Northeast and Mid-Atlantic
Nearly half of all Americans live and work in coastal counties, areas that also provide critical habitat for a diversity of fish and wildlife. Important as these places are for supporting human and natural communities, their capacity to do so in the face of rising sea levels varies widely. Coastal sites flanked by extensive lowlands have space for coastal habitats to migrate landward in response to sea level rise. However, this potential habitat migration can be impeded by human activities that physically block movement, degrade ecological condition, and disrupt key ecological processes.
TNC scientists evaluated over 10,000 sites in the Northeast and Mid-Atlantic US for the size, configuration, and tidal diversity of their migration space, and for the natural processes necessary to support the migration of coastal habitats landward as the sea level rises.
With no action, this region could see an 83% loss of existing tidal habitats to severe inundation. But with proper management, there are thousands of individual sites where tidal habitats could increase and expand through landward migration, reversing this trend. These resilient sites could offset more than 50% of tidal wetland loss, providing critical habitat for birds and wildlife, and buffering people from the effects of storms and floods. With these results, communities and resource managers can better prioritize land acquisition, identify areas for restoration, and develop effective strategies for sustaining the natural benefits provided by coastal habitats.
Estimates suggest the US coastal population will reach almost 134 million by 2020, exposing more of the population to the detrimental impacts of rising sea level and intense storms related to climate change. Damages from Hurricane Sandy, which struck the Eastern US seaboard in October 2012, amounted to $65 billion in damage for the US alone. Census data from 2008 shows the Northeast region has the second highest share of the US coastal population at 35.5%, second only to the Pacific US region with 36.6% (U.S. Census Bureau 2010). The combined effect of rising sea levels and stronger storms from climate change is expected to accelerate shoreline retreat in certain areas of the region. The coastal plains from northern New Jersey to southern Virginia, are particularly vulnerable and expected to experience significant shoreline changes over the next century. There will also be significant costs for coastal communities beyond the most obvious impacts of flooded public and private infrastructure, including salt water intrusion into drinking water, overwhelmed storm water discharge systems, and the presence of hazardous waste at sites below projected flood levels (Cooper et al. 2008). Some human responses to protect life and property from sea level rise impacts will exacerbate negative impacts to natural systems (e.g., shoreline hardening) while others may facilitate marsh resilience and the persistence of critical habitats (e.g., living shorelines, coastal retreat).
Salt marshes are intertidal wetlands typically located in low energy environments such as estuaries. They exist both as expansive meadow marshes and as narrow fringing marshes along shorelines. Considered one of the most productive ecosystems in the world, salt marshes provide numerous ecological functions, including shoreline stabilization, wildlife habitat, and nutrient cycling. North Atlantic marshes support the endemic Salt Marsh Sparrow (Ammodramus caudacutus) which has declined by 80% in the last 15 years. The uncommon and declining King Rail (Rallus elegans) and Black Rail (Laterallus jamaicensis) are also found in these marshes.
Salt marsh dependent species facilitate the export of nutrients and carbon from coastal to offshore food webs. The emerging field of valuing nature (calculating ecosystem services in economic terms) is sometimes controversial, but by any measure salt marsh is one of the most valuable habitat types on Earth. Bromberg Gedan et al. (2009) cautiously estimate that the ecosystem services of one hectare of salt marsh exceed a value of $14,000 per year.
In the past few centuries, a large portion of the Northwest Atlantic’s salt marsh habitat has been altered or destroyed. Soon after European settlement, salt marshes were ditched and drained to facilitate hay production, and subsequently to control mosquitoes. Over decades, various forms of coastal development (urban expansion, roadways, residential development, and industry) have altered and reduced the extent of marshes through diking, dredging, filling, and armoring (Greene et al. 2010).
Tidal flats are extensive, horizontal tracts of unconsolidated clays, silts, sands and organic materials that are alternately covered and uncovered by the tide, not allowing for much vegetated growth. Tidal flats have received less attention by resource managers than vegetated tidal wetlands, and therefore their importance to wildlife and humans has often been overlooked. However, the recent focus on the relationship between endangered shorebirds and sheltered beach-nesting horseshoe crabs has brought to light the ecological importance of these under-protected habitats.
