Marine eelgrass meadow Cornell Cooperative Extension of Suffolk County

Marine eelgrass meadow
Cornell Cooperative Extension of Suffolk County

System
Marine
Subsystem
Marine Subtidal
State Protection
Not Listed
Not listed or protected by New York State.
Federal Protection
Not Listed
State Conservation Status Rank
S1S2
Critically Imperiled or Imperiled in New York - Especially or very vulnerable to disappearing from New York due to rarity or other factors; typically 20 or fewer populations or locations in New York, very few individuals, very restricted range, few remaining acres (or miles of stream), and/or steep declines. More information is needed to assign either S1 or S2.
Global Conservation Status Rank
G5
Secure globally - Common in the world; widespread and abundant (but may be rare in some parts of its range).

Summary

Did you know?

Seagrass beds are some of the most productive communities on earth. In New York, eelgrass provides critical habitat for a surprising variety of fascinating marine creatures. Seahorses, puffer fish, bay scallops, hard clams, lobster, starfish, flounder, shrimp, hermit crabs, spider crabs, skates, squid, horseshoe crabs, sea turtles, and many more species spend at least part of their lives within these protective marine eelgrass meadows (NYS Seagrass Task Force 2009, Orth 2006).

State Ranking Justification

There are estimated to be over 21,000 acres of eelgrass in New York; there may be as many as 30 extant occurrences of marine eelgrass meadow statewide. The few documented occurrences of this community have good viability and are somewhat protected in the waters adjacent to public or private conservation land. The community is restricted to the ocean surrounding Long Island in the North Atlantic Coast ecoregion; it is found in the Peconic Estuary, Long Island Sound, and the South Shore Estuary. The aerial extent and ecological integrity of this community is very rapidly to severely declining; an estimated 90% of New York's eelgrass meadows have been lost between 1930 and the present. Threats to the community include decreased water quality, increased nutrient inputs, physical disturbance from fishing and shellfishing gear, and harmful algal blooms.

Short-term Trends

The aerial extent and ecological integrity of this community is very rapidly to severely declining. While historical seagrass acreage in New York has not been documented, historical photography and records indicate that there may have been 200,000 acres in 1930; today, only a little more than 20,000 acres remain. This is due, in part, to effects from historical seagrass wasting disease and current increased nutrient loading, decreased water quality and clarity, harmful phytoplankton blooms, habitat degradation, and fishing and boating disturbances (New York State Seagrass Task Force 2009).

Long-term Trends

Prior to the 1930s, marine eelgrass meadows in the waters surrounding New York are assumed to have been relatively extensive (>200,000 acres) and stable (New York State Seagrass Task Force 2009).

Conservation and Management

Threats

The greatest threats to marine eelgrass meadows in New York are decreased water quality from excess nitrogen, harmful algal blooms, increased turbidity from sedimentation, and damage from fishing/shellfishing gear and boating activities. These threats vary by estuarine system: "Long Island Sound seagrass is most threatened by excess nitrogen. Peconic Estuary seagrass is most affected by fishing and shellfishing gear and boating activities. . . . Long Island's South Shore Estuary is most threatened by harmful algal blooms" (New York State Seagrass Task Force 2009). Additional existing or expected threats include continued decline in water quality and clarity from development, hardened shorelines, polluted run-off, and potentially from a loss of filter feeders; physical disturbances from construction of marinas and docks, navigational channel dredging (which potentially destroys eelgrass beds, increases turbidity, and alters habitat suitability), storm surges, and wind/wave action (which may be exacerbated by climate change); seagrass wasting disease; bioturbation and overgrazing; increased water temperatures from climate change; and sea level rise. Some invasive exotic species, including tunicate colonies (Didemnum spp.) and macroalgae (Codium fragile), are also threatening this community (New York State Seagrass Task Force 2009, Pickerell and Schott 2004, Stephenson 2009).

