Marine Intertidal Mudflats Guide - New York Natural Heritage Program

Summary

Did you know?

Walking on mudflats can be challenging and in some cases even dangerous. It is very easy to sink up to your waist in the soft mud, unless you wear "mudders." Mudder shoes have expandable wings on the side to provide support when crossing mudflats. Worn over boots or waders, the wings expand as you step onto soft surfaces to increase boot area by four times and then retract when you lift your foot.

State Ranking Justification

There are over 100 extant occurences of marine intertidal mudflats estimated statewide with 50-100 occurrences with good viability. They can be found across Long Island in north and south shore embayments and in the Peconic estuary at the eastern end of the island, as well as around New York City. The current trend of the community is likely declining; the speed and severity of the decline varies by site. Substantial primary threats include ditching and draining, dredging and filling, shoreline hardening, poor water quality, diking and impoundment, inlet stabilization, altered sediment budget, slumping and subsidence, changes in water circulation patterns, sea level rise, restricted tidal connection, and altered tidal hydrodynamics.

Short-term Trends

Over the last several decades, there have been significant decreases in the area of extent, number, and ecological integrity of low salt marshes in New York. Marine intertidal mudflats, which are adjacent to these marshes, may have suffered equally drastic declines, particularly from direct dredging and filling for urban development and maintaining navigation channels. Sea level rise may result in permanent flooding of some occurrences.

Long-term Trends

The number, aerial extent, and integrity of marine intertidal mudflats in New York are suspected to have declined substantially from their historical state. These declines are likely correlated with coastal development; dredging, ditching, and filling; and changes in hydrology, water quality, and natural processes.

Conservation and Management

Conservation Overview

Remove shoreline armoring to increase overland sediment input; improve water quality by reducing or eliminating sewer and stormwater discharge and pesticide application; restore tidal regime by removing culverts, dikes, and impoundments, plugging ditches, and replacing static flow restriction devices with those that are calibrated for local tidal hydrology. Ensure connectivity between the open saltwater and low salt marsh.

Threats

Factors that threaten salt marsh complexes also threaten marine intertidal mudflat communities. These include dredging and filling for development, ditching and draining for mosquito control, Poor water quality (from sewage and stormwater discharge; nonpoint source runoff; landfill leachate; boat traffic; particulate aircraft, vehicular, and power plant emissions; jet fuel; ethylene glycol from aircraft deicing; and pesticides used in mosquito management), diking and impoundment, inlet stabilization, shoreline hardening, altered sediment budget (decreased sediment input), subsidence, changes in water circulation patterns because of changes in shoreline and benthic topography, restricted tidal connection, and altered tidal hydrodynamics resulting from changes to hydrology (including groundwater levels, overland flow, and in-channel volume) in the surrounding watershed, road construction, and urbanization. Sea level rise may result in permanent flooding of some occurrences.

Conservation Strategies and Management Practices

Remove shoreline armoring to increase overland sediment input; improve water quality by reducing or eliminating sewer and stormwater discharge and pesticide application; restore tidal regime by removing culverts, dikes, and impoundments, plugging ditches, and replacing static flow restriction devices with those that are calibrated for local tidal hydrology. Restoration and monitoring protocols are available (Niedowski 2000).

Development and Mitigation Considerations

Strive to minimize or eliminate hardened shorelines and maintain low-sloped shorelines within the tidal zone to increase overland sediment input. Maintain functional connectivity between the open ocean and bays with salt marsh complexes to enable full tidal flushing during each tidal cycle. For example, barriers such as railway causeways should have numerous culverts to allow sufficient hydrologic connectivity. If flow restriction devices are needed, those that are calibrated for local tidal hydrology can be used. Avoid dumping dredge spoil onto mudflats and low salt marshes. This community is best protected as part of a large salt marsh complex. Protected areas should encompass the full mosaic of low salt marsh, high salt marsh, marine intertidal mudflats, saltwater tidal creek, salt panne, and salt shrub communities to allow dynamic ecological processes (sedimentation, erosion, tidal flushing, and nutrient cycling) to continue. Connectivity to brackish and freshwater tidal communities, upland beaches and dunes, and to shallow offshore communities should be maintained. Connectivity between these habitats is important not only for nutrient flow and seed dispersal, but also for animals that move between them seasonally. Development of site conservation plans that identify wetland threats and their sources and provide management and protection recommendations would ensure their long-term viability.

