banks and sides of creeks support a similar range of species to those of intertidal mudflats. Marsh surfaces are
habitat for a range of species including large numbers of
crabs and marine gastropod molluscs. Within the sediment, there is an abundance and diverse range of
meiofauna, whose survival in anaerobic mud may be
enabled by the creation of an oxygenated rhizosphere
(only a few millimeters thick), sheathing the roots of vascular plants as a result of oxygen loss from aerenchyma
tissues (Teal and Kenwisher, 1966; Teal and Wieser,
1966; Osenga and Coull, 1983). Interactions between
larger benthic species and flora may be important. The
sediment input into marshes may contain a high proportion of fecal and pseudofecal pellets (Frey and Basan,
1985), which, as well as influencing particle size, may
be an important source of bioavailable nitrogen and phosphorus for plant growth (Long and Mason, 1983). Crab
species may be present in large numbers and, through their
burrowing, may influence microtopography, sediment aeration, and chemistry and drainage (Bertness and Miller,
1984).
The interactions between the fiddler crab Uca pugnax
and the dominant vascular plant Spartina alterniflora
were described by Bertness (1985). The crabs are absent
from the mudflats in front of the marsh, as the sediment
is insufficiently consolidated to permit burrows to be
maintained. They are also absent from areas of the short
form of Spartina alterniflora where the dense root map
precludes burrow formation. However, they are abundant
in stands of tall Spartina alterniflora where root densities
are lower. Bertness (1985) proposed that there was
a facultative mutualism between the crabs and tall Spartina such that the plant root density was sufficient to provide firm sediment to maintain burrows but not so dense
as to prevent burrowing, while improved drainage and aeration created by burrows promotes plant productivity and
maintains the tall growth form of the grass. Not all
marshes support such abundant crab populations, but the
example demonstrates the ability of invertebrates to structure the environment, and even in the absence of crabs,
other taxa may play a similar, if quantitatively lesser, role.
The spatial scale over which individual invertebrates on
saltmarshes feed may be small. Saintilan and Mazumder
(2010) took advantage of the difference in photosynthetic
pathway in the two dominants of the saltmarsh in eastern
Australia, the C 4 grass Sporobolus virginicus and the C 3
succulent subshrub Sarcocornia quinqueflora, to investigate the feeding ecology of two grazing crab species and
a marine gastropod. The different photosynthetic pathways result in the plant tissues having different carbon isotope signatures which can be traced from the plants to
herbivores. The two plants occur in a mosaic of virtually
monospecific patches. The study showed that Sporobolus
was the species directly consumed and that individual
grazers had territories of at most a few square meters. In
the Sarcocornia-dominated patches, the major energy
source for the fauna was fine organic material, rather than
living plant tissues.
Terrestrial fauna
The terrestrially derived fauna of saltmarshes is large, but
many components of it have not been as well studied as
the marine component.
Invertebrates
For many members of the public, the terrestrial fauna which
are of most concern are mosquitoes and biting insects.
There are a number of diseases which can be transmitted
to humans by mosquitoes, and with growing human
populations close to saltmarshes and the possibility of
increased insect populations and greater incidence of pathogens as a consequence of global warming, there is likely to
be greater pressure for implementation of control measures
(Dale and Breitfuss, 2009). There has been a long history of
ditch construction in saltmarshes in the United States with
the object of reducing insect populations (Gedan et al.,
2009), but the consequences of the ditching for the whole
ecosystem were not initially given consideration. In subtropical saltmarshes in Australia, shallow ditches, referred
to as runnels, have been dug and have apparently been successful in reducing mosquito populations but with few other
effects on the marshes (Dale and Breitfuss, 2009).
Many of the insects in saltmarshes do not encounter the
impacts of tidal flooding, as they utilize tall vegetation
which remains emergent even at high tide. However, herbivorous species (grazers and sap suckers) must be
adapted to process plant tissues with high salt content
and low water potentials.
There are other species which are behavioral and
physical adaptations to either survive or avoid the impacts
of tidal submergence (Treherne and Foster, 1979;
Foster WA, 2000). Some of the most challenging conditions for insects on saltmarshes are experienced by species
of aphids which live on plant roots (Foster WA, 2000).
Beetles can utilize saltmarsh pools, although not necessarily at all stages of their life cycle (Foster GN, 2000).
There is also a diversity of ground-living beetles in upper
marsh grasslands (Luff and Eyre, 2000). The food plants
of the larvae of a number of larvae can survive occasional
submergence by seawater (Agassiz, 2000). Some
saltmarsh lepidopterans are rare and of conservation concern (Agassiz, 2000; Relf and New, 2009), but others are
very abundant, for example, in Australia the small Samphire Blue Theclinesthes sulpitius whose larvae feed on
samphires (succulent shrubby chenopods) (Orr and
Kitching, 2010).
Anthills occur in other saltmarshes in northern Europe
and, although higher than the surrounding marsh surface,
may be completely submerged during spring tides (Kay
and Woodell, 1976). Anthills provide a habitat for
a number of plant species which are otherwise restricted
in the distribution in marshes (Woodell, 1974). There are
a number of reports of ants occurring in saltmarshes elsewhere. The role of ants in processes such as seed distribution and pollination in saltmarshes has not been
investigated (Adam, 1990).
