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Ecology, Disturbance and Restoration of Coastal Saltmarsh in Australia: A Review (Laegdsgaard, 2006)
Ó Springer 2006
Wetlands Ecology and Management (2006) 14:379À399
DOI 10.1007/s11273-005-8827-z
-1
Ecology, disturbance and restoration of coastal saltmarsh in Australia:
a review
Pia Laegdsgaard*
Department of Infrastructure, Planning and Natural Resources, P.O. Box 2185, Dangar, NSW 2309, Aus-
tralia; *Author for correspondence (e-mail: pia.laegdsgaard@dipnr.nsw.gov.au; phone: +61-2-4960-5029;
fax: +61-2-4960-5055)
Received 10 September 2004; accepted in revised form 12 December 2005
Key words: Conservation, Creation, Disturbance, Rehabilitation, Restoration, Saltmarsh
Abstract
It is clear that saltmarshes are a unique and important component of the coastal biosphere of Australia.
Their contribution ranges from stabilisation of fine sediments and providing an excellent protective buffer
between land and sea, to their diverse blend of terrestrial and marine fauna. Further, saltmarsh plants are
highly specialised and adapted to fill a harsh niche allowing them to act in roles that other vegetation types
cannot. Saltmarsh habitats are recognised for their importance to migratory waders under the Ramsar
convention, but it is becoming increasingly evident that they are also important to a variety of commercially
valuable fish and native mammal species. Activities that are detrimental to saltmarshes continue and need
to be addressed in order to conserve remaining saltmarsh areas. In general, urbanisation of the catchment
has lead to filling of saltmarshes, tidal restriction, use by recreational vehicles, grazing, trampling and
increased sedimentation and nutrient runnoff allowing colonisation and invasion of mangroves. These
disturbances have a number of ecological consequences ranging from weed infestation to complete changes
in the species composition and ecology. Reversing the disturbance is not always simple and can require
extensive groundwork to be successful. Rehabilitation of existing saltmarsh areas has been a successful
means to enhance this habitat. In general, it requires relatively little effort to remove weeds and fence off
areas to regenerate naturally. Saltmarsh areas have been shown to respond well to this type of manipu-
lation. Restoration and creation require substantial effort and planning to ensure a successful outcome.
However, given the right environmental combinations of elevation, tide and salinity, saltmarsh will
establish and grow. To speed the process transplantation of saltmarsh plants can be considered either from
donor sites or plants propagated in green houses.
1977; Adam 1981; Bucher and Saenger 1991; Zann
Introduction
1997; Coleman 1998; Davis and froend 1999; Fin-
Coastal saltmarshes around Australia are dimin- layson and Rea 1999). New South Wales in par-
ishing. The losses of saltmarsh around the country ticular has suffered the most alarming losses. Over
can be credited to lack of information on the the past 200 years over 60% of coastal wetlands in
importance of saltmarsh leading to reclamation for NSW have been lost or degraded (Bowen et al.
industrial, agricultural, port and residential devel- 1995). In response to its demise, saltmarsh has been
opment (Kratochvil et al. 1972; Saenger et al. listed as an Endangered Ecological Community in
380
New South wales under Part 3, Schedule 1 of the shrubs, herbs and grasses (Clarke and Hannon
1971; Kratochvil et al. 1972; Adam 1981; Bridge-
Threatened Species Conservation Act 1995.
As the profile of saltmarshes in Australia in- water et al. 1981; Kirkpatrick and Glasby 1981;
creases so does the desire to protect, restore and Wilson 1984; Clarke and Benson 1988; Adam
rehabilitate these ecosystems. Streever (1997) 1993; Latchford 1994; Zedler et al. 1995). They
identifies ten projects that are specifically aimed at can range from narrow fringes on steep shorelines
saltmarsh rehabilitation in Australia and it is likely to nearly flat expanses several kilometres wide.
that more are being formulated and instigated now. It was first suggested by Pidgeon (1940), that
The future of coastal saltmarshes is linked to estuarine wetlands develop when mudflats are
knowledge of the general ecology of saltmarsh and colonised by mangroves. As sediment accretes, the
its response to disturbance. Many activities remain mangroves move into the estuary and are replaced
that are detrimental to coastal saltmarshes and it is on the landward side by saltmarsh. As tides cover
important to recognise the types of disturbance and the area less frequently, soil salinity increases with
whether recovery is possible before commencing evaporation, which in turn limits the distribution
expensive rehabilitation works. The history of the of many species including mangroves. Mangrove
site, cause of problems within a marsh area and the propagules, although transported into highly sal-
level of perturbation can be the key to effective ine areas, do not survive (Clarke and Myerscough
decision making regarding the management of 1993; Morrisey 1995), which ultimately allows
a particular area. It is important to know saltmarshes to flourish. Evidence from cores taken
how enhancement efforts are going to affect the in existing saltmarsh areas supports this hypothe-
saltmarsh À i.e. is it going to work? How do salt- sis where mangrove root systems dated as
marshes recover after disturbance À are they 500À1700 years-old were found under the salt-
capable of recovery? What is the saltmarsh for À marsh plain (Saintilan and Hashimoto 1999).
how will it function? Some of these questions can However, the process may not be the same in every
be answered with a thorough understanding of the coastal area. Other evidence has shown that
mechanisms behind recovery and the ecology of mangroves can expand directly onto mudflats
saltmarshes and relating these to perturbations and without a saltmarsh stage. Also, where there was
restorative actions. Knowledge of successional the opportunity to observe the creation of a new
patterns, plant physiology, environmental condi- wetland, saltmarshes can be the initial colonists
tions for plant establishment and growth, fauna, (Mitchell and Adam 1989a).
amongst other ecological functions is required. In During the initial stages of saltmarsh forma-
light of this, it seems timely to consider what we tion, pioneer species are the first to establish.
know about saltmarsh ecology, disturbance and Immature saltmarshes are often relatively flat
restoration. with shallow pools. At this stage, vegetation
This paper provides an overview of the ecology, consists of succulents and small shrubs that are
threats and restoration efforts on Australian salt- tolerant to the high salinity and regular flooding
marsh. The information provided is designed to of the newly created coastal environment. As
assist in the management of existing saltmarsh deposition of sediment continues, the saltmarsh
areas and the creation of new saltmarshes in plants trap and bind fluvial and marine sediments
coastal areas. that have been transported by tidal currents (Roy
1984), and the surface of the saltmarsh grows
higher. In turn, species that are less tolerant of
flooding replace earlier pioneer species at upper
Ecology
levels until eventually the system reaches equi-
librium.
The saltmarsh environment
For colonisation and maintenance of vegetation
Establishment and development communities, saltmarsh plants exhibit two modes
Saltmarshes generally develop in areas that are of reproduction, either: sexually, by flowering and
protected from the full force of the surf, in loca- producing seeds for dispersal into bare areas; or
tions such as river mouths and sheltered bays and vegetatively (asexually), by cloning of individual
are typically vegetated by a variety of unique low plants or the extension and spreading of plant parts
381
into new areas (Redfield 1972; Nelson 1994; temperate climates, saltmarshes have a vastly dif-
Allison 1995). Vegetative spread by the means of ferent species composition compared to those in
rhizomes or stolons may produce extensive clones tropical latitudes. Temperature and rainfall are the
and cover large areas. How large, and how old most likely causes of these patterns because of
individual clones can become has not been inves- their effect on salinity. Rainfall is significant in salt
tigated (Adam 1990); but areas of saltmarsh persist circulation in communities as it reduces salinity
for many years without apparent change, and there stress. Most saltmarsh species show better growth
is potential for saltmarsh plants to be long-lived, as rates and survivorship in areas where the salinity is
demonstrated for other clonal plants (Cook 1985). lowered, at least for parts of the year. As a result,
Additionally, most saltmarsh plants flower and set the distribution of saltmarshes along the coast
seeds infrequently (Nelson 1994; Huiskes et al. tends to mimic that of higher average seasonal
1995) usually restricted to times when they are less rainfall (Figure 1). Tropical saltmarshes contain
likely to be inundated by the tide or low salinity considerably fewer plant species than those in
times to minimise the stress of acquiring water and temperate areas (Saenger et al. 1977; Specht 1981).
nutrients. This is particularly important for those Where temperatures are high, as in northern areas
species with small inconspicuous flowers that rely of Australia, the loss of moisture by evaporation is
on wind for pollination. Other saltmarsh species greatest and consequently the salinity increases.
are capable of holding their inflorescences above This coupled, with low rainfall in these areas is
the water at high tide, or have pollen that is resis- probably the major factor in determining the lim-
tant to tidal inundation. Insect pollination has also ited presence of saltmarshes on the northern tip of
been demonstrated for several species, and the Australia (Figure 1). The number of species in
most common pollinators are probably bees (e.g. in these areas is restricted to those that are more
Sarcocornia quinqueflora, Adam and Hutchings tolerant of extreme conditions of salinity. On the
1987) and flies (e.g. in Suaeda australis, Adam contrary, saltmarshes are particularly well devel-
1990). Seeds are likely to be dispersed by birds, oped in the southern, temperate areas of Australia,
insects or tides, for example, S. quinqueflora is a and these areas have a diverse floral component
prolific producer of buoyant seeds that are resistant with more than 40 species of plants being recog-
to desiccation, and are dispersed by tides (Nelson nised (Underwood and Chapman 1993).
1994).
The rate of saltmarsh expansion on substrata Vegetation
Adam et al. (1988) described 25 saltmarsh vegeta-
depends on the incline of the area and topography.
tion communities within NSW, but there is debate
That is, saltmarshes will expand more slowly
about whether saltmarshes should be so highly di-
where the incline is steeper. The older marshes of
vided or whether the mid-marsh community
Europe and North America exhibit elaborate sys-
(dominated by a few species) should be a single
tems of drainage creeks and expansive saltpans,
heterogenous community (Zedler et al. 1995).
but these are notably absent from Australian
marshes (Adam 1997). Shallow depressions with Bridgewater et al. (1981) give descriptions of 13
communities throughout Australia based on the
poorly defined boundaries may occur; and these
dominant species present in any given zone (high
are either permanently or temporarily devoid of
marsh, middle marsh or low marsh). For an ap-
vegetation, and may become hypersaline (Clarke
proach based on ecology and saltmarsh function, it
and Hannon 1967, 1969). Generally, older salt-
is beneficial to regard saltmarsh communities as
marshes in Australia exhibit a more diverse plant
groups of dominant species, especially because
assemblage with distinct zonation patterns that
fluctuations of species between years (particularly
appear as large flat expanses of low vegetation,
much like grass plains. These can however be, rare and annual species) is a common feature of
Australian systems (Adam 1993). Therefore, most
visually diverse depending on the dominant plant
of the saltmarshes found in temperate Australia
species.
can be considered as a single community complex
dominated by one, or a combination of the fol-
Temperature and climate
Regional climate is important in determining the lowing species: saltcouch (Sporobolus virginicus
location and type of saltmarsh to be expected. In (L.) Kunth), samphire (Sarcocornia quinqueflora
382
Figure 1. The average rainfall in millimetres (over a 30-year period) shown for Australia on a contour map adapted from data from the
Bureau of Meteorology. The main concentrations of saltmarsh along the coast are highlighted with an orange dotted line to show the
correlation between saltmarsh and high rainfall.
(Bunge ex Ungem-Sternberg) A.J. Scott)), creeping many areas by development (Pen 1983). In South
brookweed (Samolus repens (Forst & Forst. f) Australia, the perennial blown grass (Agrostis
Pers.) and streaked arrowgrass (Triglochin striatum limitanea J. Black) is limited to the banks of a river
Ruiz & Pav.)(Congdon and McComb 1980; Carne near Spalding in the mid-north. This species lives
1991; Clarke and Jacoby 1994; Nelson 1994; Kra- in semi-saline soils and is associated with emugrass
use 1995; Zedler et al. 1995; Turner and Streever (Distichlis distichophylla (Labill.) Fassett.) and
1999). samphire (Sarcocornia quinqueflora) (Black 1986).
Rare species should be identified for biodiversity
and conservation purposes. In Australia, several Zonation
Many studies have described the zonation patterns
saltmarsh species are rare and their distribution is
of saltmarshes in Australia (e.g. Clarke and Han-
under threat. Of these, the Wilsonia species are
non 1969; Adam and Hutchings 1987; Krause
noteworthy because they are a group that is pe-
1995; Zedler et al. 1995; Streever and Genders
culiar to Australia and New Zealand. Wilsonia
1997). Vegetation is usually zoned parallel to the
backhousei Hook.f. is a rare species in NSW but is
shoreline, and there is a general broad scale
widespread in South Australia. It has been re-
zonation from the land to the sea. The zones can
ported in Homebush Bay and Wamberal Lagoon
(Adam and Hutchings 1987). A feature of the be described as lower, mid and upper levels, usu-
ally each with a distinct mosaic of species that is
saltmarsh vegetation of Cararma Inlet in southern
often complicated by small-scale patchiness. Suc-
NSW is the presence of Sclerostegia arbuscula
culents dominate the lower marsh (e.g. Sarcocornia
(R.Br.) P.G. Wilson, which is also rare in NSW
spp.), while the mid-marsh usually contains species
(Adam and Hutchings 1987). In Western Austra-
such as Sporobolus spp. and Samolus spp. The
lia, Halosarcia spp. are important successional
upper marsh is a mosaic of species including Jun-
species that are required for seed stock to colonise
cus kraussii and Baumea juncea. The area behind
bare areas; but Halosarcia spp. are threatened in
383
the upper marsh is filled with terrestrial vegetation Saltmarsh fauna
such as eucalypts, melaleucas and casuarinas. In
Fauna is probably the least studied component of
most saltmarshes a combination of salinity, ele-
saltmarshes in Australia and information is lack-
vation and inundation is responsible for many of
the patterns seen in the distribution of saltmarsh ing. Generally, the descriptions available highlight
that it consists of several fauna groups ranging
plant species (Adam 1981a, b, 1990; King 1981;
from terrestrial to aquatic species with some
Zedler et al. 1995; Streever and Genders 1997).
specialised saltmarsh dwellers.
