Eelgrass Restoration

Phase II: Restoring Eelgrass to the Neponset River Estuary

Ashley Bulseco-McKim

11/19/2012

ABSTRACT: This document reviews the history of eelgrass restoration, and distinguishes reasons for either successes or failures in past restoration efforts. By investigating case studies from the Great Bay Estuary, NH, Chesapeake Bay, MD, and Boston Harbor, MA, we may gain a better understanding of what aspects should be applied towards a successful management plan to restore eelgrass to the Neponset River Estuary.

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INTRODUCTION.

Eelgrass (Zostera marina L.) performs a number of ecosystem services that contribute to

a healthy estuary (Short et al. 2000), such as providing habitat for fish and invertebrates (Orth

1973; Thayer et al. 1984), maintaining food web structure (Thorhaug 1986), altering water flow

(Gambi et al. 1990), filtering and cycling nutrients, stabilizing sediments (Orth 1977), and

contributing to the detritus pool (Orth et al. 2006a). Unfortunately, eelgrass has faced decline

over the past several decades due to anthropogenic impacts (e.g. dredging, eutrophication,

coastal development) (Thorhaug 1986; Short & Burdick 1996) and wasting disease (slime mold,

Labrinthula zosterae: Rasmussen 1977; Short et al. 1987), and may soon face further decreases

in response to climate change (Orth et al. 2006a).

These losses in eelgrass habitat often lead to physical and biological changes to its

estuary, so large effort has been put forth to mitigate and reverse such declines. Various methods

of transplanting, including hand-planting, frames, and seeds, have been developed in attempt to

restore eelgrass habitats around the world, in addition to several monitoring techniques that

determine the success or failure of each restoration effort. Furthermore, recent restorations have

also included community-based restoration (Short et al. 2002b), and modeling (Short et al.

2002a). The purpose of this paper is therefore to (1) review the types of transplant techniques

utilized by these restoration attempts, (2) identify the aspects of each experiment that worked and

did not work, and (3) investigate case studies in the Great Bay Estuary, NH, Chesapeake Bay,

MD, and Boston Harbor, MA to hypothesize whether or not eelgrass restoration in the Neponset

River Estuary is plausible.

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TRANSPLANT TECHNIQUES:

Since the 1940’s, beginning with the efforts of Addy (1947), scientists have worked

towards the restoration of seagrass habitats. Presently, transplantation methods can be

categorized into three general groups: (1) hand-planting, consisting of cores/plugs, the bare-root

method, and the horizontal rhizome method; (2) frames, consisting of TERFSTM and more

generic PVC frame designs placed in a checkerboard pattern; and (3) seeds, consisting of hand,

buoy, and mechanical seed distribution (summarized in Table 1).

Hand-Planting. Hand-planting of eelgrass utilizes adult shoots from a donor site (or

reference site), and transplants it to a carefully chosen recipient (or experimental) site. Core/plug

hand-planting was historically the first successful transplantation technique (Kelly 1971), in

which a core of eelgrass shoots (with sediment and rhizomes intact) was extracted from the

donor site, and moved into excavated holes in the recipient site. Various materials have been

used to act as the core extractor, including PVC pipe (Phillips & McRoy 1980), small metal cans

(Kelly 1971), sod pluggers (Fonseca et al. 1996), and shovels (Addy 1947). Once “plugged” into

the recipient site, transplant shoots are anchored with cement plug collars or U-shaped staples to

resist loss due to turbulence (Thorhaug 1986). The fact that the entire root-rhizome-sediment

system remains intact makes the core/plug transplantation technique advantageous. The method

also transplants a small amount of the nutrient pool along with the sediments, to which the plant

may already be adapted. Furthermore, this technique can be completed year-round, weather

permitting, and does not rely on seasonal variation. Unfortunately, this method is highly

intrusive, with disadvantages outweighing the advantages. Excavation in the healthy donor site

creates holes that researchers must subsequently fill in; furthermore, in the interim, the site may

still be susceptible to erosion. As a result, the technique is labor intensive, and requires a large

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monetary committment. Lastly, the physical transport of large bunches of shoots and sediment is

difficult, making the method inefficient and time costly. Generally, the use of the core/plug

technique in the Neponset River Estuary is not recommended.

Another traditional method of hand-planting is called the bare-root method, which

involves removing seagrass along with a small length of rhizome (approximately 2-20cm) from

the donor site. The eelgrass may be kept as a single or gathered in bunches, and transplanted to

the recipient site, where they may or may not be anchored. In a study by Fonseca et al. (1982),

authors bundled shoots together in groups of 10 and anchored them down with 8-gauge metal U-

shaped sods. Other researchers have since developed less environmentally obtrusive anchors,

such as mesh fabric held down by pins (Homziak et al. 1982) and biodegradable bamboo shoot

staples (Davis & Short 1997; Leschen et al. 2010). The advantage of this method is that it is

much less damaging to the donor site, but it still requires that adult shoots be excavated. As a

result, it is a time intensive method, and usually calls for SCUBA divers to complete the process.

