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Literature Review
Coastal salt marshes are an important ecological habitat for all kinds of flora and
fauna. Salt marshes are defined as areas with either sediment or peat deposits that are
colonized by herbaceous and/or small shrubby plants and are frequently washed over
by saline waters (Long, Mason, 1983). They form in mainly sheltered bays or
estuaries due to the dispersion and lowered wave energy. This leads to sedimentation
which is the most important factor of a salt marsh as without it colonization cannot
occur. Sedimentation occurs when water movement is slowed and the suspended
particles can settle. This can take from minutes to as long as a couple of days
depending on the size of the particle (stokes law)(Garzanti et al. 2008). Due to the
constant water movement in an estuarine salt marsh, only the larger particles such as
sand can settle. Once sediment has accumulated above the mean high water at neap
tide (MHWN) halophytic vegetation, such as Spatina species can start to colonize the
newly laid land. Once vegetation begins to colonize, they increase the rate of
sedimentation in a number of ways. Root/rhizome networks trap sediment and
encourage particles to settle, above ground stalks and leaves both lower wave energy
and trap particles and as a secondary outcome the halophytic plants add organic
material which appears to deter filter feeders that may rework t and de-stabilize the
sediment, all of these processes increase sedimentation further (Shen et al. 2008).
Holland and Coles (1972, 1979 cited in Long, Mason, 1983) show that another factor
that increases the sedimentation is the mucus from certain micro floral species such as
Diatoms. This binds particles together increasing their mass and so accelerating
sedimentation Due to the increase in sedimentation the land rises and so is subject to
a decrease in saline inundation, this allows more halophytic plants to colonize
increasing biodiversity of the marsh. Eventually the high zone becomes colonized by
glycophytes, such as sedges and rushes. At that stage only freak weather could destabilise the marsh. Salt marshes are most on very flat ground, ranging 1-2m at most,
this adds to the sedimentation as wave action is reduced due to length of travel over
such a flat area. Due to the nature of salt marshes most are found around the coasts of
Western Europe including the United Kingdom, Sweden, Norway and France. Other
salt marsh sites include both East and West coast of North America, South America
around Chile and Argentina, New Zealand and a few around the Russian coast line.
The total distribution is unknown but an estimation has been taken from Long and
Mason (fig.1).
Figure 1 – Estimated worldwide distribution of salt marshes.
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Salt marshes can usually be split into three zones. The first is the pioneer or low zone,
this is typically between the mean high water at neap tides (MHWN) and the mean
high water at normal tide (MHW). The pioneer zone is mainly occupied by Spartina
anglica, with a few others including Aster tripolium, Salicornia europaea and
Puccinellia maritima. All of these species are halophytic meaning there can tolerate
complete submergence in saline water. This is vital and only these types of plants can
colonize the pioneer zone. This does mean the diversity of flora in the pioneer zone is
usually very low compared to the mid and high zones. Common floras that occupy
the mid marsh are Triglochin martima, Halimione portulacoides and also some
species from the pioneer zone such as Spartina anglica and Puccinellia maritime.
This is not surprising that vegetation does overlap from zone to zone and there is no
clear cut line between the zones. Some species such as Salicornia europaea can
actually inhabit all three zones on the same marsh. The high marsh is rarely
submerged with saline water and so the floras do not have to be halophytes. High
marsh is mainly occupied by shrubby plants such as Suaeda fruticosa and Agropyron
pungens. The plants, if allowed, can grow higher and faster due to the fact they are
not covered with water or sediment twice a day.
Salt marshes are home to many different animals, from invertebrates such as
nematodes, periwinkles littorina littorea, many different types of worms and also
clams Macoma balthica to vertebrates such as lapwing species Vanellinae, avocet
species Recurvirostra, pink-footed geese Anser brachyrhynchus, whooper swans
Cygnus cygnus and many more. Salt marshes provide different micro-habitats for
these different species and also different resources. The mud flats provide
invertebrate filter feeders a stable environment in which they can dig themselves
down into and due to the almost constant cover by water food is abundant. Further up
the salt marsh the edges of the creeks also provide a suitable habitat for filter feeders,
again for the soft, muddy substrate and a high amount of water flowing through the
creeks. Salt pans provide a habitat for both vertebrates and invertebrates depending
on location. A mid marsh salt pan can be used as a nursery for both invertebrates,
such as beetles, and vertebrates, such as fish. It is vital in this instance that the salt
pan is in the mid marsh zone as to avoid it completely drying out. High salt pans are
used by ground nesting birds such as redshank Tringa tetanus, Tringa erythropus and
oystercatcher species Haematopus. Salt marshes act as a perfect environment for
these types of birds because as well as providing breeding habitats, salt marshes also
provide these birds with a good feeding habitat in the form of the mud flats. Salt
marshes also provide a safe haven for many birds from the genus Anas during the
winter months. Again it provides a good feeding habitat and also due to the flatness
of the marsh predators are easily seen and can be avoided.