Salinity is especially important in the establish-
ment of new saltmarsh as most saltmarsh plants
cannot metabolise well in seawater alone (Web
1966) particularly in terms of germination and Aquatic invertebrates
early growth. Saltmarshes can range in salinity
The sediment of saltmarshes generally contain few
from brackish to hypersaline, and salinity varies
fauna. Only three groups of fauna (oligochaetes,
according to rainfall, freshwater inputs, ground-
polychaetes and bivalves), each containing only two
water influx, soil type and extent of tidal flushing
or three species, have been identified to be wholly
(Clarke and Hannon 1969; Vernberg 1993).
contained within the sediments of saltmarshes in
Most plants, however, possess mechanisms that
Australia (Warren 1989; Berents 1993; Genders
allow them to cope with the saline environment so
1997; Laegdsgaard, unpublished data). The hostile
that they can have a competitive advantage over
nature of the environment no doubt contributes to
many other terrestrial plant species, and can oc-
this lack of fauna with some evidence that the dense
cupy a specific niche. Hypersaline conditions can
impenetrable root systems of saltmarsh can limit
lead to the death of saltcouch or the formation of
burrowing species (Marsh 1982; Laegdsgaard, un-
smaller, thicker darker leaves in samphire and
published data).
seablite communities. Some species avoid having
Crustaceans and molluscs are the most con-
to survive long periods in high soil salinity by
spicuous element of the invertebrate fauna char-
growing as ephemerals in high rainfall periods of
acteristic of saltmarshes, and in a comprehensive
the year. This is most common in the tropics where
study of 65 Sarcocornia quinqueflora marshes
seasonal flooding in the wet season decreases
around Tasmania, Richardson et al. (1997) found
salinity and allows species such as Salsola kali,
over 50 species. However, only eight of these spe-
Sclerolaena spp. and Trianthema spp. to grow
cies were unique to saltmarshes. Molluscs have
(Jacobs 1999).
received most of the attention in the literature,
In many areas Sporobolus spp. and Sarcocornia
with studies ranging from species composition and
spp. co-occur but usually either one or the other
size range to adaptations (Hutchings and Recher
genus is dominant (Nelson 1994). This is generally
1974; Roach et al. 1989; Berents 1993; CSIRO
attributed to competition. In general, Sporobolus
1994; Roach 1998; Roach and Lim 2000). Salina-
spp. have a competitive advantage on more moist
tor solida Von Martens, is the most common gas-
sites, while Sarcocornia spp. have an advantage on
tropod in saltmarsh around Australia (Hutchings
more saline sites. Biological activity can also
and Recher 1974; Hutchings et al. 1977; Roach
influence the zonation of plant species within a
et al. 1989; CSIRO 1994; Roach 1998; Roach and
saltmarsh. The presence of crab burrows can
Lim 2000). S. solida burrow into the surface of the
influence the type and density of vegetation found
mud when the tide covers the saltmarsh surface.
because of increases in aeration, nutrient avail-
When the mud dries out, the snails cluster together
ability, and decomposition of below-ground plant
at the base of vegetation or in small depressions. In
detritus, together with decreases in salinity and
a study at Kooragang Island, S. solida was found
hydrogen sulphide concentrations (Marsh 1982;
in areas that were associated with increased
Bertness 1985). By excavating sediment to main-
flushing (Genders 1997), while it was conspicu-
tain a burrow, crabs transport nutrients within the
ously absent from saltmarsh in Homebush Bay
sediment to the saltmarsh surface where it becomes
(Berents 1993) that have been tidally isolated. This
more available for vegetation (Marsh 1982).
384
species may therefore provide a useful indicator of ancestors of land snails (Richardson et al. 1997).
healthy tidal exchange. There are, however, also several amphipods that
Differences in zonation of epifaunal snail species are found in coastal habitats, including saltmars-
in saltmarsh environments have been attributed to hes, whose dependence on salt spray has been
their abilities to tolerate physical stress and pre- shown to limit their landward migration (Rich-
dation pressures (Roach et al. 1989; CSIRO 1994; ardson et al. 2001).
Talley and Levin 1999; Roach and Lim 2000). In
areas of Juncus kraussii occurring high above the
shoreline, there is a high proportion of small Terrestrial invertebrates
individuals of Ophicardelus ornatus Ferussac. It is
suggested that this may relate to these areas pro- The terrestrial invertebrates of saltmarshes have
been studied very little in Australia, with the
viding a stable microhabitat that provides the right
temperature and moisture conditions for this spe- exception of the saltmarsh mosquito (Ochlerotatus
cies (Roach et al. 1989). S. solida has a population vigilax Skuse previously Aedes vigilax). Its associ-
size age structure that varies significantly with ation with human health risks, such as Ross River
height above the shoreline. Smaller younger indi- Virus (Ryan et al. 2000), has made it a focus for
viduals dominate the mangroves, while the Sar- studies on saltmarshes in Australia (Dale et al.
cocornia habitat supports the larger older 1993; Ritchie 1994; Ritchie and Jennings 1994;
individuals (CSIRO 1994; Roach and Lim 2000). Gislason and Russell 1997; Turner and Streever
1997; Chapman et al. 1999; Turner and Streever
Additionally, growth rate and mortality decrease
with height above the shoreline. Predation has 1999; Webb and Russell 1999). It is clear, however,
been suggested as the main mechanism for this that spiders and insects from most of their orders
trend. Predators limit the size to which Salinator (Homoptera, Hemiptera, Diptera, Coleoptera,
solida can grow in the mangroves, while in the Orthoptera, Hymenoptera and Lepidoptera) are
saltmarsh they are able to attain a greater size common on saltmarshes (Hutchings and Recher
because of decreased predation. Toad fish, yellow- 1974; Marsh 1982; Clarke and Miller 1983; Lae-
finned bream and eels are identified as the major gdsgaard unpublished data).
Marsh’s (1982) research provides an indication
predators of S. solida and it is likely that these fish
species may target many of the other mollusc that there is seasonal variation in the terrestrial
species that are present on the saltmarshes at high invertebrates that use saltmarshes, despite the lack
tide. However, tides only cover the entire salt- of spring data. There is a general trend towards a
marsh surface on the highest tides (maximum three decrease in flying insects in winter because many of
to four times per year) so that for most of the time these spend winter in the egg state, while other
fish can only target those molluscs that are closer species increase in response to the decrease in pre-
to the shoreline i.e. in mangroves. Excluding pre- dators. Clarke and Miller (1983) provided a
glimpse into the spatial distribution of insects by
dators at Towra Point actually decreased the
mortality of S. solida from 82 to 0.7% (Roach and comparing areas within the saltmarsh along with
Lim 2000). other habitats such as mangrove and pasture. In
Richardson and Mulcahy (1996) identified sev- general, there was an increase in the more terrestrial
eral species of amphipods as being dominant species (e.g. grasshoppers) in drier saltmarsh, while
among Tasmanian saltmarshes, These included the diversity of spiders increased in mixed salt-
both aquatic and terrestrial species of amphipods, marsh. In comparison with mangroves, saltmarsh
and it is hypothesised that saltmarshes may have has a much greater diversity of insects (a total of 13
species in mangroves compared to 47 in saltmarsh)
provided the pathway for amphipods to colonise
the land. Saltmarsh vegetation has remained rela- Clarke and Miller 1983). Since insects are a
tively unchanged since the Cretaceous period common component of the saltmarsh fauna, these
(Adam 1990), and it is possible that other species in turn attract insectivorous animals such as birds
utilised saltmarsh as an evolutionary pathway. For and bats. Bats in particular have been identified to
example, the gastropods Ophicardelus spp. are the be active over saltmarshes of Victoria and NSW
most primitive of their family, and they show with ten species recorded including some listed as
characteristics similar to those of the primitive rare and threatened (Laegdsgaard et al. 2004).
385
by extreme high tides. Gibbs (1986) sampled sev-
Vertebrates
eral pools in saltmarshes around Wallis Lake in
Fish NSW, and found juveniles of several species,
In the past, saltmarshes have not been considered including silver biddy and yellow-finned bream.
important fisheries habitat in Australia (Connolly Smaller ponds within saltmarshes have been found
et al. 1997). Most saltmarsh areas are only to contain species such as the introduced mosquito
available for fish to use during the highest tides of fish along with the native blue-eyes and gobies
the year, and therefore their usefulness as a (Davis 1988; Morton et al. 1988; Lincoln-Smith
habitat for fish was considered limited. However, et al. 1994).
the lack of information on fish in saltmarshes is
generally related to the difficulties of sampling in
Birds
this environment (Connolly 1999). Consequently,
In the available literature, there are several good
most studies have centred on creeks because they
descriptions of birds that utilise saltmarshes, but
are easier to sample than saltmarsh flats. Morton
the information available on reptiles and mammals
et al. (1987) collected samples monthly, over a
is more rare, with only two studies mentioning
year, from a large channel draining a saltmarsh;
them (Latchford 1994; Morrisey 1995). Many ter-
and found 19 species, from 14 families, of fish
restrial birds frequent the saltmarshes, and use
that regularly used this area. The dominant spe-
them as breeding grounds (e.g. bronze cuckoos).
cies were toadfish, yellow-finned bream, yellow
They feed on the variety of insects found on the
perchlets, and flat-tail and fan-tail mullet.
saltmarsh or on the seeds of the saltmarsh plants
Another record of fish from temperate saltmars-
(e.g. galahs). All these smaller birds and mammals
hes is from Wallis Lake, where poisoning of a
on the saltmarsh form ideal prey for the hunting
small creek resulted in the capture of 11 species
birds such as brahminy kite, whistling kite and
(Gibbs 1986).
marsh harriers, which are considered to be the top
More recently, investigators have overcome
predators in the structure of the saltmarsh food
some of the difficulties of sampling on saltmarsh
web (Figure 2). Saltmarsh provides summer feed-
flats to discover that these environments in Aus-
ing and roosting grounds for migratory waders of
tralia are used by fish during flood tides (Connolly
international significance (Gosper 1981; Clarke
et al. 1997; Thomas and Connolly 2001; Crinall
and van Gessel 1983; Maddock 1983; Day et al.
and Hindell 2004; Mazumder et al. 2005). The
1989; Smith 1991; Latchford 1994). Bird species
number of fish caught on the flats is lower than in
that utilise saltmarshes as a roosting site do not
creeks (Connolly et al. 1997) but still provide a
tend to use wooded areas (including mangroves)
habitat that is utilised by many fish species most
because these areas can hide land-based predators
likely for feeding. The abundance of insects, spi-
and, more importantly, restrict landing and take
ders, crustaceans and mollusc provide ample food
off areas for birds (Clarke and van Gessel 1983;
resources (adults, nymphs and larval stages) to be
Saintilan 2003). Many wading birds feed primarily
targetted by fish (Morton et al. 1988; Mazumder
on mudflats, and it is important that roosting pla-
unpublished data). Small resident species such as
ces are close to feeding areas, to minimise energy
perchlets and gobies dominated catches, but
expended on flights during their overwintering
commercial species such as whiting, bream and
period. This makes large expanses of saltmarsh
mullet were also caught in significant numbers in
ideal roosting sites, and indeed 18 of the 42 sites
Queensland and NSW (Thomas and Connolly
throughout Australia recognised as wetlands of
2001; Mazumder unpublished data). It is not only
international importance, under the Ramsar con-
the edges of the saltmarsh flats that are used either,
vention, contain large expanses of saltmarsh that
some fish venture to the farthest reaches of a
are considered vital for several species of migratory
saltmarsh during the tidal cycle (Connolly and
wading birds. Additionally, saltmarshes have
Bass 1996; Thomas and Connolly 2001).
associated ponds of water that are flooded by the
Semi-permanent and permanent ponds in salt-
occasional high tide. These ponds contain fish that
marsh areas have been investigated as a suitable
remain after the tide has receded, and several
habitat for a nursery for juvenile fish, despite being
invertebrates which attract waterbirds such as
a relatively harsh environment that is only flushed
386
sharp-tailed sandpipers, curlew sandpipers, anced in saltmarshes with no net import or export
greenshanks and marsh sandpipers (Straw 1996). to adjacent areas. For most of the time, salt-
Saltmarsh habitats in south-eastern Australia marshes in Australia are not covered by the tide,
support the endangered bird species, the orange- facilitating exchanges with the atmosphere, rather
bellied parrot (Neophema chrysogaster Latham) than exporting nutrients and plant matter to the
which has a single breeding population containing estuary. Therefore, a relatively large proportion of
less than 200 mature adults in the wild. These rare the macrophyte production is consumed on the
parrots are confined to coastal habitats within saltmarsh by respiratory or burial processes. In
10 km of the coastline in south-eastern Australia. addition, denitrification (and thereby loss of
The parrots spend the winter around saltmarshes available nitrogen) is likely to be limited because
in Victoria, South Australia and Tasmania where this process is generally enhanced in waterlogged
they feed on the seeds of saltmarsh plants such as anoxic soils that are typical of habitats constantly
Frankenia, Sarcocornia, Sclerostegia and Suaeda. inundated by the tides. The soils of saltmarshes in
Australia are typically drier than those of nearby
mangroves (Saintilan and Williams 1999b), there-
by reducing the potential for nitrogen loss to the
Saltmarsh productivity
atmosphere. Furthermore, saltmarsh vegetation
There are very few data on productivity, and no actively transfers oxygen to the roots and conse-
detailed measurements of fluxes into and out of quently to the soil (Kaplan and Valiela 1979). This
Australian marshes. The characteristics of salt- forms the basis for nitrification processes whereby
marshes in Australia make them different from nitrogenous compounds are converted to biologi-
those that are found in North America and other cally available ammonium and nitrate that is ex-
parts of the world, which are dominated by tall ported to coastal waters and used in active plant
robust grasses and are generally considered highly growth (Boon and Cain 1988). In addition, during
productive. From the small amount of data avail- decomposition, nutrients in the plant tissue are
able it is clear that Australian marshes record lower released and recycled into new plant growth,
productivity figures than those reported for many Decomposition rates of most plants in Australian
USA marshes (Table 1). Additionally, high vari- marshes are high (61À67% in the first year, van
ability precludes consistent spatial or temporal der Valk and Attiwill 1983) compared to the USA
trends were associated with above-ground biomass (50% in the first year, de la Cruz and Hackney
of the dominant saltmarsh species (Sporobolus 1977) which probably relates to the succulent
virginicus or Sarcocornia quinqueflora) (Smith- nature of most Australian saltmarsh plants.
