Habitat description
Tidal wetlands are some of the most productive habitats in the world, considered equally as rich as rainforests and coral reefs. Massachusetts’ extensive coastline supports thousands of acres of tidal wetlands, many of which are globally renowned destinations for birding or wildlife photography. Tidal wetlands in Massachusetts support iconic vertebrate species such as the saltmarsh sparrow and diamondback terrapin while providing important nursery habitat for fish and marine invertebrates. Tidal wetlands encompass estuaries with brackish water, freshwater tidal habitats, and beach intertidal habitats that occur at the interface between the land and the sea. Tidal wetlands include a range of marsh and shrub-dominated habitats, riverine or open water habitats.
Sites in Massachusetts with extensive estuaries and tidal wetland habitat include an area near the mouth of the Merrimack River known as the Great Marsh, Nauset Marsh and Pleasant Bay on outer Cape Cod, the East Branch of the Westport River, and numerous shorter estuaries found along the south side of Cape Cod, Buzzards Bay, and the mouths of all coastal rivers. The Taunton River has an extensive estuary that flows into Mount Hope Bay and Narragansett Bay, Rhode Island.
Characteristic natural communities
Tidal wetlands in Massachusetts encompass a stunning range of significant natural communities. Perhaps the most well-known are salt marshes, which are areas flooded daily by brackish water of varying salinity depending on distance from the ocean and other factors. Further inland along rivers, there are also freshwater tidal marshes, where the tidal influence effects water level fluctuations but not salinity. Salt ponds are created in depressions at least partially isolated from the ocean by barrier beaches. In the Massachusetts habitat classification, tidal wetlands also include sandy or rocky intertidal zones associated with beaches. These areas are exposed during low tides with pools sometimes forming in low areas.
Learn more about the natural communities found in tidal wetlands:
- Fresh/brackish tidal shrubland (S1)
- Fresh/brackish tidal swamp (S1)
- Freshwater tidal marsh (S1)
- Brackish tidal marsh (S2)
- Coastal salt pond community (S2)
- Salt marsh (S3)
- Seagrass community (S3)
- Marine intertidal gravel/sand beach (S4)
- Marine intertidal rocky shore (S4)
Natural communities are given state rarity/imperilment ranks ranging from S1-S5 (S1: rarest/most imperiled).
Characteristic plants and animals
Tidal marshes are characterized by grasses, sedges, and rushes such as the iconic saltmarsh cordgrass. These tidal marshes provide important habitat for a variety of inland and marine fishes, serving as foraging and staging areas for diadromous species (species that migrate between the ocean and rivers), such as shortnose sturgeon, American eel, American shad, and river herring. Some fish are only found in tidal wetland habitats, including mummichog and spot-fin killifish. Clams, mussels, oysters, fiddler crabs, shrimp, worms, and other invertebrates are important food sources for wildlife, including the diamondback terrapin, which thrives in brackish water but is evolutionarily related to the freshwater turtles rather than sea turtles. Salt marshes provide essential habitat for, and are critical for the conservation of, the saltmarsh sparrow which feeds, breeds, and rears young within the salt marsh grasses and thatch. Intertidal beach areas are important foraging and resting areas for migrating shore birds such as least sandpipers and red knot.
Tidal wetlands provide essential habitat for many rare or migratory species including piping plover, Atlantic horseshoe crab, harlequin duck, and purple sandpiper. Four species of rare terns that nest in Massachusetts depend on marine and estuarine habitats for all their food. Red-throated and common loons are frequent migrants along the Massachusetts Coast during spring and fall migration, and both species can be found in these waters during the winter months. Many rare plants occur within tidal wetlands, particularly within freshwater and brackish transitional areas along tidal rivers.
Associated habitats
Tidal wetlands are often associated with coastal beaches and dunes, gently-sloping warm rivers, tidal streams, maritime, and marine nearshore habitats.
Ecological processes
Tidal wetlands are strongly associated with tidal processes and their nutrient cycles are driven by both terrestrial and marine inputs. For example, terrestrial environments provide inputs of sediment, nutrients, and freshwater. Coastal processes such as sediment transport, tidal inundation, and storm surges also have major influences over tidal wetland systems.
Threats
- Tidal wetlands have been negatively affected by the effects of altered hydrology associated with channelization and ditching, tidal restrictions, berm construction, beach hardening (natural system modification), as well as roads and railroads. Some of these impacts are a legacy from past agricultural land reclamation, mosquito control, and road construction, but others (such as shoreline hardening) are still occurring today. These alterations have resulted in erosion, reduction or elimination of tidal flow, salt marsh loss, the spread of invasive plants, and lower salt marsh elevations making them more susceptible to sea level rise and storm surges. Many brackish mashes have been altered by urbanization (development) due to their location at river mouths which are ideal locations for transportation and commercial hubs (i.e. ports).
