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REVIEW OF MANGROVE PLANTING ACTIVITIES IN WESTERN PORT 2004–2011

Hugh Kirkman Marine Science and Ecology 5A Garden Grove Seaholme VIC 3018 Email: hughkirkman@ozemail.com.au Paul Boon Institute for Sustainability and Innovation Victoria University Footscray Park VIC 8001 Email: paul.boon@vu.edu.au

Western Port Seagrass Partnership

May 2012

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REVIEW OF MANGROVE PLANTING ACTIVITIES IN WESTERN PORT 2004–2011 A report prepared for the Western Port Seagrass Partnership by Hugh Kirkman and Paul Boon To cite this publication: Kirkman, H. and Boon, P. 2012. Review of Mangrove Planting Activities in Western Port 2004–2011. Report prepared for Western Port Seagrass Partnership. Pp. 42 and Appendix. ISBN: 978-1-86272-696-3

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Contents  Contents ......................................................................................................................................... 4 1.  Background to this review .................................................................................................... 6 

1.2  Possible reasons for mangrove revegetation .................................................................. 13 2.  Revegetation of Avicennia marina ...................................................................................... 16 

2.1 Meaning of the terms ‘restoration’ and ‘rehabilitation’...................................................... 16 2.2 Mangrove planting review .................................................................................................. 17 2.3 Principles critical for effective rehabilitation or creating mangrove forests....................... 20 2.4 Mangrove plantings in Western Port .................................................................................. 21 2.5 Methods used in nursery ..................................................................................................... 22 2.6 Success in nursery............................................................................................................... 24 2.7 Methods used in planting .................................................................................................... 24 2.8 Recent replanting projects................................................................................................... 27 2.9 Success of plantings............................................................................................................ 31 2.10 Causes of mortality ........................................................................................................... 31 2.11 Possible solutions to lowering mortality........................................................................... 32 2.12 Strategy for future planting............................................................................................... 33 

3.  Alternatives to mangrove planting..................................................................................... 33 4.  Discussion ............................................................................................................................. 36 5.  Recommendations................................................................................................................ 38 Acknowledgments ....................................................................................................................... 39 References.................................................................................................................................... 40 Appendix 1................................................................................................................................... 44 

Mangrove Restoration in Western Port Bay Literature Review   Tom Hurst. July 2011 ..... 44 

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Executive summary Western Port has been and still is subjected to significant disturbances such as land

clearing, draining saltmarshes and swamps, straightening river and creek meanders, industrial

and urban growth in its catchment and recreational and, in the past, commercial fishing. One of

the major primary producers in Western Port is seagrass. In the 70s there were about 250 km2 of

seagrass meadows; in 1984 only 59 km2; and in 2000 154 km2. This loss and subsequent more

recent recovery, albeit not to 1970s levels, has been attributed to suspended sediment in the

water column reducing light to seagrass and precipitated sediments smothering seagrass plants.

Apart from runoff and riverine input, a major source of sediments is from eroding coastlines,

particularly the clay Lang Lang cliffs on the eastern shore of the embayment. One way of

reducing this erosion is to reduce wave energy, and an efficient and economic way of doing this

is to grow mangroves.

This report discusses the use of mangroves to reduce sediment loads and then presents the

various methods of growing mangroves in nurseries from seed to out-planting in Western Port. A

programme has been running in Western Port from 2004 to establish mangroves at various sites

along the northern and eastern shores of Western Port, and field trials have shown that the best

results are achieved by growing mangroves to a six-leaf stage in milk cartons. Before the cartons

are planted the tops are stapled, to prevent wave-induced loss of sediment from the container.

Many of the seedlings planted out have been in places where mangroves did not grow in the

recent past; this is warned against in many overseas experiences, but in Western Port there

seemed no other way to achieve the desired outcome of stablising eroding coastlines, especially

along the eastern shore.

Nevertheless, there may be other ways than mangrove establishment to reduce wave

action and these alternatives are briefly reviewed. Seawalls and rock deposits, for example, are

an expensive way of preventing erosion, and so efforts to date have concentrated into using

mangroves. We question the current method, because of the time needed to grow mangroves

sufficiently tall to survive in the field and reduce wave action, and because losses require

constant replanting and attention to alleviate processes that threaten mangrove survival, such as

seagrass drift, detritus, and accumulation of fishing lines around young plants. There was also

some community backlash and removal of many plants by disaffected locals.

Growing bands of mangrove that have been protected from waves by walls or sand bags

may be a useful way of starting the protective barriers, but these measures also will take time.

Volunteer groups have been mostly responsible for the mangrove plantings, but professionals are

needed to record survival, fitness and disturbance to new plants.

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Some recommendations as to further actions are proposed. These include the need for a

strategic plan for Western Port to guide research and on-ground activities, greater media

coverage to communicate the threats and need for remedial action, and the creation of a database

that covers all mangrove plantings to date, with consistent reporting on success rates and

concomitant effects on rates of shoreline erosion and seagrass recovery. We recommend also that

research on methods to create or recreate mangrove stands in Western Port not be confused with

on-ground works involved with planting mangrove to prevent erosion, and consistent biennial

measurements of erosion rates

1. Background to this review 

This review is to establish the reasons for and success of planting mangroves along the

northern and eastern shores of Western Port. It also reviews the mangrove planting efforts

undertaken since 2004 and refers to a comprehensive review on mangrove rehabilitation in

temperate regions (Morrisey et al., 1999) and a review of the mangrove information specifically

for Western Port (Hurst, 2011 Appendix 1).

Avicennia marina var. australasica is the only mangrove to grow in Victoria where, in

fact, it forms the southern-most occurrence of mangroves in the world (Duke, 2006). It is known

commonly as either the ‘grey mangrove’ or, less frequently, the ‘white mangrove’. Mangroves

provide habitat for birds, fish, crabs, barnacles other invertebrates, and substrata for macroalgae

(Harty, 2011). However, one of their most important attributes in Western Port is as a barrier to

high-energy waves and swell (Badola and Hussain, 2005). The area of mangroves in Western

Port (not including those on French Island, with 475 ha) was recently measured as 1230 ha, with

an additional 8 ha around The Inlets on the northern shore, 15 ha around the Bass River estuary,

and 2 ha along the Lang Lang coast (Boon et al., 2011). Figure 1 shows the map sheets prepared

as part of that study, and Figures 2 and 3 more detailed information for map sheets 30 (northern

shore of Western Port) and 32 (Jam Jerrup region). The pre-European distribution of coastal

wetlands—mangroves, coastal saltmarsh and Juncus kraussii dominated wetlands—is shown in

light grey on the detailed maps.

The 2011 estimate of there being 1230 ha of mangroves in Western Port matches closely

with the estimate of mangrove area made in the 1975 Shapiro study: Table 4.3.7 (e) of Shapiro

(1975) shows the area of mangroves as 12.1 km2 (= 1210 ha). Somewhat oddly, two State

Government reports cite the 1975 Shapiro study as providing estimates of the area of mangroves

in Western Port as 12,100 ha (Department of Natural Resources and Environment 1997, page 3;

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Environment Protection Authority 1996, page 60). Presumably this is an error in converting ha

from km2.

Fig. 1 Mapping of coastal wetlands around Western Port undertaken by Boon et al. (2011)

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Fig. 2 Current(~2008) distribution of coastal wetlands around the northern shore of Western Port.

Mangroves are shown in dark green. Source: Boon et al. (2011)

Fig. 2 Current(~2008) distribution of coastal wetlands around the northern shore of Western Port.

Mangroves are shown in dark green. Source: Boon et al. (2011)

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There is good evidence that mangroves, although abundant along the western and

northern shores, were never common along much of the eastern shore of Western Port. The draft

Western Port mangrove replenishment strategy (1997) of the Department of Natural Resources

and Environment, for example, concluded there was sparse coverage of mangroves from The

Gurdies south to Grantville and west to Corinella. Figure 8.1 of the recently released Western

Port scientific review (Melbourne Water 2011) similarly shows mangroves almost completely

lacking from the western shore in the surveys of Smyth in 1842 and again in the surveys of Bird

in 1984. Ross (2000), in her review of Western Port mangroves, makes similar points about the

absence of mangroves along these parts of Western Port.

Figures 3–5 below show changes in distribution of mangroves from the earliest mapping

of Smyth in 1842, through to the mapping done in 1939, and finally from the maps of Bird in

1984, reproduced from EPA (1996). It appears that mangroves had disappeared from Pioneer

Bay by 1939 but showed some return in 1984. There is less mangrove on Phillip Island, Stony

Point and the western side of French Island in 1984 than there was in 1842. These maps are only

indicative and the original articles should be used to determine finer-scale changes in mangrove

distributions.