The main technique used to management a salt marsh is to moderately graze it. This
keeps important habitats available, such as around the edges salt pans for the breeding
birds. However grazing does have impacts on the other aspects of the salt marsh
ecosystem. For instance the primary production of the salt marsh is reduced due to
the loss in amount of flora, detris production is reduced and also invertebrate
populations (crabs) are reduced (Reimold et al. 1975). A study carried out in
Germany by Kiehl et al, in 1996 also states that when grazing was stopped, the salt
marsh developed a higher biodiversity over a two year period. Contradicting these
studies are studies carried out by Esselink et al. who found that moderate grazing of a
salt marsh (40-80 individuals per hˉ¹) increased the floral diversity. Also grazing is a
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natural management scheme (Dijkema, 1990) and so may seem the ideal way to
management a salt marsh. Other techniques include spraying and replanting.
Spraying is mainly used when a salt marsh is overrun with invasive species such as
Spatina species, by killing off the invasive species there is a chance for native species
to reclaim the salt marsh. On the opposite side replanting of invasive species have
been used as a form of management to speed up the marsh formation however once a
marsh has been developed invasive species do become a problem.
As salt marshes are an important habitat for many different plants and animals it is
important to know how the salt marsh ecosystem interacts and develops. Also more
information is needed on how grazing affects the secondary consumers such as the
soil invertebrates. As every single salt marsh differs slightly in composition or
formation or both it is important to look at each individual site and record data that
may be used with other data to create the best possible management plan.
Reference list
 Coles, S.M. (1979) “Benthic microalgal populations on intertidal sediments and their
role as precursors to salt marsh development.” Estuarine Interactions (ed. M. L. Wiley),
Academic press, New York, pg 93-113
Cited in: Long, S.P. and Mason C.F. (1983) Saltmarsh Ecology. Blackie – USA:
Chapman and Hall, New York
 Dijema, K.S. (1990) “Salt and brackish marshes around the Baltic Sea and adjacent parts
of the north sea: Their vegetation and management.” Biological Conservation, Vol.51,
pg 191-209
 Esselink, P., Fresco, L.F.M. and Dijkema, K.S. (2002) “Vegetation change in a manmade salt marsh affected by a reduction in both grazing and drainage.” Applied
Vegetation Science, Vol. 5, pg 17-32
 Frid, C and James, R. (1989) “The marine invertebrate fauna of a British coastal salt
marsh.” Holarctic Ecology, Vol. 12 (1) pg 9-15.
 Garzanti, E. Andò, S. And Vezzoli, G. (2008) “Settling equivalence of detrital
minerals and grain-size dependence of sediment composition.” Earth and Planetary
Science letters, Vol. 273 (1-2) pg138-151.
 Holland, A.F., Zingmark, R. G. And Dean J.M. (1974) Quantitative evidence concerning
the stabilization of sediments by marine benthic diatoms. Marine Biology. Vol. 27 (3), pg
191-196
Cited in: Long, S.P. and Mason C.F. (1983) Saltmarsh Ecology. Blackie – USA:
Chapman and Hall, New York
 Kiehl, K., Eischeid, I., Gettner, S. And Walter, J. (1996) “Impact of different sheep
grazing intensities on salt marsh vegetation in northern Germany.” Journal of Vegetation
Science, Vol. 7, pg 99-106.
 Long S.P. and Mason C.F. (1983) Saltmarsh Ecology. Blackie – USA: Chapman and
Hall, New York
 Reimold, R.J., Linthurst, R.A. and Wolf, P.L. (1975) “Effects of grazing on a salt marsh.”
Univeristy of Georigia
 SHEN, Yong-Ming. YANG, Jing-Song. WANG, Yan-Hong. FENG, Nian-Hua. ZHOU,
Qin and ZENG, Hua, (2008) “Impact of sediment supply on Spatina Salt Marshes.” Soil
Science society of China, Vol. 18 (5) pg 593-598.