Rhode Island Habitat Restoration Strategy: Seagrasses

 

   SEAGRASS

    Worldwide, estuaries are experiencing water quality problems with an accompanying reduction in seagrass habitat (Den Hartog and Polderman 1975, Giensen et al. 1990, Walker and McComb 1992). Highly valued as a refuge, nursery ground, and food resource for a number of commercially important fin and shellfish (Thayer et al. 1984, Kenworthy et al. 1988, Orth and Van Montfrans 1987), seagrasses also stabilize sediments by buffering the erosive force of waves and currents (Fonseca and Cahalan. 1992, Worcester 1995). In many locations along the east coast (USA), seagrass coverage has declined by fifty percent or more since the 1970’s (Thayer et al. 1975, Orth and Moore 1983, Costa 1988, Dennison et al. 1993, Short et al. 1993, Short et al. 1996, Short and Burdick 1996). Loss of seagrasses is attributed to reduced water quality and clarity resulting from elevated inputs of nutrients or other pollutants such as suspended solids and disturbances such as dredging (Kemp et al. 1983, Kenworthy and Haunert 1991, Short et al. 1996, Short and Burdick 1996).

Because of the widely recognized importance of seagrass habitat, significant resources are now being expended to restore seagrass beds in relatively non-impacted areas or to recreate beds in systems where pollution inputs have been reduced. There is evidence that eelgrass was historically much more abundant in Narragansett Bay than it is at present (Kopp et al. 1995), and there is reason to believe that the loss was due to nutrient enrichment (Nixon 1997). However, nutrient inputs to the bay have diminished during the recent past as a result of at least two developments: (i) Fields Point Sewage Treatment Plant servicing the city of Providence has been upgraded to include secondary treatment and its management has been markedly improved, and (ii) various management policies reducing nutrient runoff from watersheds which drain into the bay have been implemented. Recent policy changes in Rhode Island to upgrade effluent treatment facilities such as going from secondary to tertiary treatment and the capture and treatment of rain water in Providence will further reduce nutrient inputs to Narragansett Bay. The ensuing improvement in water quality and clarity presents an unprecedented opportunity for seagrass restoration in areas of the bay where eelgrass, Zostera marina L once flourished. 

 

Goals and Objectives

            As the wastewater treatment plant upgrades take effect, water quality improvements can be expected in Narragansett Bay. Improved water quality can result in an expansion of potential transplant sites to areas further north in the Bay. The goal is to improve water quality, particularly in the upper bay, to the extent that a large-scale restoration effort can be successfully conducted in Greenwich Bay and other mid- and upper-bay areas.   

           

Status, Trends, and Opportunities

Status

Eelgrass restoration primarily began in Rhode Island in 1996. Many of the initial projects were funded with mitigation settlement funds from the World Prodigy oil spill. At this time a number of people from the University of Rhode Island, RI DEM, Narragansett Bay Estuary Program, Save The Bay, and NOAA embarked on projects to investigate various methods of eelgrass restoration.   A complete summary of these projects is listed on the RI Habitat Restoration Portal website http://www.edc.uri.edu/restoration/.

In 2001, URI received funding from CICEET (Cooperative Institute for Coastal and Estuarine Environmental Technology) to investigate the use of seed-based techniques for eelgrass restoration. Seeds offer some distinct advantages over the use of whole plants such as being less detrimental to the donor site, easier to transport, easier to collect - collection of millions of seeds can be done with minimal investment of time and labor, and increased genetic diversity of the restored site.   With CICEET funding URI conducted experiments in eelgrass seeding density, germination, planting depth, and seedling survival. The results of these initial experiments were used to guide the development of a mechanized eelgrass seeding machine. This patented seeding machine uses a specialized pump to transfer a seed/gel mixture from the boat to a sled that rides on the sediment surface. Steel tines attached to the sled open furrows and the seed/gel mixture is pumped into the furrow through stainless steel injection needles. The preliminary results from early spring germination counts were promising. However, predation in late spring caused large losses of seedlings by the summer. These losses resulted in the failure of the seeded restoration sites.