Fig. 3 Mangrove distribution in Western Port in 1842. Source: Bird and Barson (1975)

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Fig. 4 Mangrove distribution in Western Port in 1939. Source: Bird and Barson (1975)

Fig. 5 Mangrove distribution in Western Port in 1984. Source: Bird (1986)

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Fig. 6 Clay cliffs at Lang Lang. Note rows of planted mangrove (yellow arrow) and one self-

seeded plant (red arrow).

Sediment is entering at the eastern end of Western Port from the erosion of cliffs (Fig. 6).

This process has been going on for many years, at least since 1842 (Bird and Barson, 1975).

Other sediment loads into Western Port come from rivers, drains, canals and non point-source

inputs that drain the highly modified catchment. Increased sediment has reduced light enough to

seriously affect the photosynthetic capacity of seagrasses. This reduced light has caused loss and

decline in growth of seagrass which, in turn has reduced its ability to hold sediment, creating a

positive feedback loop that results in further increases in sediment load and reductions in the

underwater light regime (Bulthius, 1984).

There are two reasons mangrove rehabilitation might need to be pursued in Western Port.

The first relates to the poor—and worsening—ecological condition of the aquatic habitats in

Western Port and the decrease in the quality of ecosystem services that they can provide. In a

recent review Understanding the Western Port Environment: a summary of current knowledge

and priorities for future research (Melbourne Water 2011) the authors began by suggesting that

some of the changes to Western Port and its catchment are irreversible, so it will never return to

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some of its past states. Expansion in urban areas has changed land use on the northern bay shores

altering runoff and river discharges. Commercial fishing is being phased out. Climate change

will bring rising sea levels, changes to catchment discharges and wind and storm patterns,

requiring adaptation, rather than mitigation

(http://www.melbournewater.com.au/westernportreview).

The second relates to climate change and sea-level rise. Faced with strong likely impacts

on the Western Port ecosystem as a result of climate change and sea-level rise, the Department of

Sustainability and Environment published a report outlining predicted climatic changes in Port

Phillip and Western Port areas under a medium carbon dioxide emissions scenario for 2030 and a

low and high emissions scenario for 2070 (DSE, 2008). It suggests that the number of frost days

(when temperature falls below 2°C) will decrease while days over 30°C, 35°C and 40°C will

increase under all emissions scenarios.

Table 1 shows the monthly average rainfall and minimum and maximum temperatures for

Western Port. This increase in temperature generally translates into increased evaporation rates.

Rainfall is generally expected to decrease under all emissions scenarios but intensity of rainfall is

expected to increase and will fall on fewer days. Global sea-levels are predicted to rise by 0.18 to

0.79 m by 2095 with greater rises possible due to polar and Greenland ice sheet collapse (Church

et al., 2008). Intense rain events combined with sea-level rise could result in storm surges that

would lead to more coastal erosion and cause widespread damage to coastal cliffs (DSE, 2008).

There is now a sizeable literature that links the value of coastal wetlands and their ability to

(partially) control coastal erosion with the likely impacts of climate change and, in particular,

sea-level rise (e.g., see Gedan et al. 2011; Shepard et al. 2011)

Table 1: Climate statistics for Rhyll. Source: BOM (2010) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual Mean maximum temperature (°C)

23.5 24.2 22.3 19.4 16.2 13.8 13.2 14.3 15.9 17.6 19.9 21.5 18.5

Mean minimum temperature (°C)

15.2 15.8 14.5 12.4 10.6 8.8 8.1 8.3 9.3 10.4 12.1 13.5 11.6

Mean number of days ≥ 35 °C

0.6 0.4 0.2 0 0 0 0 0 0 0 0.1 0.2 1.5

Mean number of days ≤ 2 °C

0.1 0.1 0.2 0.2 0.3 0.2 0.1 0.1 0.1 0.1 0.1 0.2 1.8

Mean number of days ≤ 0 °C

0 0 0 0 0.2 0.2 0.1 0 0.1 0.1 0.1 0 0.8

Mean rainfall (mm) 35.7 38.1 36.2 61.3 65.2 57.5 65.2 78.3 67.2 59.4 56.4 42.5 665.9

A programme has existed since 2004 to establish mangroves in Western Port, but it has

had mixed results. In this report we review the successes and failures of these planting efforts

and, by reviewing the literature on planting of mangrove and creation (or re-creation) of coastal

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wetlands more generally, make some suggestions for successfully establishing mangroves alone

the shore of Western Port. Finally we investigate alternatives to growing mangroves to protect

the cliffs on the eastern edge of Western Port and facilitate the recovery of seagrass beds within

the embayment.

1.2  Possible reasons for mangrove revegetation 

To be successful, any ecological rehabilitation programme needs a vision that is

unequivocal and unambiguous and has an attainable aim or set of aims directly related to that

vision (Ryder et al., 2008). Thus the first question to ask when starting this review task is: What

is the reason for planting mangroves in Western Port?

We can imagine that there might have been a number of reasons for mangrove plantings:

1. Recreate mangrove stands from areas where mangroves had been lost since European

colonization, e.g., as a result of clearing to improve access, or of collection of plants for

barilla-ash production, in order to provide better and more extensive high-quality habitat

for fish, invertebrates, birds, etc;

2. Rehabilitate mangrove stands along the north-eastern shore of Western Port specifically

in order to reduce the wave action that causes coastal erosion and the loss of valuable

farming land;

3. Rehabilitate mangrove stands along the coastline more generally, in order to reduce

wave-induced sediment resuspension, thus decreasing the turbidity of the water column

and facilitating the recovery of seagrass beds; or

4. Rehabilitate mangroves stands along the coastline more generally, in order to capture

sediment coming from the broader catchment as suspended particles during storms and

other periods of high runoff, also with an eye to facilitating the recovery of seagrass beds.

Thus, it would seem that there are at least four partly related reasons that mangrove

creation or rehabilitation might be desired:

1. Create habitat for aquatic biota in Western Port, including fish and invertebrates and

more terrestrial organisms that use mangroves to roost, nest or feed, such as many species

of coastal birds;

2. Reduce shore erosion and the loss of valuable grazing land;

3. Reduce sediment loads to the waterbody of Western Port, thereby limiting the potential

for smothering of seagrasses beds and thus to facilitate seagrass recovery;

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4. Reduce sediment loads to the waterbody of Western Port, thereby improving water

clarity, thus permitting more rapid seagrass photosynthesis and growth, and hence also

helping facilitate seagrass recovery.

For rationales 3 and 4, we can see a further set of bay-wide consequences that might arise

from mangrove plantings: once sediment loads in the water column have been reduced and the

underwater light regime improved, seagrass, particularly Zostera muelleri, could return naturally

and this submerged vegetation would, in itself, reduce sedimentation by slowing overlying water

that would then release its sediment. The less turbid water would then allow Heterozostera

nigricaulis to grow in subtidal areas. The result would be an improvement in the area and

condition of seagrass beds, and related improvements in the ecosystem services provided by

Western Port, e.g., recreational fishing.

We stress that it is important from the onset of this review to decide on why mangroves

are being planted around Western Port. Once this decision has been made, an assessment of the

plantings’ success can be made and an assessment as to whether the monitoring methods being

used to gauge that success are also appropriate. Success might only be survival of mangrove

seedlings, but if that is the case then it does not bear much relationship with why the planting

was done in the first place. In other words, although survival would be an essential component of

the monitoring programme it is not a sufficient measure of success. A set of quantitative

measures should be developed to gauge whether those aims had been achieved, i.e. whether the

project was ‘successful’, as discussed later.

It seems that a primary objective for growing mangrove is to reduce suspended sediment

in the waters of Western Port by reducing coastal erosion. However, cliff erosion is not the only

source of sediment and we found that maritime processes are not the only ones contributing to

coastal erosion of the Western Port shoreline. To emphasize and find examples of the need for

mangroves to prevent cliff erosion, we examined the cliffs at Jam Jerrup. According to the Lang

Lang Foreshore Reserve Coastal Management Plan (Anon, 2012) “Recent erosion of the Red

Bluff area has been significant, with an estimated 10 metres of cliff falling in some areas during

the last three years. This erosion threatens the viability of the cliff top walk that goes through

this area”. The erosion from these cliffs may not be caused by waves from the sea, but rather

from water flow from the top of the cliffs after heavy rain (Fig. 7). Although large amounts of

rock have been placed on the beach 100 m further north, it is evident that freshwater erosion of

the cliffs has occurred (Fig. 8). The eroded sediment from these cliffs can easily pass through the

rocks and into Western Port. An earlier DSE report (Department of Sustainability and

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Environment, 2011) showed a photo of this cliff without the rocks and a collapse of part of the

cliff could be seen. This collapse is obviously reduced by the rock deposits but the landward

erosion continues.