Intertidal sand and mud flats of the sheltered coasts can be fringing or expansive, depending on bathymetry and tidal amplitude. Sediment size, sediment chemistry, inundation cycle, salinity, frequency of disturbance, and latitude are all determinants of the biotic community within flats. These flats are habitat for shellfish such as blue mussel (Mytilus edulis), Eastern oyster (Crassostrea virginica), hard clam (Mercenaria mercenaria) and soft shell clam (Mya arenaria). In addition to the typical resident invertebrate communities of annelids, crustaceans, and bivalves, tidal flats are foraging grounds for marine organisms such as eels, crabs, fish, snails, and shrimp at high tide and terrestrial organisms, particularly shorebirds, at low tide. During low tide, shorebirds congregate in tidal flats, sometimes in vast numbers, to feast on their abundant burrowing invertebrates. A variety of algal species often grow or float among the shells, rocks, and other structures present in the intertidal areas. The algae and bacteria that grow here provide additional food for fish, shellfish, and other animals using this habitat. However, in some areas of anthropogenic eutrophication, excessive growth of certain green algae species can suffocate the infauna of the mudflats below (Greene et al. 2010).
The results and data from the Resilient Coastal Sites study can be used in different ways to protect and manage valuable coastal resources for both people and nature. Each of the strategies below can be visually and geographically explored through an interactive story map.
- Prioritize land acquisition by focusing on the unsecured migration space of resilient marshes.
- Influence future development to prevent it from occurring in the boundary of a coastal marsh or directly in the migration space to enable marsh movement as the sea level rises.
- Identify areas for restoration where sites with relatively large amounts of migration space but in poor ecological condition can be improved by local management and conservation efforts.
- Maintain coastal productivity by conserving resilient sites whose migration space is larger than the current marsh and are thus expected to be more productive in the future.
- Invest in Natural Solutions by identifying resilient marshes that could potentially mitigate the effects of storm surge and sea level rise on densely populated areas.
- Identify resilient and biodiverse sites with internationally or regionally significant biodiversity.
- Sustain Important Bird Areas by identifying climate resilient sites that also have global or regional significance for birds, based on an ecoregional assessment for the Northwest Atlantic (Greene et al. 2010).
- Conservation Gateway Page: Resilient Coastal Sites in the Northeast and Mid-Atlantic. https://www.nature.org/resilientcoasts
- Map Viewer: Resilient Coastal Sites in the Northeast and Mid-Atlantic. http://nature.org/ECoastalResilienceMap
- Strategy Map: Resilient Coastal Sites in the Northeast and Mid-Atlantic. https://arcg.is/0GS9Sz
- Resilient Lands Tool: http://maps.tnc.org/resilientland/
Anderson, M.G, J. Odell, M. Clark, Z. Ferdaña, and J.K. Greene. 2010. The Northwest Atlantic Marine Ecoregional Assessment: Identifying Conservation Areas in the Northwest Atlantic Marine Region. Phase Two. The Nature Conservancy, Eastern U.S. Division, Boston, MA.
Bromberg Gedan, K. D., B. R. Silliman, and M. D. Bertness. 2009. Centuries of human-driven change in salt marsh ecosystems. Annual Review of Marine Science. 1:117-141.
Cooper, M. J. P., M. D. Beevers, and M. Oppenheimer. 2008. The potential impacts of sea level rise on the coastal region of New Jersey, USA. Climate Change. 90: 475-492.
Greene, J.K., M.G. Anderson, J. Odell, and N. Steinberg, eds. 2010. The Northwest Atlantic Marine Ecoregional Assessment: Species, Habitats and Ecosystems. Phase One. The Nature Conservancy, Eastern U.S. Division, Boston, MA.
U.S. Census Bureau, “Coastline Population Trends in the United States: 1960 to 2008,” Population Estimates and Projections, P25-1139, May 2010, pg. 14. Available at: http://www.census.gov/prod/2010pubs/p25-1139.pdf.