White 1981; Clarke 1986; Clarke and Jacoby 1994; Decomposition of more woody saltmarsh plants
Seliskar 1998), This may be attributed to natural such as Juncus Kraussii is very slow (approxi-
variation, fluctuations in soil salinity (Smith-White mately 20% in the first year) (van der Valk and
1981) or disturbance. It has been shown that Attiwill 1983). Additionally, above ground litter
above-ground biomass can be lower in sites that decomposes faster than below-ground litter (Dick
have been affected by urban development (Lae- 1999). Therefore, very little litter is left on the
gdsgaard unpublished data). surface of the marsh to be exported with the rare
Although saltmarsh plants utilise nutrients for full tidal inundation.
growth, nitrogen concentration within the tissue of The litter decomposed by microorganisms pro-
plants such as Sarcocornia quniqueflora is only vides energy to invertebrates and higher trophic
around 2% (Clarke 1983; van der Valk and Atti- levels in the foodweb. A great number of ani-
will 1983; Dick 1999), and phosphorus is less than mals found in the saltmarsh can be classified as
1% (van der Valk and Attiwill 1983; Dick 1999). detritivorous or decomposers (e.g. protozoans and
This means very little of the nutrients brought into nematodes). These fauna convert the wealth of
the saltmarsh system are actually incorporated plant matter in saltmarshes to detrital food sour-
into the plant material at any one time (estimated ces. Such food sources are utilised by a rich and
at around 15%), so the plants themselves do not diverse invertebrate community that may in turn
act as a nitrogen source (Clarke 1986). It has been support other marine and terrestrial species in a
suggested that nitrogen and phosphorus are bal- foodweb that climaxes with hunting birds as the
387
top predators (Figure 2). In Australia, Boon et al. the surface level of the saltmarsh. This favours the
(1997) found that the saltmarsh plant Sarcocornia establishment and spread of such species as com-
quinqueflora did not contribute as a food source mon reed (Phragmites australis [Cav.] Trin ex
for two intertidal callinassid shrimps in Western Steud), water couch (Paspalum vaginatum) and
Port southern Australia. However, Irving (2001) river clubrush Schoenoplectus validus [Vahl] A & D
found that Sporobolus virginicus was a basis of the Love), and the loss of saltmarsh species (Roman
¨
foodweb of the common gastropod of saltmarshes et al. 1984). The common reed (Phragmites aus-
(Salinator solida), the semaphore crab (Heleocius tralis) is tenacious and recruits easily to areas that
cordiformis) and several fish species (e.g. mullet have become tidally isolated. If allowed to persist,
and stingrays). In addition, bream were found to it can form extensive stands that restrict the
derive nutrition from Sarcocornia quinqueflora. movement of aquatic life and alter the ecology and
Many fish species feed on amphipods such as Or- function of the entire saltmarsh (Adams and Bate
chestia spp., which are common in (Berents 1993; 1994; Windham 1995; Weinstein and Balletto
Richardson et al. 1997) throughout Australia, and 1999). Dense monotypic Phragmites stands gener-
are primary consumers of halophytes (Lefeuvre ally provide unsuitable or less preferred habitat
et al. 2000). It has also been demonstrated that fish and food for wildlife and waterfowl (Roman et al.
feeding in saltmarshes at high tide targeted mainly 1984).
saltmarsh crabs (Morton et al. 1987).
Agricultural practices
Response of saltmarsh to disturbance
In areas that are adjacent to wetlands and have been
Saltmarsh have to cope with a variety of natural reclaimed for agriculture, pasture species exclude
and anthropogenic disturbances (Laegdsgaard saltmarsh plants to a point where the pasture spe-
2001) to which they are particularly susceptible. It cies can no longer cope with the salinity. Saltmarsh
is important to understand the ecological conse- plants cannot compete with pasture species, and
quences of disturbance in order to reverse or halt it. therefore their expansion is limited by competition
(Genders 1996) in these altered environments.
In addition to being replaced, many saltmarsh
areas in Australia occur on private land and are
Changes to hydrology
used as pasture for livestock. Grazing and tram-
Alterations to drainage and hydrology can have pling are particularly detrimental to saltmarsh
devastating effects on saltmarsh communities. plants. Where trampling is high saltmarsh plants
These range from habitat destruction to modifica- are unable to regenerate or re-establish. Fauna
tion of the ecology. When estuaries are closed or that is native to Australia is unique and does not
tidally blocked, water levels rise as a result of posses hard hooves; therefore, constant trampling
localised freshwater run-off, leading to the inun- by hard hoofed farm animals can easily disrupt a
dation of saltmarshes for extended periods. Many saltmarsh area. Hoofed animals in saltmarsh
succulent saltmarsh plants such as Sarcocornia spp. habitats disrupt the dense vegetation and root
can only withstand short periods of inundation system, often destroying delicate succulent cheno-
before the plants quickly rot and decompose pods, such as Sarcocornia spp. and Suaeda spp.,
(Adams and Bate 1994). Naturally occurring flood and allowing tidal water to pool. Such pools form
events cause a similar effect; however, the water excellent habitat for biting insects (mosquitoes and
does not remain to cause permanent damage. Some midges) or other plant species (e.g. Triglochin
plants may appear to die because of prolonged striata) which are more tolerant of waterlogging
submergence; but if the stems of the plant remain and lowered salinity (Zedler et al. 1995). Tram-
alive, despite leaf decomposition, it is possible that pling also introduces gaps where weeds can
the plant will survive and regenerate once water establish (Bridgewater 1982), which can affect the
levels drop and the tidal influence is restored. If the dynamics of saltmarsh communities. In areas
tidal movement is not restored, the water table is where trampling is high, regeneration of the salt-
substantially lowered, and there is a relative drop in marsh plants is generally slow. Alterations in
388
typical saltmarsh species distributions can occur with various diseases and is therefore a priority for
because some plants are grazed selectively in control. This is achieved either through pesticide
preference to unpalatable species. For example, application, which may be harmful to non-target
the reduction of cover of rare species (e.g., Scler- insect populations, or habitat modification. Run-
ostegia arbuscula) has been linked to selective nelling is a type of habitat modification using
grazing (Kirkpatrick and Glasby 1981; Bridgewa- shallow channels in the saltmarsh to increase the
ter 1982) in saltmarsh areas. tidal flushing of the area to reduce mosquito
breeding and is likely to affect the plant species
distribution and faunal communities in the salt-
Urban encroachment
marsh (Connolly and Bass 1996). Runnelling was
Where saltmarsh is adjacent to urban development not found to have any significant impacts on the
it can be subject to mowing which can disrupt the wetland environment over a 6.5-year study period
by Dale et al. (1993). However, its effect on salt-
flowering of grasses while destroying succulent
marsh crabs was the subject of a study in
species. Watering of lawns adjacent to saltmarsh
Queensland, where it was concluded that although
also reduces their competitive advantage and leads
runneling did not affect the total number of crabs
to terrestrial grass species eradicating saltmarsh
it did have an effect on the species distribution of
species (Genders 1996). Halophytes are not com-
crabs (Chapman et al. 1998). Significantly greater
petitive in non-saline conditions (Zedler et al.
1990; Genders 1996; Wilson et al. 1996). So, numbers of Parasesarma erythodactyla Hess. were
fresher conditions allow exotic species to invade found at the runnelled site while Helograpsus
haswellianus Whit. was more abundant at the un-
and conquer the otherwise harsh saltmarsh envi-
runnelled site (Chapman et al. 1998). Additionally,
ronment. The competition between saltmarsh
it has been found that the overall effect of run-
plants and terrestrial vegetation is not restricted to
nelling appears to be a reduction in the abun-
above-ground; root competition is just as impor-
dances of nekton in the immediate vicinity of
tant. In a study on the ability of Sarcocornia
runnels thereby adversely affecting the saltmarsh
quinqueflora seedlings to invade areas where pas-
ture species had been removed, Genders (1996) environment (Connolly 2005). The tidal penetra-
found that S. quinqueflora were only successful in tion also increases the chance of mangrove incur-
sion with propagules transported high into the
plots that had been weeded to remove above- and
marsh by runnels (Breitfuss et al. 2003). The in-
below-ground vegetation. Plots that were simply
creased flushing may also decrease the high salinity
mown, remained free of saltmarsh plants.
in the marsh and allow mangroves seedlings to
Proximity to urban development has also pre-
establish and grow (Clarke and Myerscough 1993;
cipitated the need for increased mosquito man-
Morrisey 1995).
agement. The saltmarsh mosquito is associated
Table 1. Published values of above-ground productivity levels for dominant, wide-spread saltmarsh species in south eastern Australia
compared to species that dominate the marshes of the USA.
Species Location Above-ground Reference
production (g mÀ2)
South-eastern Australia 148À852 Clarke and Jacoby (1994)
Sprobolus virginicus
172À1600 Laegdsgaard, unpub. data
South-eastern Australia 1116 Clarke and Jacoby (1994)
Juncus Kraussii
300À1300 Congdon and McComb (1980)
210À3300 Congdon and McComb (1981)
South-eastern Australia 800 Congdon and McComb (1981)
Sarcocornia quinqueflora
317 Clarke and Jacoby (1994)
88À2411 Laegdsgaaerd, unpub. data
South-eastern Australia 400 Congdon and McComb (1981)
Samolus repens
South-eastern Australia 1100 Congdon and McComb (1981)
Scirpus maritimus
USA 600À1000 Mahall and park (1976)
Salicornia virginica
USA 500À2500 Taylor and Allanson (1995)
Spartina alterniflora
389
The proximity of saltmarshes to urban settle- the salinity would increase thereby eliminating the
ments increases their attractiveness to drivers of mangroves again (Outhred and Buckney 1983).
recreational vehicles. Off-road vehicles (e.g. The view that salinity is the driving force for
mountain bicycles, 4-wheel drive vehicles, trail maintaining mangrove distribution remains a
motorbikes) traversing saltmarsh vegetation can hypothesis. Clarke and Allaway (1993) suggest
cause localised and widespread damage. Decrease that upslope delimitation of the grey mangrove
of saltmarsh in areas of NSW and Tasmania has (Avicennia marina) is related to desiccation that
been directly attributed to recreational vehicle use may suggest that inundation frequency is the
(Kirkpatrick and Glasby 1981; Clarke 1993; critical factor. The fact that mangroves are
Kelleway in press). The type of disturbance to the threatening to over run many saltmarsh areas,
saltmarsh depends greatly on the nature and pur- suggests there is a mechanism operating to allow
pose of the driving. Effects like stein-height mangroves to flourish where they would normally
reductions and stem breakage are common with be stressed or absent.
light traversing (restricted to a set of wheel ruts) of
saltmarsh areas. However, continuous, heavy
usage can cause a complete removal of vegetation, Fragmentation
soil compaction and removal of mollusc and crab
populations (Kelleway in press). Fragmentation is another major contributing fac-
tor for saltmarsh habitat decline, however, it is not
clear what the ecological consequences might be.
Fragmentation in other habitats such as forests
Mangrove incursion
and grasslands has been shown to cause degrada-
An imminent threat to saltmarshes around Aus- tion of habitat quality and decreases in biodiver-
tralia is mangrove incursion. Over the last few sity (Collinge 1996; Harrison and Bruna 1999;
decades colonisation and invasion of mangroves Mazluff and Ewing 2001; Tschantke et al. 2002).
into south-eastern Australian saltmarsh areas has Rare or specialised species and species with lower
been documented (Buckney 1987; Mitchell and dispersal capabilities are most affected (Tscharntke
Adam 1989a, b; Morton 1993; West 1993; Fenech et al. 2002). Although it has not been tested,
1994; Coleman 1998; Saintilan and Hashimoto fragmentation is likely to affect the foodweb
1999; Saintilan and Williams 1999; Saintilan and structure of saltmarsh significantly. Many of the
Wilton 1999). There are a number of hypotheses predators require space for prey capture, particu-
that have been put forward to explain this phe- larly those that feed on the wing such as bats and
nomenon. These include sea level rise, increased hunting birds. Large saltmarsh habitats with a
rainfall, increased freshwater inputs into saltmarsh diverse array of molluscs and crabs produce a
or altered tidal regimes most of which need to be large amount of plankton that is exported with the
tested. Wilton (2002) was unable to find a corre- tide when the saltmarsh is inundated which is an
lation between the degree of mangrove encroach- important food source for fish (Mazumder,
ment with sea level rise or degree of urbanisation, unpublished data). In this way, saltmarshes are
which suggests that other physical factors within important in sustaining other estuarine species,
the environment may be driving the changes being many of which may be of commercial significance.
observed. Salinity is a major driving factor in Many of the crabs and molluscs are generally ab-
maintaining wetland communities. Normally, sent from small fragmented saltmarsh habitats and
saltmarshes flourish because soil salinity increases these do not have the capacity to supply larval
with evaporation, which in turn may limit the zooplankton to estuarine fish species. It is pre-
distribution of many species including mangroves, dicted that with increasing fragmentation and re-
Mangrove propagules, although transported into duced Patch size of saltmarsh habitat the foodweb
highly saline areas, do not survive (Clarke and will become limited to small predators and few
Myerscough 1993; Morrisey 1995). Nevertheless, insects as shown in Figure 3. This would be par-
during a succession of wetter years soil salinity ticularly true if the saltmarsh patch also becomes
may fall to an extent where mangroves can tidally isolated (Figure 3b). In grassland, frag-
establish and grow, but in subsequent dry periods ments can become too small even to maintain
390
Figure 2. Representation of the foodweb of a typical coastal saltmarsh in Australia. Arrows represent the direction of the links in the
foodweb with respect to consumers.
viable populations of small birds (Johnson 2001). been positively correlated to the area of saltmarsh
This could also be true for saltmarshes, which within 20 km radius of the breeding colony
would reduce the top predators to spiders and (Baxter 1998).
insects of a very small fragment (Figure 3d). Where saltmarshes are fragmented by the
Urbanisation of many coastal areas has seen the presence of roads, contamination is also likely to
reduction of saltmarsh areas to minute patches affect biodiversity. Contaminants may cause
that are likely to be utilised only by insects. physiological stress in some plants and make
Migratory birds are generally attracted to lar- them more susceptible to pest attack, Saltmarshes
ger areas of saltmarsh to give better visual pro- contain a high number of insects that may be
tection from predators (Straw 1996; Saintilan reduced by the lead in combustion gases in cars
2003). The size of breeding colonies of egrets has (Spellerberg 1998).