Fig. 7 Slump from land at Jam Jarrup from terrestrial erosion.

Fig. 8 Rocks to protect cliffs at Jam Jarrup, note stripes of erosion in the cliffs, this erosion

is caused by rain, not waves from the sea. Suggested solution—stop run off down the cliffs. The

sediment washed away here will go into Western Port.

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Further north, again according to the Lang Lang Foreshore Reserve Coastal Management

Plan (Anon, 2012), “the majority of erosion at Lang Lang typically occurs during storm events

and high tides when water levels are raised. There was a significant storm in April 2009, which

considerably eroded the cliffs along the foreshore, and inundated the caravan park. Foreshore

erosion is a natural coastal process and does not always require protection options to be

implemented. The costs and benefits of erosion mitigation and protection must be balanced with

the risk involved which must be assessed for each site. There have been several reports and

investigations into erosion undertaken, the most recent being a Geotechnical Risk Assessment

(Parsons Brinkerhoff, 2009)”.

The implication from these points is that the planting of mangroves reviewed in our

critique is only part of what is required to reduce the loss of agricultural land, loss of mangroves,

and adverse effects on seagrasses and other fully aquatic elements of the Western Port biota. Any

amount of mangrove planting will not resolve erosion from coastal movement and loss of the

hinterland if it is caused by rain and overland flow.The effect of cumulative and diverse types of

impacts needs to be evaluated.

There is a scarcity of information for ecosystem-scale processes in the mangroves of

Western Port (Melbourne Water, 2011). Data gaps on benthic communities, plant-animal

interactions, animal-sediment interactions and food-web studies are challenges that need to be

addressed. Some of the research needs and knowledge gaps are described in Dittmann (2011).

2. Revegetation of Avicennia marina 

2.1 Meaning of the terms ‘restoration’ and ‘rehabilitation’ 

There is considerable confusion in the natural-resource management field about the terms

‘rehabilitation’ and ‘restoration’. Dictionaries generally tend not to differentiate between the two

(e.g., see Shorter Oxford English Dictionary) nor do many learned articles on wetland creation

(e.g., Lewis 1989), but there is a distinction worth making, especially with degraded ecosystems.

Bradshaw (1997) argued that the term ‘restoration’ should mean “reversion of a degraded

ecosystem to its original condition”. Lake (2001, page 110) referred to this process as “inducing

and assisting abiotic and biotic components of an environment to recover to the state that they

existed in the unimpaired or original state” In most cases the original condition is equated with

pre-European condition, but even that end-point has its conceptual and pragmatic problems.

In contrast, ‘rehabilitation’ describes an acceptable improvement in ecological condition

(see discussion in Lake, 2001) and, in most cases, is a more realistic management objective. The

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term is used in the same way as it is in a rehabilitation hospital for the war-wounded: the

intention of medical care and intervention in rehabilitation hospitals is not (indeed cannot) be the

complete recovery of, say double amputees or those made blind by gas, but their treatment with

prostheses, physiotherapy etc in order that the patient can become a useful and functioning

member of society. Much the same argument holds for the rehabilitation of damaged, i.e.

degraded, natural systems, where management interventions are expected to markedly improve

the ecological condition of the system and allow it to again deliver, in broad terms, the sorts of

ecosystem services the community expects but are never intended to return the system to some

notional ‘pristine’ condition. Hobbs (2005) developed the argument further, and distinguished

among three types of management outcomes: i) maintenance; ii) improvement; and iii)

reconstruction. In his scheme, reconstruction broadly equates with restoration, and improvement

with rehabilitation.

The Society for Ecological Restoration’s International Primer on Ecological Restoration

(SER, 2002) defines ecological restoration as “the process of assisting recovery of an ecosystem

that has been degraded, damaged or destroyed”, but it is a much broader concept. The goal of

ecological restoration, according to the SER report, is a resilient ecosystem that is self-sustaining

with respect to structure, species composition, and function, while integrated into a larger

landscape and congenial to low-impact human activities. According to Aronson et al. (2007), an

associated discipline is ecological engineering, which involves restoring and creating sustainable

ecosystems that have value to humans and nature. Ecological engineering should

restore/rehabilitate damaged ecosystems and create new sustainable systems in a cost-effective

way.

In the light of this material on terminology, we take ‘restoration’ to mean the recreation

of an ecosystem to a pristine condition, usually defined under Australian conditions to some pre-

European model. In contrast, ‘rehabilitation’ is an improvement in ecological condition, whether

measured in terms of structure, e.g., floristics, function, e.g., ecological processes, or value, e.g.,

the provision of ecosystem services.

2.2 Mangrove planting review 

Almost all of the studies into mangrove ecology have been done in the tropics, and

temperate mangroves are not structurally or functionally equivalent to those in the north of

Australia. Thus, it was refreshing to find a comprehensive review of the ecology and

management of temperate mangroves by Morrisey et al. (2010). Lewis (2005) gives a sensible

account of the necessary hydrology required for growing mangrove with a review of successful

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mangrove restoration, and other articles on mangrove establishment in temperate climatic zones

have been written by Field (1998, 1999) and McManus (2006).

Lewis (2009) is a strong advocate of not growing mangroves where they never were in

the recent pass (100–200 years). If it is necessary, as the current case in Western Port may be, he

suggests that aside from the need to understand the existing hydrology as it relates to topography

of a mangrove stand nearby as a reference site, it is also important to understand the natural

recovery process in damaged mangrove areas also known as ‘secondary succession’. The natural

secondary succession process in damaged mangrove forest often begins with the appearance of a

‘nurse species’ which is typically an herbaceous plant species like Sarcocornia quinqueflora or

in Lewis’ (2011) case Spartina. Fig. 9 shows volunteer mangrove seedlings behind a strip of S.

quinqueflora, which in turn is fronted by a dense band of mangroves on the seaward side.

Fig. 9. Pioneer Bay—mangrove fringed by saltmarsh. Note mangrove seedlings behind saltmarsh

consisting of Sarcocornia quinqueflora.

As mentioned above, the planting efforts on the eastern edge of Western Port are not

efforts at restoration but new plantings. Propagules from grey mangrove have rarely been shown

to disperse more than 10 km but there are stands of mangrove less than 10 km from the

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mangrove plantings (Clarke, 1993), so if it were possible to establish seedlings at the plantings

site, there should be some evidence of mangroves there already. Growing mangroves where they

have not recently been growing is fraught with danger and most often discouraged (Lewis, 2009;

Samson and Rollon, 2008). In Victoria, in Port Phillip Bay in the Stony Creek Backwash of the

Yarra River, mangroves were planted about 25 years ago and have been very successful in filling

the area; they propagate, are highly productive, and flower annually (Harty, 2011; Appendix 1 of

this report). An alternative view, however, has been proposed by restoration ecologists such as

Hobbs (2005), who argue that the impacts of climate-change are likely to be so pervasive and

unpredictable that land- and water-managers should be ready to consider the value of entirely

novel ecosystems and communities of organisms taking the place of existing assemblages.

In an excellent review of mangrove restoration in Western Port, Hurst (2012 see

Appendix I) describes Western Port and its mangroves. The embayment covers an area of 680

km2, of which around 270 km2 are intertidal mudflats. There is approximately 263 km of

coastline in the bay, 40% of which is fringed by a band of Avicennia marina mangrove trees

growing in the intertidal zone (Clough and Attiwill, 1975). The mangrove fringe is generally less

than 100 m wide, but in some areas can be up to 300 m wide (Bird, 1986: see also Fig. 10).

There are also receding clay cliffs up to 2 m high in the vicinity of the Lang Lang River mouth

on the eastern shores of the Bay (Fig. 6).

Fig. 10. Wide bands of mangroves growing on the northern shore of Western Port, near

Tooradin.

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The sediment dynamics in Western Port were investigated by Wallbrink et al. (2003),

who found that fine sediment in the Bay was reworked daily by tidal and wave action, causing

high turbidity. The clockwise transport of this sediment around the bay means that sediment

deposited in the northern sections is resuspended and can affect water quality in the seagrass

meadows in the eastern and southern parts of Western Port. Wallbrink et al. (2003) also traced

the origin of sediments and found that most deposited sediment is derived from channel and

gully erosion occurring in the Bunyip and Lang Lang River catchments. However, the tracing

study also indicated that up to 30% of sediments originate from the eroding clay cliffs along the

eastern coast around the Lang Lang River mouth (Wallbrink et al., 2003). This study

recommended that, despite the unlikely existence of mangroves historically in this area (Boon et

al., 2011), replanting of mangroves to stabilise these eroding cliffs could help to reduce some of

the possible causes of seagrass decline in Western Port.