SALTMARSHES
525
habitat for a range of species including large numbers of
crabs and marine gastropod molluscs. Within the sediment, there is an abundance and diverse range of
meiofauna, whose survival in anaerobic mud may be
enabled by the creation of an oxygenated rhizosphere
(only a few millimeters thick), sheathing the roots of vascular plants as a result of oxygen loss from aerenchyma
tissues (Teal and Kenwisher, 1966; Teal and Wieser,
1966; Osenga and Coull, 1983). Interactions between
larger benthic species and flora may be important. The
sediment input into marshes may contain a high proportion of fecal and pseudofecal pellets (Frey and Basan,
1985), which, as well as influencing particle size, may
be an important source of bioavailable nitrogen and phosphorus for plant growth (Long and Mason, 1983). Crab
species may be present in large numbers and, through their
burrowing, may influence microtopography, sediment aeration, and chemistry and drainage (Bertness and Miller,
1984).
The interactions between the fiddler crab Uca pugnax
and the dominant vascular plant Spartina alterniflora
were described by Bertness (1985). The crabs are absent
from the mudflats in front of the marsh, as the sediment
is insufficiently consolidated to permit burrows to be
maintained. They are also absent from areas of the short
form of Spartina alterniflora where the dense root map
precludes burrow formation. However, they are abundant
in stands of tall Spartina alterniflora where root densities
are lower. Bertness (1985) proposed that there was
a facultative mutualism between the crabs and tall Spartina such that the plant root density was sufficient to provide firm sediment to maintain burrows but not so dense
as to prevent burrowing, while improved drainage and aeration created by burrows promotes plant productivity and
maintains the tall growth form of the grass. Not all
marshes support such abundant crab populations, but the
example demonstrates the ability of invertebrates to structure the environment, and even in the absence of crabs,
other taxa may play a similar, if quantitatively lesser, role.
The spatial scale over which individual invertebrates on
saltmarshes feed may be small. Saintilan and Mazumder
(2010) took advantage of the difference in photosynthetic
pathway in the two dominants of the saltmarsh in eastern
Australia, the C 4 grass Sporobolus virginicus and the C 3
succulent subshrub Sarcocornia quinqueflora, to investigate the feeding ecology of two grazing crab species and
a marine gastropod. The different photosynthetic pathways result in the plant tissues having different carbon isotope signatures which can be traced from the plants to
herbivores. The two plants occur in a mosaic of virtually
monospecific patches. The study showed that Sporobolus
was the species directly consumed and that individual
grazers had territories of at most a few square meters. In
the Sarcocornia-dominated patches, the major energy
source for the fauna was fine organic material, rather than
living plant tissues.
Terrestrial fauna
The terrestrially derived fauna of saltmarshes is large, but
many components of it have not been as well studied as
the marine component.
Invertebrates
For many members of the public, the terrestrial fauna which
are of most concern are mosquitoes and biting insects.
There are a number of diseases which can be transmitted
to humans by mosquitoes, and with growing human
populations close to saltmarshes and the possibility of
increased insect populations and greater incidence of pathogens as a consequence of global warming, there is likely to
be greater pressure for implementation of control measures
(Dale and Breitfuss, 2009). There has been a long history of
ditch construction in saltmarshes in the United States with
the object of reducing insect populations (Gedan et al.,
2009), but the consequences of the ditching for the whole
ecosystem were not initially given consideration. In subtropical saltmarshes in Australia, shallow ditches, referred
to as runnels, have been dug and have apparently been successful in reducing mosquito populations but with few other
effects on the marshes (Dale and Breitfuss, 2009).
Many of the insects in saltmarshes do not encounter the
impacts of tidal flooding, as they utilize tall vegetation
which remains emergent even at high tide. However, herbivorous species (grazers and sap suckers) must be
adapted to process plant tissues with high salt content
and low water potentials.
There are other species which are behavioral and
physical adaptations to either survive or avoid the impacts
of tidal submergence (Treherne and Foster, 1979;
Foster WA, 2000). Some of the most challenging conditions for insects on saltmarshes are experienced by species
of aphids which live on plant roots (Foster WA, 2000).
Beetles can utilize saltmarsh pools, although not necessarily at all stages of their life cycle (Foster GN, 2000).
There is also a diversity of ground-living beetles in upper
marsh grasslands (Luff and Eyre, 2000). The food plants
of the larvae of a number of larvae can survive occasional
submergence by seawater (Agassiz, 2000). Some
saltmarsh lepidopterans are rare and of conservation concern (Agassiz, 2000; Relf and New, 2009), but others are
very abundant, for example, in Australia the small Samphire Blue Theclinesthes sulpitius whose larvae feed on
samphires (succulent shrubby chenopods) (Orr and
Kitching, 2010).
Anthills occur in other saltmarshes in northern Europe
and, although higher than the surrounding marsh surface,
may be completely submerged during spring tides (Kay
and Woodell, 1976). Anthills provide a habitat for
a number of plant species which are otherwise restricted
in the distribution in marshes (Woodell, 1974). There are
a number of reports of ants occurring in saltmarshes elsewhere. The role of ants in processes such as seed distribution and pollination in saltmarshes has not been
investigated (Adam, 1990).
SALTMARSHES
525