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Design Considerations

Seagrass - Salt Marsh - Anadromous Fish Habitat

Seagrass

Design considerations of particular importance for seagrass beds include transplant spacing, light attenuation, and patterns of current flow in the vicinity of the transplant site. Careful attention must be paid to the spacing of individual planting units in order to achieve site coalescence. Seagrass transplant projects conducted in the eastern Gulf of Mexico have achieved coalescence in as little as nine months or as long as three to four years, depending on planting distance between individual units. In high-energy areas, coalescence of beds may never fully occur. Separation of planting units by one half meter is ideal, but results in greater impacts to donor beds. Trade-offs between rapid transplant coalescence and impacts to donor beds must be considered on a project-specific basis.

Light availability is one of the most important determinants of eelgrass bed health. Generally, eelgrass requires 15 to 25 percent of the light available at the water's surface. Because of this, eelgrass rarely occurs at depths exceeding five meters. For the Rhode Island South Shore Habitat Restoration Study, various restoration alternatives were compared using a predictive model developed by Fred Short at the University of New Hampshire (UNH). The model requires inputs of baseline data such as light attenuation, turbidity, water temperature, and nutrient levels. The output from the model is the amount of eelgrass biomass that can be produced at various depths. The UNH model predicted optimum eelgrass growth at a depth of 0.75 to one meter (USACE-NED 2002).

An appropriate current regime is critical for eelgrass transplant success. If current velocities are high in the vicinity of the transplant site, transplant success will be poor, due to loss of transplant units, and coalescence may never occur. If current velocities are low, sedimentation may occur and suffocate the newly transplanted beds. A hydrodynamic model was developed by the U.S. Army Corps of Engineers New England District (USACE-NED) for the South Shore Habitat Restoration Study and used to predict the effects of sediment removal on tidal current velocity and direction, tidal elevation and sediment transport. Inputs to this model included detailed topographic and hydrographic surveys and measurement of water surface levels and current velocity throughout the tidal cycle (USACE-NED 2002).

Potential Obstacles to Restoration | Equipment Sources and Contacts

Potential Obstacles to Restoration
Seagrass restoration projects are subject to a variety of potential obstacles; however, many of these obstacles can be avoided or minimized through careful pre-project planning and post-construction monitoring.

Brant goose, a grazer of eelgrass.
Brant goose, a grazer of eelgrass.
Courtesy: E. Marks, Audubon Society of Rhode Island

Grazing by waterfowl is a potential problem in eelgrass restoration projects. Ducks and geese may eat newly transplanted shoots and leaves in restored eelgrass beds. Various types of nets and cages have been deployed in eelgrass transplant projects to protect the new transplants from direct grazing by waterfowl and other animals.

When eelgrass is newly transplanted, the shoots are highly susceptible to bioturbation effects, especially by green crabs (Carcinus maenus), an introduced species that has become abundant in New England waters in recent years. Caging may help minimize the presence of adult green crabs in the project areas; however, larvae and juvenile crabs are able to recruit into the beds. Careful attention to site selection, and monitoring crab density and the degree of disturbance are the best solutions to this potential problem.

There is a potential threat of direct physical damage of restored eelgrass beds from dredging, aquaculture, and propeller scarring from recreational and commercial vessels. Ideally, most of these threats would be eliminated or significantly reduced through proper planning, coordination, and site selection prior to conducting an eelgrass restoration project.

Public awareness is an important component of a comprehensive eelgrass restoration program in Rhode Island. According to a Bay Habitat Public Opinion Research Study conducted by Save The Bay in 1996, approximately 70 percent of Rhode Islanders do not know what eelgrass is. Save The Bay has developed several initiatives to promote eelgrass restoration among communities in Rhode Island.

Seagrass restoration projects in shallow coastal habitats can potentially conflict with historic and cultural resources, including Native American sites of significance. Rhode Island Coastal Resources Management Council (CRMC) coordinates with the Rhode Island Historical Preservation and Heritage Commission and with the Narragansett Indian Tribe, Tribal Historic Preservation Office in order to address potential conflicts. If conflicts arise, these agencies work with the applicant to resolve the issue.

