Dam blocking fish passage in Maine. Photo credit: NOAA Crab caught in derelict fishing gear. Photo credit: NOAA

Coastal and marine habitats around the nation are in jeopardy due to loss and degradation. Of the 221 million acres of wetlands estimated to have existed in the contiguous United States at the time of European arrival, less than 49 percent remain (Dahl 1990, 2006). Natural, non-armored shorelines in coastal areas have decreased by up to 60 percent on the Pacific Coast since the early 1990s (NOAA 2005). Although regulations such as the Clean Water Act have slowed the rate of loss in some areas, a net loss of habitat continues due to population growth and new development.

The loss and degradation of these habitats are the result of various human activities, including agriculture, aquaculture, flood control, waste disposal, mosquito abatement, and residential and commercial development. The damaging components of these activities may involve actions such as wetland dredging and filling, water diversions, shoreline armoring (e.g., sea walls and docks), subsidence, and erosion. Dikes, tidegates, culverts, and dams have also altered hydrologic connections, thus impairing habitat function . Dam building has especially limited fish migration and disrupted energy, nutrient, temperature, and sediment flows downstream. Additional impacts include the introduction of nutrients, toxic chemicals, oil, pathogens, and contaminated sediments, as well as invasive species. Commercial and recreational boating and fisheries activities cause damage to habitat due to vessel groundings, anchoring, harvest techniques, and derelict fishing gear. Impacts also occur from intensive and cumulative levels of recreational activities (e.g., around coral reefs and on beaches). In addition, natural processes that may or may not be exacerbated by human activities (e.g., hurricanes, droughts, floods, disease, predation, and sea-level rise) can also impair habitat.

The information below highlights a few examples of habitat loss rates in various regions of the United States (NOAA 2005; RAE and NOAA 2002).

Great Lakes

• More than two-thirds of wetlands filled or drained.
• Southeast Michigan: 90 to 97 percent of original emergent coastal wetlands lost.
• Detroit River: 87 percent of river's U.S. shoreline filled and bulkheaded.

Northeast

• Approximately 90 percent of coastal marshes ditched to control mosquitoes by 1930s.
• Maine: Only 52 percent of spawning and nursery habitat for Atlantic salmon remains.
• Narragansett Bay: 33 percent of shellfish beds closed to harvest due to pathogens.
• Long Island Sound: Tidal wetlands decreased by more than 35 percent over the past century, and submerged aquatic vegetation (SAV) beds decreased by 65 percent since the 1950s.

Mid-Atlantic

• Delaware Estuary: More than 25 percent of historical wetlands lost, and more than 33 percent of tidal wetlands invaded with Phragmites.
• Chesapeake Bay: 60 percent of historical wetlands, 88 percent of SAV, and 98 percent of native oyster reefs lost.

Southeast

• From European settlement to 1980, 78 percent of wetlands lost.
• Nearly half of protected barrier island beaches and dunes, and intact saltwater and freshwater marshes, lost.
• South Carolina: Approximately one-third of shellfish areas permanently closed.

Gulf Coast

• Most estuaries lost 20 to 100 percent of seagrass habitat.
• More than half of oyster-producing areas permanently or conditionally closed.
• Louisiana: Marsh the size of a football field lost every 30 minutes since 1930.
• Tampa Bay: Nearly 80 percent of seagrass and half of salt marsh and mangrove habitat lost. 

Pacific Northwest

• Washington: 50 to 90 percent riparian habitat lost or extensively modified since early 1800s.
• Oregon: Nearly half of historic tidal wetlands lost.
• Alaska: More than half of culverts obstruct fish passage; Exxon Valdez oil spill contaminated 1,500 miles of coastline in 1989.
• Willapa Bay: Spartina sp. estimated to increase from 3,200 to 30,000 acres between 1997 and 2030.

California

• San Francisco Bay: 95 percent of historic wetlands and riparian habitat damaged or destroyed.
• Southern California: Estuarine wetlands eliminated by 75 to 90 percent.

Pacific Islands

• Hawaii: Coastal plain wetlands decreased by 31 percent over a 200-year period.
• Saipan and American Samoa: 64 percent and 25 percent of estuarine wetlands lost, respectively.

References Cited