Using this technique may be appropriate for the Neponset River Estuary if it is done in

collaboration with other transplantation methodologies.

The last well-known hand-planting technique is called the horizontal-rhizome method as

adapted by Davis & Short (1997) in their attempt to restore eelgrass to the Great Bay Estuary in

New Hampshire. Similar to the bare-root method, the horizontal-rhizome method harvests adult

eelgrass shoots and anchors two at a time with a biodegradable staple, which is less expensive

and avoids hazard to human health. Their rhizomes are then aligned in a parallel fashion facing

opposite directions, and are pressed horizontally into the top two centimeters of the recipient

sediment. Each group of shoots is called a planting unit (PU), and is created in the field

immediately before deploying linearly, parallel to the shoreline – this eliminates the difficulty of

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intermediate preparation and degradation due to excessive handling. Subsequent studies have

adapted the horizontal-rhizome method by ignoring the use of anchors altogether. For instance,

Orth et al. (1999) simplified the technique by gently inserting the rhizome shoot into the

sediment at an angle to a depth of 25 to 50 mm. The resulting position of the plant is similar to

what occurs in natural eelgrass beds, where the rhizome is buried parallel relative to sediment

surface and the shoot is erect in the water column (Orth et al. 1999). The advantages of the

horizontal-rhizome method and its adaptations include less destruction to the donor site, more

environmentally friendly anchors (when used), and a method more representative of what may

occur in nature. Perhaps its biggest advancement is the use of 80% less donor shoots in Davis &

Short (1997) than in more widely used transplant techniques (Fonseca et al. 1982), and an even

further 50% decrease in donor shoots from Davis & Short (1997) (Orth et al. 1999), leading to

progressively more efficient transplantation techniques. In contrast, disadvantages again include

labor intensive work, high time commitment, and the requirement for SCUBA divers.

Additionally, in the event of an intense disturbance (e.g. extreme meteorological events) or high

levels of bioturbation, unanchored shoots would be uprooted. Overall, transplantation success

should be significantly higher if disturbances can be avoided within the first few weeks of

transplanting (Orth et al. 1999).

Frames. Frame transplantation is considered practical and fairly cost-effective. Because

they require repetitive material constructions, frames are also ideal for encouraging community

involvement. A common frame design in the northeastern United States is called the TERFSTM,

which stands for “Transplanting Eelgrass Remotely with Frame Systems” (Fig. 1; Short et al.

2002b). The TERFSTM method uses dissolving paper ties to attach 25 PU’s (pairs of eelgrass

shoots placed opposite of each other) to a weighted rubber-coated wire frame.

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Fig. 1. TERFSTM as designed by Short et al. 2002b, University of New Hampshire

One 60 cm x 60 cm frame holds 50 eelgrass shoots, totaling 200 shoots per m2 (Short et al.

2002b). Volunteers and scientists prepare the TERFSTM onshore, and frames are subsequently

placed on the seafloor by either wading in the water or leaning over the side of a small boat. It is

important that the eelgrass roots contact the sediment, and the leaf blades extend into the water

column, so that they have the highest probability of growing successfully. The bricks in the

TERFSTM design ensure that the eelgrass shoots stay in place, and the frame prevents

bioturbating organisms from disturbing the newly transplanted individuals. The TERFSTM are left

on the sediment surface at the recipient site for three to five weeks, which should allow for

enough time for the eelgrass shoots to sufficiently penetrate the sediment surface (timing

depends on the location – if the frames are removed too early, then the eelgrass shoots will not

remain securely in the sediment; however, if the frames are removed too late, then the shoots

may have grown around the frame and removal will lead to eelgrass damage).

A number of adaptations have been made to the TERFSTM design to adhere to site

specificity. Leschen et al. (2010) combined the TERFTM concept with a polyvinyl chloride

(PVC)/jute frame, in a recent restoration project in Boston Harbor, MA. The frames consisted of

0.25 m2 of PVC pipe with jute landscape mesh stretched over and held in place with cable ties.

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Eelgrass shoots were tied to the jute by volunteers, and galvanized spikes and bamboo staples

were used to hold the jute securely in the seafloor. After the eelgrass was rooted into the

sediment, the jute was cut away, and the PVC frames were collected for re-use (Leschen et al.

2010).

TERFSTM and PVC/jute frames are typically deployed in a checkerboard grid pattern,

accomplished by alternating planted and unplanted 0.25 m2 quadrats (Fig. 2; according to Save

the Bay in Rhode Island, Short et al. 2002b, Leschen et al. 2010).

Fig. 2. Planting pattern utilizing a checkboard grid of alternating planted (black) and unplanted (white) 0.25 m2

quadrats. Planted quadrats are typically 30-50 m apart (Leschen et al. 2010)

Quadrats are spaced 30 to 50 m apart, effectively covering more ground than continuous planting

of shoots alone. This method also allows for the possible growth of eelgrass by providing voids

between plots (Leschen et al. 2010).

