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).
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.
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).
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).
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).
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).
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).
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.
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).
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.
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).
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.
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).
Known examples of this community have been found at elevations between -12 feet and -2 feet.
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.
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.
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.
Zostera marina (eel-grass)
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%.
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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.