391
Invasive species Restoration efforts
Several invasive species have the potential to Restoration of saltmarsh in Australia is a rela-
completely overrun a natural saltmarsh. These tively new concept. As the profile of saltmarshes
species form a priority for rehabilitation efforts. Of increases so do restoration efforts. Unfortunately,
particular note are the common cordgrass and rehabilitation efforts generally go undocumented
spiny rush. The invasive common cordgrass and there is little measure of their success. Nev-
(Spartina anglica) was introduced into Tasmania ertheless, examples do exist that allow confidence
and Victoria specifically for reclamation of land in rehabilitation efforts.
and stabilisation of mudflats. In Tasmania, it has Actions such as fencing to remove cattle from
completely taken over the Tamar Estuary (Adam saltmarsh areas, diversion of stormwater away
1981). Despite attempts to establish it in NSW it from saltmarsh and weed removal are the most
has not become a problem in this State (Adam and common rehabilitation methods for saltmarsh. A
Hutchings 1987). The common cordgrass can have good example of a saltmarsh restoration project,
several detrimental effects on natural environments where these have been employed, is the Kooragang
in Australia. These effects include invading mudfl- Wetland Rehabilitation Project on the central
ats that are rich in invertebrates and producing coast of NSW. The project was initiated in 1993 to
dense monotypic stands that replace more diverse compensate for the loss of estuarine habitat due to
plant communities. Species such as Sarcocornia 200 years of clearing and filling (Buckney 1987).
quinqueflora and Samolus repens are particularly The project covers three sites, Tomago, Ash Island
prone to competitive exclusion by Spartina anglica and Stockton and it is one of the major environ-
(Simpson 1995; Hedge and Kriwoken 2000). Birds mental projects in NSW. The main area for reha-
have been observed to avoid S. anglica (Simpson bilitating estuarine habitats has been Ash Island
1995; Hedge and Kriwoken 2000), and species where tidal flushing is being restored through the
richness and total abundance of fauna are greater removal of culverts. In areas where tidal restriction
in saltmarshes dominated by native plants, com- has been removed there has been an observed
pared to those dominated by S. anglica (Hedge and reversal of the habitat degradation brought about
Kriwoken 2000). by the tidal restriction and reclamation for agri-
Spiny rush (Juncus acutus) is another introduced culture (Streever et al. 1996), with a return and
species, from the Mediterranean, that has become expansion of native saltmarsh and mangrove spe-
widespread throughout saltmarshes and on saline- cies. Additionally, evidence from a large area im-
affected pasturelands in southeastern Australia pacted by cattle grazing at Kooragang Island in
(Milford and Simons 2002; Zedler and Adam NSW, where cattle had been excluded to allow
2002). It has been so successful at invasion that it rehabilitation, suggests that Sarcocornia quin-
has been listed as a noxious weed for Australia queflora is able recover naturally in around five
(NAWC 2003). This species occupies the same years once the disturbance is removed (Kooragang
niche as the native rush, Juncus krausii but is Wetland Rehabilitation Project unpublished data).
tougher and more resilient and easily out-competes Weed removal is particularly important in the
the native species. The introduction of J. acutus rehabilitation of many saltmarsh habitats as there
into saltmarshes has altered the structure and are several introduced species that plague salt-
complexity of these environments. Once J. acutus marshes around Australia, and the way in which
becomes established, its sharp tough cylindrical most have arrived is unknown. Common intro-
leaves form dense impenetrable thickets so that the duced species include buck’s horn plantain (Plan-
native rush is displaced or unable to establish. tago coronopus), rock sea-lavender (Limonium
Many gastropods and other invertebrate fauna are binervosurn), grasses (Polypogon monspeliensis.)
believed to depend on J. krausii for completion of and daisy (Aster subulatus). All these species have
their lifecycle and the same function is not affor- been introduced from the Northern Hemisphere,
ded by J. acutus due to its harsher habit. There- and the majority have the ability to out-compete
fore, the ecosystem may be severely impacted by native saltmarsh species (Callaway and Zedler
the invasion of J. acutus as it displaces J. krausii in 1998). Generally, these are simple to eradicate from
many saltmarsh ecosystems of coastal Australia. saltmarsh areas. The removal of spiny rush (Juncus
392
Figure 3. Predicted changes to the typical saltmarsh foodweb with disturbance and fragmentation. (a) Reduction in size of the
saltmarsh limits the ability of birds of prey to feed thereby eliminating them from the foodweb. Top predators become small birds, fish
and small mammals. (b) Tidal restriction coupled with decreased habitat size eliminates fish, crustaceans and molluscs from the
saltmarsh foodweb. (c) A fragment of saltmarsh approximately the size of a house block are likely to support only small ground feeding
birds and insects. (d) Minute fragments of saltmarsh (1À2 m2) can only support arthropods. Predatory insects and spiders take on the
role of top predators in this scenario.
acutus) however has become a focus for manage- cies in order to formulate effective and permanent
ment in some areas but it is proving particularly eradication methods.
difficult to eradicate. More information is required Where land needs reshaping in order to restore
on the general biology and physiology of this spe- tidal inundation for saltmarshes to grow and
393
flourish, it is important to understand that salt- back to saltmarsh in this way (Personal Observa-
marsh species can be sensitive to changes of a few tion).
centimetres in elevation and tidal inundation. It is usually assumed that if hydrology is re-
Zonation of saltmarsh plants requires a specific stored that vegetation, soil and animals will come
combination of land gradients (to ensure inunda- naturally. In many areas, this is true but may not
tion) and soil salinity (Clarke and Hannon 1970; always be the case and may require assistance. If
Adam 1990; Zedler et al. 1995). This may be par- the site is excavated and the surface soils removed
ticularly difficult to achieve. Callaway et al. (1997) it may take longer for organic carbon levels at
established that hydrology and substratum are the depth (where it is needed) to return to similar
key elements in restoration. Porous substratum levels to natural marshes (Havens et al. 2002). It
drains and dries too quickly to be conducive to the may be necessary to add organic substrate back to
growth of dominant saltmarsh species. Addition- the marsh surface at the time of construction when
ally, saltmarsh areas planted with Salicornia virg- re-levelling is complete to speed the development
inica (a species similar to Sarcocornia quinqueflora) of a sediment profile similar to natural marshes. In
did not thrive in areas that were infrequently tid- addition, soil salinity is a major factor determining
ally flooded but retained water (Callaway et al. seed germination and the ability of plants to ma-
1997). Where this has been trialled and access to ture in saltmarshes so the right balance of tide and
tidal water restored through excavation and rele- freshwater are essential. Table 2 provides toler-
velling, saltmarsh has establish naturally. Several ances for the most common species associated with
sites in Sydney have been reverted from parks to Australian saltmarsh.
saltmarsh that is floristically mature and attracting Natural recovery of saltmarsh communities oc-
bird species (Eckstein 2004; Sainty and Roberts curs after disturbance via establishment of seed-
2004) and areas of Kooragang Island in NSW lings. The degree of isolation from natural habitats
have been successfully converted from pasture will affect recolonisation. Sarcocornia quinqueflora,
Table 2. Dominant saltmarsh species and their requirements for growth in early and mature stages.
Species Appearance Germination and early growth Mature conditions
A small erect leafless herb with Requires conditions of low salinity Flowering in late summer is trig-
Sarcocornia
succulent jointed stems. Can vary to trigger germination (Chapman gered by high salinity conditions
quinqueflora
in colour from green to red and 1960). (Clarke and Hannon 1970). Die
purple. back in winter
Grass like Narrow imrolled leaves Low salinity periods are required Can tolerate periods of high salin-
Sporobolus
are stiff, erect and green. for establishment. Responds well ity (Gallagher 1979), flooding and
virginicus
to increased nutrients Waterlog- hypoxic soils (Donovan and
ging can hasten the onset of flow- Gallagher 1984; Donovan and
ering (Clarke and Hannon 1970) Gallagher 1985). However, hy-
persaline and constant inundation
leads to little or no growth (Clarke
and Hannon 1970).
Low growing herb Newly pro- High mortality and retarded Plants in full sun become pink or
Suaeda
duced foliage is soft green and may growth in seedlings is common in purple while those in shaded posi-
australis
become pink or purple well-drained areas suggesting wet tions remain green (Cribb and
conditions are necessary for ger- Cribb 1985). With age and matu-
mination and early growth (Clarke rity, it can tolerate drier conditions.
and Hannon 1970).
Non-tuberous annual plant with Opportunistic and will invade areas Plants die down to underground
Triglochin
succulent leaves rounded in cross that become waterlogged. Water- rhizomes in dry conditions and will
striata
section logging hastens the onset of flow- only flower once they are flooded.
ering (Clarke and Hannon 1970).
A herb with creeping lower stems Can be planted in most soils but Occurs in saline conditions on the
Samolus
and erect upper stems to 30 cm tall. grows best with some moisture. edge of estuaries
repens
White star flowers.
394
is a prolific producer of buoyant seeds dispersed by their natural densities in small plots varies with
the tide (Nelson 1994). If an entire saltmarsh field species and location within the saltmarsh. In a
is removed and no saltmarsh habitats are nearby, study using small, denuded, plots of Sporobolus
then it is likely that the saltmarsh will be very slow virginicus and Sarcocornia quinqueflora. NSW, it
to recover. Seeds would need to be transported was found that access to tidal inundation was
from areas further afield. important for recovery of S. quinqueflora. It took
Several studies in Australia have examined the longer (estimated 4À5.5 years) at higher elevations
active transplantation of saltmarsh plants culti- than at lower positions (14À17 months) (Lae-
vated in greenhouses or taken from donor popu- gdsgaard 2002). S. virginicus, it is estimated at
lations (Table 3). In short, several species of 4À5 years regardless of position (Laegdsgaard
saltmarsh plants can be propagated and grown for 2002).
transplantation purposes (Burchett et al. 1998). Saltmarsh areas that are restored using trans-
Saltmarsh plants that are transplanted from donor plants from donor sites may establish a compli-
sites into rehabilitation areas survive and spread, ment of fauna faster as some may be transported
although often slowly (Nelson 1996; Dick 1999). in with the transplant. This is effectively inoculat-
The best results from restoration are generally ing the site with fauna. This has been shown to be
achieved where the environment has been prepared an effective way to speed up the faunation of sites
for the natural recolonisation or regeneration of in the USA (Brady et al. 2002). It may also be
saltmarsh plants (Nelson 1996; Burchett et al. possible to stock the site with some of the inver-
1998; Dick 1999). Plants that appear spontaneously tebrates known to occur in natural saltmarshes.
in areas tend to grow better than transplanted This requires collection of fauna from nearby
individuals (Burchett and Pulkownik 1995). natural sites, which may not be appropriate in
In transplantation from natural sites, it is many cases. It may be useful where a created or
important to consider the impacts to the donor restored saltmarsh area is far removed from other
sites and that the effects of harvesting may take natural areas and therefore the recruitment
some time to recover also. It has been found that capacity of fauna may be limited. Direct stocking
the time required for saltmarsh plants to recover to of target taxa has been successful and can allow
Table 3. Propagation and replanting trials from the literature with different species of saltmarshes.
Saltmarsh species Methods Reference
Propagated in a greenhouse. Transplanted into res- Burchett et al. (1998), Seliskar
Sporobolus virginicus
toration site and growth recorded (1998)
Removed from donor site and transplanted onto Nelson (1994), Burchett and
varying substrata and spread to cover sites Pulkownik (1995)
Seeding no shoots emerged Burchett and Pulkownik (1995)
Propagated in a greenhouse and transplanted onto Burchett and Pulkownik (1995),
Sarcocornia quinqueflora
bare natural sites or onto slag deposited in natural Dick (1999)
sites and spread to cover sites
Transplants from donor site onto prepared levelled Nelson (1994)
and cleared pasture site. but did not expand
Seeding no shoots emerged Burchett and Pulkownik (1995)
Transplants of 8 cm cores from donor sites. Some Kay (2004)
fertilised. Some planted in topsoil with 50À100%
survival. Survival poor in unreplaced soil and where
tidal influence reduced
Suaeda australis, Halosarcia sp., Propagated in a greenhouse and transplanted but did Burchett and Pulkownik (1995)
not expand
Wilsonia baekhousei, Lampranthus tegens
Transplants from donor site onto prepared levelled Nelson (1994)
Triglochin striata
and cleared pasture site Did not survive transplant-
ing
Transplanting of clumps of Juncus. After 10 months Pen (1983)
Juncus krausii
were expanding and setting seed
395
restored areas to function like natural systems Bowen R., Stephens N. and Donnelly P. 1995. SEPP-14 wetland
protection and the role of mitigation. Wetlands (Australia)
more quickly by facilitating the establishment of
14: 6À12.
key species (Bradshaw 1996). Bradshaw A. 1996. Underlying principles of restoration. Can.
J. Fish. Aquat. Sci. 53(Suppl. 1): 3À9.
Brady V., Cardinale B., Gathman J. and Burton T. 2002. Does
facilitation of faunal recruitment benefit ecosystem restora-
Acknowledgments
tion? An experimental study of invertebrate assemblages in
wetland mesocosms Restor. Ecol. 10(4): 617À626.
Thanks go to Dr. Kylee Wilton and Dr. Nicole Breitfuss M.J., Connolly R.M. and Dale P.E.R. 2003. Man-
Hacking for comments on an earlier draft of this grove distribution and mosquito control: transport of Avi-
cennia marina propagules by mosquito-control runnels in
manuscript. I am grateful to Peggy Svoboda for
southeast Queensland saltmarshes. Estuar. Coast. Shelf Sci.