The advantages of TERFSTM and PVC/jute frames are that they are simple, cost effective,

and can easily involve volunteers in the case of a community-based restoration project. They

also require less intensive labor from scientists, as SCUBA is not a pre-requisite for deploying

frames, and can be re-used once the frames are removed. However, experiments have found that

the success of these frames is highly site-specific. For example, although the TERFSTM design

worked well for Short et al. (2002b) in the Great Bay Estuary, its use attracted high numbers of

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bioturbators in Boston Harbor (Leschen et al. 2010), and thus had to be eliminated from the

study. The use of TERFSTM or PVC/jute frames will work well in the Neponset River Estuary, as

the restoration effort will likely be community-based, but again should be completed in addition

to another transplantation technique (e.g. seeds).

Seeds. One major disadvantage of the previously discussed transplantation methods is

that they all rely on the use of adult eelgrass shoots, which may lead to a possible loss in genetic

diversity when used to re-establish large populations (Williams et al. 2001). Preserving genetic

diversity is considered an important component of ecosystem restoration (Booy et al. 2000)

because genetically diverse assemblages may be fitter and more resistant to anthropogenic

disturbances (Williams 2001; Hughes & Stachowicz 2004, 2001) and climate change (Ehlers et

al. 2008). In a study spanning restoration efforts in the Chesapeake Bay, Virginia Bay, and

Chincoteague Bay, researchers found that by using a largely adequate number of seeds, both

donor beds and restoration sites had the same level of genetic diversity. This result indicated that

after reaching equilibrium, the restored eelgrass had the same capability as the reference site to

adapt to environmental forcing and various disturbances (Orth et al. 2012; Reynolds et al. 2012).

Therefore, transplantation via seed dispersal has become a common choice when looking to

restore eelgrass in highly disturbed estuaries.

Eelgrass reproduces sexually by producing seeds in addition to rhizome expansion.

Traditional seeding techniques began to take advantage of sexual reproduction through studies

by Addy (1947) and Lewis & Phillips (1980). Seeds are collected by taking reproductive shoots

from donor sites and are held in flowing seawater until the seeds ripen and drop from the leaves.

Large quantities of seed can be collected in this manner, and are then planted into the sediment

of the recipient site by SCUBA divers or are simply mass-broadcasted from a boat on the water’s

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surface (Thorhaug 1986; Leschen et al. 2010). However, this manual process is laborious and

often constrained due to spatio-temporal variability, so recent studies have investigated more

efficient methodologies to use seed in eelgrass restoration (Fishman et al. 2004).

One alternative to manual seed transplants has attempted to automate deployment by use

of a mechanized planter. In a study by Orth et al. (2009), a planter (Fig. 3) consisting of a benthic

Fig. 3. Mechanical planter used in Orth et al. (2009) consisting of a benthic sled (upper left), a seed hopper fitted with a peristaltic pump (upper right), a seed suspension gel made with Knox ® gelatin (bottom left), and injection

nozzles (bottom right)

sled fitted with a seed-gel mixture, a weighted pad, and a pump that mixed Knox® gelatin with

eelgrass seeds, was used to inject seeds into the sediment at 300 seeds m-2 in replicate plots

around Chesapeake Bay. Overall, burying seeds using this mechanical planter resulted in a

positive effect in seedling establishment, but the mean effectiveness tended to vary depending on

the site. For example, seedling establishment for machine-planted seeds was significantly

greater than simple broadcast planting at some sites, but not for others. The study

concluded that burial via mechanical planting might show promise, but further investigation is

needed to justify the cost associated with process (Orth et al. 2009, Marion et al. 2010).

Another alternative to manual planting is buoy-deployed seeding, a relatively low-cost,

simple, and efficient method easily taught to local communities (Fig. 4; Pickerell et al. 2005).

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Fig. 4. A single seed buoy line showing the net and block attachment (Pickerell et al. 2005)

Reproductive shoots are collected after the second week of seed release via SCUBA. Meanwhile,

the buoy system (Fig. 4) is prepared, using commercial aquaculture 9 mm nets, a 12.7cm x 28

cm lobster buoy, a 39.4 cm x 19 cm x 8.9 cm cement block for anchorage, a 3.3 m floating

polypropylene line to secure the net and buoy to the anchor, a recycled garden hose to protect the

line, and a 22.7 kg capacity wire tie to attach the net to the buoy. The nets are then stocked with

approximately 100 reproductive shoots on the same day of collection, and are sewn shut using

polyethylene thread. Pickerell et al. (2005) used this method and found that these detached

reproductive shoots had the natural ability to release viable seeds, potentially re-establishing the

phenological timing of seed maturation and dispersal in situ. Overall, the simplicity of the

method and the effectiveness (at least 6.9% recruitment per net) suggests that buoy-deployment

of seeds may provide a simple, community-friendly method towards eelgrass restoration. Further

studies do need to be conducted in order to understand how far seeds can disperse from the buoy

(although it is attached to a brick, the net itself can still revolve around the base) to determine if

buoy-deployment will be efficient in the Neponset River Estuary.

