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Chapter 2 - Coastal EcosystemsData, Analysis, and Areas ofImportanceShoreline Habitat DiversityThe shoreline habitats and intertidal NWI type characterizationcorroborated stratification by CMECS class.For example, rocky shorelines are essentially non-existentin the lagoon and riverine types, but prominent in fjordtypes. Swamp shorelines are only a small percentage of anyCSU shoreline, but do not occur at all in fjord or FundyCSUs. Marshes make up the highest percentage of shorelinehabitats in lagoons and riverine CSUs. Beach and flatshorelines are found in the highest percentages in embaymentsand fjord CSUs. However unconsolidated intertidalhabitats of mud make up more than 50% of intertidalhabitats in most fjords while unconsolidated shores ofsand, gravel, and cobble make up over 50% of intertidalhabitats in most embayments. Although these differencesbetween CMECS classes were evident, significant differencesamong CSUs of the same CMECS class were alsoobserved. For example, some embayment CSUs have >50% beach shorelines, while others have only 10% - 15%beach shorelines. Differences were also observed amongsubregions (Gulf of Maine, Southern New England, andMid-Atlantic Bight). Although the 8,000 km of beachshoreline in the region were surprisingly evenly distributedacross the three subregions, beaches of fjords are mostoften small pocket or cove beaches whereas those of thelagoon and embayment areas are often very long, nearlycontinuous barrier beaches. Salt marshes are also found tooccur in all subregions and CMECS estuarine types. As apercent of shoreline length, there are not such marked differenceswithin CMECS types or subregions. However, inareal extent they make up over 70% of intertidal habitat inmost lagoons and riverine types and < 35% in other groups.The total area of salt marshes in lagoon types of the Mid-Atlantic Bight is orders of magnitude greater than in therest of the region, especially Gulf of Maine fjords (Figure2-13, 2-14, and 2-15).Seagrass beds occur along the entire Atlantic coast (Figure2-16). Based on the most recent data available fromeach state, the largest seagrass bed coverage occurs in thePamlico Sound CSU (36,429 hectares), although otherCSUs have significant amounts of seagrass habitat (e.g.,Casco Bay, 3,331 hectares; Nantucket Sound, 6,462 hectares;Long Island South Shore, 9,861 hectares; ChesapeakeBay Eastern, 24,838 hectares). By CMECS type, the vastmajority of seagrass in the region occurs within CSUs ofthe lagoon (63,459 hectares) and riverine types (44,087hectares). However, there is substantial variation withineach CMECS class. For example, Chesapeake Bay Innerhas 9,710 hectares of seagrass, whereas several otherCSUs of the riverine type have only several hundredhectares. The regional seagrass dataset includes historicaltime series snapshots of eelgrass coverage and presentsa new opportunity to evaluate loss and identify spatiallyexplicit restoration priorities. Areas mapped as coastal saltponds only occur in the embayment type. Among the 10CSUs of this type, five had no coastal salt ponds andothers had as many as six or eight.Not surprisingly, these differences in characteristic habitatextend to the immediate offshore zone. At the scale of individualCSUs, calculating the percent of various benthicclasses within the 1,000 m zone would not be accurateenough to fairly compare one CSU to another. However,when combined into CMECS classes, the average percentagesdo seem meaningful. The benthic zone just offshorefrom fjords includes significant areas deeper than 31 mand is characterized by steep canyon seabed forms, largelyabsent from the offshore zones of other CSUs. In contrast,benthic zones immediately offshore of lagoons and riverineCSUs have extensive areas within the seagrass growingdepth zone of 1 to 3 m. The benthic zones offshore oflagoons are characterized by clays, silt, and fine sands andhave zero mapped areas of pebble or cobble, which areabundant in the nearshore of the Gulf of Maine.Abundance and variety of stream habitats feeding theCSUs, particularly relevant for diadromous fish, were notincluded because of the challenges of identifying comparablemetrics across the region. Diadromous fish habitatuse and distribution is addressed in a separate chapter.Note: Further characterizations of spatial complexity, sinuosity,and functional connectivity among habitats could2-32Northwest Atlantic Marine Ecoregional Assessment • Phase 1 Report