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Webb C.E. and Russell R.C. 1999. Towards management of mosaics and potential causes. Wetlands (Australia) 14: 1À18.
mosquitoes at Homebush Bay, Sydney, Australia. I. Seasonal Zedler J.B., Paling E. and McComb A. 1990. Differential re-
activity and relative abundance of adults of Aedes vigilax, sponses to salinity help explain the replacement of native
Culex sitiens, and other salt-marsh species, 1993À94 through Juncus krausii by Typha orientalis in Western Australia salt
1997À98. J. Amer. Mosq. Contr. Assoc. 15(2): 242À249. marshes. Austr. J. Ecol. 15: 57À72.
Wetlands Ecology and Management (2006) 14:379À399
DOI 10.1007/s11273-005-8827-z
-1
Ecology, disturbance and restoration of coastal saltmarsh in Australia:
a review
Pia Laegdsgaard*
Department of Infrastructure, Planning and Natural Resources, P.O. Box 2185, Dangar, NSW 2309, Aus-
tralia; *Author for correspondence (e-mail: pia.laegdsgaard@dipnr.nsw.gov.au; phone: +61-2-4960-5029;
fax: +61-2-4960-5055)
Received 10 September 2004; accepted in revised form 12 December 2005
Key words: Conservation, Creation, Disturbance, Rehabilitation, Restoration, Saltmarsh
Abstract
It is clear that saltmarshes are a unique and important component of the coastal biosphere of Australia.
Their contribution ranges from stabilisation of fine sediments and providing an excellent protective buffer
between land and sea, to their diverse blend of terrestrial and marine fauna. Further, saltmarsh plants are
highly specialised and adapted to fill a harsh niche allowing them to act in roles that other vegetation types
cannot. Saltmarsh habitats are recognised for their importance to migratory waders under the Ramsar
convention, but it is becoming increasingly evident that they are also important to a variety of commercially
valuable fish and native mammal species. Activities that are detrimental to saltmarshes continue and need
to be addressed in order to conserve remaining saltmarsh areas. In general, urbanisation of the catchment
has lead to filling of saltmarshes, tidal restriction, use by recreational vehicles, grazing, trampling and
increased sedimentation and nutrient runnoff allowing colonisation and invasion of mangroves. These
disturbances have a number of ecological consequences ranging from weed infestation to complete changes
in the species composition and ecology. Reversing the disturbance is not always simple and can require
extensive groundwork to be successful. Rehabilitation of existing saltmarsh areas has been a successful
means to enhance this habitat. In general, it requires relatively little effort to remove weeds and fence off
areas to regenerate naturally. Saltmarsh areas have been shown to respond well to this type of manipu-
lation. Restoration and creation require substantial effort and planning to ensure a successful outcome.
However, given the right environmental combinations of elevation, tide and salinity, saltmarsh will
establish and grow. To speed the process transplantation of saltmarsh plants can be considered either from
donor sites or plants propagated in green houses.
1977; Adam 1981; Bucher and Saenger 1991; Zann
Introduction
1997; Coleman 1998; Davis and froend 1999; Fin-
Coastal saltmarshes around Australia are dimin- layson and Rea 1999). New South Wales in par-
ishing. The losses of saltmarsh around the country ticular has suffered the most alarming losses. Over
can be credited to lack of information on the the past 200 years over 60% of coastal wetlands in
importance of saltmarsh leading to reclamation for NSW have been lost or degraded (Bowen et al.
industrial, agricultural, port and residential devel- 1995). In response to its demise, saltmarsh has been
opment (Kratochvil et al. 1972; Saenger et al. listed as an Endangered Ecological Community in
380
New South wales under Part 3, Schedule 1 of the shrubs, herbs and grasses (Clarke and Hannon
1971; Kratochvil et al. 1972; Adam 1981; Bridge-
Threatened Species Conservation Act 1995.
As the profile of saltmarshes in Australia in- water et al. 1981; Kirkpatrick and Glasby 1981;
creases so does the desire to protect, restore and Wilson 1984; Clarke and Benson 1988; Adam
rehabilitate these ecosystems. Streever (1997) 1993; Latchford 1994; Zedler et al. 1995). They
identifies ten projects that are specifically aimed at can range from narrow fringes on steep shorelines
saltmarsh rehabilitation in Australia and it is likely to nearly flat expanses several kilometres wide.
that more are being formulated and instigated now. It was first suggested by Pidgeon (1940), that
The future of coastal saltmarshes is linked to estuarine wetlands develop when mudflats are
knowledge of the general ecology of saltmarsh and colonised by mangroves. As sediment accretes, the
its response to disturbance. Many activities remain mangroves move into the estuary and are replaced
that are detrimental to coastal saltmarshes and it is on the landward side by saltmarsh. As tides cover
important to recognise the types of disturbance and the area less frequently, soil salinity increases with
whether recovery is possible before commencing evaporation, which in turn limits the distribution
expensive rehabilitation works. The history of the of many species including mangroves. Mangrove
site, cause of problems within a marsh area and the propagules, although transported into highly sal-
level of perturbation can be the key to effective ine areas, do not survive (Clarke and Myerscough
decision making regarding the management of 1993; Morrisey 1995), which ultimately allows
a particular area. It is important to know saltmarshes to flourish. Evidence from cores taken
how enhancement efforts are going to affect the in existing saltmarsh areas supports this hypothe-
saltmarsh À i.e. is it going to work? How do salt- sis where mangrove root systems dated as
marshes recover after disturbance À are they 500À1700 years-old were found under the salt-
capable of recovery? What is the saltmarsh for À marsh plain (Saintilan and Hashimoto 1999).
how will it function? Some of these questions can However, the process may not be the same in every
be answered with a thorough understanding of the coastal area. Other evidence has shown that
mechanisms behind recovery and the ecology of mangroves can expand directly onto mudflats
saltmarshes and relating these to perturbations and without a saltmarsh stage. Also, where there was
restorative actions. Knowledge of successional the opportunity to observe the creation of a new
patterns, plant physiology, environmental condi- wetland, saltmarshes can be the initial colonists
tions for plant establishment and growth, fauna, (Mitchell and Adam 1989a).
amongst other ecological functions is required. In During the initial stages of saltmarsh forma-
light of this, it seems timely to consider what we tion, pioneer species are the first to establish.
know about saltmarsh ecology, disturbance and Immature saltmarshes are often relatively flat
restoration. with shallow pools. At this stage, vegetation
This paper provides an overview of the ecology, consists of succulents and small shrubs that are
threats and restoration efforts on Australian salt- tolerant to the high salinity and regular flooding
marsh. The information provided is designed to of the newly created coastal environment. As
assist in the management of existing saltmarsh deposition of sediment continues, the saltmarsh
areas and the creation of new saltmarshes in plants trap and bind fluvial and marine sediments
coastal areas. that have been transported by tidal currents (Roy
1984), and the surface of the saltmarsh grows
higher. In turn, species that are less tolerant of
flooding replace earlier pioneer species at upper
Ecology
levels until eventually the system reaches equi-
librium.
The saltmarsh environment
For colonisation and maintenance of vegetation
Establishment and development communities, saltmarsh plants exhibit two modes
Saltmarshes generally develop in areas that are of reproduction, either: sexually, by flowering and
protected from the full force of the surf, in loca- producing seeds for dispersal into bare areas; or
tions such as river mouths and sheltered bays and vegetatively (asexually), by cloning of individual
are typically vegetated by a variety of unique low plants or the extension and spreading of plant parts
381
into new areas (Redfield 1972; Nelson 1994; temperate climates, saltmarshes have a vastly dif-
Allison 1995). Vegetative spread by the means of ferent species composition compared to those in
rhizomes or stolons may produce extensive clones tropical latitudes. Temperature and rainfall are the
and cover large areas. How large, and how old most likely causes of these patterns because of
individual clones can become has not been inves- their effect on salinity. Rainfall is significant in salt
tigated (Adam 1990); but areas of saltmarsh persist circulation in communities as it reduces salinity
for many years without apparent change, and there stress. Most saltmarsh species show better growth
is potential for saltmarsh plants to be long-lived, as rates and survivorship in areas where the salinity is
demonstrated for other clonal plants (Cook 1985). lowered, at least for parts of the year. As a result,
Additionally, most saltmarsh plants flower and set the distribution of saltmarshes along the coast
seeds infrequently (Nelson 1994; Huiskes et al. tends to mimic that of higher average seasonal
1995) usually restricted to times when they are less rainfall (Figure 1). Tropical saltmarshes contain
likely to be inundated by the tide or low salinity considerably fewer plant species than those in
times to minimise the stress of acquiring water and temperate areas (Saenger et al. 1977; Specht 1981).
nutrients. This is particularly important for those Where temperatures are high, as in northern areas
species with small inconspicuous flowers that rely of Australia, the loss of moisture by evaporation is
on wind for pollination. Other saltmarsh species greatest and consequently the salinity increases.
are capable of holding their inflorescences above This coupled, with low rainfall in these areas is
the water at high tide, or have pollen that is resis- probably the major factor in determining the lim-
tant to tidal inundation. Insect pollination has also ited presence of saltmarshes on the northern tip of
been demonstrated for several species, and the Australia (Figure 1). The number of species in
most common pollinators are probably bees (e.g. in these areas is restricted to those that are more
Sarcocornia quinqueflora, Adam and Hutchings tolerant of extreme conditions of salinity. On the
1987) and flies (e.g. in Suaeda australis, Adam contrary, saltmarshes are particularly well devel-
1990). Seeds are likely to be dispersed by birds, oped in the southern, temperate areas of Australia,
insects or tides, for example, S. quinqueflora is a and these areas have a diverse floral component
prolific producer of buoyant seeds that are resistant with more than 40 species of plants being recog-
to desiccation, and are dispersed by tides (Nelson nised (Underwood and Chapman 1993).
1994).
The rate of saltmarsh expansion on substrata Vegetation
Adam et al. (1988) described 25 saltmarsh vegeta-
depends on the incline of the area and topography.
tion communities within NSW, but there is debate
That is, saltmarshes will expand more slowly
about whether saltmarshes should be so highly di-
where the incline is steeper. The older marshes of
vided or whether the mid-marsh community
Europe and North America exhibit elaborate sys-
(dominated by a few species) should be a single
tems of drainage creeks and expansive saltpans,
heterogenous community (Zedler et al. 1995).
but these are notably absent from Australian
marshes (Adam 1997). Shallow depressions with Bridgewater et al. (1981) give descriptions of 13
communities throughout Australia based on the
poorly defined boundaries may occur; and these
dominant species present in any given zone (high
are either permanently or temporarily devoid of
marsh, middle marsh or low marsh). For an ap-
vegetation, and may become hypersaline (Clarke
proach based on ecology and saltmarsh function, it
and Hannon 1967, 1969). Generally, older salt-
is beneficial to regard saltmarsh communities as
marshes in Australia exhibit a more diverse plant
groups of dominant species, especially because
assemblage with distinct zonation patterns that
fluctuations of species between years (particularly
appear as large flat expanses of low vegetation,
much like grass plains. These can however be, rare and annual species) is a common feature of
Australian systems (Adam 1993). Therefore, most
visually diverse depending on the dominant plant
of the saltmarshes found in temperate Australia
species.
can be considered as a single community complex
dominated by one, or a combination of the fol-
Temperature and climate
Regional climate is important in determining the lowing species: saltcouch (Sporobolus virginicus
location and type of saltmarsh to be expected. In (L.) Kunth), samphire (Sarcocornia quinqueflora
382
Figure 1. The average rainfall in millimetres (over a 30-year period) shown for Australia on a contour map adapted from data from the
Bureau of Meteorology. The main concentrations of saltmarsh along the coast are highlighted with an orange dotted line to show the
correlation between saltmarsh and high rainfall.
(Bunge ex Ungem-Sternberg) A.J. Scott)), creeping many areas by development (Pen 1983). In South
brookweed (Samolus repens (Forst & Forst. f) Australia, the perennial blown grass (Agrostis
Pers.) and streaked arrowgrass (Triglochin striatum limitanea J. Black) is limited to the banks of a river
Ruiz & Pav.)(Congdon and McComb 1980; Carne near Spalding in the mid-north. This species lives
1991; Clarke and Jacoby 1994; Nelson 1994; Kra- in semi-saline soils and is associated with emugrass
use 1995; Zedler et al. 1995; Turner and Streever (Distichlis distichophylla (Labill.) Fassett.) and
1999). samphire (Sarcocornia quinqueflora) (Black 1986).
Rare species should be identified for biodiversity
and conservation purposes. In Australia, several Zonation
Many studies have described the zonation patterns
saltmarsh species are rare and their distribution is
of saltmarshes in Australia (e.g. Clarke and Han-
under threat. Of these, the Wilsonia species are
non 1969; Adam and Hutchings 1987; Krause
noteworthy because they are a group that is pe-
1995; Zedler et al. 1995; Streever and Genders
culiar to Australia and New Zealand. Wilsonia
1997). Vegetation is usually zoned parallel to the
backhousei Hook.f. is a rare species in NSW but is
shoreline, and there is a general broad scale
widespread in South Australia. It has been re-
zonation from the land to the sea. The zones can
ported in Homebush Bay and Wamberal Lagoon
(Adam and Hutchings 1987). A feature of the be described as lower, mid and upper levels, usu-
ally each with a distinct mosaic of species that is
saltmarsh vegetation of Cararma Inlet in southern
often complicated by small-scale patchiness. Suc-
NSW is the presence of Sclerostegia arbuscula
culents dominate the lower marsh (e.g. Sarcocornia
(R.Br.) P.G. Wilson, which is also rare in NSW
spp.), while the mid-marsh usually contains species
(Adam and Hutchings 1987). In Western Austra-
such as Sporobolus spp. and Samolus spp. The
lia, Halosarcia spp. are important successional
upper marsh is a mosaic of species including Jun-
species that are required for seed stock to colonise
cus kraussii and Baumea juncea. The area behind
bare areas; but Halosarcia spp. are threatened in
383
the upper marsh is filled with terrestrial vegetation Saltmarsh fauna
such as eucalypts, melaleucas and casuarinas. In
Fauna is probably the least studied component of
most saltmarshes a combination of salinity, ele-
saltmarshes in Australia and information is lack-
vation and inundation is responsible for many of
the patterns seen in the distribution of saltmarsh ing. Generally, the descriptions available highlight
that it consists of several fauna groups ranging
plant species (Adam 1981a, b, 1990; King 1981;
from terrestrial to aquatic species with some
Zedler et al. 1995; Streever and Genders 1997).
specialised saltmarsh dwellers.