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Table 1. Summary of advantages and disadvantages of transplantation techniques as discussed in this paper (adapted from Short et al. 2002a)

Method Advantages Disadvantages Reference

Hand: Core/Plug- Roots/rhizome remain intact- Sediment/nutrient poolmaintained

- Labor intensive- Holes in healthy donor bed- SCUBA- Highest cost per PU- low genetic diversity

- Fonseca et al. 1996- Philips 1990- Harrison 1990

Hand: Bare-root Technique

- Minimizes impact to donor site- No site preparation- Low time cost

- Requires PU- Requires handling- SCUBA- Must adapt quickly- low genetic diversity

- Foncesa et al. 1996- Merkel and Hoffman 1990

Hand: Horizontal rhizome method

- Minimizes impact to donorsite- Minimizes number of shootsharvested- No PU or site preparation- Low time cost

- SCUBA- Must adapt quickly- low genetic diversity

- Short et al. 2002a

Frame: TERFSTM

- cost-effective- community-based method- simple, straight forward- can re-use frames

- success is highly site-specific- known to attract bioturbators- low genetic diversity - Short et al. 2002b

Frame: PVC/jute(adapted from TERFSTM)

- effectively guarded againstBioturbators- cost-effective- community-based method

- success is highly site-specific- low genetic diversity - Leschen et al. 2010

Seed: Basic

- No plants uprooted- Seeds can be dispersed overlarge areas quickly- Maintains high geneticdiversity

- Variable seed viability- Reduces natural recruitmentat donor bed- Long term survival unknown- Location unpredictable

- Orth et al. 1994- Harrison 1991

Seed: Mechanical- Maintains high geneticDiversity-Increased efficiency

- Inconsistent effectiveness

- Fishman et al. 2004- Orth et al. 2009- Marion et al. 2010

Seed: Buoy- Maintains high geneticDiversity- community-based method

- Difficult to determine seed dispersal

- Pickerell et al.2005

To reiterate, the use of seeds in eelgrass restoration is being encouraged in recent articles

due to the importance of maintaining genetic diversity (Williams 2001; Orth et al. 2012;

Reynolds et al. 2012). Generally, eelgrass donor beds vary in genetic diversity, and may be

further reduced upon transplantation, if donor plants are collected from small areas (Williams

2001). Furthermore, success of transplants, especially that of seeds, are highly site-specific.

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Therefore, a thorough understanding of how to select sites for eelgrass restoration plays a large

role in determining the success of a transplant. The next section will take site selection into

consideration, offering greater insight as to where eelgrass (if anywhere) may be restored in the

Neponset River Estuary.

IMPORTANCE OF SITE SELECTION.

The success of transplantation varies due to a number of factors (Davis & Short 1997;

Fonseca et al. 1998), with poor site selection perhaps being the most prominent. In light of this

discovery, scientists have since attempted to create models that estimate the most optimal

restoration sites in order to increase the success of costly transplant efforts by considering their

requirements for survival and growth. This section will review a model created specifically for

the northeastern United States (Short et al. 2002a), resulting in transplant success much higher

than the country average (25%).

Short Model. This model was created particularly for eelgrass transplantation in the

northeastern United States. Researchers reviewed results from other eelgrass studies (Davis &

Short 1997), and developed a quantitative site selection model based on the physical and

biological characteristics that led to a successful (or failed) restoration effort. Once the goals and

physical boundaries of the project has been set, the site selection model progresses through three

major phases; (1) Phase I identifies potential eelgrass habitat and assigns each area a

‘Preliminary Transplant Suitability Index’ (PTSI); (2) Next, small-scale field assessments are

completed to groundtruth and narrow down results from Phase I; and (3) Phase III culminates

with a final calculation of the ‘Transplant Suitability Index’ (TSI), a multiplicative index. At

each step, various factors of a particular habitat are assigned a score of 0-2, with 0 representing

no likelihood of restoring eelgrass. Since the model is a multiplicative index, if at any step

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between Phase I and Phase III a habitat receives a 0, it is eliminated from any further

consideration.

To describe the model in more detail, Phase I considers historical eelgrass distribution

(1= previously unvegetated, 2 = previous vegetated), current eelgrass distribution (0 = currently

vegetated, 1 = currently unvegetated), proximity to natural eelgrass bed (0 = less than100m, 1 =

greater than 100 m), sediment (0 = rock/cobble, 1 = over 70% silt/clay, 2 = cobble free with less

than 70% silt/clay), wave exposure (0 = over mean plus 2 standard deviations, SD, 1 for less than

or equal to mean plus 2 SD), water depth (0 = too shallow or too deep, 1 = shallow edge of

reference bed, 2 = average for reference bed, 1 = deep edge of reference bed), and water quality

(0 = poor, 1 = fair, 2 = good based on phytoplankton pigments, DIN, TON, secchi depth,

eutrophication index, or habitat requirements). The PTSI score is then calculated by multiplying

the ratings of each parameter, with 0 being the lowest possible score and 16 being the highest

possible score. Sites with a PTSI less than 2 were eliminated from consideration and those

remaining were ranked numerically for suitability.