Conservation Strategies and Management Practices

Improve water quality by reducing or eliminating sewer and stormwater discharge and pesticide/herbicide application. Set guidelines and gear restrictions to minimize disturbances from shellfishing, boating, and dredging. Reduce or mitigate shoreline development and armoring as much as possible. Monitor the spread of invasive exotic species in this community, particularly tunicate colonies (Didemnum spp.) and macroalgae (Codium fragile) and, as needed, control their encroachment. Include marine eelgrass meadow restoration and long term monitoring in Harbor Management Plans, as appropriate. A comprehensive management plan for the Peconic Estuary is available as a model (Stephenson 2009).

Development and Mitigation Considerations

Strive to minimize or eliminate hardened shorelines and maintain low-sloped shorelines within the tidal zone; healthy marine eelgrass meadows will slow ocean currents and reduce shoreline erosion. Maintain functional connectivity between the open ocean and bays with marine eelgrass meadows 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. This community is best protected as part of a large complex. Protected areas should encompass coastal, nearshore, and deepwater marine habitats to ensure connectivity and allow dynamic ecological processes to continue. Connectivity to brackish and freshwater tidal communities, upland beaches and dunes, and to shallow offshore communities should also 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 local threats and their sources and provide management and protection recommendations would ensure their long-term viability. Address seagrass protection in Local Waterfront Revitalization Programs where appropriate (NYS Seagrass Task Force 2009).

Inventory Needs

Extensive inventory is needed, with focus on the Peconic Estuary, Long Island Sound, and the South Shore Estuary. Existing digital maps of the three estuaries (Long Island Sound and South Shore Estuary circa 2002 and Peconic Estuary circa 2000) should be used as leads. The New York State Seagrass Task Force recommends that inventories be repeated every three years.

Research Needs

A significant amount of research on marine eelgrass meadow threats and stressors, recolonization, disturbance, restoration, genetics, and ecology has been suggested (from New York State Seagrass Task Force 2009). Studies are needed to determine impacts from channel dredging operations, specifically whether local operations actually improve water quality through increased tidal flushing. The ability of eelgrass beds to migrate in response to sea level rise, particularly in areas with hardened shorelines, should be investigated, as should their carbon dioxide uptake potential. Potential impacts of recently-arrived exotic species, like Didemnum spp. (a filter-feeding, colonial tunicate that forms dense, smothering mats), need to be explored. Research should be conducted to determine the effects of multiple stressors on eelgrass, to determine the genetic diversity of eelgrass in and between estuarine systems, and to determine the causes of exacerbated wasting disease or other potential diseases affecting eelgrass. The concentration at which pesticides and herbicides become toxic to eelgrass should be determined. Relationships, (positive, negative, and neutral) between biota (including epiphytes, grazers, and bioturbators) and eelgrass should be established. Ground- and surface-water monitoring should be conducted to determine whether inputs are negatively affecting eelgrass meadows, either directly or indirectly. Causes of eelgrass disappearance from seemingly suitable sites in the Peconic Estuary (Southold Bay, Three Mile Harbor, and Northwest Harbor) should be conclusively determined (Pickerell and Schott 2008). More data on other marine shallow water communities with very little or no eelgrass (e.g., marine macroalgae beds) are needed (Edinger et al. 2002).

Rare Species

Range

New York State Distribution

Marine eelgrass meadow occurs in the ocean surrounding Long Island in the North Atlantic Coast ecoregion. It is known from the eastern Peconic Estuary; from multiple bays on the south shore of Long Island including Great South Bay, Moriches Bay, and Shinnecock Bay; and from the north shore of Long Island bordering Long Island Sound. Small occurrences are suspected from bays on Staten Island.

Global Distribution

This community occurs in subtidal habitat along the north and mid-Atlantic coast. It has a wide distribution in coastal waters from Maine to North Carolina and occurs in large patches in sheltered near-shore estuarine waters (NatureServe 2009).

Best Places to See

  • Mashomack Preserve (TNC) (Suffolk County)

Identification Comments

General Description

A community of subtidal aquatic beds typically occurring in quiet, shallow (2 to 30 feet deep), polyhaline (18 to 30 ppt salinity) waters of temperate tidal embayments below the lowest tide level, where fluctuations in salinity are minor. Plant species composition is known to vary with different rates of exchange with marine waters. As salinity decreases, eelgrass beds may grade into brackish subtidal aquatic beds dominated by widgeon grass (Ruppia maritima) (Macomber et al. 1979). Eelgrass meadows are highly productive, provide habitat for a rich variety of marine organisms, and enhance sediment stability. They typically occur on sands to sandy loam soils at 0.6-4.5 m (2 to 15 ft) below mean sea level.