            In 2001, Save The Bay used a site selection model adopted from Short et. al , and conducted 19 test transplants throughout Narragansett Bay to identify suitable transplant sites. In 2002 the USDA Natural Resources Conservation Service (NRCS) began funding Save The Bay to conduct large-scale restoration projects around Narragansett Bay. The restoration sites were based upon the findings of the site selection model and the results of the test transplants. Save The Bay has conducted large-scale restoration efforts at 6 sites since 2002, including Poplar Point and Sauga Point in North Kingstown, Prudence Island, Coggeshall Point, and Hog Island in Portsmouth, and Fogland Point in Tiverton. Table 1 summarizes the large-scale restoration activities at each of these sites from 2002 to present. In addition to large scale sites, Save The Bay has also conducted small scale test transplants throughout the bay since 2001. Table 2 through Table 6 illustrate percent survival and shoot densities of the transplant sites from 2001-2008. Save The Bay also conducted monitoring of transplants and natural beds with funding from National Marine Fisheries Service Community-Based Restoration Center Partnership with Restore America’s Estuaries (NOAA-RAE) . Monitoring projects have included a benthic fauna study, a growth tagging study, a biomass study, and SeagrassNet monitoring. SeagrassNet is a global monitoring program that tracks and documents the status of seagrass resources as well as threats to this important habitat. 

            In 2003 URIGSO received funding from the USEPA to develop the first eelgrass mariculture facility. This facility was the first in the nation to begin raising a large number of eelgrass plants from seed to be used for restoration. The eelgrass mariculture facility was developed to be an alternative to whole plant transplanting. This facility was composed of 4 saltwater tanks, three 13 m3 (4600 gal) tanks and one 45 m3 (12,000 gal) tank, holding 40, 0.9 m x 1.2m (3 ft x 4 ft), sediment trays seeded with approximately 1,800 seeds each.  During the first year of raising seedlings the facility produced 27,000 eelgrass plants which were transplanted in August 2004. The mariculture-raised seedlings had a similar survival rate as adult shoots transplanted from donor beds over the first winter. In the second year, the facility produced 12,000 plants for eelgrass restoration in 2005. In 2006, URIGSO grew approximately 29,000 shoots from seed that were planted in conjunction with Save The Bay.  Funding for the mariculture facility was depleted in 2006 and is currently not being used for large-scale restoration. Save The Bay discontinued use of mariculture grown eelgrass after 2006 for this reason. The seed grown transplants still remain at the Prudence Island and Coggeshall Point sites. However, these seed grown shoots do not appear to be expanding as quickly as the natural bed harvested whole plants.

 

Trends

           

Narragansett Bay

Seven years of large scale transplants in the Bay have not provided any predictable trends with regards to survival. Survival rates have varied from site to site and from year to year (Figure 1). One of the most successful sites in 2002, Fogland Point in Tiverton, failed the following year, and by 2004 no planted eelgrass remained at the site. It is possible that some of the plants were lost to ice scouring from a very cold 2003/2004 winter; however, the 2004 transplant had high epiphyte cover and low survival. As a result, this site is no longer used for large-scale transplants. The site at Sauga Point had the highest survival in 2004 at 68%.. Monitoring efforts in 2006 indicated a significant portion of that transplant was lost due to crab predation during a summer heat wave. Data from 2005 to 2007 showed high crab densities in this area. Monitoring efforts in 2007 found most of the transplants at Sauga had been lost. This included the majority of the 2003 and 2004 transplants, which had previously been expanding over the previous few growing seasons. Monitoring in 2008 found the entire 2007 transplant failed to survive into the next growing season. Only a few small isolated plots from 2004 remain at this location. As a result, Sauga Point has been eliminated as a transplant site.       