Phase II involves conducting test-transplants at sites with high PTSI scores from Phase I,

which has been recommended for projects larger than 0.2 ha (Fonseca et al. 1998). During and

after small-scale transplants, bottom light levels, presence of bioturbators, survival, and leaf

nitrogen content are measured and compared to a nearby reference site. Survival, shoot growth,

and leaf nitrogen may be measured in as little as four weeks, but it is recommended that

evaluation of each test-transplant be made a full year after initiation to thoroughly assess the

site’s suitability. Phase III then uses another multiplicative index to calculate the PTI for each

test-transplant site by considering results from both Phase I (PTSI) and Phase II (see Short et al.

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2002a ). Sites with the highest TSI score (highest = 64) at the end of Phase III are then chosen

for full-scale eelgrass restoration.

The Short model was applied to a study by Davis & Short (1997) in the Great Bay

Estuary, NH post hoc, and correctly identified 62% of the sites where transplants were

successful. In addition, a nearby study (Leschen et al. 2010) in Boston Harbor, MA utilized used

the model to identify potential sites of restoration, which will be reviewed later in the paper.

Overall, no model can account for every detail, but using it to help eliminate poor sites rather

than using “best professional judgment” (Short et al. 2002a) will undoubtedly save money and

time when taking on large-scale eelgrass restoration projects.

REDUCING BIOTURBATION.

A number of studies have shown that bioturbation (e.g. the reworking of soil by

organisms) plays a significant role in reducing the survival of both naturally occurring and

transplanted eelgrasses (Table 2; Orth 1975; Suchanek 1983; Fonseca et al. 1996); therefore, a

major component of successful restoration is to actively prevent uprooting caused by

bioturbators.

In the Great Bay Estuary, NH, Horseshoe crabs (Limulus polyphemus) and Green crabs

(Carcinus maenus) have foraging habitats that uproot unprotected transplanted eelgrass. In an

attempt to circumvent negative effects from these common bioturbators, Davis & Short (1997)

constructed temporary cages that were hammered into the sediment with oak stakes around the

perimeter of the transplanted eelgrass plots. A monofilament gill netting was attached to the

stakes, sealed with cable ties, and the extra netting at the bottom was then stretched out to create

a skirt protecting the sediment. Once this setup was secure, the researchers placed unbaited crab

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pots inside the cages, which were emptied twice a week. Although the gill netting successfully

protected against crab bioturbation, clam worms (Neanthes virens) may have caused severe

decline in eelgrass biomass due to their ability to pull blade distal ends into their burrows (Davis

& Short 1997). These results emphasize the need to assess not only the physical environment

when selecting a site for eelgrass restoration, but also the biological environment in order to

understand what bioturbating organisms may threaten the restoration effort.

Table 2. Bioturbating organisms known to reduce survival and growth of natural and restored eelgrass sites (adapted from Short et al. 2002a)

Bioturbators Species Impact Location ReferenceCownose ray Rhinoptera bonasus Excavation Chesapeake Bay,

USAOrth 1975

Horseshoe crabs Limulus polyphemus Excavation New Hampshire, USA

Short

Green crabs Carcinus maenus Clipping New Hampshire, USA

Davis et al. 1988

Spider crabs Libinia spp. Clipping Massachusetts, USA Kopp

Clamworm Neanthes virens Lodging New Hampshire, USA

Davis & Short 1997

Lugworm Arenciola marina Burial The Netherlands Philippart 1994

Burrowing shrimp Callianassa californiensis

Burial Washington, USA Harrison 1987

Green urchin Stronglyocentrotus spp

Grazing Alaska, USA Short

Canada geese Branta canadensis Grazing New England, USA Buchsbaum 1987

Brant Branta bernicla Grazing British Columbia, Canada

Baldwin & Lovvorn 1994

Trumpeter swan Cygnus olor Grazing New England, USA Short

Whooper swan Cygnus cygnus Grazing Japan Albertsen & Mukai 1998

OUTREACH & COMMUNITY-BASED RESTORATION.

Although seagrasses have far-reaching distributions, they generally receive little to no

attention in the public media (Duarte et al. 2008). In order to change this trend and emphasize the

importance of the ecosystem services provided by eelgrass habitats, it is crucial that any

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restoration effort, especially the Neponset River Estuary, include community involvement. A

paper by Short et al. (2002b) entitled A Manual for Community-Based Eelgrass Restoration

provides a simple, straight-forward guide to organizing a volunteer-based restoration program. It

outlines the reasons restoration should be community-based, and gives step-by-step instructions

on how to contact volunteers, how to organize a volunteer day, and how to proceed towards

restoring a particular site with the community involved.