Salinity is especially important in the establish-
ment of new saltmarsh as most saltmarsh plants
cannot metabolise well in seawater alone (Web
1966) particularly in terms of germination and Aquatic invertebrates
early growth. Saltmarshes can range in salinity
The sediment of saltmarshes generally contain few
from brackish to hypersaline, and salinity varies
fauna. Only three groups of fauna (oligochaetes,
according to rainfall, freshwater inputs, ground-
polychaetes and bivalves), each containing only two
water influx, soil type and extent of tidal flushing
or three species, have been identified to be wholly
(Clarke and Hannon 1969; Vernberg 1993).
contained within the sediments of saltmarshes in
Most plants, however, possess mechanisms that
Australia (Warren 1989; Berents 1993; Genders
allow them to cope with the saline environment so
1997; Laegdsgaard, unpublished data). The hostile
that they can have a competitive advantage over
nature of the environment no doubt contributes to
many other terrestrial plant species, and can oc-
this lack of fauna with some evidence that the dense
cupy a specific niche. Hypersaline conditions can
impenetrable root systems of saltmarsh can limit
lead to the death of saltcouch or the formation of
burrowing species (Marsh 1982; Laegdsgaard, un-
smaller, thicker darker leaves in samphire and
published data).
seablite communities. Some species avoid having
Crustaceans and molluscs are the most con-
to survive long periods in high soil salinity by
spicuous element of the invertebrate fauna char-
growing as ephemerals in high rainfall periods of
acteristic of saltmarshes, and in a comprehensive
the year. This is most common in the tropics where
study of 65 Sarcocornia quinqueflora marshes
seasonal flooding in the wet season decreases
around Tasmania, Richardson et al. (1997) found
salinity and allows species such as Salsola kali,
over 50 species. However, only eight of these spe-
Sclerolaena spp. and Trianthema spp. to grow
cies were unique to saltmarshes. Molluscs have
(Jacobs 1999).
received most of the attention in the literature,
In many areas Sporobolus spp. and Sarcocornia
with studies ranging from species composition and
spp. co-occur but usually either one or the other
size range to adaptations (Hutchings and Recher
genus is dominant (Nelson 1994). This is generally
1974; Roach et al. 1989; Berents 1993; CSIRO
attributed to competition. In general, Sporobolus
1994; Roach 1998; Roach and Lim 2000). Salina-
spp. have a competitive advantage on more moist
tor solida Von Martens, is the most common gas-
sites, while Sarcocornia spp. have an advantage on
tropod in saltmarsh around Australia (Hutchings
more saline sites. Biological activity can also
and Recher 1974; Hutchings et al. 1977; Roach
influence the zonation of plant species within a
et al. 1989; CSIRO 1994; Roach 1998; Roach and
saltmarsh. The presence of crab burrows can
Lim 2000). S. solida burrow into the surface of the
influence the type and density of vegetation found
mud when the tide covers the saltmarsh surface.
because of increases in aeration, nutrient avail-
When the mud dries out, the snails cluster together
ability, and decomposition of below-ground plant
at the base of vegetation or in small depressions. In
detritus, together with decreases in salinity and
a study at Kooragang Island, S. solida was found
hydrogen sulphide concentrations (Marsh 1982;
in areas that were associated with increased
Bertness 1985). By excavating sediment to main-
flushing (Genders 1997), while it was conspicu-
tain a burrow, crabs transport nutrients within the
ously absent from saltmarsh in Homebush Bay
sediment to the saltmarsh surface where it becomes
(Berents 1993) that have been tidally isolated. This
more available for vegetation (Marsh 1982).
384
species may therefore provide a useful indicator of ancestors of land snails (Richardson et al. 1997).
healthy tidal exchange. There are, however, also several amphipods that
Differences in zonation of epifaunal snail species are found in coastal habitats, including saltmars-
in saltmarsh environments have been attributed to hes, whose dependence on salt spray has been
their abilities to tolerate physical stress and pre- shown to limit their landward migration (Rich-
dation pressures (Roach et al. 1989; CSIRO 1994; ardson et al. 2001).
Talley and Levin 1999; Roach and Lim 2000). In
areas of Juncus kraussii occurring high above the
shoreline, there is a high proportion of small Terrestrial invertebrates
individuals of Ophicardelus ornatus Ferussac. It is
suggested that this may relate to these areas pro- The terrestrial invertebrates of saltmarshes have
been studied very little in Australia, with the
viding a stable microhabitat that provides the right
temperature and moisture conditions for this spe- exception of the saltmarsh mosquito (Ochlerotatus
cies (Roach et al. 1989). S. solida has a population vigilax Skuse previously Aedes vigilax). Its associ-
size age structure that varies significantly with ation with human health risks, such as Ross River
height above the shoreline. Smaller younger indi- Virus (Ryan et al. 2000), has made it a focus for
viduals dominate the mangroves, while the Sar- studies on saltmarshes in Australia (Dale et al.
cocornia habitat supports the larger older 1993; Ritchie 1994; Ritchie and Jennings 1994;
individuals (CSIRO 1994; Roach and Lim 2000). Gislason and Russell 1997; Turner and Streever
1997; Chapman et al. 1999; Turner and Streever
Additionally, growth rate and mortality decrease
with height above the shoreline. Predation has 1999; Webb and Russell 1999). It is clear, however,
been suggested as the main mechanism for this that spiders and insects from most of their orders
trend. Predators limit the size to which Salinator (Homoptera, Hemiptera, Diptera, Coleoptera,
solida can grow in the mangroves, while in the Orthoptera, Hymenoptera and Lepidoptera) are
saltmarsh they are able to attain a greater size common on saltmarshes (Hutchings and Recher
because of decreased predation. Toad fish, yellow- 1974; Marsh 1982; Clarke and Miller 1983; Lae-
finned bream and eels are identified as the major gdsgaard unpublished data).
Marsh’s (1982) research provides an indication
predators of S. solida and it is likely that these fish
species may target many of the other mollusc that there is seasonal variation in the terrestrial
species that are present on the saltmarshes at high invertebrates that use saltmarshes, despite the lack
tide. However, tides only cover the entire salt- of spring data. There is a general trend towards a
marsh surface on the highest tides (maximum three decrease in flying insects in winter because many of
to four times per year) so that for most of the time these spend winter in the egg state, while other
fish can only target those molluscs that are closer species increase in response to the decrease in pre-
to the shoreline i.e. in mangroves. Excluding pre- dators. Clarke and Miller (1983) provided a
glimpse into the spatial distribution of insects by
dators at Towra Point actually decreased the
mortality of S. solida from 82 to 0.7% (Roach and comparing areas within the saltmarsh along with
Lim 2000). other habitats such as mangrove and pasture. In
Richardson and Mulcahy (1996) identified sev- general, there was an increase in the more terrestrial
eral species of amphipods as being dominant species (e.g. grasshoppers) in drier saltmarsh, while
among Tasmanian saltmarshes, These included the diversity of spiders increased in mixed salt-
both aquatic and terrestrial species of amphipods, marsh. In comparison with mangroves, saltmarsh
and it is hypothesised that saltmarshes may have has a much greater diversity of insects (a total of 13
species in mangroves compared to 47 in saltmarsh)
provided the pathway for amphipods to colonise
the land. Saltmarsh vegetation has remained rela- Clarke and Miller 1983). Since insects are a
tively unchanged since the Cretaceous period common component of the saltmarsh fauna, these
(Adam 1990), and it is possible that other species in turn attract insectivorous animals such as birds
utilised saltmarsh as an evolutionary pathway. For and bats. Bats in particular have been identified to
example, the gastropods Ophicardelus spp. are the be active over saltmarshes of Victoria and NSW
most primitive of their family, and they show with ten species recorded including some listed as
characteristics similar to those of the primitive rare and threatened (Laegdsgaard et al. 2004).
385
by extreme high tides. Gibbs (1986) sampled sev-
Vertebrates
eral pools in saltmarshes around Wallis Lake in
Fish NSW, and found juveniles of several species,
In the past, saltmarshes have not been considered including silver biddy and yellow-finned bream.
important fisheries habitat in Australia (Connolly Smaller ponds within saltmarshes have been found
et al. 1997). Most saltmarsh areas are only to contain species such as the introduced mosquito
available for fish to use during the highest tides of fish along with the native blue-eyes and gobies
the year, and therefore their usefulness as a (Davis 1988; Morton et al. 1988; Lincoln-Smith
habitat for fish was considered limited. However, et al. 1994).
the lack of information on fish in saltmarshes is
generally related to the difficulties of sampling in
Birds
this environment (Connolly 1999). Consequently,
In the available literature, there are several good
most studies have centred on creeks because they
descriptions of birds that utilise saltmarshes, but
are easier to sample than saltmarsh flats. Morton
the information available on reptiles and mammals
et al. (1987) collected samples monthly, over a
is more rare, with only two studies mentioning
year, from a large channel draining a saltmarsh;
them (Latchford 1994; Morrisey 1995). Many ter-
and found 19 species, from 14 families, of fish
restrial birds frequent the saltmarshes, and use
that regularly used this area. The dominant spe-
them as breeding grounds (e.g. bronze cuckoos).
cies were toadfish, yellow-finned bream, yellow
They feed on the variety of insects found on the
perchlets, and flat-tail and fan-tail mullet.
saltmarsh or on the seeds of the saltmarsh plants
Another record of fish from temperate saltmars-
(e.g. galahs). All these smaller birds and mammals
hes is from Wallis Lake, where poisoning of a
on the saltmarsh form ideal prey for the hunting
small creek resulted in the capture of 11 species
birds such as brahminy kite, whistling kite and
(Gibbs 1986).
marsh harriers, which are considered to be the top
More recently, investigators have overcome
predators in the structure of the saltmarsh food
some of the difficulties of sampling on saltmarsh
web (Figure 2). Saltmarsh provides summer feed-
flats to discover that these environments in Aus-
ing and roosting grounds for migratory waders of
tralia are used by fish during flood tides (Connolly
international significance (Gosper 1981; Clarke
et al. 1997; Thomas and Connolly 2001; Crinall
and van Gessel 1983; Maddock 1983; Day et al.
and Hindell 2004; Mazumder et al. 2005). The
1989; Smith 1991; Latchford 1994). Bird species
number of fish caught on the flats is lower than in
that utilise saltmarshes as a roosting site do not
creeks (Connolly et al. 1997) but still provide a
tend to use wooded areas (including mangroves)
habitat that is utilised by many fish species most
because these areas can hide land-based predators
likely for feeding. The abundance of insects, spi-
and, more importantly, restrict landing and take
ders, crustaceans and mollusc provide ample food
off areas for birds (Clarke and van Gessel 1983;
resources (adults, nymphs and larval stages) to be
Saintilan 2003). Many wading birds feed primarily
targetted by fish (Morton et al. 1988; Mazumder
on mudflats, and it is important that roosting pla-
unpublished data). Small resident species such as
ces are close to feeding areas, to minimise energy
perchlets and gobies dominated catches, but
expended on flights during their overwintering
commercial species such as whiting, bream and
period. This makes large expanses of saltmarsh
mullet were also caught in significant numbers in
ideal roosting sites, and indeed 18 of the 42 sites
Queensland and NSW (Thomas and Connolly
throughout Australia recognised as wetlands of
2001; Mazumder unpublished data). It is not only
international importance, under the Ramsar con-
the edges of the saltmarsh flats that are used either,
vention, contain large expanses of saltmarsh that
some fish venture to the farthest reaches of a
are considered vital for several species of migratory
saltmarsh during the tidal cycle (Connolly and
wading birds. Additionally, saltmarshes have
Bass 1996; Thomas and Connolly 2001).
associated ponds of water that are flooded by the
Semi-permanent and permanent ponds in salt-
occasional high tide. These ponds contain fish that
marsh areas have been investigated as a suitable
remain after the tide has receded, and several
habitat for a nursery for juvenile fish, despite being
invertebrates which attract waterbirds such as
a relatively harsh environment that is only flushed
386
sharp-tailed sandpipers, curlew sandpipers, anced in saltmarshes with no net import or export
greenshanks and marsh sandpipers (Straw 1996). to adjacent areas. For most of the time, salt-
Saltmarsh habitats in south-eastern Australia marshes in Australia are not covered by the tide,
support the endangered bird species, the orange- facilitating exchanges with the atmosphere, rather
bellied parrot (Neophema chrysogaster Latham) than exporting nutrients and plant matter to the
which has a single breeding population containing estuary. Therefore, a relatively large proportion of
less than 200 mature adults in the wild. These rare the macrophyte production is consumed on the
parrots are confined to coastal habitats within saltmarsh by respiratory or burial processes. In
10 km of the coastline in south-eastern Australia. addition, denitrification (and thereby loss of
The parrots spend the winter around saltmarshes available nitrogen) is likely to be limited because
in Victoria, South Australia and Tasmania where this process is generally enhanced in waterlogged
they feed on the seeds of saltmarsh plants such as anoxic soils that are typical of habitats constantly
Frankenia, Sarcocornia, Sclerostegia and Suaeda. inundated by the tides. The soils of saltmarshes in
Australia are typically drier than those of nearby
mangroves (Saintilan and Williams 1999b), there-
by reducing the potential for nitrogen loss to the
Saltmarsh productivity
atmosphere. Furthermore, saltmarsh vegetation
There are very few data on productivity, and no actively transfers oxygen to the roots and conse-
detailed measurements of fluxes into and out of quently to the soil (Kaplan and Valiela 1979). This
Australian marshes. The characteristics of salt- forms the basis for nitrification processes whereby
marshes in Australia make them different from nitrogenous compounds are converted to biologi-
those that are found in North America and other cally available ammonium and nitrate that is ex-
parts of the world, which are dominated by tall ported to coastal waters and used in active plant
robust grasses and are generally considered highly growth (Boon and Cain 1988). In addition, during
productive. From the small amount of data avail- decomposition, nutrients in the plant tissue are
able it is clear that Australian marshes record lower released and recycled into new plant growth,
productivity figures than those reported for many Decomposition rates of most plants in Australian
USA marshes (Table 1). Additionally, high vari- marshes are high (61À67% in the first year, van
ability precludes consistent spatial or temporal der Valk and Attiwill 1983) compared to the USA
trends were associated with above-ground biomass (50% in the first year, de la Cruz and Hackney
of the dominant saltmarsh species (Sporobolus 1977) which probably relates to the succulent
virginicus or Sarcocornia quinqueflora) (Smith- nature of most Australian saltmarsh plants.