Characters Most Useful for Identification

This community is characteristically dominated or codominated by eelgrass (Zostera marina). Characteristic associated plants include a diverse array of attached (rooted and epiphytic) and unattached (suspended) marine algae. Rooted red algae are especially common, including graceful red weed (Gracilaria tikvahiae), tubed weed (Polysiphonia denudata), Grinnell's pink leaf (Grinnellia americana), Agardh's red weed (Agardhiella subulata), Rhodomela confervoides, pod weed (Chondria baileyana), Spyridia filamentosa, banded weed (Ceramium spp.), and rough tangle weed (Stilophora rhizoides). Abundant and characteristic epiphytic marine algae include barrel weed (Champia parvula), tubed weed (Polysiphonia stricta), Cladophora sericea, and Pneophyllum fragile. Other associated marine algae include the green algae sea lettuce (Ulva lactuca), hollow green weed (Enteromorpha spp.), Cladophora gracilis, and the brown algae gulfweed (Sargassum filipendula). A common exotic species is the marine green algae, green fleece (Codium fragile). Characteristic fauna include fish such as fourspine stickleback (Apeltes quadracus), mummichog (Fundulus heteroclitus), northern pipefish (Syngnathus fuscus), threespine stickleback (Gasterosteus aculeatus), silversides (Menidia spp.), naked goby (Gobiosoma bosci), menhaden (Brevoortia tyrannus), winter flounder (Pseudopleuronectes americanus), and northern puffer (Sphoeroides maculatus); marine mollusks such as bay scallop (Aequipecten irradians), common Atlantic slippershell (Crepidula fornicata), and northern quahog (Mercenaria mercenaria); crustaceans such as nine-spine spider crab (Libinia emarginata), mud crabs (e.g., Dyspanopeus sayi, Panopeus herbstii and Rithropanopeus harrisii), broken-back shrimp (Hippolyte pleurocantha); and other marine invertebrates, such as short-spine brittle star (Ophioderma brevispina), bamboo worms (Polychaeta), and counterclockwise coiled worm (Spirobis spirillum). Comb jellies (Beroe spp., Mnemiopsis leidyi) are common plankton species. Waterfowl known to extensively feed on eelgrass include brant (Branta bernicla) and American black duck (Anas rubripes) (Good et al. 1978).

Elevation Range

Known examples of this community have been found at elevations between -12 feet and -2 feet.

Best Time to See

Marine eelgrass meadows can be explored year-round. Snorkel through the meadows in mid- to late summer to observe associated species like hermit crabs foraging and hiding amongst the blades of grass. Flowering eelgrass can also be seen in mid- to late summer.

Marine Eelgrass Meadow Images

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.

NatureServe Ecological Systems

This New York natural community falls into the following ecological system(s). Ecological systems are often described at a coarser resolution than New York's natural communities and tend to represent clusters of associations found in similar environments. The ecological systems project is developed and maintained by NatureServe.

  • Northern Atlantic Coastal Plain Seagrass Bed (CES203.246 )

Characteristic Species

Nonvascular plants

Agardhiella subulata

Ceramium spp.

Champia parvula

Chondria baileyana

Cladophora sericea

Codium fragile

Gracilaria tikvahiae

Grinnellia americana

Pneophyllum fragile

Polysiphonia denudata

Polysiphonia stricta

Rhodomela confervoides

Sargassum filipendula

Spyridia filamentosa

Stylophora rhizoides

Submerged aquatics

Zostera marina (eel-grass)

