Coastal Habitats of the Gulf of Mexico. The coastal strand and its associated vegetated marine habitats consist of several characteristic habitats that are qualitatively similar throughout the world. These habitats include supratidal barrier islands and beaches; intertidal saline wetlands, including salt marshes and mangroves; subtidal seagrasses; and intertidal flats and subtidal soft bottoms (Christensen 2. Mendelssohn and Mc. Kee 2. 00. 0; Hester et al. These habitats provide a suite of societal benefits as described in Section 6. Introduction to Vegetated Marine Habitats. The Barrier Strand. The barrier strand, composed of shore- parallel accumulations of sand and shell in the form of barrier islands, beaches, and related shoreline types, is best considered a habitat- complex. Several unique habitats, such as beach, dune, swale, maritime shrub and forest, salt pan, back barrier marsh, and submerged seagrass occur as part of the barrier strand complex (Figure 6. Although the physiography of the barrier strand may differ in specific geographical locations in the Go. M, the habitats therein and the primary factors controlling their biotic communities are quite similar. This introduction draws examples from the Deltaic Coastal Marshes and Barrier Islands Terrestrial Ecoregion (Figure 6. Figure 6. 7. 1(a) Barrier strand habitats in the northern Go. M (from Mendelssohn et al. Every organism needs to obtain energy in order to live. For example, plants get energy from the sun, some animals eat plants, and some animals eat other animals. ASCE). (b) Oblique aerial photo of a segment of the Chandeleur Islands (photo credit: I. A. Mendelssohn)The beach habitat is a strip of generally sandy substrate that extends from the low tide line to the top of the foredune, or in the absence of a foredune, to the farthest inland reach of storm waves (Barbour 1. Figure 6. 7. 2). This habitat is characterized by shifting sands, intense salt- spray, periodic saltwater inundation, and sand- washover. Only those plant species highly adapted to these stressors (e. Cakile edentula (sea rocket)) can survive on the beach. Figure 6. 7. 2Beach habitat includes the foreshore and backshore of the barrier strand and is subject to periodic wave runup, shifting sands, and saltwater from salt spray and surf (photo credit: I. A. Mendelssohn)Landward of the beach, sand dunes, which can vary greatly in height, form as accumulations of aeolian transported sand and fine shell (Figure 6. Some dunes remain unvegetated and mobile, while those that are more stable become vegetated, which further promotes stability. Dune vegetation is usually distinct from beach vegetation. Because sand dune habitat seldom experiences saltwater inundation, the substrate, although infertile, has little salt accumulation, and thus, plant salt tolerance is not necessary. However, salt spray, the salt- laden aerosol generated from onshore winds blowing across breaking waves, is a common environmental stressor on primary dunes, and vegetation, like Uniola paniculata (sea oats), must be adapted to this stressor to survive in the sand dune habitat. Urbanization and industrial development pressures have seriously impacted coastal ecosystems, including vegetated intertidal and subtidal marine habitats such as.Figure 6. 7. 3Dune habitat is characterized by accumulations of sand, either mobile or stabilized, depending on the extent of vegetation cover. As such, vegetation must be adapted to sand burial and salt spray, as well as moisture deficiency, to survive (photo credit: I. A. Mendelssohn)Landward of the primary dune, and between secondary and tertiary dunes, are low elevation depressions called swales or dune slacks (Figure 6. Swales have greater soil moisture than beach or dune habitats, and the types of vegetation occurring in swales are more flood- tolerant than beach and dune vegetation. Because of generally greater plant growth in the swale habitat and the lesser probability of plant- derived litter being removed by tides, soils in the swale are relatively high in organic matter (compared to the dune and beach), and therefore, have a greater water holding capacity and are more fertile for plant growth (Dougherty et al. Many of the mostly herbaceous plants that dominate the swale occur only, or primarily, in this habitat. On wider and more stable barrier islands, protected portions of the swale are usually dominated by shrubs and trees, e. Express Helpline- Get answer of your question fast from real experts. 