- Salt marshes, brackish marshes, and small coastal bays are uniquely vulnerable to nutrient inputs (especially nitrogen) from fertilizers, septic leach fields, and other sources (pollution). These nutrients can result in reduction in root mass loss and accelerated rates of decomposition, resulting in bank collapse. Strong storm events are likely to increase pollutants, including residues from roads, sewage from combined sewage overflows, and nutrients from lawns and septic systems. High levels of nutrients can also increase the magnitude and frequency of algal blooms in these systems which can deprive the water column of oxygen and result in fishkills.
- Invasive species: Massachusetts tidal wetlands are negatively affected by common reed (Phragmites australis) as well as pepperweed (Lepidium latifolium), purple loosestrife (Lythrum salicaria), and many other species, including green crab (Carcinus maenas).
- Climate change: Tidal wetlands are threatened by changes associated with climate change including sea-level rise, large, more frequent storms, increasing summer temperatures, and prolonged periods of drought. Sea level rise will exacerbate the effects of existing legacy agricultural features, mosquito ditches, and tidal restrictions in the marsh, rapidly contributing to water logging and loss of salt marsh vegetation. Sea level rise is also changing the chemical gradients that shape these habitats. Salt marsh areas may transition to “megapools” and mudflats; brackish marshes and salt ponds may become more saline. Warmer air temperatures are increasing heat stress in intertidal organisms resulting in limited ranges and lower abundance of some organisms. Warmer temperatures and ocean acidification may affect ocean currents and primary production and may alter foraging opportunities in intertidal zones. Freshwater inputs may decrease significantly during droughts while large rainfall events also may periodically inundate these habitats. Strong storms, storm surges, increasing temperatures and sea level rise are already affecting tidal wetlands. Stronger storms increase wave energy which is depleting sand deposits in some beaches and dislodging organisms from rocky intertidal habitats. Current estimates are that about 50% of beaches worldwide will be lost by 2100.
Conservation actions
- Proactive habitat protection. Protect tidal wetlands in conjunction with other coastal habitats to maintain healthy and resilient landscapes for people and biodiversity conservation. Prioritize sites supporting state-listed animals and plants and other SGCN, as well as other protection priorities identified in BioMap and other conservation planning tools (e.g., municipal open space plans).
- Habitat restoration and management. See recommendations below.
- Law and policy. Regulate and limit the impacts of development and shoreline hardening. Innovative approaches to incentivizing compatible development should be considered where applicable.
- Conservation planning. Include key tidal wetlands in conservation planning efforts at multiple spatial scales. See BioMap as an example. Identify coastal areas that are most vulnerable to flooding and erosion and develop plans to mitigate impacts from flooding. Habitat considerations should be carefully considered when engaging in coastal resilience planning tied to sea level rise and climate change.
- Monitoring and research. Monitor and conduct surveys of SGCN in marine and estuarine waters, so that changes in abundance and distribution can be detected and threats evaluated. This would include the temporal and spatial use of the marine habitats by birds and bats; documenting stranded or oiled sea turtles (including carcasses), marine mammals, and birds; and investigating interactions between fisheries/aquaculture harvests and SGCN abundance and productivity. Other actions include mapping eelgrass beds through aerial surveys and working with non-governmental organizations on volunteer wetland assessment programs.
- Public outreach. Include information about the role of tidal wetlands and associated coastal landscapes in biodiversity conservation, flood mitigation, water filtering, and climate resiliency as part of broader communication strategies. Provide technical advice and outreach on pollution, unrestricted access, and stormwater issues to coastal municipalities and the public along coastal Massachusetts.
Restoration & management recommendations
Due to their importance to Species of Greatest Conservation Need and vulnerability to stressors, tidal wetlands have been designated as very high priority (tier 1) for restoration and management.
Massachusetts tidal wetlands can benefit from coordinated management and restoration by state and federal agencies working with non-governmental organizations, municipalities, and universities. Numerous partners are deeply involved in representative projects around the state, including: Northeast Climate Adaptation Science Center, Great Marsh Coalition, Mass Audubon, Buzzard’s Bay Coalition, UMass Dartmouth, UMass Amherst, and many others. Additional decision support could help partners decide whether, where, and when management is appropriate; what scale restoration is meaningful for the community group, how landscape context should be considered, and how habitats are likely to change in the future. This could include an interactive GIS-based map of past, current, and future coastal restoration projects to evaluate, track, and prioritize actions.
Typical tidal wetland restoration activities include removal of tidal restrictions such as undersized culverts, salt marsh ditch remediation, installation of runnels, use of nature-based solutions such as thin layer deposition of sediment to raise salt marsh elevations, eel grass restoration, and invasive species control. Better management of non-point and point source pollution to improve water quality is also an important restoration activity.