Rogers et al. (2006) found that there was some localized expansion, of up to 60% of the

mangrove fringe, in areas where mangroves were already well established. The expansion

occurred partly by mangroves encroaching into the saltmarsh and partly due to the fringe moving

seaward. The seaward expansion of mangrove forests is usually related to the accretion of

sediments and subsequent increased elevation of the mudflats on which they grow (Harty, 2010).

Mangroves in Western Port have been shown to contribute to accretion processes within the

mangrove forest through pneumatophores and tree trunks locally slowing currents and enabling

suspended sediments to settle (Bird, 1986). It is also thought possible that the existence of

mangroves in Western Port can lead to accretion in adjacent mudflats by providing wind

protection from offshore winds for around 6 m seaward of the mangrove fringe, allowing

sediment to settle more easily (Bird, 1986).

2.3 Principles critical for effective rehabilitation or creating mangrove forests. 

Like most plants, mangrove stands flourish in conditions to which they have adapted over

millions of years. Obviously they need seawater, a muddy substratum and a particular

temperature range. Then what distinguishes a good from a bad restoration/rehabilitation

programme? Zedler (2006) listed a number of principles critical for the effective rehabilitation of

degraded wetlands, we adapt this list to restoring and creating mangrove stands. The points made

explicit by Zedler (2006) were:

1. Consider the hydrological, geomorphological and ecological landscape, along with the

prevailing climate. Seedlings cannot survive in extremely vigorous water conditions.

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They will not tolerate long periods of exposure or cold. Consideration should be given to

the substrate stability paying particular attention to soil types, water depths, tidal ranges

and planting schedules.

2. Adopt a dynamic landscape-scale perspective.

3. Restore or develop naturally variable hydrologic conditions.

4. Where possible, choose to rehabilitate rather than to create a wetland. Some of the

seedling planting was done in areas where mangroves never grew in the past. The reason

for their not being there should be ascertained and limiting conditions changed, if

necessary.

5. Avoid over-engineered structures. Geotextile® sausages were used to protect the

mangroves from strong waves at one site where mangroves had not grown. If these are to

be laid for long distances, e.g., kilometres, they should allow water to pass between them

with tides.

6. Provide suitably heterogeneous topography, i.e. small pools or concave areas where

opportunistic seedlings can settle.

7. Pay attention to sub-surface conditions, including sediment biogeochemistry and runoff

issues.

8. Consider the complications associated with rehabilitation or mangrove creation in

seriously degraded sites.

9. Undertake monitoring early in the adaptive management process. Survival counts should

be made as a minimum but some form of productivity measure, such as new leaf counts

or shoot additions over time would be a useful measure of health and ability to grow.

Generally, in Western Port, a qualitative assessment seems to have been made that the

area for creating mangroves fulfills these principles. Soil types, salinity, tide range, exposure to

the atmosphere, insolation, storm frequency and intensity and a check on pathogens, insects and

disease should also be documented.

2.4 Mangrove plantings in Western Port 

The initiative to grow mangroves in Western Port was begun by Dr Tim Ealey, a local

retired scientist, whose energy since 2004 has been largely responsible for the scale and

continuity of the plantings. He aimed to grow and transplant into the field thousands of

mangroves (Ealey, 2011b).

22

Beginning in 2004, as part of a joint project with DSE the Western Port Seagrass

Partnership became interested in planting mangroves south of the Lang Lang River where

erosion was severe. Seedlings were transplanted from Pioneer Bay in May 2005. Some of these

survived, especially where protected in erosion depressions, and produced seeds in 2010. The

project north of the Lang Lang River was supported by the Alternative Penalties Provision of the

Environmental Protection Act 1973. This is a grant that enables a magistrate to choose between a

set fine that goes to consolidated revenue or to order a convicted company to pay a sum of

money to a community group to undertake offsetting environment improvement projects. A

project target to transplant 7,000 plants carried out by the Bass Valley Land Care Group during

2006–2007 would have fulfilled the project target if the plants had survived, however all but a

handful disappeared. This mortality was probably because stunted, older plants were transplanted

instead of more vigorous seedlings.

Several staking arrangements, group plantings and single plantings were tried. Plants tied

to stakes broke off at the tie. Some plants, grown from seeds planted in the mud, appeared to do

well but often the seeds were eaten by crabs Ealey, 2011b). Seeds planted in peat pots, even

though they were staked, washed away. Thousands of seeds collected in December 2008 grown

by the Mornington Peninsular Youth Enterprises nurseries were killed by an exceptionally cold

autumn in 2009. The nursery later built a plastic, igloo-shaped greenhouse to protect the plants.

Growing viable cuttings was attempted but not one cutting survived. In 2010 the nursery

produced 7,000 seedlings in an igloo and 4,063 were planted out along 3 km of the coast.

The Coastcare Victoria Community Grants Programme is a partnership between the

Australian Government’s ‘Caring for our Country’ and the Victorian Government’s Department

of Sustainability and Environment’s Coast Action/Coastcare’. Grants are usually open to any

incorporated community group (including Coastcare and Coast Action groups), indigenous and

community service organizations and clubs and education institutions. This source of funds was

used to support the second project, undertaken along the Grantville coast.

Melbourne Water has planted mangroves along the eroding coastline north of the Lang

Lang River. The main purpose of this project is to attempt establishing mangroves for

stabilisation of the eroding north-east coastline

2.5 Methods used in nursery 

Mature fruit from mangrove trees were collected in December each year from mangrove

stands at Pioneer Bay (recently) but earlier also from Tooradin. Some years, e.g., 2009, there

were very few fruit to collect. When fruit are available, about 60 healthy fruit are placed in trays

23

(measuring 300 mm x 800 mm and 40 mm deep), nestled among wet seagrass (Fig. 11). Care for

the seedlings is variable. School children germinate the seeds in trays of seagrass, which teachers

take home to maintain during school holidays. The fruit are left to continue germinating until a

root and cotyledon are well established (Fig. 11). The seedling is then placed in a 600 ml

cardboard milk carton with a fertile soil. The schools use sandy loam or potting mix. At the

nursery, seeds or germinated seeds are planted directly into milk cartons. The nursery has

experimented with a range of substrata but now uses a sandy soil. The seedlings are then grown

in the carton in a plastic greenhouse until six leaves have emerged. The cartons are stapled for

further security for the seedlings (primarily to prevent the outwashing of surface soils by waves

or storms) and planted in the field (see Appendix 1 Hurst, 2012).

During 2004–2008 various experimental procedures were tried to ascertain planting and

germination procedures and whether seawater or freshwater should be used to keep planting

media moist. A few schools participated in the planting exercises. There are little quantitative

data available for this period but there is some information on survival rate and planting

quantities during the early stages of the project from 2004–2008. This gap in knowledge and

record keeping may be significant in providing answers to the questions now being addressed.

The nurseries of Mornington Peninsular Youth Enterprises, using thousands of seeds collected in

December 2008, grew several thousand plants in the following year. An exceptionally cold

autumn in 2009 killed most of the seedlings before they were planted. In December 2009,

although the nursery built a plastic greenhouse to protect the plants from cold, there were hardly

any seeds produced and less than 2,000 were collected.

This setback stimulated experiments with cuttings assisted by a professional

horticulturalist. Over 600 cuttings were planted using several cutting media and potting mixes.

No cuttings survived, so the team leading the revegetation efforts was obliged to wait for the

next seeding season. The following year—2010—was an excellent year for seeds and the nursery

germinated 7,000 in the plastic greenhouse. However, heavy rain in late summer of 2010 flooded

the nursery and many plants were washed out of their containers and lost.

24

Fig. 11 Seedling tray with seedlings held in wet seagrass. Seawater is added to keep the seagrass

moist.

2.6 Success in nursery 

By experimenting, Dr Ealey has managed to determine optimum conditions for

germinated fruit to develop into plantable seedlings (Appendix 1 Hurst 2012). Using the trays

and seagrass as a medium (Fig. 11), nearly 100% of germinated fruit collected from local

mangroves grow into plantable seedlings. The largest of these fruit or the seeds from them are

chosen and have shown to germinate best. The trays are watered with 30% seawater, which is the

salinity at which temperate Avicennia marina seedlings grow best (Morrisey et al., 2010)).

2.7 Methods used in planting 

The methods used and some of the pitfalls of planting are explained in Appendix 1

(Hurst, 2012). In 2004, as part of a joint project with DSE, the Western Port Seagrass Partnership

became interested in planting mangroves south of the Lang Lang River where there is much

erosion. Dr Ealey became the ’champion’ of mangrove planting and it is through his efforts that

much of the mangrove planting has been done.