To briefly summarize the Short et al. (2002b) document on community outreach: A

number of community groups can benefit from involvement in eelgrass restoration, but first and

foremost elementary and middle school students. Not only will these students learn the

importance of eelgrass beds, but also the next generation of restoration scientists will be trained

early on in the methodologies of transplantation. In addition to school groups, other community

groups, including Boy or Girl Scouts, environmental advocacy groups, and various other

volunteer associations, can benefit from involvement in restoration. The primary goal of

community-based restoration is to increase awareness, so the more exposure the project can

receive the better. Short et al. (2002b) also recommends that upcoming eelgrass restoration

projects be advertised in the media, and that even a reporter/journalist become involved

themselves in order to further advocate the cause. Overall, it is important that the volunteers

leave with a sense of accomplishment, a heightened knowledge of the value of eelgrass beds, and

lastly the reason for eelgrass restoration world-wide. With a positive experience, volunteers may

gain a better appreciation for their coast, and will hopefully educate their peers regarding the

ecological significance of eelgrass in their estuaries (Short et al. 2002b). Large numbers of

volunteers will become especially useful when conducting long-term monitoring of already

restored sites, a topic covered in the next section.

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LONG-TERM MONITORING.

In order to assess which aspects of restoration projects are successful and which are not,

and to improve our state of knowledge regarding the value of restored vs. natural eelgrass beds,

long-term monitoring programs must be used regularly (Sheridan 2004). A number of studies in

other ecosystems such as salt marshes, coral reefs, and mangroves, have conducted long-term

monitoring; however, high resolution records are rare in seagrass habitats (Fonseca 1990;

Sheridan 2004). Therefore, this section will discuss the types of eelgrass monitoring projects

undertaken so far and the ultimate outcome of each.

A study by Fonseca et al. (1990) looked at numerical abundance, species composition,

and size of shrimp/fish among vegetated, unvegetated, transplanted, recently seeded, and mature,

natural eelgrass habitats in southern Core Sound, NC to assess functional equivalence among

different habitat types. By developing vector-graphical analysis, the researchers were able to plot

measures of the above fauna against measures of eelgrass to compare ecological function.

Ultimately, this allowed for managers to assess whether or not restoration was positive – even if

eelgrass is restored structurally, if it does not have the same ecosystem function, then it could

result in a loss of important fauna; therefore, this monitoring scheme is useful in understanding

how restored eelgrass might support (or not support) normal levels of biologically productivity.

Moreover, Davis & Short (1997) recognized the importance of monitoring, and sampled

vegetation, benthic invertebrates, and fish from transplanted and reference beds on a yearly basis.

Subsequent sampling also included production (leaf biomass), shoot density, 2-sided leaf area,

and aerial photography to asses bed continuity and areal extent of transplanted beds. By

recording as much useful information as possible, scientists can use models to assess and predict

how restoration efforts might fare, depending on a number of these factors.

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Lastly, in a study by Evan & Short (2005) conducted in the Great Bay Estuary, NH, the

authors used functional trajectory modeling to show the development of restored eelgrass

ecological function over time in relation to reference sites. Ideally, the model would show the

ecosystem trajectory for the restored habitat steadily increasing over time, and eventually

matching that of the natural system (the ultimate goal of restoration is to obtain the same

ecosystem services as a natural eelgrass bed). This result would indicate a successful restoration.

In the case the restored site trajectory never reaches the same level as the natural system, then it

can be concluded that their ecosystem function is not equal, and restoration may not have been

successful. Using trajectory models as a quantitative comparison between transplanted and

natural sites can contribute towards an improved design of both restoration and monitoring

programs. In the case eelgrass is restored in the Neponset River Estuary, I propose that we use

this model to assess the ecosystem function of the transplanted site over time.

CASE STUDIES.

Great Bay Estuary, New Hampshire. Davis & Short (1997) worked to restore eelgrass in

the Great Bay Estuary, NH when Port Authority pier facilities in Portsmouth were proposed to

expand. Expansion would have led to loss of eelgrass habitat, so in order to prevent further loss,

the authors created an experimental restoration framework specific to the area. The study site, the

Piscataqua River, runs naturally between southern Maine and New Hampshire, USA, with the

southern side experiencing heavily industrialized impacts and the northern side consisting of

naturally occurring eelgrass beds.

The researchers identified the naturally occurring 6 ha donor bed on the Maine side of the

river, and collected large, healthy shoots, ensuring to confine collection to three adjacent 150 m x

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300 m large rectangles in order to minimize impacts to the donor beds. Collectors knelt in only

unvegetated area, and carefully uprooted approximately 3 -5 cm of the rhizome by digging

underneath the sediment by hand. The shorts were then stored in large coolers filled with

seawater to prevent dessication, and were transported to the recipient sites within 72 hours. Over

the course of two years (length of the study), 250,000 shoots were collected from the donor site.

At the recipient site, the horizontal rhizome method was used to plant the shoots (see pg. 3) from

June to September of 1993 and May to July of 1994, and PU’s were transplanted at 0.5 m

intervals. As discussed on pg. 13, Davis & Short (1997) also took action to prevent negative

impacts by bioturbators by placing unbaited crab pots around the transplant.

It was found that approximately one person hour was required to collect 300 shoots, and

an average of 4.5 person hours were required to transplant a 100 m2 area at the recipient site

(depending on visibility). Furthermore, an average of 5.5 person hours were required to construct

subtidal cages by SCUBA, and 4.5 person hours were required to construct intertidal cages.