Inventory Needs

Inventory needs are to continue to search for large marine intertidal mudflats in good condition (A- to AB-ranked), prioritizing mudflats that are associated within high quality salt marsh complexes. Surveys and documentation of additional occurrences are needed, as are data on rare and characteristic animals, especially benthic invertebrates.

Research Needs

Future research on marine intertidal mudflats should include monitoring community response to sea level rise, sediment starvation, and permanent flooding and studying nutrient exchange processes and relationships to adjacent marine and estuarine communities.

Rare Species

Ardea alba (Great Egret) (guide)
Diplachne fusca ssp. fascicularis (Salt-meadow Grass) (guide)

Range

New York State Distribution

Marine intertidal mudflats are often adjacent to low salt marshes and saltwater tidal creeks. These communities have a similar distribution in the state and are restricted to sheltered areas of the seacoast in the the Coastal Lowlands and Manhattan Hills ecozones in Bronx, Westchester, Kings, Queens, Nassau, and Suffolk counties. Marine intertidal mudflats can be found across Long Island in north and south shore embayments and in the Peconic estuary at the eastern end of the island, as well as around New York City, in Westchester County on Long Island Sound, and in the Hudson River north to approximately the Tappan Zee Bridge.

Global Distribution

These intertidal mudflats extend along the Atlantic Coast, especially in the back-barrier bays, from Maine to New York and New Jersey.

Best Places to See

Gateway National Recreation Area (Queens County)
Great South Bay (Nassau, Suffolk Counties)

Identification Comments

General Description

The marine intertidal mudflats community is located in quiet waters, with substrates composed of silt or sand that is rich in organic matter and poorly drained at low tide. This community is almost completely unvegetated. Cordgrass (Spartina alterniflora) can occur sporadically, colonizing from adjacent low salt marsh communities. The marine alga sea lettuce (Ulva lactuca) can cover 40% or more of the exposed substrate.

Characters Most Useful for Identification

This intertidal community is almost completely unvegetated on exposed mudflats adjacent to low salt marshes and saltwater tidal creeks where the salinity is greater than 18 ppt. This community is submerged during high tide, and exposed at low tide.

Elevation Range

Known examples of this community have been found at elevations between -1 feet and 9 feet.

Best Time to See

Marine intertidal mudflats are viewable year round, but are best viewed at low tide from a distance on firm ground or a boat.

Marine Intertidal Mudflats Images

Marine intertidal mudflats in Jamaica Bay, Gateway National Recreation Area.
Gregory J. Edinger

Air photo of marine intertidal mudflats on tidal marsh island in Jamaica Bay.
NYS Orthoimagery from Spring 2010. Color Infrared.

Marine intertidal mudflats in Jamaica Bay, Gateway National Recreation Area.
Gregory J. Edinger

Classification

International Vegetation Classification Associations

This New York natural community encompasses all or part of the concept of the following International Vegetation Classification (IVC) natural community associations. These are often described at finer resolution than New York's natural communities. The IVC is developed and maintained by NatureServe.

Intertidal Mudflats Sparse Vegetation (CEGL006614 )

Characteristic Species

Herbs

Spartina alterniflora (smooth cord grass)

Nonvascular plants

sea lettuce (Ulva lactuca)

Unvegetated

American oystercatcher (Haematopus palliatus)

blue mussel (Mytilus edulis)

mudsnail (Ilyanassa obsoleta)

polychaete (Heteromastus filiformis)

polychaete (Lumbrinereis tenuis)

polychaete (Nereis virens)

polychaete (Polydora ligni)

polychaete (Streblospio benedicti)

softshell clam (Mya arenaria)

willet (Catoptrophorus semipalmatus)

Similar Ecological Communities

Low salt marsh (guide)

Low salt marshes and marine intertidal mudflats are often adjacent to each other, or can form a patchy mosaic within an embayment. Both communities are influenced by diurnal tides and often have similar muddy substrates. However, marine intertidal mudflats are almost completely unvegetated compared to low salt marshes that have diverse and often dense vegetation cover dominated by cordgrass (Spartina alterniflora).
Marine intertidal gravel/sand beach (guide)

