Seagrass - Salt
Marsh - Anadromous
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
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.
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
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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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,
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.
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
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
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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