 

The transplant site on the west side of Prudence Island has been fairly consistent since 2002. Survival rates tend to range from 50 to 60 percent each year. All the transplant years have survived and continue to expand with the exception of the 2003 transplant. Coggeshall Point in Portsmouth is another site that is rapidly expanding and continues to do well. Transplanting began here in 2005 and monitoring has shown consistent survival rates ranging from 60 to 80 percent. Hog Island is the newest transplant site, beginning in 2007. Survival rates for Hog are the highest of the three remaining sites, ranging between 65 and 80 percent . Save The Bay monitors each transplant site for five years.

 

It is difficult to fully understand why a transplant does well one year and not the next, though water quality is believed to be a large factor. During the 2003 field season, water quality in the Bay was very poor. There was low dissolved oxygen in a number of areas in the Bay which led to a fish and clam kill in Greenwich Bay. It is likely that these water quality issues were the cause of poor survival rates for the 2003 transplants. Fish kills occurred again in 2008 in Wickford Harbor, less than a mile southwest of Sauga Point and at other sites in Narragansett Bay. Monitoring in 2008 of the 2007 Sauga transplant found little to no surviving eelgrass. This suggests that water quality issues may have caused the 2007 transplant to fail. During the spring of 2009, the Bay experienced 26 days of rain out of 30. The Prudence Island transplants that took place at this time had dramatically reduced percent survival rates of  37% , while the Hog Island spring transplants had their most successful survival rate of 76%. Increased turbidity in the water column caused by the daily addition of fresh water may have affected the deeper Prudence transplant by reducing light penetration, but had no negative affect on the Hog Island transplants. 

 

Salt Ponds

The South Coast Habitat Restoration Project was initiated in 1997. The project goals were to restore 57 acres of eelgrass in the three largest coastal ponds, Ninigret, Quonochontaug and Winnapaug in Charlestown and Westerly. Studies show a marked acceleration in delta growth since the construction of the Charlestown Breachway. As the delta expanded into the pond, the formerly lush eelgrass beds that covered the pond bottom were buried under rapidly accumulating sand deposits. Breachways were constructed into Winnapaug and Quonochontaug Ponds in the mid 1950s and early 1960s with the same results. After an eelgrass restoration site selection study was completed in Ninigret Pond, a first phase of dredging was completed in 2005 to remove sand that formerly buried eelgrass. Once proper elevations had been reestablished, seeding occurred in 2006. Hand transplanting was planned following the second phase of dredging in 2007, but eelgrass reestablished very quickly and was deemed not necessary. 

 

In 2008, Save the Bay collaborated with The Nature Conservancy to hand plant 10,000 shoots each  in Quonochontaug Pond and Ninigrit Pond. Test plots were planted in both ponds in the spring of 2008, but only the Quonochontaug test plots showed adequate survival. A transplant of 10,000 shoots was completed in 2008 in Quonochontaug Pond. Monitoring of the Quonochontaug transplant in 2009 showed a 76% reduction in transplant density. There are no additional eelgrass transplants planned in either pond at this time.     

 

Restoration Techniques and Lessons Learned

Whole-Plant Restoration Techniques

Seagrass restoration techniques fall into two categories, whole plant transplants and seeding. Currently, whole plant transplantation is the most commonly used eelgrass restoration method in Rhode Island. With this technique, adult shoots harvested from existing healthy beds are transplanted to restoration sites. The harvested plants are anchored in place at the new site until they have firmly rooted. The whole-plant restoration techniques used in Narragansett Bay include the TERF© method and anchored individual plants, or hand planting.