Both communities are intertidal and essentially unvegetated. However, marine intertidal mudflat substrates are composed of silt or sand that is rich in organic matter and poorly drained at low tide. Mudflats are usually adjacent to low salt marshes and saltwater tidal creeks. Whereas, marine intertidal gravel/sand beaches are composed of sand or gravel substrates that are well-drained at low tide; and they are usually adjacent to maritime beaches.
Marine rocky intertidal (guide)

Unlike marine rocky intertidal communities, which have high-energy wave action and rocky substrates, marine intertidal mudflats are characterized by quiet waters and unconsolidated soils. Marine intertidal mudflats occur on fine silt or sand that is rich in organic material. They are exposed at low tide, and have a diverse array of invertebrates that provide important fuel for migrating and breeding shorebirds.
Maritime beach (guide)

Marine intertidal mudflat substrates are composed of silt or sand that is rich in organic matter and poorly drained at low tide. Mudflats are usually adjacent to low salt marshes and saltwater tidal creeks. Whereas, maritime beaches are terrestrial and are located above the high tide line. Maritime beaches are usually adjacent to marine intertidal gravel/sand beaches offshore and maritime dunes or bluffs landward.
Saltwater tidal creek (guide)

Saltwater tidal creeks and marine intertidal mudflats are often adjacent to each other within a salt marsh complex. Both communities are influenced by diurnal tides and often have similar muddy substrates. However, marine intertidal mudflats are submerged during high tide, and exposed at low tide, whereas saltwater tidal creeks have a permanently flooded subtidal channel.

Vegetation

Herbs

Nonvascular plants

40%

Unvegetated

100%

Percent cover

This figure helps visualize the structure and "look" or "feel" of a typical Marine Intertidal Mudflats. Each bar represents the amount of "coverage" for all the species growing at that height. Because layers overlap (shrubs may grow under trees, for example), the shaded regions can add up to more than 100%.

Additional Resources

References

Brown, B. 1993. A classification system of marine and estuarine habitats in Maine: An ecosystem approach to habitats. Part 1: benthic habitats. First iteration. Maine Natural Areas Program. Department of Economic and Community Development. Augusta, ME.

Edinger, G. J., A. L. Feldmann, T. G. Howard, J. J. Schmid, E. Eastman, E. Largay, and L. A. Sneddon. 2008. Vegetation Classification and Mapping at Gateway National Recreation Area. Technical Report NPS/NER/NRTR—2008/107. National Park Service. Northeast Region. Philadelphia, PA.

Edinger, G. J., D. J. Evans, S. Gebauer, T. G. Howard, D. M. Hunt, and A. M. Olivero (editors). 2014. Ecological Communities of New York State. Second Edition. A revised and expanded edition of Carol Reschke’s Ecological Communities of New York State. New York Natural Heritage Program, New York State Department of Environmental Conservation, Albany, NY. https://www.nynhp.org/ecological-communities/

New York Natural Heritage Program. 2023. New York Natural Heritage Program Databases. Albany, NY.

Reschke, Carol. 1990. Ecological communities of New York State. New York Natural Heritage Program, New York State Department of Environmental Conservation. Latham, NY. 96 pp. plus xi.

Townes, H. K. Jr. 1939. Ecological studies on the Long Island marine invertebrates of importance as fish food or bait. In: A biological survey of the salt waters of Long Island, 1938. Suppl. to the 28th Annual Report, 1938. A joint survey with the US Bureau of Fisheries. NYS Conservation Dept., Albany, NY.

Whitlatch, R. B. 1982. The ecology of New England tidal flats: a community profile. US Fish and Wildlife Service, Biological Services Program, US Dept. of Interior, Washington, DC FWS/OBS-81/01. 125 pp.

About This Guide

This guide was authored by: Gregory J. Edinger

Information for this guide was last updated on: May 15, 2020

Please cite this page as:
New York Natural Heritage Program. 2023. Online Conservation Guide for Marine intertidal mudflats. Available from: https://guides.nynhp.org/marine-intertidal-mudflats/. Accessed March 31, 2023.