Similar Ecological Communities

  • Brackish subtidal aquatic bed (guide)
    Brackish subtidal aquatic beds are dominated by widgeon grass (Ruppia maritima), a submerged, rooted vascular plant that grows in slightly shallower water than eelgrass. The brackish water of these subtidal aquatic beds has salinity values that range from 0.5 to 18 parts per thousand (ppt) in contrast to marine eelgrass meadows, which are saline at 18-30 ppt.
  • Freshwater subtidal aquatic bed
    Like marine eelgrass meadows, freshwater subtidal aquatic beds are continuously flooded communities dominated by rooted vegetation. The freshwater system is primarily found along the Hudson River and possibly on small tidal rivers of Long Island, and is dominated by tapegrass (Vallisneria americana), whereas the marine system is found in the ocean off of Long Island and is dominated by eelgrass.
  • Marine intertidal gravel/sand beach
    Marine intertidal gravel/sand beaches, unlike marine eelgrass meadows, are periodically exposed and flooded by semidiurnal tides. They are washed by rough, high-energy waves and have sand or gravel substrates that are well-drained at low tide. They are largely unvegetated.
  • Marine intertidal mudflats
    Marine intertidal mudflats, unlike marine eelgrass meadows, are periodically exposed and flooded by semidiurnal tides. They may be covered with marine algae, such as sea lettuce, but would not support submerged eelgrass.
  • Marine rocky intertidal (guide)
    Unlike marine eelgrass meadows, which are charaterized by quiet waters and unconsolidated sandy to sandy loam soils, marine rocky intertidal communities have high-energy wave action, occur on rocky substrates, and are dominated by marine algae, not eelgrass.
  • Saltwater tidal creek (guide)
    Saltwater tidal creeks are permanently flooded, like marine eelgrass meadows, but they tend to be shallower. Their submerged areas average less than 2 m deep at low tide, but they can be deeper in main channel reaches. They are also dominated by species like widgeon grass, not eelgrass.

Vegetation

Nonvascular plants
10%
Submerged aquatics
55%

Percent cover

This figure helps visualize the structure and "look" or "feel" of a typical Marine Eelgrass Meadow. 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

Briggs, P.T. and J.S. O'Connor. 1971. Comparison of shore-zone fishes over naturally vegetated and sand-filled bottoms in Great South Bay. NY. Fish and Game J. 18: 15-41.

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.

Cashin Associates, P.C. 1996. Peconic Estuary Program. Final submerged aquatic vegetation study. Unpublished report. Hauppague, New York. 116 pp.

Day, C.H. 1987. Life on Intertidal Rocks. Nature Study Guild, Rochester, New York.

Dumais, S. and C. Smith. 1999. Peconic Estuary Program. 1998 Eelgrass (Zostera marina) Long Term Monitoring Program. Progress Report 2. Marine Program, Cornell Cooperative Extension. Riverhead, NY. 19 pp.

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. http://www.dec.ny.gov/docs/wildlife_pdf/ecocomm2014.pdf

Edinger, Gregory J., D.J. Evans, Shane Gebauer, Timothy G. Howard, David M. Hunt, and Adele M. Olivero (editors). 2002. Ecological Communities of New York State. Second Edition. A revised and expanded edition of Carol Reschke's Ecological Communities of New York State. (Draft for review). New York Natural Heritage Program, New York State Department of Environmental Conservation. Albany, NY. 136 pp.

Good, R.E., J. Limb, E. Lyszczek, M. Miernik, C. Ogrosky, N. Psuty, J. Ryan, and F. Sickels. 1978. Analysis and delineation of the submerged vegetation of coastal New Jersey. A case study of Little Egg Harbor. Rutgers University. Center for Coastal and Environmental Studies. New Brunswick, N.J.

Gosner, K.L. 1978. A Field Guide to the Atlantic Seashore. Peterson Field Guides. Houghton Mifflin Company, New York, New York.

Kunstler, D. and P. Capainolo. 1987. Huckleberry Island: Premier waterbird colony of western Long Island. Kingbird 37:178-188.

Macomber, R.T. and D. Allen. 1979. The New Jersey submersed aquatic vegetation distribution atlas final report. Prepared for the New Jersey Department of Env. Protection, Division of Coastal Resources, Bureau of Coastal Planning and Development. Trenton, New Jersey.