White 1981; Clarke 1986; Clarke and Jacoby 1994; Decomposition of more woody saltmarsh plants
Seliskar 1998), This may be attributed to natural such as Juncus Kraussii is very slow (approxi-
variation, fluctuations in soil salinity (Smith-White mately 20% in the first year) (van der Valk and
1981) or disturbance. It has been shown that Attiwill 1983). Additionally, above ground litter
above-ground biomass can be lower in sites that decomposes faster than below-ground litter (Dick
have been affected by urban development (Lae- 1999). Therefore, very little litter is left on the
gdsgaard unpublished data). surface of the marsh to be exported with the rare
Although saltmarsh plants utilise nutrients for full tidal inundation.
growth, nitrogen concentration within the tissue of The litter decomposed by microorganisms pro-
plants such as Sarcocornia quniqueflora is only vides energy to invertebrates and higher trophic
around 2% (Clarke 1983; van der Valk and Atti- levels in the foodweb. A great number of ani-
will 1983; Dick 1999), and phosphorus is less than mals found in the saltmarsh can be classified as
1% (van der Valk and Attiwill 1983; Dick 1999). detritivorous or decomposers (e.g. protozoans and
This means very little of the nutrients brought into nematodes). These fauna convert the wealth of
the saltmarsh system are actually incorporated plant matter in saltmarshes to detrital food sour-
into the plant material at any one time (estimated ces. Such food sources are utilised by a rich and
at around 15%), so the plants themselves do not diverse invertebrate community that may in turn
act as a nitrogen source (Clarke 1986). It has been support other marine and terrestrial species in a
suggested that nitrogen and phosphorus are bal- foodweb that climaxes with hunting birds as the
387
top predators (Figure 2). In Australia, Boon et al. the surface level of the saltmarsh. This favours the
(1997) found that the saltmarsh plant Sarcocornia establishment and spread of such species as com-
quinqueflora did not contribute as a food source mon reed (Phragmites australis [Cav.] Trin ex
for two intertidal callinassid shrimps in Western Steud), water couch (Paspalum vaginatum) and
Port southern Australia. However, Irving (2001) river clubrush Schoenoplectus validus [Vahl] A & D
found that Sporobolus virginicus was a basis of the Love), and the loss of saltmarsh species (Roman
¨
foodweb of the common gastropod of saltmarshes et al. 1984). The common reed (Phragmites aus-
(Salinator solida), the semaphore crab (Heleocius tralis) is tenacious and recruits easily to areas that
cordiformis) and several fish species (e.g. mullet have become tidally isolated. If allowed to persist,
and stingrays). In addition, bream were found to it can form extensive stands that restrict the
derive nutrition from Sarcocornia quinqueflora. movement of aquatic life and alter the ecology and
Many fish species feed on amphipods such as Or- function of the entire saltmarsh (Adams and Bate
chestia spp., which are common in (Berents 1993; 1994; Windham 1995; Weinstein and Balletto
Richardson et al. 1997) throughout Australia, and 1999). Dense monotypic Phragmites stands gener-
are primary consumers of halophytes (Lefeuvre ally provide unsuitable or less preferred habitat
et al. 2000). It has also been demonstrated that fish and food for wildlife and waterfowl (Roman et al.
feeding in saltmarshes at high tide targeted mainly 1984).
saltmarsh crabs (Morton et al. 1987).
Agricultural practices
Response of saltmarsh to disturbance
In areas that are adjacent to wetlands and have been
Saltmarsh have to cope with a variety of natural reclaimed for agriculture, pasture species exclude
and anthropogenic disturbances (Laegdsgaard saltmarsh plants to a point where the pasture spe-
2001) to which they are particularly susceptible. It cies can no longer cope with the salinity. Saltmarsh
is important to understand the ecological conse- plants cannot compete with pasture species, and
quences of disturbance in order to reverse or halt it. therefore their expansion is limited by competition
(Genders 1996) in these altered environments.
In addition to being replaced, many saltmarsh
areas in Australia occur on private land and are
Changes to hydrology
used as pasture for livestock. Grazing and tram-
Alterations to drainage and hydrology can have pling are particularly detrimental to saltmarsh
devastating effects on saltmarsh communities. plants. Where trampling is high saltmarsh plants
These range from habitat destruction to modifica- are unable to regenerate or re-establish. Fauna
tion of the ecology. When estuaries are closed or that is native to Australia is unique and does not
tidally blocked, water levels rise as a result of posses hard hooves; therefore, constant trampling
localised freshwater run-off, leading to the inun- by hard hoofed farm animals can easily disrupt a
dation of saltmarshes for extended periods. Many saltmarsh area. Hoofed animals in saltmarsh
succulent saltmarsh plants such as Sarcocornia spp. habitats disrupt the dense vegetation and root
can only withstand short periods of inundation system, often destroying delicate succulent cheno-
before the plants quickly rot and decompose pods, such as Sarcocornia spp. and Suaeda spp.,
(Adams and Bate 1994). Naturally occurring flood and allowing tidal water to pool. Such pools form
events cause a similar effect; however, the water excellent habitat for biting insects (mosquitoes and
does not remain to cause permanent damage. Some midges) or other plant species (e.g. Triglochin
plants may appear to die because of prolonged striata) which are more tolerant of waterlogging
submergence; but if the stems of the plant remain and lowered salinity (Zedler et al. 1995). Tram-
alive, despite leaf decomposition, it is possible that pling also introduces gaps where weeds can
the plant will survive and regenerate once water establish (Bridgewater 1982), which can affect the
levels drop and the tidal influence is restored. If the dynamics of saltmarsh communities. In areas
tidal movement is not restored, the water table is where trampling is high, regeneration of the salt-
substantially lowered, and there is a relative drop in marsh plants is generally slow. Alterations in
388
typical saltmarsh species distributions can occur with various diseases and is therefore a priority for
because some plants are grazed selectively in control. This is achieved either through pesticide
preference to unpalatable species. For example, application, which may be harmful to non-target
the reduction of cover of rare species (e.g., Scler- insect populations, or habitat modification. Run-
ostegia arbuscula) has been linked to selective nelling is a type of habitat modification using
grazing (Kirkpatrick and Glasby 1981; Bridgewa- shallow channels in the saltmarsh to increase the
ter 1982) in saltmarsh areas. tidal flushing of the area to reduce mosquito
breeding and is likely to affect the plant species
distribution and faunal communities in the salt-
Urban encroachment
marsh (Connolly and Bass 1996). Runnelling was
Where saltmarsh is adjacent to urban development not found to have any significant impacts on the
it can be subject to mowing which can disrupt the wetland environment over a 6.5-year study period
by Dale et al. (1993). However, its effect on salt-
flowering of grasses while destroying succulent
marsh crabs was the subject of a study in
species. Watering of lawns adjacent to saltmarsh
Queensland, where it was concluded that although
also reduces their competitive advantage and leads
runneling did not affect the total number of crabs
to terrestrial grass species eradicating saltmarsh
it did have an effect on the species distribution of
species (Genders 1996). Halophytes are not com-
crabs (Chapman et al. 1998). Significantly greater
petitive in non-saline conditions (Zedler et al.
1990; Genders 1996; Wilson et al. 1996). So, numbers of Parasesarma erythodactyla Hess. were
fresher conditions allow exotic species to invade found at the runnelled site while Helograpsus
haswellianus Whit. was more abundant at the un-
and conquer the otherwise harsh saltmarsh envi-
runnelled site (Chapman et al. 1998). Additionally,
ronment. The competition between saltmarsh
it has been found that the overall effect of run-
plants and terrestrial vegetation is not restricted to
nelling appears to be a reduction in the abun-
above-ground; root competition is just as impor-
dances of nekton in the immediate vicinity of
tant. In a study on the ability of Sarcocornia
runnels thereby adversely affecting the saltmarsh
quinqueflora seedlings to invade areas where pas-
ture species had been removed, Genders (1996) environment (Connolly 2005). The tidal penetra-
found that S. quinqueflora were only successful in tion also increases the chance of mangrove incur-
sion with propagules transported high into the
plots that had been weeded to remove above- and
marsh by runnels (Breitfuss et al. 2003). The in-
below-ground vegetation. Plots that were simply
creased flushing may also decrease the high salinity
mown, remained free of saltmarsh plants.
in the marsh and allow mangroves seedlings to
Proximity to urban development has also pre-
establish and grow (Clarke and Myerscough 1993;
cipitated the need for increased mosquito man-
Morrisey 1995).
agement. The saltmarsh mosquito is associated
Table 1. Published values of above-ground productivity levels for dominant, wide-spread saltmarsh species in south eastern Australia
compared to species that dominate the marshes of the USA.
Species Location Above-ground Reference
production (g mÀ2)
South-eastern Australia 148À852 Clarke and Jacoby (1994)
Sprobolus virginicus
172À1600 Laegdsgaard, unpub. data
South-eastern Australia 1116 Clarke and Jacoby (1994)
Juncus Kraussii
300À1300 Congdon and McComb (1980)
210À3300 Congdon and McComb (1981)
South-eastern Australia 800 Congdon and McComb (1981)
Sarcocornia quinqueflora
317 Clarke and Jacoby (1994)
88À2411 Laegdsgaaerd, unpub. data
South-eastern Australia 400 Congdon and McComb (1981)
Samolus repens
South-eastern Australia 1100 Congdon and McComb (1981)
Scirpus maritimus
USA 600À1000 Mahall and park (1976)
Salicornia virginica
USA 500À2500 Taylor and Allanson (1995)
Spartina alterniflora
389
The proximity of saltmarshes to urban settle- the salinity would increase thereby eliminating the
ments increases their attractiveness to drivers of mangroves again (Outhred and Buckney 1983).
recreational vehicles. Off-road vehicles (e.g. The view that salinity is the driving force for
mountain bicycles, 4-wheel drive vehicles, trail maintaining mangrove distribution remains a
motorbikes) traversing saltmarsh vegetation can hypothesis. Clarke and Allaway (1993) suggest
cause localised and widespread damage. Decrease that upslope delimitation of the grey mangrove
of saltmarsh in areas of NSW and Tasmania has (Avicennia marina) is related to desiccation that
been directly attributed to recreational vehicle use may suggest that inundation frequency is the
(Kirkpatrick and Glasby 1981; Clarke 1993; critical factor. The fact that mangroves are
Kelleway in press). The type of disturbance to the threatening to over run many saltmarsh areas,
saltmarsh depends greatly on the nature and pur- suggests there is a mechanism operating to allow
pose of the driving. Effects like stein-height mangroves to flourish where they would normally
reductions and stem breakage are common with be stressed or absent.
light traversing (restricted to a set of wheel ruts) of
saltmarsh areas. However, continuous, heavy
usage can cause a complete removal of vegetation, Fragmentation
soil compaction and removal of mollusc and crab
populations (Kelleway in press). Fragmentation is another major contributing fac-
tor for saltmarsh habitat decline, however, it is not
clear what the ecological consequences might be.
Fragmentation in other habitats such as forests
Mangrove incursion
and grasslands has been shown to cause degrada-
An imminent threat to saltmarshes around Aus- tion of habitat quality and decreases in biodiver-
tralia is mangrove incursion. Over the last few sity (Collinge 1996; Harrison and Bruna 1999;
decades colonisation and invasion of mangroves Mazluff and Ewing 2001; Tschantke et al. 2002).
into south-eastern Australian saltmarsh areas has Rare or specialised species and species with lower
been documented (Buckney 1987; Mitchell and dispersal capabilities are most affected (Tscharntke
Adam 1989a, b; Morton 1993; West 1993; Fenech et al. 2002). Although it has not been tested,
1994; Coleman 1998; Saintilan and Hashimoto fragmentation is likely to affect the foodweb
1999; Saintilan and Williams 1999; Saintilan and structure of saltmarsh significantly. Many of the
Wilton 1999). There are a number of hypotheses predators require space for prey capture, particu-
that have been put forward to explain this phe- larly those that feed on the wing such as bats and
nomenon. These include sea level rise, increased hunting birds. Large saltmarsh habitats with a
rainfall, increased freshwater inputs into saltmarsh diverse array of molluscs and crabs produce a
or altered tidal regimes most of which need to be large amount of plankton that is exported with the
tested. Wilton (2002) was unable to find a corre- tide when the saltmarsh is inundated which is an
lation between the degree of mangrove encroach- important food source for fish (Mazumder,
ment with sea level rise or degree of urbanisation, unpublished data). In this way, saltmarshes are
which suggests that other physical factors within important in sustaining other estuarine species,
the environment may be driving the changes being many of which may be of commercial significance.
observed. Salinity is a major driving factor in Many of the crabs and molluscs are generally ab-
maintaining wetland communities. Normally, sent from small fragmented saltmarsh habitats and
saltmarshes flourish because soil salinity increases these do not have the capacity to supply larval
with evaporation, which in turn may limit the zooplankton to estuarine fish species. It is pre-
distribution of many species including mangroves, dicted that with increasing fragmentation and re-
Mangrove propagules, although transported into duced Patch size of saltmarsh habitat the foodweb
highly saline areas, do not survive (Clarke and will become limited to small predators and few
Myerscough 1993; Morrisey 1995). Nevertheless, insects as shown in Figure 3. This would be par-
during a succession of wetter years soil salinity ticularly true if the saltmarsh patch also becomes
may fall to an extent where mangroves can tidally isolated (Figure 3b). In grassland, frag-
establish and grow, but in subsequent dry periods ments can become too small even to maintain
390
Figure 2. Representation of the foodweb of a typical coastal saltmarsh in Australia. Arrows represent the direction of the links in the
foodweb with respect to consumers.
viable populations of small birds (Johnson 2001). been positively correlated to the area of saltmarsh
This could also be true for saltmarshes, which within 20 km radius of the breeding colony
would reduce the top predators to spiders and (Baxter 1998).
insects of a very small fragment (Figure 3d). Where saltmarshes are fragmented by the
Urbanisation of many coastal areas has seen the presence of roads, contamination is also likely to
reduction of saltmarsh areas to minute patches affect biodiversity. Contaminants may cause
that are likely to be utilised only by insects. physiological stress in some plants and make
Migratory birds are generally attracted to lar- them more susceptible to pest attack, Saltmarshes
ger areas of saltmarsh to give better visual pro- contain a high number of insects that may be
tection from predators (Straw 1996; Saintilan reduced by the lead in combustion gases in cars
2003). The size of breeding colonies of egrets has (Spellerberg 1998).