Although cumbersome, this type of information is useful for planning future transplanting

efforts. Overall, the eelgrass transplanting project was successful, and of the five sites planted at

the recipient site, three still have eelgrass (as of time of publication, 1997). In most cases of

eelgrass death, ice damage was to blame. By 1995, 1.2 ha of newly restored eelgrass habitat was

successfully growing in the estuary.

A post-hoc model (Short et al. 2002a) was applied to the study (pg. 13), which

successfully identified sites that were ultimately successful in restoring eelgrass habitat. This

result underscores the need to use some sort of site-selection model to determine locations best

suitable for restoration before taking action and using time/money. Additionally, Davis & Short

only attempted restoration at sites historically known to have had eelgrass in order to maximize

Bulseco-McKimEelgrass Restoration

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success. Although this is logical reasoning, and historical eelgrass distribution is part of the Short

model, limiting restoration efforts to small areas only makes success less obtainable. Lastly,

bioturabtion caused a large portion of eelgrass loss – future studies should try and lessen these

negative effects by experimenting with mitigation techniques before following through with

restoration projects.

Chesapeake Bay Region. Eelgrass is much less widespread in areas spanning Delmarva

Bay and Chesapeake Bay, largely due to wasting disease in the 1930’s (Rasmussen 1977). In

1978, an eelgrass restoration program was initiated, beginning a large-scale effort to explore

methods of transplanting. During the past 25 years, eelgrass has been transplanted using several

techniques; although this paper will not cover the entire history of eelgrass restoration in

Chesapeake Bay, it will review the overall suggestions made my researchers throughout this

long-term experiment (Orth et al. 2003).

In 1979, eelgrass plants were dug with shovels and transplanted to recipient sites (bare-

root technique). Due to rough weather, nearly 95% of eelgrass shoots were lost within one

month. In 1979 and 1980, 10 cm diameter cores of both eelgrass and sediment were collected

and plugged. As long as anchoring was adequate, 100% of the PU’s survived for a one to two

month period, while 57% survived for up to one year. Beginning in 1983 to 184, researchers

used sods (both eelgrass and sediment), which ended up leading to 94% survival after one

month, and 77% survival for up to five to six months; however, there was extremely low

survivability after nine months due to water quality issues. After years of hand-planting,

Williams (2001) brought up the issue of lack of genetic diversity by using adult shoots (pg. 7).

Orth et al. 2008 therefore compared the effectiveness of mechanized vs. manual seed planting,

and found the effectiveness to not be worth the cost.

Bulseco-McKimEelgrass Restoration

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Overall, it has been found that the optimal transplantation season for the Chesapeake Bay

is in the fall between mid-September to mid-November (where the temperature ranges from 20 to

10 degrees Celsius). This allowed for the longest period to establish and grow before facing

stress associated with the summer season. Additionally, researchers discovered that addition of

fertilizer to plants increased shoot density and spread of the PU, although cost must be weighed

against benefit (as fertilizer use is costly). Lastly, the effectiveness of transplantation is highly

site-specific. These techniques may have worked in the Chesapeake region, but could lead to

ultimate failure in other geographic locations. As a result, it is important that high resolution site-

selection models be used to determine suitability before attempting restoration efforts (Orth et al.

2003).

Boston Harbor, Massachusetts. Perhaps the most useful study for us to review is a recent

restoration effort by Leschen et al. 2010 and the Massachusetts Division of Marine Fisheries in

Boston Harbor, MA from spring 2004 to fall 2007. The harbor was targeted for eelgrass

restoration as a mitigation attempt following the construction of the HubLine natural gas

pumpline. In addition, the relatively shallow estuary (average 4.9m depth) and wind-driven

current patterns makes natural re-populations of eelgrass unlikely; therefore, this study aimed to

restore eelgrass at various sites around the harbor (Fig. 5).

Bulseco-McKimEelgrass Restoration

21

Fig. 5. Boston Harbor, located on the western edge of Massachusetts Bay within the Gulf of Maine (Leschen et al. 2010)

Researchers began by adapting the Short et al. (2002a) site-selection model for Boston

Harbor (herein “Short model”). Six parameters were measured to determine preliminary site

suitability (PSTI), including water depth, exposure to northeast winter storm winds, historical

eelgrass distribution, current eelgrass distribution, water quality, and sediment type (using USGS

seafloor maps; open file 99-439). As discussed on pg. 11, parameters were assigned scores

ranging from 0 to 2 (0 = not suitable for eelgrass growth, 2 = most suitable for eelgrass growth),

and results were used to determine which sites might be acceptable for field assessment.

According to Phase II of the Short model, each potential transplant site was groundtruthed for

characteristics such as water depth, the presence of human disturbance (e.g. marinas, mooring

fields), the presence of bioturbators, and sediment type by use of an underwater camera, SCUBA

diving, and sediment cores. Finally, Phase III utilized the multiplicative index to determine

which sites had potential for eelgrass restoration.