Muenscher, W.C. 1939. Aquatic vegetation of Long Island waters. In: A biological survey of the fresh waters of Long Island. Suppl. to the 28th Ann. Rep., 1938. New York State Conservation Department, Albany, NY. pp 88-101.

NatureServe. 2009. NatureServe Explorer: An online encyclopedia of life [web application]. Version 7.1. NatureServe, Arlington, Virginia. Available http://www.natureserve.org/explorer. (Data last updated October, 2009)

New York Natural Heritage Program. 2019. New York Natural Heritage Program Databases. Albany, NY.

New York State Seagrass Task Force. 2009. Final Report of the New York State Seagrass Task Force: Recommendations to the New York State Governor and Legislature.

Orth, Robert J., T.J.B. Carruthers, W.C. Dennison, C.M. Duarte, J.W. Fourqurean, K.L. Heck Jr., A.R. Hughes, G.A. Kendrick, W.J. Kenworthy, S. Olyarnik, F.T. Short, M. Waycott, and S.L. Williams. 2006. A Global Crisis for Seagrass Ecosystems. BioScience 56(12): 987-996.

Pickerell, Christopher and Stephen Schott. 2004. Peconic Estuary Program long-term eelgrass monitoring program: Eelgrass trends analysis report: 1997-2002. Cornell University Cooperative Extension of Suffolk County for The Peconic Estuary Program Office, Suffolk County Department of Health Services, Office of Ecology.

Pickerell, Christopher and Stephen Schott. 2008. Peconic Estuary Program 2007 eelgrass (Zostera marina) long-term monitoring program: Progress Report 8. Cornell University Cooperative Extension of Suffolk County for The Peconic Estuary Program Office, Suffolk County Department of Health Services, Office of Ecology.

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.

Schlesinger, M.D., E.L. White, S.M. Young, G.J. Edinger, K.A. Perkins, N. Schoppmann, and D. Parry. 2016. Biodiversity Inventory of Plum Island, New York. New York Natural Heritage Program, Albany, New York, and SUNY College of Environmental Science and Forestry, Syracuse, NY.

Stephenson, Laura B. 2009. Eelgrass management plan for the Peconic Estuary. New York State Department of Environmental Conservation, Peconic Estuary Program, Yaphank, NY.

Strieb, M.D., V.M. Bricelj, and S.I. Bauer. 1995. Population biology of the mud crab, Dyspanopeus sayi, an important predator of juvenile bay scallops in Long Island (USA) eelgrass beds. Journal of Shellfish Research 14(2): 347-357.

Thayer, G.W., W.J. Kenworthy, and M.S. Fonseca. 1984. The ecology of eelgrass meadows of the Atlantic Coast: a community profile. U.S. Fish and Wildlife Service. FWS/OBS- 84/02. 147 pp.

Thorne-Miller, B., M. M. Harlin, G. B. Thursby, M. M. Brady-Campbell, and B. A. Dworetsky. 1983. Variations in the distribution and biomass of submerged macrophytes in five coastal lagoons in Rhode Island, USA. Botanica Marina 26:231-242.

Tiner, R., H. Bergquist, T. Halavik, and A. MacLachlan. 2003. Eelgrass survey for Eastern Long Island Sound, Connecticut and New York. U.S. Fish and Wildlife Service, National Wetlands Inventory Program, Northeast Region, Hadley, MA. National Wetlands Inventory report. 14 pp plus appendix.

Tiner, R., H. Bergquist, T. Halavik, and A. MacLachlan. 2007. 2006 Eelgrass survey for Eastern Long Island Sound, Connecticut and New York. U.S. Fish and Wildlife Service, National Wetlands Inventory Program, Northeast Region, Hadley, MA. National Wetlands Inventory report. 24 pp plus appendix.

Links

About This Guide

This guide was authored by: Shereen Brock

Information for this guide was last updated on: May 3, 2019

Please cite this page as:
New York Natural Heritage Program. 2019. Online Conservation Guide for Marine eelgrass meadow. Available from: https://guides.nynhp.org/marine-eelgrass-meadow/. Accessed September 23, 2019.

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