391
Invasive species Restoration efforts
Several invasive species have the potential to Restoration of saltmarsh in Australia is a rela-
completely overrun a natural saltmarsh. These tively new concept. As the profile of saltmarshes
species form a priority for rehabilitation efforts. Of increases so do restoration efforts. Unfortunately,
particular note are the common cordgrass and rehabilitation efforts generally go undocumented
spiny rush. The invasive common cordgrass and there is little measure of their success. Nev-
(Spartina anglica) was introduced into Tasmania ertheless, examples do exist that allow confidence
and Victoria specifically for reclamation of land in rehabilitation efforts.
and stabilisation of mudflats. In Tasmania, it has Actions such as fencing to remove cattle from
completely taken over the Tamar Estuary (Adam saltmarsh areas, diversion of stormwater away
1981). Despite attempts to establish it in NSW it from saltmarsh and weed removal are the most
has not become a problem in this State (Adam and common rehabilitation methods for saltmarsh. A
Hutchings 1987). The common cordgrass can have good example of a saltmarsh restoration project,
several detrimental effects on natural environments where these have been employed, is the Kooragang
in Australia. These effects include invading mudfl- Wetland Rehabilitation Project on the central
ats that are rich in invertebrates and producing coast of NSW. The project was initiated in 1993 to
dense monotypic stands that replace more diverse compensate for the loss of estuarine habitat due to
plant communities. Species such as Sarcocornia 200 years of clearing and filling (Buckney 1987).
quinqueflora and Samolus repens are particularly The project covers three sites, Tomago, Ash Island
prone to competitive exclusion by Spartina anglica and Stockton and it is one of the major environ-
(Simpson 1995; Hedge and Kriwoken 2000). Birds mental projects in NSW. The main area for reha-
have been observed to avoid S. anglica (Simpson bilitating estuarine habitats has been Ash Island
1995; Hedge and Kriwoken 2000), and species where tidal flushing is being restored through the
richness and total abundance of fauna are greater removal of culverts. In areas where tidal restriction
in saltmarshes dominated by native plants, com- has been removed there has been an observed
pared to those dominated by S. anglica (Hedge and reversal of the habitat degradation brought about
Kriwoken 2000). by the tidal restriction and reclamation for agri-
Spiny rush (Juncus acutus) is another introduced culture (Streever et al. 1996), with a return and
species, from the Mediterranean, that has become expansion of native saltmarsh and mangrove spe-
widespread throughout saltmarshes and on saline- cies. Additionally, evidence from a large area im-
affected pasturelands in southeastern Australia pacted by cattle grazing at Kooragang Island in
(Milford and Simons 2002; Zedler and Adam NSW, where cattle had been excluded to allow
2002). It has been so successful at invasion that it rehabilitation, suggests that Sarcocornia quin-
has been listed as a noxious weed for Australia queflora is able recover naturally in around five
(NAWC 2003). This species occupies the same years once the disturbance is removed (Kooragang
niche as the native rush, Juncus krausii but is Wetland Rehabilitation Project unpublished data).
tougher and more resilient and easily out-competes Weed removal is particularly important in the
the native species. The introduction of J. acutus rehabilitation of many saltmarsh habitats as there
into saltmarshes has altered the structure and are several introduced species that plague salt-
complexity of these environments. Once J. acutus marshes around Australia, and the way in which
becomes established, its sharp tough cylindrical most have arrived is unknown. Common intro-
leaves form dense impenetrable thickets so that the duced species include buck’s horn plantain (Plan-
native rush is displaced or unable to establish. tago coronopus), rock sea-lavender (Limonium
Many gastropods and other invertebrate fauna are binervosurn), grasses (Polypogon monspeliensis.)
believed to depend on J. krausii for completion of and daisy (Aster subulatus). All these species have
their lifecycle and the same function is not affor- been introduced from the Northern Hemisphere,
ded by J. acutus due to its harsher habit. There- and the majority have the ability to out-compete
fore, the ecosystem may be severely impacted by native saltmarsh species (Callaway and Zedler
the invasion of J. acutus as it displaces J. krausii in 1998). Generally, these are simple to eradicate from
many saltmarsh ecosystems of coastal Australia. saltmarsh areas. The removal of spiny rush (Juncus
392
Figure 3. Predicted changes to the typical saltmarsh foodweb with disturbance and fragmentation. (a) Reduction in size of the
saltmarsh limits the ability of birds of prey to feed thereby eliminating them from the foodweb. Top predators become small birds, fish
and small mammals. (b) Tidal restriction coupled with decreased habitat size eliminates fish, crustaceans and molluscs from the
saltmarsh foodweb. (c) A fragment of saltmarsh approximately the size of a house block are likely to support only small ground feeding
birds and insects. (d) Minute fragments of saltmarsh (1À2 m2) can only support arthropods. Predatory insects and spiders take on the
role of top predators in this scenario.
acutus) however has become a focus for manage- cies in order to formulate effective and permanent
ment in some areas but it is proving particularly eradication methods.
difficult to eradicate. More information is required Where land needs reshaping in order to restore
on the general biology and physiology of this spe- tidal inundation for saltmarshes to grow and
393
flourish, it is important to understand that salt- back to saltmarsh in this way (Personal Observa-
marsh species can be sensitive to changes of a few tion).
centimetres in elevation and tidal inundation. It is usually assumed that if hydrology is re-
Zonation of saltmarsh plants requires a specific stored that vegetation, soil and animals will come
combination of land gradients (to ensure inunda- naturally. In many areas, this is true but may not
tion) and soil salinity (Clarke and Hannon 1970; always be the case and may require assistance. If
Adam 1990; Zedler et al. 1995). This may be par- the site is excavated and the surface soils removed
ticularly difficult to achieve. Callaway et al. (1997) it may take longer for organic carbon levels at
established that hydrology and substratum are the depth (where it is needed) to return to similar
key elements in restoration. Porous substratum levels to natural marshes (Havens et al. 2002). It
drains and dries too quickly to be conducive to the may be necessary to add organic substrate back to
growth of dominant saltmarsh species. Addition- the marsh surface at the time of construction when
ally, saltmarsh areas planted with Salicornia virg- re-levelling is complete to speed the development
inica (a species similar to Sarcocornia quinqueflora) of a sediment profile similar to natural marshes. In
did not thrive in areas that were infrequently tid- addition, soil salinity is a major factor determining
ally flooded but retained water (Callaway et al. seed germination and the ability of plants to ma-
1997). Where this has been trialled and access to ture in saltmarshes so the right balance of tide and
tidal water restored through excavation and rele- freshwater are essential. Table 2 provides toler-
velling, saltmarsh has establish naturally. Several ances for the most common species associated with
sites in Sydney have been reverted from parks to Australian saltmarsh.
saltmarsh that is floristically mature and attracting Natural recovery of saltmarsh communities oc-
bird species (Eckstein 2004; Sainty and Roberts curs after disturbance via establishment of seed-
2004) and areas of Kooragang Island in NSW lings. The degree of isolation from natural habitats
have been successfully converted from pasture will affect recolonisation. Sarcocornia quinqueflora,
Table 2. Dominant saltmarsh species and their requirements for growth in early and mature stages.
Species Appearance Germination and early growth Mature conditions
A small erect leafless herb with Requires conditions of low salinity Flowering in late summer is trig-
Sarcocornia
succulent jointed stems. Can vary to trigger germination (Chapman gered by high salinity conditions
quinqueflora
in colour from green to red and 1960). (Clarke and Hannon 1970). Die
purple. back in winter
Grass like Narrow imrolled leaves Low salinity periods are required Can tolerate periods of high salin-
Sporobolus
are stiff, erect and green. for establishment. Responds well ity (Gallagher 1979), flooding and
virginicus
to increased nutrients Waterlog- hypoxic soils (Donovan and
ging can hasten the onset of flow- Gallagher 1984; Donovan and
ering (Clarke and Hannon 1970) Gallagher 1985). However, hy-
persaline and constant inundation
leads to little or no growth (Clarke
and Hannon 1970).
Low growing herb Newly pro- High mortality and retarded Plants in full sun become pink or
Suaeda
duced foliage is soft green and may growth in seedlings is common in purple while those in shaded posi-
australis
become pink or purple well-drained areas suggesting wet tions remain green (Cribb and
conditions are necessary for ger- Cribb 1985). With age and matu-
mination and early growth (Clarke rity, it can tolerate drier conditions.
and Hannon 1970).
Non-tuberous annual plant with Opportunistic and will invade areas Plants die down to underground
Triglochin
succulent leaves rounded in cross that become waterlogged. Water- rhizomes in dry conditions and will
striata
section logging hastens the onset of flow- only flower once they are flooded.
ering (Clarke and Hannon 1970).
A herb with creeping lower stems Can be planted in most soils but Occurs in saline conditions on the
Samolus
and erect upper stems to 30 cm tall. grows best with some moisture. edge of estuaries
repens
White star flowers.
394
is a prolific producer of buoyant seeds dispersed by their natural densities in small plots varies with
the tide (Nelson 1994). If an entire saltmarsh field species and location within the saltmarsh. In a
is removed and no saltmarsh habitats are nearby, study using small, denuded, plots of Sporobolus
then it is likely that the saltmarsh will be very slow virginicus and Sarcocornia quinqueflora. NSW, it
to recover. Seeds would need to be transported was found that access to tidal inundation was
from areas further afield. important for recovery of S. quinqueflora. It took
Several studies in Australia have examined the longer (estimated 4À5.5 years) at higher elevations
active transplantation of saltmarsh plants culti- than at lower positions (14À17 months) (Lae-
vated in greenhouses or taken from donor popu- gdsgaard 2002). S. virginicus, it is estimated at
lations (Table 3). In short, several species of 4À5 years regardless of position (Laegdsgaard
saltmarsh plants can be propagated and grown for 2002).
transplantation purposes (Burchett et al. 1998). Saltmarsh areas that are restored using trans-
Saltmarsh plants that are transplanted from donor plants from donor sites may establish a compli-
sites into rehabilitation areas survive and spread, ment of fauna faster as some may be transported
although often slowly (Nelson 1996; Dick 1999). in with the transplant. This is effectively inoculat-
The best results from restoration are generally ing the site with fauna. This has been shown to be
achieved where the environment has been prepared an effective way to speed up the faunation of sites
for the natural recolonisation or regeneration of in the USA (Brady et al. 2002). It may also be
saltmarsh plants (Nelson 1996; Burchett et al. possible to stock the site with some of the inver-
1998; Dick 1999). Plants that appear spontaneously tebrates known to occur in natural saltmarshes.
in areas tend to grow better than transplanted This requires collection of fauna from nearby
individuals (Burchett and Pulkownik 1995). natural sites, which may not be appropriate in
In transplantation from natural sites, it is many cases. It may be useful where a created or
important to consider the impacts to the donor restored saltmarsh area is far removed from other
sites and that the effects of harvesting may take natural areas and therefore the recruitment
some time to recover also. It has been found that capacity of fauna may be limited. Direct stocking
the time required for saltmarsh plants to recover to of target taxa has been successful and can allow
Table 3. Propagation and replanting trials from the literature with different species of saltmarshes.
Saltmarsh species Methods Reference
Propagated in a greenhouse. Transplanted into res- Burchett et al. (1998), Seliskar
Sporobolus virginicus
toration site and growth recorded (1998)
Removed from donor site and transplanted onto Nelson (1994), Burchett and
varying substrata and spread to cover sites Pulkownik (1995)
Seeding no shoots emerged Burchett and Pulkownik (1995)
Propagated in a greenhouse and transplanted onto Burchett and Pulkownik (1995),
Sarcocornia quinqueflora
bare natural sites or onto slag deposited in natural Dick (1999)
sites and spread to cover sites
Transplants from donor site onto prepared levelled Nelson (1994)
and cleared pasture site. but did not expand
Seeding no shoots emerged Burchett and Pulkownik (1995)
Transplants of 8 cm cores from donor sites. Some Kay (2004)
fertilised. Some planted in topsoil with 50À100%
survival. Survival poor in unreplaced soil and where
tidal influence reduced
Suaeda australis, Halosarcia sp., Propagated in a greenhouse and transplanted but did Burchett and Pulkownik (1995)
not expand
Wilsonia baekhousei, Lampranthus tegens
Transplants from donor site onto prepared levelled Nelson (1994)
Triglochin striata
and cleared pasture site Did not survive transplant-
ing
Transplanting of clumps of Juncus. After 10 months Pen (1983)
Juncus krausii
were expanding and setting seed
395
restored areas to function like natural systems Bowen R., Stephens N. and Donnelly P. 1995. SEPP-14 wetland
protection and the role of mitigation. Wetlands (Australia)
more quickly by facilitating the establishment of
14: 6À12.
key species (Bradshaw 1996). Bradshaw A. 1996. Underlying principles of restoration. Can.
J. Fish. Aquat. Sci. 53(Suppl. 1): 3À9.
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Acknowledgments
tion? An experimental study of invertebrate assemblages in
wetland mesocosms Restor. Ecol. 10(4): 617À626.
Thanks go to Dr. Kylee Wilton and Dr. Nicole Breitfuss M.J., Connolly R.M. and Dale P.E.R. 2003. Man-
Hacking for comments on an earlier draft of this grove distribution and mosquito control: transport of Avi-
cennia marina propagules by mosquito-control runnels in
manuscript. I am grateful to Peggy Svoboda for
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