The Short model outputted a total of 12 potential sites, all of which received a test-

transplant. Transplants were conducted in a stepwise series to avoid excessive failure, starting

with preliminary transplants (12 sites using TERFSTM at 200 shoots site-1). Based on the success

Bulseco-McKimEelgrass Restoration

22

of the 12 sites, a subset was carried over to a medium-scale transplant (using PVC/jute frames

and the horizontal rhizome method at 1000 shoots site-1). Lastly, a total of four sites were

considered suitable for eelgrass restoration, where transplanting occurred at a large-scale

(PVC/jute frames, hand-planting, 3,600 to 7,200 shoots site-1, and 300,000 seeds). The

researchers encouraged the help from the community on the PVC/jute frames, and continuously

monitored restoration sites by assessing shoot density, plot size, mean areal cover, and biological

attributes (faunal habitat use as epibenthic/demersal and infaunal fish and invertebrate abundance

(N), species richness (S), Pielou’s evenness (J) and Shannon diversity (H’)).

Following the small-scale test transplant, shoot survival ranged from 5-90%. In four sites,

external disturbances such as excessive wind or macroalgae/gravel caused eelgrass death. An

additional four sites looked unhealthy, but not due to the same reasons, so the researchers

analyzed sediment size and found that at sites with < 35% silt/clay, eelgrass was successful;

however, at sites > 57% silt/clay, the eelgrass transplant failed. This result suggests that we do

extensive sediment analysis before attempting restoration in the Neponset River Estuary, since

sediment characteristics is primarily fine-grained. The sites which remained after the small-scale

transplant were then moved into the medium-scale test. It was discovered that the use of

TERFSTM actually attracted burrowing crabs that uprooted eelgrass shoots and led to a lower

transplantation success rate. In response, the authors switched from the TERFSTM to a flat

PVC/jute design (pg. 5) to avoid further bioturbation. It is important to note here that

transplantation methods are highly site-specific – even though TERFSTM worked well for Short

et al. (2002b) in the Great Bay Estuary, they led to transplantation failure in Boston Harbor due

to differences in biological characteristics. Lastly, the four sites considered suitable for large-

scale transplant showed either comparable or even larger values of eelgrass biomass and density

Bulseco-McKimEelgrass Restoration

23

when compared to the natural beds/control sites. Furthermore, the diversity indices (N, S, J, H’)

of the restored sites were comparable to that of the natural sites, suggesting that eelgrass

restoration is possible in formerly eutrophic estuaries, and its ecosystem function can be restored

as well.

Overall, this study in Boston Harbor successfully restored over 2 ha of eelgrass to

carefully selected sites around the estuary. A number of factors likely contributed to this success,

including the significant improvement of water quality from the Deer Island secondary treatment

plant, careful site selection via the Short Model, and stepwise transplantation experiments at

various suitable sites around the harbor. Hand-planting (e.g. horizontal rhizome method) tended

to be the most efficient method of plant transplanting, yet it required SCUBA divers; on the other

hand, frame planting was less efficient, but took advantage of the availability of community

volunteers. In addition, checkerboard planting minimized initial human effort while still

achieving maximum areal coverage. To review what did not work in their study, TERFSTM,

though shown to be successful at other sites, actually attracted bioturbators to transplant sites.

To improve upon this study, we need better information on physical requirements (e.g.

wave exposure and sediment characteristics) to be used in a site selection model. Also, because

of the imbalance between the amount of eelgrass restored and eelgrass lost, we should not only

consider eelgrass restoration, but also broaden our view to watershed management. For example,

during the same time a restoration project successfully brought back 4 ha of eelgrass, a total of

760 ha were lost simultaneously. It is clear that a more holistic management plan will be useful

in restoring eelgrass by both improving water quality and preventing loss, and transplanting new

eelgrass to currently unvegetated areas. Lastly, Leschen et al. (2010) present a strong point that

areas with compromised water or sediment quality may not actually be ready for eelgrass

Bulseco-McKimEelgrass Restoration

24

restoration. We need to consider this possibility and conduct field experiments assessing physical

and biological characteristics before we can confidently say eelgrass restoration is possible in the

Neponset River Estuary. Alternative mitigation strategies may be a better option if suitable sites

cannot be located, including management of water quality and minimization of boat impacts.

SUMMARY & RECOMMENDATIONS.

After reviewing the wide range of transplantation techniques and a number of case

studies, here are some suggestions for the restoration of eelgrass in the Neponset River Estuary:

(1) The Short model (or an adaptation of it) should be used to determine site suitability before

taking on large-scale eelgrass restoration efforts; (2) As suggested by the success of the Leschen

et al. (2010) study in Boston Harbor, we should use a combination of transplantation techniques

to increase chances of success (an alternative would be to conduct small-scale experiments and

assess what might be most effective in the Neponset River Estuary); (3) Gain a better

understanding of our site’s physical characteristics (e.g. wave and wind exposure, sediment

characteristics) (especially since Boston Harbor is primarily silty/clay); (4) Survey the types of

bioturbators present in the estuary; (5) involve the community and promote a greater awareness

of eelgrass habitat; and (6) conduct long-term monitoring of physical and biological

characteristics, structural and functional attributes of the transplanted and natural eelgrass

habitats, and GIS is possible (MassGIS).

Bulseco-McKimEelgrass Restoration

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