145 energy flOw thrOugh an eCOsysteM • aCtivity 7 getting started 1 7Project Transparency 7.1, “Organisms in an Ecosystem.” Ask students what the diagram shows. Myrica cerifera (wax myrtle) and Quercus virginiana (live oak), respectively, and have been termed maritime forests (Christensen 2. Figure 6. 7. 4Swale habitat is an interdunal topographical depression that occurs landward of the primary dune. Because the environment is more benign here, species diversity is generally high (photo credit: I. A. Mendelssohn)On larger, more stable barrier islands, dune and swale topography often repeats multiple times, but when moving landward, elevation decreases and seawater inundation from backbarrier lagoons and bays occurs. This portion of a barrier island system is dominated by backbarrier salt marshes and in the more tropical climates, mangroves (Figure 6. Salt pan habitat (Figure 6. This is an area where infrequent tidal incursions result in salt accumulation in the soil and thus high soil salinities. Where salinities are exceptionally high (more than twice sea- strength), salt pans can be devoid of vegetation. However, more often than not, sparse populations of the most salt- tolerant halophytes dominate salt pans. At somewhat lower elevations, tidal incursions occur more frequently, but still not on a daily basis. This is the high marsh, which consists of salt- tolerant plants that can only withstand intermittent flooding, usually only on spring or wind tides. Further bayward is the low marsh, where tidal inundation occurs daily. Salt marshes and mangroves that occur in regularly flooded portions of backbarrier environments reach their greatest development here. Intertidal flats are only exposed at very low water, and therefore are generally unvegetated by macrophytes. Figure 6. 7. 5Backbarrier marsh (a) occurs on the landward side of a barrier island/beach and is composed of both regularly flooded low marsh, dominated by Spartina alterniflora or Avicennia germinans, and (b) infrequently flooded high marsh, dominated by S. Distichlis spicata, among other species (photo credit: I. A. Mendelssohn)Figure 6. Salt pan habitat has hypersaline soils in which few plant species can survive, and those that do are stunted and of low productivity (photo credit: I. A. Mendelssohn)Within shallow waters landward of the barrier strand, seagrass beds may occur where turbidity conditions permit. Their presence is determined primarily by water clarity and low- nutrient conditions. Also associated with the barrier strand are intertidal flats (Figure 6. Go. M, and are herein considered an independent coastal habitat (see Section 6. Often they are associated with barrier islands, but they also occur along shorelines in bays and lagoons. Figure 6. 7. 7Unvegetated tidal flats, adjacent to vegetated salt marshes, are exposed at low tides and provide habitat for wading birds and benthic fauna (photo credit: I. A. Mendelssohn)6. Marine Intertidal Wetlands. Salt marshes, mangroves, and reed beds generally are low- energy coastal shoreline intertidal wetlands. Salt marshes are dominated by halophytic forbs, graminoids, and shrubs that periodically flood with seawater as a result of lunar (tidal) and meteorological (primarily wind) water level changes. Like other wetlands, salt marshes are characterized by a pronounced hydrology, soil development under flooded conditions (hydric soils), and the dominance of vegetation (hydrophytes) adapted to saturated soil conditions (Lyon 1. Salt marshes (Figure 6. Costa and Davy 1. Mangrove habitats (Figure 6. The word, mangrove, is an ecological term used to describe salt- and flood- tolerant trees and shrubs that inhabit the intertidal zone (Mendelssohn and Mc. Kee 2. 00. 0). In addition to the typical saline wetlands that occur along the Go. M coastline, reed beds, dominated by Phragmites australis, are a unique habitat of the northern Go. M. The largest expanse of coastal reed beds in North America occurs along the coastal shorelines of the Mississippi River Birdfoot Delta (Figure 6. Because it is a shoreline coastal habitat and occupies the position of saline wetlands elsewhere in the Gulf, it is included in this review of coastal habitats. The Phragmites reed habitat at the terminus of the Mississippi River is structured by the Mississippi River and the high subsidence rates that occur there. Salinities are fresh to intermediate and both native and European strains of Phragmites australis occur (Lambertini et al.
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