“The main objective of the programme was to grow a strip of mangroves along the coast

two metres wide. It was important to construct a continuous barrier for erosion protection rather

than a series of experimental plots which could be by passed by waves. Therefore each set of

planting was added to the survivors of the last planting(s) replacing losses and using different

methods each time. We monitored what we could when we could access the plants but this was

really of no use as almost all ultimately disappeared. The few that survived usually could not be

25

associated with an individual planting. The methods by now have been much improved so the

small survival rates of earlier plantings are meaningless as regards future planning. The

important facts are that hundreds have actually survived for 4–5 years where mangroves have

never grown before, have pneumatophores and are producing flowers. Therefore the substrate

and level on the mud flats is usually appropriate and once established, mangroves will survive

the harsh conditions. However we need thousands”. This is a section of a personal

communication from Dr Ealey in 2012.

Seedlings were transplanted from nurseries, in May 2005, to south of the Lang Lang

River by a number of local schools and other volunteer groups. Seedlings were transported in

trays with sixty seedlings in each tray and they were individually planted. A number survived,

especially where they were protected in erosion pockets and some produced seeds in 2010.

Large numbers of what was assumed to be seedlings under the adult trees at Blind Bight

were the basis of the project north of the Lang Lang River, using a grant from the Alternative

Penalties Provision of the Environmental Protection Act 1973. Using volunteers and the Bass

Valley Landcare work crew, over 7,000 plants, singly or in groups, were transplanted during

2006–2007. All but a handful disappeared, probably because most transplants were not young

seedlings but stunted older plants and died in the field. Others were torn out by the waves.

Because wave energy seemed to be the main cause of seedling mortality, several staking

arrangements and group plantings were attempted. Plants tied to stakes broke off at the tie. Some

plants, grown from seeds planted in the mud, seemed to do well but often the seeds were eaten

by crabs (Tim Ealey, Pers. Comm.) Seeds in peat pots with support stakes were washed away.

Successful experiments growing mangroves in milk cartons supplied by Visy™ seemed a

reliable method although milk cartons were bulky and heavy when filled with soil. The milk

carton allows a large plant with a good root system to develop. The carton is then staked into the

mud using a milk carton shaped tool (Fig. 12) that allowed them to be embedded very securely in

the mud, as the carton is held fast by suction (Ealey, 2011a).

Fig. 12 Mangrove planting tool.

26

In 2010 about 5,000 seedlings were salvaged after the greenhouse flooding and 4,063

were planted along 3 km of the eastern coast of Western Port.

There is now evidence that the methods developed over this time are effective for the

germination, seedling-growth and early establishment of young plants. Koo Wee Rup Secondary

School, for example, planted 300 large seedlings on 28 March 2011 at Jam Jerrup, of which only

seven were missing after nearly four months of winter storms in an area where waves of 2 m

have been observed. These were strong, healthy plants with at least six leaves. Furthermore, in

20 July 2011, an additional 500 plants were planted north of the Lang Lang River in milk cartons

that had the top openings stapled together, thus firmly but gently holding the plants and

preventing them being torn out by waves (Fig.13). Almost all have survived the winter storms, in

contrast to other nearby plantings which were not in stapled containers and died.

Fig. 13 Stapled milk carton showing healthy mangrove plant planted in clay mud along the shore of

Western Port, near the Lang Lang River.

27

2.8 Recent replanting projects 

The past two years (2011–2012) saw a consolidation of efforts to reduce wave-driven

cliff erosion along the north-east coastline of Western Port by mangrove plantings at various

points along the shoreline. There currently three major projects being undertaken:

1. Lang Lang coastline project

2. Grantville coastline project

3. Melbourne Water mangrove revegetation project.

Project 1: Lang Lang coastline

Along the south side of the Lang Lang River a project funded by an EPA/ Alternative

Penalties Provision of the Environmental Protection Act 1973 grant set out to grow mangrove

along the high energy environment of the Lang Lang cliffs. Here special techniques are required

as two metre high waves can occur. Part of the work was devoted to testing different staking and

tying methods in different substrates. Unless stakes were buried deeply they washed out. When

plants were tightly tied to the stakes they broke off. Loose ties allowed plants to wash out.

Unless planting was carried out in very firm mud there were losses, even though softer mud

would have been ideal in calmer conditions (Fig. 14).

Using two stakes with ties which allowed some movement but gave support provided

better results.This project changed from a simple planting project to a research project because of

the difficulty of planting mangroves on a high energy coast. A number of innovations were tried

with varied success. Thousands of seedlings in milk cartons were planted but success was limited

because, although the milk cartons remain in place, the plants were often torn out by the waves.

A trial using 500 cartons with their tops stapled had some success and a large scale trial was

carried out in 2012. It is not clear that the distance from the cliffs that the mangrove seedlings

were planted is the optimal tide depth for successful growth. Experiments were not carried out to

determine the best depth considering the backwash from the cliffs that occurs in storms.

28

Fig. 14 Soft surface ooze at the Lang Lang cliffs. The author of Appendix 1, Tom Hurst,

demonstrates the softness of the mud.

Project 2: Grantville coastline

The Coastcare Victoria Community Grants Programme funding was used to support the

second project, undertaken along the Grantville coast. In October 2009 a barrier of Geotextile®

bags was constructed to protect mangrove planting and prevent erosion (Fig. 15). In November

2009 mangrove seedlings were planted about 10 m along the lee side of the Geotextile® bags

and in a control area without protection. Very early the control plants were lost due to a strong

wash-out from a nearby creek but these were replaced. More mangroves survived in the

protected area than in the replanted control. However, other conditions may have affected the

result. Part of the kilometre of coastal planting specified in the project was completed by school

children and the remainder will be completed in 2012.

29

Fig. 15. Geotextile® sausage to protect mangrove growing on their lee side, along the

Grantville shoreline of eastern Western Port.

Building on the success of the current schools’ engagement programme, which initially

used a small amount of corporate funding to assist some schools to grow and plant mangroves,

the Western Port Seagrass Partnership received a grant from the Commonwealth Community

Coastcare grants programme. The new project is titled ‘Mangroves and Mud’, and allows

expansion of the initial successful activities to include:

1. The production of a manual for schools about mangrove raising and planting

(Ealey, 2011a).

2. More visits to local schools.

3. A programme for schools to plant their mangroves and care for them.

Some of the ten schools involved have already produced mangrove seedlings and planted

them. The schools’ programme indicated some improvement in the process of preparing and

planting mangrove seedlings:

1. Only large ripe seeds should be planted.

2. If possible plants should be raised in shelters such as plastic glasshouses.

30

3. Rich sandy soil or good quality potting mix should be used.

4. Seedlings should not be planted out until they have six leaves at which stage they are more

likely to survive infestations by barnacles or smothering by sea wrack. A strong root system

will have developed by this stage.

5. Tops of cartons should be stapled together before planting out to give plants further support.

Project 3: Melbourne Water Project

All planting undertaken by Melbourne Water (with Tom Hurst as the project manager)

has been along the eroding coastline north of the Lang Lang River. The main purpose of this

project is to attempt establishing mangroves for stabilisation of the eroding north-east coastline

as recommended by Wallbrink et al. (2003). It is predicted that this will reduce the amount of

sediments entering the bay and benefit the health of seagrass populations.

Melbourne Water planted about 13,000 seedlings over about 4 km of shoreline in

May/June 2011 and plan to put in another 10,000 starting in April 2012. No final survival count

has been made, but two preliminary counts indicate a 30% survival rate. The method used by

Ealey (2011b) in stapling the milk carton tops yielded a better survival rate (around 70–80%,

Hurst pers. comm.) than cartons without staples or seedlings planted without carton protection.

Melbourne Water will be using this technique for the coming plantings.

Over summer 2011/12, a direct seeding technique was trialled that worked very well in

some smaller trials. But there were problems with crabs eating the seeds at Lang Lang and

further work is continuing to overcome this source of seedling mortality. There are important

logistical advantages to direct seeding over planting established young seedlings, largely arising

from the smaller volumes that need to be transported to the field sites. Only propagules are

transported, and 60 of these fit into a tray (Fig. 11) compared with seedlings in milk cartons,

which weigh around 1 kg each.

More than 3000 seedlings were planted around Grantville and Corinella as part of the

Tom Hurst’s MSc project and separate to the Melbourne Water undertakings outlined above.

These plantings are testing the effects of different intertidal zones and proximities to existing

mangroves on their survival and growth. They have been planted in areas where mangroves once

flourished but were removed and have been gone for many years. Survival rates are below 30%,

but low survival rates are not uncommon in mangrove restoration projects—this is also the case

in many restoration projects in tropical areas, let alone at the southern limit of their distribution.