TERFs©:  Dr Fred Short at the University of New Hampshire developed a method of tying eelgrass plants to a weighted frame called TERFs© (Transplanting Eelgrass Remotely with Frames). The plants are attached to the frame with a biodegradable paper tie and then dropped from a boat or placed by a snorkler in the water. The weighted frame holds the plants in place until they have firmly rooted in the bottom. The frames are retrieved 3-5 weeks after placement and can be used again. This method does help to reduce some of the costs and logistics of using divers and is very good for smaller, educational restoration projects. However, TERF© based projects become very difficult on large scales. The large numbers of frames required for a major restoration makes this process very labor intensive and requires the use of a large vessel to transport the frames to and from the restoration sites. During TERF© transplants in Narragansett Bay in 2002-2003, significant difficulties arose with the paper ties not biodegrading quickly enough. This resulted in large numbers (30-50%) of the eelgrass shoots being pulled up when the frames were recovered. Divers were then needed to replant the uprooted shoots, making retrieval more difficult.

Anchored individual plants: Currently, the most widely used method of restoration in Rhode Island is conducted using whole plants which are planted by divers and are anchored in place by a bamboo skewer bent in to a U-shape. Divers collect shoots from natural beds and then bundle the shoots into groups of 50. Each bundle of 50 shoots is transplanted into a 50 cm x 50 cm square quadrat. Because of the nature of how these plants grow, many of the plants are joined together by a complex system of rhizomes. Every effort is made to keep this system of rhizomes intact for planting. This allows for better rooting of the plants and fewer stakes are required.  

Seed-based Restoration Techniques

            Eelgrass is a marine angiosperm that produces flowering shoots annually. Each flower will first attempt to cross pollinate with pollen from a neighboring plant, if this does not occur it will self pollinate. This ensures that the majority of flowering shoots will produce viable seed. Once a flowering plant has released its seeds, the shoot senesces and dies. Eelgrass seeds can offer an alternative to adult shoot transplantation and have some advantages over whole plant transplanting. One advantage of seeds is that harvesting is less detrimental to the donor bed, since only flowering shoots need to be collected from natural beds. Primarily eelgrass bed maintenance is conducted through clonal reproduction where the mother plant drops off genetically identical daughter shoots; eelgrass seeds are primarily used to recolonize large gaps in the bed or to establish in new areas. For these reasons, the removal of the flowering shoots has very little effect on the survival of the donor bed. Another advantage of seeds is that through cross pollination they have increased genetic diversity. Collecting seeds from many different donor sites, then, will result in a restored bed with increased genetic diversity. This will aid in the longevity of the bed. 

Mechanical delivery: This technique involves the use of a machine to mechanically deliver the seed into the sediment. This method reduces the potential for seed predation or resuspension while planting. Through mechanical seeding it is also possible to control the planting depth and density which optimizes germination.   See the above project summary section for more details on the mechanical delivery method used in Rhode Island.

Mariculture: Eelgrass seeds are collected from donor beds and planted in seawater tanks. The seeds germinate and mature in the controlled seawater environment. Once mature the plants are harvested and transplanted to the restoration site using any of the whole plant transplant methods described above. This is the most labor intensive of all the seeding techniques but has some very promising results. This method combines the advantages associated with seeding such as reduced impacts to the donor beds and increased genetic diversity, along with the increased success seen with whole plant transplantation.  See the above project summary section for more details on the mariculture facility in Rhode Island.

Other Potential Restoration Techniques

There are a number of other restoration techniques that have been used in U.S. estuaries including Puget Sound, Biscayne Bay, Long Island Sound, and Chesapeake Bay.  Below are some additional techniques for restoring eelgrass that have not been successfully used in Rhode Island.

Mats: The method for anchoring shoots has varied through the years. Early projects were successful moving large mats of eelgrass plants that kept the sediment and roots intact as they were transported and planted at the new site. This gave the plants an early advantage because of increased nutrients and organics incorporated in the sediments. However, this technique is laborious as the heavy mats were difficult to collect and transport.

Planting Units: More recent methods involve tying between 2-5 shoots to a metal or wooden stake creating a planting unit. The planting units are placed with regular spacing by SCUBA divers. This technique has been relatively successful and can be done at a much larger scale than that of the eelgrass mats. However, this technique is very labor intensive to sort and tie each planting unit and extensive diver time is required to conduct the actual planting. 

