Noteworthy The great majority of coastal species show medium or high vulnerability to climate change. The quality and quantity of coastal habitats is likely to decrease as a result of sea-level rise, increased storm damage, and effects on marine productivity. Losses of habitat and food sources due to climate change are the largest concerns for coastal birds. Populations may decline if climate change disconnects the timing of prey availability or abundance with coastal birds’ breeding or migration cycles.
	Image: Black Oystercatcher by Roy Lowe

Observations and Predictions

Observed and predicted impacts of rising sea levels vary depending on latitude, marine currents, and subsidence or elevation of land mass. In the United States, the Gulf of Mexico and mid-Atlantic coasts have experienced the highest rates of relative sea level rise and recent wetland loss. Continued sea-level rise is expected to inundate or fragment existing low-lying habitats such as salt marshes, barrier islands, and mudflats. Movement of coastal wetlands may offset some losses; however, this possibility is limited in areas with cliffs and steeper topography, such as areas on the Pacific Coast, or where shorelines are extensively developed, such as around San Francisco Bay.

On all coasts, flooding and erosion are predicted to increase with more frequent and severe storms, as a result of rising ocean temperatures. Loss of sea ice buffers around Alaska leaves its coasts more exposed to storms. For example, the Bering Sea had a 39% reduction in the extent of sea ice in the last decade that has led to loss of coastal habitat.

The trend toward heavier rainfall events is likely to increase the harmful effects of runoff that introduces excess nutrients or salinity changes in coastal areas. Warmer temperatures and increased nutrient inputs may exacerbate phytoplankton blooms that can cause coastal dead zones. Warmer temperatures are also causing a northward shift in the distribution of marine organisms and facilitating the introduction of invasive species to new areas.

Bonaparte's Gull by Philina English

Many of the coastal species that show medium or high vulnerability to climate change are coastal seabirds such as the arctic Ivory Gull, Aleutian Tern, and Kittlitz’s Murrelet. These species are vulnerable to climate change because they rely on marine food webs and because they have low reproductive potential. Beach-nesting Black and American oystercatchers and specialized Saltmarsh Sparrows are among the most vulnerable coastal birds because they rely heavily on limited, low-elevation coastal habitats.

Potential Impacts

Like many other organisms, coastal bird species are expected to shift distributions northward, as warmer temperatures cause shifts in food resources and nesting opportunities. If coastal habitats are lost, bird populations may decline. Based on projections of marsh habitat loss in Chesapeake Bay, significant declines of many marsh species are predicted. Birds such as the rare Black Rail that relies solely on irregularly flooded high marsh could disappear from the Bay if breeding sites are submerged.

The great majority of coastal species (74 of 84 assessed) have medium or high vulnerability to climate change.

Saltmarsh Sparrow by Kenneth V. Rosenberg

Seabirds breeding on coasts may be unsuccessful in raising chicks if their hatch dates do not match patterns in the availability of food resources. Migrating shorebirds stopping at coastal feeding grounds with reduced numbers of invertebrates may be unable to gain the body weight necessary to reach their breeding grounds and raise their young.

Some large ecosystems may fundamentally change. For example, Everglades National Park is very vulnerable to sea-level rise because the park lies at or near sea level. Some projections show a loss of tidal flats and inland freshwater marshes, which would adversely impact some wading birds and the federally endangered Cape Sable Seaside Sparrow. However, these same projections show an increase in the area of shallow basins, mangroves, and brackish marshes, which could favor some species.

Key Steps

Conserving coastal habitats already extensively altered by development requires strategic planning and management. Communities must take climate change into account as they develop zoning and building codes. In areas with rising sea levels, development plans should avoid restricting the inland migration of coastal beaches, marshes, mangroves or other wetlands. The placement of hard barriers for construction or flood control on shorelines can squeeze wetlands out of existence. Some coastal states, including Massachusetts and Rhode Island, have restricted the construction of seawalls and other barriers in some estuaries, and other states should as well. 

American Avocet by John Bedell

A number of strategies can make existing coastal habitats more resilient to sea-level rise. For example, at the Alligator River National Wildlife Refuge in North Carolina, The Nature Conservancy and U.S. Fish and Wildlife Service are removing ditches to restore the hydrologic regime and limit saltwater intrusion, assisting vegetation movement by planting salt-tolerant species, and building oyster reefs to buffer shorelines from waves and storms. Along the Pacific Coast, dikes and drainage ditches are being removed from Bandon Marsh, Nisqually, and several other National Wildlife Refuges to restore natural hydrology and expand tidal marsh habitat.

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