Direct planting of seeds with bird wire cages to prevent crabs eating the seeds has had some

31

success. We should point out that the survival rates obtained by Ealey (2011a) in areas not

previously supporting mangrove, are very impressive.

2.9 Success of plantings 

Planting success may be defined in a number of ways. First, sometimes success is

claimed if seedlings grow sufficiently to produce their own seedlings and their canopy, covering

the area planted, is similar to a nearby unaffected mangrove forest. Second, criteria, preferably

measurable as quantitative values, could be established prior to the commencement of planting

activities. Success can then be defined as the successful integration of plant material

establishment with fishery and wildlife habitat establishment and water quality improvements

(Lewis, 1989). This habitat equivalence can be measured with quantitative measures such as

species presence in conjunction with plant cover. The habitat measurements are compared with a

proximate mangrove forest. A third approach might be to set a numerical target for survival over

a given period: e.g., 70+ % survival of planted seedlings after one year.

2.10 Causes of mortality 

Mangrove seedlings in southern Victoria face one main obstacle that other mangroves

usually do not—cold. They are killed or considerably damaged by frost and growth rates may be

reduced by long spells of cold weather. The result is that growth rates are not as fast as in

tropical mangrove forests.

It is likely that a range of other environmental factors may also come into play as

mortality factors. First, the elevational band occupied by mangroves in Western Port is quite

narrow (Boon et al., 2010), and it is not clear from the planting so far carried out whether the

plants are being placed at the correct elevation with an appropriate tidal inundation. Moreover,

slightly raised areas may exist that allow mangroves to growth successfully in zones that would

otherwise be too deep for them: the role of such subtle microtopographic variations in the

success of wetland revegetation has recently been shown with the wetlands that fringe the

Gippsland Lakes (Raulings et al., 2010, 2011; Boon, 2011).

Second, waves and erosion (including backwash from cliffs) may remove plants.

Protection was given in some cases but stapled milk cartons and wood planks to protect

seedlings have not been entirely successful.

Third, physical damage is increased by fishing lines, debris and seagrass drift all

accumulate on seedlings. Their increased surface area then provides more resistance to waves

32

and increases the likelihood of the seedlings being washed out. If heavy enough, this debris

reduces photosynthesis.

Fourth, consumption by insects and smothering by barnacles growing on the leaves may

cause some problems. It is noteworthy that Hong (1996) and Satumanatpan and Keough (1999)

have marshaled empirical evidence to show that barnacles are not a significant cause of seedling

mortality., and this is in contrast to the observations of Ealey (2011b).

Clarke and Allaway (1993) commented that herbivory of post-dispersal mangrove

propagules by crabs was less important in temperate than tropical parts of Australia. Consistent

with this suggestion, individuals of the temperate Australian mangrove crab Helograpsus

haswellianus did not consume propagules of Avicennia marina when offered them in laboratory

experiments (Imgraben and Dittmann, 2008). In the research of Ealey (2011b) it was found that

some plants grown from seeds directly planted in the mud seemed to do well but often the seeds

were eaten by crabs.

Another source of irritation to the efforts of planting mangrove and mortality to seedlings

is direct human vandalism of planted mangrove seedlings. This is often attributed to people who

do not want mangrove stands in front of their properties or who consider that mangroves are a

haven for and attract mosquitoes.

2.11 Possible solutions to lowering mortality 

Before solutions to improve survival can be devised, it is necessary to first determine the

cause(s) of mortality. In the absence of this information, we can only propose as possible

solutions the follow options.

A cost-effective method for attenuating wave energy to protect a coastal mangrove

plantation was developed by Halide et al. (2004) in Indonesia. The design used bamboo poles, a

strong, cheap, environmentally friendly and widely available material in tropical developing

countries. The bamboo poles were pushed into the sediment offshore from the coastal mangrove

plantation. A numerical model was used to determine performance in reducing incidental wave

energy. A field experiment on a mud bank suggested that the bamboo be pushed in no less than

600 mm to avoid scouring and dislodging with 1 m protruding above the bank surface. Although

bamboo is not as readily available in Victoria, some other natural product might be used, e.g., tea

tree (Melaleuca ericifolia) or wooden pickets. At the same time these are deployed, records of

cliff position should be taken as the barriers may also be protecting eroding cliffs.

The problems of drift detritus being caught in newly planted seedlings are partially

overcome when seedlings are only planted when they have six leaves (Ealey, 2011b). He

33

suggests that this robustness allows plants to withstand barnacle infestation and be strong enough

to hold seagrass wrack.

The stapled milk carton used by Dr Ealey’s team is a useful addition to making a hole

and placing the seedling in it. A specially designed tool, shaped as a milk carton base, is pushed

into the substrate and the milk carton containing a mangrove seedling is then placed in the

resultant hole. The carton has been stapled at its top to prevent the seedling washing out yet an

opening is left to allow leaves to receive sunlight.

Planting mangrove in clumps, rather than in rows a metre apart may be useful in their self

protection but experiments are needed to test this idea.

2.12 Strategy for future planting 

More plantings are planned in 2012 with available seedlings and it is anticipated that all

will be done with stapled milk cartons. Much of the planting will be done by school children,

which has the benefit of raising the awareness of mangroves among the wider community,

showing the problems with working in estuarine environments, and illustrates the range of other

marine issues and value of team work for these children.

There is, however, no long-term strategy or plan for mangrove planting in Western Port.

Departments responsible have not developed a strategic plan for erosion control, reducing

sediment, mangrove revegetation or establishment in areas where mangroves seemingly did not

occur in the recent past, or rehabilitation in areas that they did. There are many reports

suggesting future plans and activities but, until now, no concerted effort has been made to reduce

sediments and sedimentation at the northern end of Western Port. A recent summary of current

knowledge and priorities for future research is useful in directing a strategic plan but it falls short

of actually providing a strategic plan (Melbourne Water, 2011). Until such a plan becomes

available, it is likely that mangrove revegetation will remain uncoordinated and sporadic.

3.  Alternatives to mangrove planting 

The clay banks along the eastern edge of Western Port are about 1–2 m high (Fig. 6). As

we have noted above, it is not clear whether the primary goal of the mangrove revegetation

activities is to prevent erosion of these clay banks or cliffs and other coastal erosion hotspots, or

whether it is to provide coastal habitat, or even to protect the seagrass beds that lie offshore.

Until the underlying reason for planting becomes clarified, it is difficult to suggest alternatives.

34

Notwithstanding this caveat, it may be appropriate to assume that the plantings are

designed to protect the hinterland. If so, one valid alternative is to design structures to protect

this land. Any structure should be constructed parallel to the shoreline, probably on the existing

erosion scarp. Areas below the cliffs clay mud and ooze may not be suitable for mangrove

establishment.

Structures such as revetments and seawalls are designed to halt further landward

progression of the shoreline by providing a hard shoreline for waves to break onto whilst also

retaining the soils behind the structure. They can also have a supplementary use in minimising

the inundation, through overtopping, of land areas by waves and storm surges, and thus protect

the land from erosion and from salinization. These structures range from vertical faced structures

such as massive concrete or masonry walls, e.g., the current wall along the Lang Lang foreshore,

sheet piled walls and gabions, to sloping structures made from Geotextile® bags, stone rubble,

concrete armour units or concrete panels. The large range of materials available for seawall

construction requires careful selection to suit the specific circumstances and site conditions.

Whilst structures such as these can be effective at preventing shoreline recession, they

also generally accelerate erosion of the seabed immediately in front of the structure due to

increased wave reflection directly caused by the structure. This results in increased depths that

allow larger waves to reach (and break on) the structure, and can discourage the natural

deposition of beach sediments. As a consequence, structures such as seawalls that are not well

founded may be at risk of instability caused by erosion of the seabed at the toe of the structure,

and by an increase in direct wave breaking, run-up, and overtopping. Because of their potential

vulnerability to toe scour, seawalls need to be founded below the predicted future erosion level,

or are sometimes used in conjunction with other erosion control techniques such as groynes and

beach nourishment. Seawalls also tend to create a stronger littoral current which may result in

localised scour at the down drift end of the structure, known as a ‘terminal scour’ zone.

Whilst the recycling of concrete for use in structures may be desirable, there can be

significant environmental and aesthetic impacts associated with its use. It has some of the ‘hard’

characteristics desirable for use in a seawall, its practical use is limited as most rubble is not

specifically designed for use in harsh marine environments and it will progressively deteriorate.

Evidence of this from the existing concrete rubble on the shoreline area is shown in Fig. 16.