Hand-cast: Flowering plants are collected by divers or snorklers and the seeds are extracted. In the fall, the collected seeds are then cast either from a boat or by a diver on the restoration site. The seeds will move around on the sediment for usually up to 1 meter until they find a small depression. Once in the depression, natural processes bury the seed.   The seed will germinate over the course of the winter and spring. This technique has shown great promise in the Chesapeake Bay area and requires the least amount of effort to complete. However, to date hand casting of seeds has produced very low germination in Narragansett Bay. Because of the low germination, other methods of seed delivery have been investigated for Rhode Island.

Moored bags: With this method, flowering shoots collected by divers are stuffed into mesh bags. These bags are hung from buoys and moored at the restoration site. As the seeds mature they are released and drop to the bottom under the bag. This seeds a circular area around the moored bag. This method was developed by Chris Pickerell of the Peconic Bay National Estuarine Research Reserve. To date this method has not been tested in Narragansett Bay.

Lessons Learned

Site selection is the most critical component of any eelgrass restoration project. The first site suitability model was created to select initial eelgrass restoration sites. This early model incorporated a single set of light measurements, wave exposure, and an historical analysis of eelgrass locations (Kopp et al. 1995). In 2001 this model was updated to be similar to a GIS based site selection model developed by Fred Short for New Hampshire restoration. This newer model has two parts, a preliminary transplant suitability index and a test transplant suitability index. The first incorporates a series of physical and environmental parameters in a GIS database to screen areas of potential eelgrass restoration success. The later part involves conducting small scale (200-250 shoots) test plantings. The test transplants are monitored for success through one growing season. Those sites that show good overall success, preferably over two growing seasons, are then selected for large scale restoration projects (Lipsky 2002).

 

            There has been a lot of change in eelgrass restoration techniques since 1996. Most importantly, the site selection process has been refined. This is one of the most critical steps in large-scale restoration projects. The current GIS based model and method of test transplanting have increased the large-scale success rate from less than 25% survival to better than 75% survival. The efficiency of planting has gone up steadily and is now beginning to level off. It is becoming evident that whole plant transplants are currently the best restoration technique for restoration projects in Rhode Island. This is due primarily to the effects of predation on small seedlings. Transplant survival averages around 50% and can greatly vary with transplant years and locations. Spacing techniques for the 0.25m2 transplant plots have also changed. Plots were once placed along transect lines 5 m apart; however, results have shown that the transplants are much less vulnerable when spaced closer together, particularly at higher energy sites. The current transplant protocol involves planting twenty-four 0.25 m2 plots in a close checkerboard pattern. This spacing technique has improved planting efficiency, diver safety, and monitoring efforts.

 

Recommended Next Steps     

           

            The GIS based site selection model created in 2001 is in need of updating. Of primary importance is the updating of the bathymetry and the sediment data for Narragansett Bay. Much of the bathymetry data for the Bay dates back to the 1960s and earlier and has very limited coverage around shallower shoreline areas. Since the bathymetry is a critical layer in the mode it is very important to have the most recent and accurate data in use.    In addition, it would be a useful tool to have a map of all sites where test plots and large-scale transplants have occurred since 2001 along with the survival data for each year. Save The Bay has set up a master spreadsheet with all the available data. The next step would be incorporating this data into GIS. 

            One of the largest unexplored areas in SAV restoration in Narragansett Bay is the combination of shellfish aquaculture and eelgrass planting. Studies show the beneficial effects of shellfish filtration on water column clarity. The increased clarity translates to more light being received by the transplanted plants and the increased growth rates. The Nature Conservancy’s shellfish and eelgrass restoration project tested this technique in Quonochontaug Pond in 2008 and results are being analyzed.

