworts of the genus Mar- 

 supella are included in this Subclass. 



Rooted Vascular.— Rooted Vascular Beds include a 

 large array of vascular species in the Marine and Estu- 

 arine Systems. They have been referred to by others as 

 temperate grass flats (Phillips 1974); tropical marine 

 meadows (Odum 1974); and eelgrass beds, turtlegrass 

 beds, and seagrass beds (Akins and Jefferson 1973; 

 Eleuterius 1973; Phillips 1974). The greatest number of 

 species occur in shallow, clear tropical, or subtropical 

 waters of moderate current strength in the Caribbean and 

 along the Florida and Gulf Coasts. Principal Dominance 

 Types in these areas include turtle grass (Thalassia testu- 

 dinum), shoalgrass (Halodule wrightii), manatee grass 

 (Cymodoceafiliformis), widgeon grass (Ruppia maritima), 

 sea grasses (Halophila spp.), and wild celery (Vallisneria 

 americana). 



Five major vascular species dominate along the tem- 

 perate coasts of North America: shoalgrass, surf grasses 

 (Phyllospadix scouleri, P. torreyi), widgeon grass, and eel- 

 grass (Zostera marina). Eelgrass beds have the most ex- 

 tensive distribution, but they are limited primarily to the 

 more sheltered estuarine environment. In the lower salin- 

 ity zones of estuaries, stands of widgeon grass, pondweed 

 (Potamogeton), and wild celery often occur, along with 

 naiads (Najas) and water milfoil (Myriophyllum). 



In the Riverine, Lacustrine, and Palustrine Systems, 

 rooted vascular aquatic plants occur at all depths within 

 the photic zone. They often occur in sheltered areas where 

 there is little water movement (Wetzel 1975); however, 

 they also occur in the flowing water of the Riverine 

 System, where they may be streamlined or flattened in 

 response to high water velocities. Typical inland genera 

 include pondweeds, horned pondweed (Zannichellia 

 palustris), ditch grasses (Ruppia), wild celery, and water- 

 weed (Elodea). The riverweed (Podostemum ceratophyl- 

 lum) is included in this class despite its lack of truly 

 recognizable roots (Sculthorpe 1967). 