35

Fig. 16. Concrete rubble used to prevent erosion along the Lang Lang clay cliffs

Within Western Port there are many examples of seawalls, including some that have

failed and some that have been successful in stopping the advancement of coastal erosion (Fig.

17). In the example shown in Fig. 17, a low wall has prevented erosion along a section of the

coast south of the ramp and the effects of erosion can be seen to the north where Melaleuca trees

have fallen down.

36

Fig. 17 Ramp at Malcolm Drive in Pioneer Bay. Note the vegetation and level of the beach on the RHS where a low cement wall was built compared with the LHS where trees are uprooted and the

erosion has receded further. This in not thought to be due to longshore drift.

A typical rubble mound seawall includes several layers of materials such as outer armour

(rocks or sandbags), and internal filter layers to allow the dissipation of groundwater without

allowing the retained soil to be extracted through the wall. Construction of seawalls will also

generally require the use of heavy earthmoving equipment and excavations to develop an

appropriate foundation. The other major disadvantage of these structures is the substantial cost of

materials and construction. In general, structures such as seawalls and revetments are considered

to be ‘the last line of defence’, and due to their considerable expense, tend to be mainly used for

public safety purposes or to protect important infrastructure that is not able to be relocated (taken

from GHD, 2010 report).

4.  Discussion This review was commissioned by the Western Port Seagrass Partnership to determine

the usefulness of planting mangroves at the northern end of Western Port. By reducing water

column sediment load it is hoped that seagrass will return to this area. During March 2012, we

visited field sites of mangrove planting and saw eroded cliffs e.g., see Fig. 6. We had interviews

37

with people involved in actually planting mangroves and we examined the many reports that

have appeared on sedimentation, erosion, light reduction and mangrove planting.

Our conclusions are that, although mangrove restoration and creation may eventually

reduce erosion of the Lang Lang cliffs, stabilise some sediment moving around on unvegetated

mudflats and add to biodiversity and bird life, it will not, in the immediate future, save the

seagrass beds nor help increase light availability to the seagrasses. At the very first, what is

required is a thorough understanding and agreement on the scale of the problem(s), their

ecological, social and financial costs, and the range of actions that can be implemented to reduce

the problems and thus offset the associated costs. It can be argued that what is required is a large

financial investment in structures to reduce wave action onto the coast. These may be as simple

as Geotextile® sausages or low seawalls. The more costly structures are probably prohibitively

expensive.

It appeared to us that much encouragement was given to the enormous efforts of

dedicated people in growing mangroves and little in kind or funding assistance to actually solve

the problem of sedimentation and turbidity in Western Port. Government agencies seem to

sponsor and encourage many reports, seminars and meetings but fail to come to the real terms of

the problem and provide suitable funding to solve it.

Although a large financial investment is required to improve water quality, plant

mangrove, restore seagrass and make some engineering changes, funding from offsets that will

be required for the new port development at Hastings should be considered for this purpose.

As mentioned earlier some attempts to grow mangroves are in areas where mangrove has

not grown in the recent past (100–20years). Lewis (pers. comm.) recommends test plantings, and

planting along a topographic gradient to test survival. This suggestion is consistent with the

findings of recent research into the rehabilitation of coastal brackish-water in the Gippsland

region (Raulings et al., 2010, 2011; Boon, 2011). He also suggests choosing locations where

mangroves can self-seed and can thrive (given of course the issue of propagule limitation, a topic

of his 2005 paper (Lewis, 2005). That location, by necessity, has not been identified for this area.

Lewis (pers. comm.) also suggests zonal test plantings over a range of topographic elevations

from what appears to be ‘too high’ to ‘too low’ and following them quantitatively over time.

This would help solve the issue of topographical gradient. It does not appear that this ‘zone of

likely success’ approach has been implemented in the current trials..

Based on figures from real estate sales advertisements in the Lang Lang area we

estimated that the current value of grazing ground near the Lang Lang cliffs is about $13,000 per

hectare. If, as Anon (2012) estimates, there are 10 m of coast being eroded in three years and the

38

eroded coast is 11 km long the value of land lost per year, assuming three metres are lost, is

$429,000. Management agencies and farmers should keep this in mind when they are

considering investment decisions and on-ground actions.

5.  Recommendations 

1. Despite the recent comprehensive reviews of Western Port and its mangroves (Boon et

al., 2011; Melbourne Water, 2011), there is still no strategic plan for this coastline and

this remains a priority.

2. Management arrangements for coastal wetlands in Victoria are complex and mostly

insufficient to the task (Boon et al., 2011) and need to be considered when devising

revegetation activities and associated attempts at shoreline protection.

3. A recent media release and seminars hosted by Melbourne Water are the first efforts to

get better attention to the issues of seagrass decline, mangrove planting and coastal

erosion, but media coverage must be increased, targeted and improved. This coverage

should take into account the social marketing research undertaken by Boon et al. (2011)

and adopt a ‘stages of behavioural change’ model. The current level of understanding of

coastal wetlands is rudimentary and at a base ‘pre-contemplation’ stage (Fig. 17).

Pre-Contemplation

People do not know about coastal saltmarsh communities, let alone the issues.

Action: raise awareness

Contemplation

People know about the issues and are thinking about the benefits to action, but are not yet convinced.

Action: demonstrate benefits, cost savings

Action

People are starting to take action to protect coastal saltmarshes & mangroves and know the consequences of their actions.

Action: advocate, improve ability to act

Maintenance

People are committed but need feedback & reminders of the benefits / impacts of their actions from time to time.

Action: reward/remind

Fig 17: Four stages in the ‘stage of behavioural change’ model used to interpret community perceptions of coastal wetlands in Victoria. Outcomes of the focus-group workshops indicate that the general community is in the ‘pre-contemplation’ stage, indicated in red in the above

schematic. Source: Figure 3.2 of Boon et al. (2011).

4. A crucial first step is that the rationale for mangrove planting be made explicit; e.g., is it

for shoreline protection, creation of coastal habitat, or to facilitate seagrass re-

establishment?

39

5. Planting activities should be planned within an explicit framework that sets out testable

hypotheses as to the effects of plant age, planting method, and position in the landscape,

e.g., elevation and tidal inundation.

6. Explicit measures of revegetation success need to be established, using criteria that are

measurable, realistic and amenable to rigorous statistical analysis.

7. All reporting on the success of mangrove plantings should be quantitative and quantify

the same suite of variables, so that a comparison can be made across different areas,

times and methods. A database should be established where all operations of all

organizations are mandated to be entered, including their planting data, dates,

survivorship, planting methods, position, reason for planting.

8. Specific experiments should be undertaken to determine the best elevation and/or tidal

regime to plant and the best position along the eroded Lang Lang cliffs to have successful

survival of seedlings and subsequent growth of adults. We have seen very little research

on planting density and it may be useful to test densities and clump sizes for best

survival.

9. More rigorous experimental procedures should be used. A distinction between growing

mangrove along the coast to potentially prevent erosion of the cliffs and research to

decide on density and position of seedling planting and most efficient methods should be

made.

10. Careful biannual measurement of erosion from the cliffs is required. This should

distinguish between erosion by freshwater from runoff down cliff faces and erosion by

wave action from the sea.

Acknowledgments 

Sincere thanks are given by the authors to Dr Tim Ealey who advised on his planting

techniques and took us out to see the mangrove plantings at the northern end of Western Port.

His enthusiasm for the wider mangrove revegetation project is to be commended and built upon.

Tom Hurst also took us to the Lang Lang cliffs and showed us the saltmarsh and mangrove

plantings. His skill and rigour are also to be commended; we are also indebted to him for

allowing us to put a draft copy of his mangrove review as an appendix to this report. This is a

draft literature review undertaken as part of an MSc at Deakin University and can only be cited

after gaining his permission.

40

References Anon. 2012. Lang Lang Foreshore Reserve Coastal Management Plan. Department of

Sustainability and Environment. 60 pp.

Aronson, J., Milton, S.J. and Blignaut, J.N. 2007. Restoring natural capital: definition and

rationale. In: Restoring Natural Capital: Science, Business and Practice. Eds: Aronson, J.,

Milton, S.J. and Blignaut, J.N. Society for Ecological Restoration International, Island Press,

Washington, DC. Pages 3–8.

Badola, R. and Hussain, S.A. 2005. Valuing ecosystem functions: an empirical study on

the storm protection function of Bhitarkanika mangrove ecosystem, India. Environmental

Conservation 32: 1–8.

Bird, E.C.F. 1986. Mangroves and intertidal morphology in Westernport Bay, Victoria,

Australia. Marine Geology 69: 251–271.

Bird, E.C.F. and Barson, M.M. 1975. Shoreline changes in Westernport Bay. Proc. Roy.

Soc. Victoria 87: 15–28.