Regular monitoring of natural eelgrass beds is necessary to monitor the health of this habitat in Narragansett Bay. Currently, the state of Rhode Island does not have a comprehensive plan for monitoring this habitat. Routine monitoring and mapping of Rhode Island’s seagrass habitat will be essential for coastal managers and researchers by making it possible to follow trends in health and aerial extent of the local populations. In order to assess trends in the overall gain or loss of eelgrass, it is necessary to repeat aerial mapping on a regular basis. It would be most useful for Rhode Island to conduct an eelgrass habitat mapping every five years to document large-scale changes (losses or gains) in eelgrass habitat, in accordance with NOAA Coastal Change Analysis Protocol (C-CAP). The most recent mapping effort occurred in August 2006 and groundtruthing was completed in 2007. The final report with updated maps was completed in early 2008, and the report is available at  http://www.savebay.info/Eelgrass_MappingReport.pdf

            Annual field monitoring of seagrass could be used to document the year to year variability in the existing populations. Trends in this data such as loss of biomass or a shallowing of the deep water edge can be an early indicator of ecosystem trouble. Yearly monitoring, compatible with the internationally accepted SeagrassNet protocol (Short, McKenzie et al. 2004), will make it possible to assess the overall health of our existing SAV beds. With funding from NOAA-RAE, Save The Bay has begun monitoring natural beds in Jamestown and at the south end of Prudence Island under SeagrassNet protocols; however, regular future funding must be secured for long-term monitoring.

            Most importantly, continued efforts to improve water quality are essential for a successful eelgrass restoration program. Efforts to reduce nitrogen inputs in the bay must continue to ensure eelgrass recovery in Narragansett Bay. As of 2009, most wastewater treatment plants in the upper Bay have been upgraded, and several more are on track for implementing upgrades. The treatment plants of Cranston, Warwick, West Warwick, and East Greenwich have all implemented biological nitrogen reduction strategies. However, water quality in Greenwich Bay remains poor. Water quality is expected to improve with upgrades at Fields Point and Bucklin facilities, estimated to be online by 2013. The major barrier left to improved water quality in the upper Bay remains the wastewater treatment plant in Worcester. The plant is appealing an EPA permit to reduce nitrogen, and resolution of the situation is a long way off.  Small scale test transplants will occur each year to monitor changes in water and habitat quality due to upgrades in wastewater treatment and to assess the potential for large scale restoration in mid to upper bay locations.

 

Resources Needed

            Natural Resources Conservation Service’s Wildlife Incentive Program (WHIP) has been the largest funder of eelgrass restoration in Narragansett Bay, however with the new language of the 2008 Farm Bill, this source of funding for eelgrass restoration is no longer available. Eelgrass restoration has also received funding from additional federal and state programs listed below. These may be potential sources to look to for future funding as well.

Funders of Eelgrass restoration included:

RI Aquafund                                       Site Suitability Study 2000-2001

CICEET                                              URI mechanical seeding 2001

NOAA-RAE Partnership                  STB Restoration 2002/monitoring projects 2003-present

NRCS (WHIP)                                   STB restoration efforts 2003-present

USEPA                                              URI mariculture facility 2003

NOAA                                                 NBNERR Aerial imagery analysis 2005

RI Habitat Trust Fund                                    Aerial overflight data collection 2005

            In addition to funding needs, large-scale restoration efforts are very labor intensive. Currently Save The Bay uses over 200 volunteers each season to conduct large-scale restoration efforts. A substantial volunteer base makes it possible to transplant on a larger-scale while educating the public on the importance of eelgrass habitat.

 

References cited

Costa, J. 1988. Distribution, production and historical changes in the abundance of eelgrass (Zostera marina L.) in southeastern Massachusetts. PhD. dissertation. Boston University, Boston Massachusetts.

Den Hartog, C. and P.J.G. Polderman. 1975. Changes in seagrass populations of the Dutch Waddenzee. Aquatic Botany 1:141-147.

