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Rhode Island's Coastal HabitatsSeagrass - Salt Marsh - Anadromous Fish Habitat SeagrassHistory and Impacts | Healthy vs. Degraded | Eelgrass Restoration | Case Study | Related Links
Rhode Island's primary seagrass is eelgrass. Eelgrass provides many ecologically valuable functions. It produces organic material that becomes part of the marine food web; helps cycle nutrients; stabilizes marine sediments; and provides important habitat. Many species of fish and wildlife depend on eelgrass. Eelgrass beds provide protection for bay scallops, quahogs, blue crabs and lobsters. Tautog and other fish lay their eggs on the surface of eelgrass leaves, and young starfish, snails, mussels, and other creatures attach themselves to the plant. Waterfowl such as brant feed on eelgrass. Studies in New England have documented the occurrence of 40 species of fish and 9 species of invertebrates in eelgrass beds. As new growth replaces older eelgrass leaves, the dead leaves decay, becoming a valuable source of organic matter for microorganisms at the base of the food chain (NOAA Damage Assessment and Restoration Program, 2001). Eelgrass reduces shoreline erosion caused by storms and wave energetics thus protecting adjacent coastal properties. Eelgrass meadows can stabilize sediments and filter nutrients from the water column. Eelgrass also provides a unique habitat for recreational SCUBA divers and snorklers to explore (Chesapeake Bay Program, 2000). History and ImpactsEelgrass was widespread in Narragansett Bay as late as the 1860s. Historical accounts record eelgrass beds in the lower Providence River, at the head of the Bay. During the 1930s wasting disease, a widespread infection partly attributed to the slime mold Labryinthula zosterae decimated Atlantic coast eelgrass populations (Short et al. 1987, 1988). Some recovery was documented up until the 1960's. Since 1960, there has been a 40% decline in Narragansett Bay's eelgrass beds. Approximately 100 acres of eelgrass remain in Narragansett Bay today (Save The Bay 2002). Nine coastal ponds located along Rhode Island's South Shore are managed by the CRMC through a Special Area Management Plan (SAMP). The ponds were historically maintained as brackish systems through natural, seasonal breaches in the barrier beaches, which separate them from the open ocean. Permanent breachways were constructed at 5 of the 9 ponds (Point Judith, Ninigret, Winnapaug, Quonochontaug and Green Hill) during the 1950s and early 1960s. Construction of the permanent breaches has resulted in significant changes to the ecology of the ponds. Salinity has increased changing the ponds from a fresh/seasonally brackish system dominated by widgeon grass (Ruppia maritima) to a marine system dominated by eelgrass. Faunal changes have accompanied the changes in the submerged aquatic vegetation community and salinity regime. Sedimentation has increased as a result of the permanent breachways. Flood tidal shoals are expanding within the ponds, encroaching upon eelgrass and shellfish bed habitat. Attempts to dredge the tidal shoals have only been partly successful in reducing the rate of encroachment upon the existing eelgrass beds (USACE-NED 2002). Seagrass beds are susceptible to an array of human-induced degradations. Dredge and fill operations associated with navigation channel maintenance have taken a significant toll. Deterioration of water quality conditions (increased turbidity, increased nutrient concentrations) associated with human population density in coastal areas remains a primary cause of seagrass bed degradation. Increases in surface water nutrient loads result in phytoplankton blooms and excessive growth of macroalgae, which shades eelgrass beds, and inhibits plant growth and colonization. Physical damage to seagrass beds may result from recreational and commercial propellers in shallow waters. Residential dock structures often shade eelgrass beds in nearshore areas. Healthy vs. Degraded Eelgrass Habitats Eelgrass can form large meadows or small separate beds, which range in size from many acres to just a yard across. Found in depths up to 20 feet in some areas, eelgrass growth and survival is dependent on clear water to provide light for photosynthesis. Eelgrass beds are susceptible to destruction and degradation by increased turbidity, increased nutrient loading from urban runoff, and destruction by boat propellers or invasive predators (Save the Sound, Inc., 1998). The most significant threats to the remaining eelgrass beds in Narragansett Bay, and a deterrent to their long-term recovery, are nutrient pollution from sewage and polluted runoff from the land. Specific sources of these nutrients are septic systems, fertilizer runoff from lawns, and wastewater treatment plant discharges. Declining water quality also increases the opportunity for wasting disease, which is caused by a marine slime mold that thins eelgrass beds and makes them more vulnerable to environmental stresses. The chronic presence of wasting disease has been tied to increases in water temperature and salinity.
