Eelgrass Restoration
Phase II: Restoring Eelgrass to the Neponset River
Estuary
Ashley Bulseco-McKim
11/19/2012
, 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. 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
Bulseco-McKim 1
Eelgrass Restoration
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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Eelgrass Restoration
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
Bulseco-McKim 3
Eelgrass Restoration
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 Ushaped 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
Bulseco-McKim 4
Eelgrass Restoration
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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Eelgrass Restoration
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.
Bulseco-McKim 6
Eelgrass Restoration
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 m 2
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
Bulseco-McKim 7
Eelgrass Restoration
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
Bulseco-McKim 8
Eelgrass Restoration
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).
Bulseco-McKim 9
Eelgrass Restoration
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.
Bulseco-McKim 10
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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
Hand: Core/Plug
- Roots/rhizome remain intact
- Sediment/nutrient pool
maintained
Hand: Bare-root
Technique
- Minimizes impact to donor
site
- No site preparation
- Low time cost
Hand: Horizontal
rhizome method
Frame: TERFSTM
Frame: PVC/jute
(adapted from
TERFSTM)
Seed: Basic
- Minimizes impact to donor
site
- Minimizes number of shoots
harvested
- No PU or site preparation
- Low time cost
- cost-effective
- community-based method
- simple, straight forward
- can re-use frames
- effectively guarded against
Bioturbators
- cost-effective
- community-based method
- No plants uprooted
- Seeds can be dispersed over
large areas quickly
- Maintains high genetic
diversity
Disadvantages
- Labor intensive
- Holes in healthy donor bed
- SCUBA
- Highest cost per PU
- low genetic diversity
- Requires PU
- Requires handling
- SCUBA
- Must adapt quickly
- low genetic diversity
- SCUBA
- Must adapt quickly
- low genetic diversity
- success is highly site-specific
- known to attract bioturbators
- low genetic diversity
- success is highly site-specific
- low genetic diversity
- Variable seed viability
- Reduces natural recruitment
at donor bed
- Long term survival unknown
- Location unpredictable
Reference
- Fonseca et al. 1996
- Philips 1990
- Harrison 1990
- Foncesa et al. 1996
- Merkel and
Hoffman 1990
- Short et al. 2002a
- Short et al. 2002b
- Leschen et al. 2010
- Orth et al. 1994
- Harrison 1991
Seed: Mechanical
- Maintains high genetic
Diversity
-Increased efficiency
- Inconsistent effectiveness
- Fishman et al.
2004
- Orth et al. 2009
- Marion et al. 2010
Seed: Buoy
- Maintains high genetic
Diversity
- 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.
Bulseco-McKim 11
Eelgrass Restoration
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
Bulseco-McKim 12
Eelgrass Restoration
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.
Bulseco-McKim 13
Eelgrass Restoration
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 usedthe
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 habits 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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Eelgrass Restoration
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
Cownose ray
Species
Rhinoptera bonasus
Impact
Excavation
Location
Chesapeake Bay,
USA
New Hampshire,
USA
New Hampshire,
USA
Massachusetts, USA
Reference
Orth 1975
Horseshoe crabs
Limulus polyphemus
Excavation
Green crabs
Carcinus maenus
Clipping
Spider crabs
Libinia spp.
Clipping
Clamworm
Neanthes virens
Lodging
Davis & Short 1997
Burial
New Hampshire,
USA
The Netherlands
Lugworm
Arenciola marina
Burrowing shrimp
Burial
Washington, USA
Harrison 1987
Grazing
Alaska, USA
Short
Canada geese
Callianassa
californiensis
Stronglyocentrotus
spp
Branta canadensis
Grazing
New England, USA
Buchsbaum 1987
Brant
Branta bernicla
Grazing
Trumpeter swan
Cygnus olor
Grazing
British Columbia,
Canada
New England, USA
Baldwin & Lovvorn
1994
Short
Whooper swan
Cygnus cygnus
Grazing
Japan
Albertsen & Mukai
1998
Green urchin
Short
Davis et al. 1988
Kopp
Philippart 1994
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
Bulseco-McKim 15
Eelgrass Restoration
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.
Bulseco-McKim 16
Eelgrass Restoration
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.
Bulseco-McKim 17
Eelgrass Restoration
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
Bulseco-McKim 18
Eelgrass Restoration
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-McKim 19
Eelgrass Restoration
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 (bareroot 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-McKim 20
Eelgrass Restoration
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 siteselection 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-McKim 21
Eelgrass Restoration
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 testtransplant. 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-McKim 22
Eelgrass Restoration
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 largescale transplant showed either comparable or even larger values of eelgrass biomass and density
Bulseco-McKim 23
Eelgrass Restoration
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-McKim 24
Eelgrass Restoration
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-McKim 25
Eelgrass Restoration
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