Equipment Sources and Contacts
There are a variety of sources and professional contacts to assist restoration practitioners in gathering information and forming partnerships. Several comprehensive literature reviews and guidebooks are available from organizations involved in eelgrass restoration.

Local experts can be accessed at state environmental resource agencies and at academic research institutions. Many of these include the Coastal Resources Management Council, Save The Bay, and the University of Rhode Island. Contacts for these groups and others are available from this Web site.

Many companies specialize in the manufacture and sale of environmental monitoring equipment used in conducting baseline and monitoring studies of seagrass restoration projects. Equipment includes nets, water quality testing kits and dataloggers, and turbidity meters.

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References

Fonseca, M.S. 1994. A guide to transplanting seagrasses in the Gulf of Mexico. Texas A&M University Sea Grant College Program, TAMU-SG-94-601, College Station, Texas.

Fonseca, M.S., W.J. Kenworthy, D.R. Colby, K.A. Rittmaster, and G.W. Thayer. 1990. Comparisons of fauna among natural and transplanted eelgrass Zostera marina meadows: criteria for mitigation. Marine Ecology Progress Series 65:251-264.

Fonseca, M.S., W.J. Kenworthy, and G.W. Thayer. 1998. Guidelines for the conservation and restoration of seagrasses in the United States and adjacent waters. NOAA Coastal Ocean Program Decision Analysis Series No. 12. NOAA Coastal Ocean Office, Silver Spring, Maryland.

Hoffman, R.S. 1988. Fishery utilization of natural versus transplanted eelgrass beds in Mission Bay, San Diego, California. Proceedings of the California Eelgrass Symposium. Chula Vista, California. 58-64.

Homziak, J., M.S. Fonseca, and W.J. Kenworthy. 1982. Macrobenthic community structure in a transplanted eelgrass meadow. Marine Ecology Progress Series 9:211-21.

Moore, K.A. and R. J. Orth. 1982. Transplantation of Zostera marina L. into recently denuded areas. pp. 92-148 in: R.J. Orth and K.A. Moore, (Eds.), The Biology and Propogation of Zostera marina, eelgrass, in the Chesapeake Bay, Virginia. Special Report No. 265 in Applied Marine Science and Ocean Engineering, Virginia Institute of Marine Sciences, Gloucester Point,Virginia.

Orth, R.J., M. Luckenbach, and K.A. Moore. 1994. Seed dispersal in a marine macrophyte: implications for colonization and restoration. Ecology 75:1927-39.

Phillips, R.C. and R.R. Lewis, III. 1983. Influence of environmental gradients on variations in leaf widths and transplant success in North American seagrasses. Marine Technology Society Journal 17:59-68.

Smith, I., M.S. Fonseca, J.A. Rivera, and K.A. Rittmaster. 1989. Habitat value of natural versus recently transplanted eelgrass, Zostera marina, for the bay scallop, Argopecten irradians. Fishery Bulletin 87:189-96.

Thayer, G.W., S.M. Adams, and M.W. LaCroix. 1975. Structural and functional aspects of a recently established Zostera marina community. pp. 518-540 in: L.E. Cronin (Ed.) Estuarine Research. Academic Press, New York.

Thom, R.M. 1997. System-development matrix for adaptive management of coastal ecosystem restoration projects. Ecological Engineering 8:219-232.

Thom, R.M. 2000. Adaptive management of coastal ecosystem restoration projects. Ecological Engineering 15:365-372.

Thom, R.M. and K.F. Wellman. 1997. Planning aquatic ecosystem restoration monitoring programs. Evaluation of Environmental Investments Research Program. U.S. Army Corps of Engineers Institute for Water Resources, IWR Report 96-R-23, Alexandria, VA.

USACE-NED. 2002. Rhode Island South Shore Habitat Restoration Feasibility Report and Environmental Assessment (Draft). U.S. Army Corps of Engineers, New England District, Concord, Massachusetts.

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Project Partner web pages - RIHRT, CRMC, NBEP, STB

This site was created through a partnership of the:

Coastal Resources Management Council
Narragansett Bay Estuary Program
Save The Bay®