The first attempts to restore eelgrass in Rhode Island were undertaken in 1996 by the Narragansett Bay Estuary Program. Since that time, a number of organizations have undertaken seagrass restoration projects in Rhode Island waters, using a variety of restoration techniques. Seagrass restoration is complicated by the fact that seagrass beds are extremely sensitive to water quality. Most coastal ecologists agree that declines in water quality have been largely responsible for the loss of seagrass. Therefore, many areas that once supported seagrass beds are unsuitable for restoration. Some practitioners argue that seagrass restoration efforts should focus exclusively on water quality improvement, in the belief that once the right conditions are established, seagrass will naturally recolonize. Many others believe that in areas where water quality is improving, physical restoration of seagrass through transplantation or seeding can accelerate the plant's re-establishment. Additionally, seagrass restoration is threatened by physical damage of restored eelgrass beds through dredging, aquaculture, and propeller scarring. In developing eelgrass restoration projects, site selection is critical. Water clarity, depth, and salinity are among the most important factors determining where eelgrass can survive, since the plants need sufficient light in order to photosynthesize. This is why eelgrass mainly occurs in the well-flushed areas of lower Narragansett Bay, where the maximum depth at which it grows is generally about 15 feet.
Eelgrass restoration methods to date have focused primarily on transplantation of either small clusters of plants or denser, sod-like sections. The transplants may be grown in aquaria or taken from healthy donor beds. In Narragansett Bay, Save The Bay is restoring eelgrass using the Transplanting Eelgrass Remotely with Frames (TERF) method, in which clusters of plants are temporarily tied with degradable crepe paper to a weighted frame of wire mesh. Once the plants have become established, the frame is taken off the bottom for re-use elsewhere. Transplantation has met with some success, but is extremely labor intensive, as it requires divers to plant the eelgrass by hand. Researchers at the University of Rhode Island Graduate School of Oceanography are experimenting with sowing eelgrass seeds mechanically. This method is being used at McAllister Point, off Newport, in the restoration of a coastal hazardous waste site, and will also be employed in south shore coastal ponds as part of the South Shore Ecosystem Restoration. For more details on seagrass restoration techniques, please refer to the Restoration Methods section of this Web site. Eelgrass Restoration Case Study: Wickford Harbor
To restore eelgrass beds in historic Wickford Harbor, Rhode Island, a public-private partnership has been developed to improve water quality and to re-plant eelgrass. The University of Rhode Island (URI) is using computer modeling and digital mapping to find the nutrient pollution problems within the harbor's watershed. Save The Bay and the Town of North Kingstown are working with URI to develop water quality solutions through better management and treatment of waste and storm water. As its water quality improves, Wickford Harbor will become more hospitable to eelgrass, allowing existing beds to expand. To accelerate this process, the project is directly restoring eelgrass to the harbor through transplanting. Save The Bay has developed an innovative program to involve school children in this effort. Through its "Seagrasses in Classes" program, Save The Bay teaches the kids about the plant, and helps them to propagate it in classroom tanks. Volunteer divers then transplant the new shoots of eelgrass into the harbor bottom in hopes of establishing a new bed. The project builds on the experience of earlier transplants by the Narragansett Bay Estuary Program, the National Marine Fisheries Service, and URI. Save The Bay is applying the knowledge gained from the Wickford Harbor project to eelgrass transplants in other areas of Narragansett Bay.
ReferencesChesapeake Bay Program. 2000. (http://www.chesapeakebay.net/baygras.htm). Annapolis, Maryland. NOAA Restoration Center. 2001. NOAA Restoration Center Web site: Are restored habitats as productive as the previously unperturbed habitats were? (http://www.nmfs.noaa.gov/habitat/restoration). Save The Bay. 2002. Restoration projects throughout the Narragansett Bay watershed. (http://www.savebay.org/bayissues/restoreprojects.htm). Save The Bay, Inc., People for Narragansett Bay. 2001. Save The Bay Web site: What is Habitat Restoration? (http://www.savebay.org/). Save the Sound, Inc. 1998. "The Long Island Sound Conservation Blueprint: Building the Case for Habitat Restoration In and Around the Sound." Stamford, CT. Save the Sound, Inc. Short, F.T., L.K. Muehlstein, and D. Porter. 1987. Eelgrass wasting disease: Cause and recurrence of a marine epidemic. Biological Bulletin 173:557-62. Short, F.T., B.W. Ibelings, and C. Den Hartog. 1988. Comparison of a current eelgrass disease to the wasting disease of the 1930's. Aquatic Botany 30:295-304. USACE-NED. 2002. Rhode Island South Shore Habitat Restoration Feasibility Report and Environmental Assessment (Draft). U.S. Army Corps of Engineers, New England District.
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