Dennison, W.C., R.J. Orth, K.A. Moore, J.C. Stevenson, V. Carter, P.W. Kollar, P.W. Bergstrom, and R.A. Batiuk. 1993. Assessing water quality with submersed aquatic vegetation. BioSience 143:86-94.

Fonseca, M.S. and J.A.  Cahalan. 1992. A preliminary evaluation of wave attenuation by four species of seagrass. Estuar. Coast. Shelf Sci. 35:565-576.

Giesen, W.B., M.M. Van Katwijk, and C.Den Hartog. 1990. Eelgrass condition and turbidity in the Dutch Wadden Sea. Aquat. Bot. 37: 71-85.

Kemp W.M., W.R. Boynton, J.C. Stevenson, R.R. Twilley, and J.C. Means. 1983. The decline of submerged vascular plants in upper Chesapeake Bay: Summary of results concerning possible causes. Marine Technology Society Journal 17:78-89.

Kenworthy, W.J. and D.E. Haunert (eds.). 1991. The light requirements for seagrasses: proceedings from a workshop to examine the capability of water quality criteria, standards and monitoring programs to protect seagrasses. NOAA Technical Memorandum NMFS-SER C-287.

Kenworthy, W.J., G.W. Thayer, and M.S. Fonseca. 1988. The utilization of seagrass meadows by fishery organisms. In D.D. Hook et al.(eds.), The Ecology of Wetlands, pp. 548-560.

Kopp, B., A.M. Doherty, and S.W. Nixon. 1995. A guide to site-selection for eelgrass restoration projects in Narragansett Bay, Rhode Island. Final report submitted to the Rhode Island Aqua Fund Program of the R.I Department of Environmental Management, Division of Water Resources, Providence, R.I.

Lipsky, A. 2002. Development of an Eelgrass Restoration Site Selection Model for Narragansett Bay. University of Rhode Island. unpublished.

Orth, R.J. and K.A. Moore. 1983. Chesapeake Bay: An unprecedented decline in submerged aquatic vegetation. Science 222:51-53.

Orth, R.J. and J. Van Montfrans. 1987. Utilization of a seagrass meadow and tidal creek by blue crabs Callinectes sapidus. I. Seasonal and annual variations in abundance with emphasis on post-settlement juveniles. Mar. Ecol. Prog. Ser. 41: 283-294.

Nixon, S.W. 1997. Prehistoric nutrient inputs and productivity in Narragansett Bay. Estuaries 20(2): 252-261.

Short, F.T. and D.M. Burdick. 1996. Quantifying eelgrass habitat loss in relation to housing development and nitrogen loading in Waquoit Bay, Massachusetts. Estuaries 19:730-739.

Short, F.T., D. Burdick, S. Granger, and S. Nixon. 1996. Long-term decline in eelgrass, Zostera marina L., linked to increased housing development. In: Seagrass Biology: Proceedings of an International Workshop. J. Kuo, R. Phillips, D. Walker, and H. Kirkman, eds. pp. 291-298.

Short, F.T., D.M. Burdick, J. Wolfe, and G.E. Jones. 1993. Eelgrass in estuarine research reserve along the East Coast, U.S.A., Part I: Declines from pollution and disease and Part II: Management of eelgrass meadows. NOAA- Coastal Oceans Program Publ. 107 pp.

Short, F. T., L. J. McKenzie, et al. 2004. SeagrassNet Manual for Scientific Monitoring of Seagrass Habitat- Western Pacific Edition. Durham, NH, University of New Hampshire.

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.

Thayer, G.W., D.A. Wolfe, and R.B. Williams. 1975. The impact of man on seagrass systems. Am Sci. 63:288-296.

Walker, D.I. and A.J. McComb. 1992. Seagrass degradation in Australian coastal waters. Mar. Poll. Bull. 25:191-195.

Worcester, S.E. 1995. Effects of eelgrass beds on advection and turbulent mixing in low current and low shoot density environments. Mar. Ecol. Prog. Ser. 126:223-232.