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Chapter 2 - Coastal Ecosystems© Robert H. Pos/USFWShighest spring tides. The dominant plant species in thehigh salt marsh community is the salt-meadow grass ormarsh hay (Spartina patens). Spikegrass (Distichlis spicata),black-grass (Juncus gerardii), and glassworts (Salicorniaspp.) are also common in the high marsh. Characteristicinvertebrates of the salt marsh include ribbed mussels(Geukensia demissa) and fiddler crabs (Uca spp.), both ofwhich boost productivity of marsh plants.As sea level has very gradually risen since the last glaciationsperiod, salt marshes have grown both horizontallyand vertically (Redfield 1965 and 1972). Horizontalgrowth occurs via migration into adjacent upland areasand vertical growth occurs through the accumulation ofmineral and biologic sedimentary materials that form thepeat substrate (Bertness 2006). Each year’s new growthbuilds on these two types of sediments that form themarsh peat. Historically, this type of accretion has more orless kept pace with changing relative sea level in most partsof our region. However, human alterations such as shorelinehardening and development can impede this growth.In regions where rivers bring large quantities of freshwater,salt water tidal marshes may grade to brackish andeven completely fresh. Long bands of freshwater tidalmarsh occur along the shores of the Hudson, Connecticut,and Kennebec River estuaries, for instance. Here, thegraminoid (grass and grass-like) species shift from cordgrassto cattails, rushes, wild rice, and numerous forbs,many of which are restricted to this habitat and thus rarein the region. Brackish and freshwater tidal marshes areimportant for migrating waterfowl and anadromous fishesand, like salt marshes, contribute considerable carbonto the estuaries of which they are part. In some parts ofthe region, these wetlands have been heavily impacted byindustrial development of major ports or by dams whichhave shifted the tidal flooding and salinity regimes. Risingsea level will be a particularly important factor indetermining future trends in tidal marsh health anddistribution.A very small percentage of the overall shoreline in thisregion is classified by National Oceanic and AtmosphericAdministration (NOAA) Environmental SensitivityIndex (ESI) as “swamp,” mostly in the Southern NewEngland and Mid-Atlantic subregions. According to ESI,freshwater tidal swamps are forested or shrub-dominatedtidal wetlands, a classification used in the United StatesFish and Wildlife Service (USFWS) National WetlandsInventory (NWI), that occur along freshwater tidal portionsof large river systems characterized by gentle slopegradients coupled with tidal influence over considerabledistances. The swamp substrate is always wet andis subject to semidiurnal flooding by fresh tidal water(salinity less than 0.5 ppt). The characteristic trees areash (Fraxinus) and tupelo (Nyssa and Taxodium species)(Reschke 1990).Sandy Beach and Dune systemsThere are three primary types of sandy beach systemsfound within the region: barrier island and barrier beaches,primarily found in the south, and pocket beaches, generallyfound in the north at the head of small bays.Sandy ocean beaches especially in the southern half of theregion are often associated with barrier island systems. Intheir natural state, sand-derived barrier islands and barrierbeaches attached to the mainland are highly dynamicsystems, constantly shaped and reshaped by winds, stormsand ocean currents. Generally speaking, prevailing windsand nearshore currents cause North Atlantic barrier is-Northwest Atlantic Marine Ecoregional Assessment • Phase 1 Report 2-13