IT 



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 

 substrates characterized by a wide range of sediment 

 depths and textures. They occur in both the Subtidal 

 and Intertidal 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. Domi- 

 nance types such as the rockweeds Fucus and Asco- 

 phyllum and the kelp Laminaria are common along 

 both coasts. In tropical regions, green algae, including 

 forms containing calcareous particles, are more 

 characteristic; Halimeda and Penicillus are common 

 examples. The red alga Laurencia, and the green algae 

 Caulerpa, Enteromorpha, and Ulva are also common 

 Estuarine and Marine dominance types; Entero- 

 morpha and Ulva are tolerant of fresh water and flour- 

 ish near the upper end of some estuaries. The stone- 

 wort Chara is also found in estuaries. 



Inland, the stoneworts Chara, Nitella, 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 intermittently exposed parts of some 

 Lacustrine Systems. The most important dominance 

 types include genera such as Fissidens, Drepano- 

 cladus, and Fontinalis. Fontinalis may grow to depths 

 as great as 120 m (394 feet) (Hutchinson 1975). For 

 simplicity, aquatic liverworts of the genus Marsupella 

 are included in this subclass. 



Rooted Vascular.— Rooted Vascular beds include a 

 large array of vascular species in the Marine and 

 Estuarine 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 Jeffer- 

 son 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. Prin- 

 cipal dominance types in these areas include turtle 

 grass (Thalasia testudinum), shoalgrass (Halodule 



wrightii), manatee grass (Syringodium filiformis), 

 widgeon grass (Ruppia maritima), sea grasses (Halo- 

 phila 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 eelgrass (Zostera marina). Eelgrass beds 

 have the most extensive distribution, but they are 

 limited primarily to the more sheltered estuarine 

 environment. In the lower salinity 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 

 pondweeds (Zannichellia), ditch grasses (Ruppia), wild 

 celery, and waterweed (Elodea). The riverweed (Podo- 

 sternum ceratophyllum) is included in this class despite 

 its lack of truly recognizable roots (Sculthorpe 1967). 



Some of the Rooted Vascular species are charac- 

 terized by floating leaves. Typical dominants include 

 water lilies (Nymphaea, Nuphar), floating-leaf pond- 

 weed (Potamogeton natans), and water shield (Bra- 

 senia 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 considered either emer- 

 gents 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 System. The plants float freely either in the 

 water or on its surface. Dominant plants that float on 

 the surface include the duckweeds (Lemna, Spirodela), 

 water lettuce (Pistia stratiotes), water hyacinth (Eich- 

 hornia crassipes), water nut (Trapa natans), water 

 fern (Salvinia rotundifolia), and mosquito 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 (Wolffiella) 

 (Sculthorpe 1967; Hutchinson 1975). 



Reef 



Definition. The class Reef includes ridge-like or 

 mound-like structures formed by the colonization and 

 growth of sedentary invertebrates. Water regimes are 