BOM. 2010. Climate Data Online, Commonwealth of Australia, retrieved Jan 2012,

<http://www.bom.gov.au/climate/data/>.

Boon, P.I., White, M. and Sinclair, S. 2010. Climate change impacts on Victoria's

Coastal Vegetation (Mangroves and Saltmarsh): Western Port Case Study. Paper presented to

Practical Responses to Climate Change National Conference 2010, Melbourne.

Boon, P.I. 2011. The rehabilitation of coastal wetlands: why small-scale variations in

topography are critical to success. Australasian Plant Conservation 20: 9–10.

Boon, P.I., Allen, T., Brook, J., Carr, G., Frood, D., Hoye, J., Harty, C., McMahon, A.,

Mathews, S., Rosengren, N., Sinclair, S., White, M. and Yugovic, J. 2011. Mangroves and

coastal saltmarsh of Victoria: distribution, condition, threats and management. Report to DSE

(Bendigo) by Institute for Sustainability and Innovation, Victoria University, Melbourne. 513 pp.

Bradshaw, A.D. 1997. What do we mean by restoration? In: Restoration ecology and

sustainable development. Ed: Urbanska, K.M. et al. Cambridge University Press, Cambridge.

Pages 8–14.

Bulthius, D., Brand, G.W. and Mobley, M.C. 1984. Suspended sediments and nutrients in

water ebbing from seagrass-covered and denuded tidal mudflats in a southern Australian

embayment. Aquatic Botany 20: 257–266

Church, J.A., White, N.J., Hunter, J.R. and Lambeck, K. 2008. Briefing: a post-IPCC

AR4 update on sea-level rise. The Antarctic Climate and Ecosystems Cooperative Research

Centre, Hobart.

41

Clarke, P.J. 1993. Dispersal of grey mangrove (Avicennia marina) propagules in

southeastern Australia. Aquatic Botany 45: 195–204.

Clough, B.F. and Attiwill, P.M. 1975. Nutrient cycling in a community of Avicennia

marina in a temperate region of Australia. In: International Symposium on Biology and

Management of Mangroves. Eds: Walsh, G.E., Snedaker S.E. and Teas, H.J. University of

Florida, pages 137–146.

DSE. 2008. Climate Change in Port Phillip and Westernport. Department of

Sustainability and Environment., Victorian Government.

DSE. 2011. The Lang Lang Foreshore Reserve Coastal Management Plan. Department

of Sustainability and Environment., Victorian Government. pp. 62.

Dittmann, S. 2011. Mangroves. In: Understanding the Western Port Environment. A

Summay of Current Knowledge and Priorities for Future Research. Melbourne Water

Corporation. Pages 106–115.

Clarke, P.J. and Allaway, W.G. 1993. The regeneration niche of the grey mangrove

(Avicennia marina): effects of salinity, light and sediment factors on establishment, growth and

survival in the field. Oecologia 93: 548–556.

Ealey, T. 2011a. Mangrove Planting Manual. Western Port Seagrass Partnership. pp. 16

Ealey, T. 2011b. Brief History of the Lang Lang Mangrove Project (Revised). A report to

Western Port Seagrass Partnership. pp. 5.

Field, C. 1998. Rehabilitation of mangrove ecosystems: an overview. Marine Pollution

Bulletin 37: 383–392.

Field, C. 1999. Mangrove rehabilitation: choice and necessity. Hydrobiologia 413: 47–

52.

Gedan, K.B., Kirwan, M.L., Wolanski, E., Barbier, E. B and Silliman, B.R. 2011. The

present and future role of coastal wetland vegetation in protecting shorelines: answering recent

challenges to the paradigm. Climatic Change 106: 7–29.

GHD. 2002. Western Port Erosion Project. Report prepared for the Department of

Natural Resources and Environment, Victorian Government.

GHD. 2010. Cardinia Shire Council Management Plan for Lang Lang Clay Banks

Stabilisation. December 2010. pp 72.

Halide, H., Brinkman, R. and Ridd, P. 2004. Designing mangrove wave attenuators for

mangrove plantations. Indian Journal of Marine Sciences 33: 220–225.

Harty, C. 2010. Mangroves in Western Port Discussion Paper. Department of

Sustainability and Environment, Victorian Government.

42

Harty, C. 2011. Mangroves of Victoria Information Kit. Parks Victoria. 22 pp.

Hobbs, R.J. 2005. Restoration ecology and landscape ecology. In: Issues and

Perspectives in Landscape Ecology. Eds: Weins, J.A. and Moss, M.R. Cambridge University

Press, Cambridge.

Hurst, T. 2011. Mangrove Restoration in Western Port Literature Review. See Appendix

1.

Imgraben, S. and Dittmann, S. 2008. Leaf litter dynamics and litter consumption in two

temperate South Australian mangrove forests. Journal of Sea Research 59: 83–93.

Lake, P.S. 2001. On the maturing of restoration: linking ecological research and

restoration. Ecological Management and Restoration 2: 110–115.

Lewis, R.R. III. 1989. Wetland restoration/creation/enhancement terminology:

suggestions for standardization. In: Wetland Creation and Restoration: The Status of the Science.

Eds Kusler, J.A. and Kentula, M.E. Island Press, Washington DC. Pages 417–422.

Lewis, R.R.III. 2005. Ecological engineering for successful management and restoration

of mangrove forests. Ecological Engineering 24: 403–418.

Lewis, R.R.III. 2009. Knowledge overload, wisdom underload. Ecological Engineering

35: 341–342.

Lewis, R.R.III. 2011. How successful mangrove forest restoration informs the process of

successful general wetland restoration. National Wetlands Newsletter 33:23–25.

McManus, P. (2006). Mangrove battlelines: culture/nature and ecological restoration.

Australian Geographer 37: 57–71.

Melbourne Water. 2011. Understanding the Western Port Environment. A Summary of

Current Knowledge and Priorities for Future Research. Melbourne Water Corporation, Victoria.

pp. 224.

Morrisey, D.J., Swales, A., Dittmann, S., Morrison, M.A., Lovelock, C.E. and Beard,

C.M. 2010. The ecology and management of temperate mangroves. Oceanography and Marine

Biology: An Annual Review 48: 43–160.

Parsons Brinkerhoff. 2009. Geotechnical Risk Assessment – Coastal Crown Land in West

and South Gippsland.

Raulings, E., Morris, K, Roache, M. and Boon, P.I. 2011. Is hydrological manipulation an

effective management tool for rehabilitating chronically flooded, brackish-water wetlands?

Freshwater Biology 56: 2347–2369.

43

Raulings, E., Morris, K, Roache, M. and Boon, P.I. 2010. The importance of water

regimes operating at small spatial scales for the diversity and structure of wetland vegetation.

Freshwater Biology 55: 701–715.

Rogers, K, Wilton, KM and Saintilan, N. 2006. Vegetation change and surface elevation

dynamics in estuarine wetlands of southeast Australia. Estuarine, Coastal and Shelf Science 66:

559–569.

Ryder, D., Brierley, G.J., Hobbs, R., Kyle, G. and Leishman, M. 2008. Vision generation:

what do we seek to achieve in river rehabilitation? In: River Futures. An Integrative Scientific

Approach to River Repair. Eds: G.J. Brierley and K.A. Fryiers. Island Press, Washington. Pages

16–27.

Samson, M.S. and Rollon, R.N. 2008. Growth performance of planted mangroves in the

Philippines: revisiting forest management strategies. Ambio 37: 234–240.

Satumanatpan, S. and Keough, M. 1999. Effect of barnacles on the survival and growth

of temperate mangrove seedlings. Marine Ecology Progress Series 181: 189–199.

SER (Society for Ecological Restoration International). 2002. Society for Ecological

Restoration International’s Primer of Ecological Restoration. http://www.ser.org/Primer

Shepard, C.C., Crain, C.M. and Beck, M.W. 2011. The protective role of coastal marshes:

a systematic review and meta-analysis. PlosOne 6: e27374.

Wallbrink, P.J., Hancock, G.J., Olley, J.M., Hughes, A., Prosser I. P, Hunt, D., Rooney,

G., Coleman, R. Stevenson, J. 2003. The Western Port Sediment Study. CSIRO Consultancy

report, 2003.

Wallbrink P.J. and Hancock G. 2003. Western Port Sediment Study: Background and

Literature Review. Technical Report 12/03, CSIRO.

Zedler, J.B. 2006. Wetland restoration. In: Wetlands. Eds: Mitsch, W.J. and Gosselink,

J.G. 2nd edition. Van Nostrand Reinhold, New York. Pages 348–406.

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Appendix 1.  

Mangrove Restoration in Western Port Bay Literature Review      Tom Hurst. July 2011