substrates, they can be sandy, muddy sand, or muddy,
depending on sediment supply and local hydrodynamics.
The tidal parts of flood-tidal deltas tend to be underlain
by sand and have marine salinities. The tidal parts of
intra-estuarine riverine deltas can be brackish to freshwater,
varying between the seasons (and even marine water during
the dry season) and, depending on the nature of the delta,
can be underlain by sand, muddy sand, or mud (see Estuarine Deltaic Wetlands and Deltas). The crests and flanks of
middle-of-estuary shoals reside in water that varies from
marine at seaward parts of the estuary to brackish/freshwater in riverine parts of an estuary. Again, depending on sediment supply, the tidal flats can be underlain by sand,
muddy sand, or mud. The tidal parts of protected lagoons,
leeward of spits, tend to be in seaward parts of the estuary
(though they can occur widely) and, as such, waters usually
are marine salinity. Their substrates are sandy. However, if
there is abundant mud in suspension in the estuarine waters,
the low-energy protected leeward zone results in mud accumulation and the tidal flats are mud floored.
With all these tidal flats, except generally for the floodtidal delta, if there is both sand and mud available, the sand
and mud commonly are partitioned in different parts of the
environment because of hydrodynamic processes, and as
such, there can be depth-related mud tidal flats grading
to sand tidal flats.
Biota of tidal flats within estuaries
There are various factors that influence the structure and
composition of biota that inhabit a tidal flat. These include
biogeography and climate, inundation frequency, substrates, moisture, salinity, hydrochemistry, herbivory, and
predation (Verwey, 1954; Paine, 1974; Lubchenco, 1978;
Semeniuk, 1983; Reise, 1985; Reise et al., 1994; Reise,
2000; Cronin et al., 2010).
Biogeography and climate are major determinants of
the composition of biota of tidal flats in estuaries. The
range of biota includes mangroves and their associated
fauna in tropical and subtropical environments, rushes,
sedges, samphire, and other saltmarsh plants and their
associated fauna in tropical, subtropical, and temperate
environments, with different species in the various biogeographic regions (Tomlinson, 1986; Adams, 1990;
Pen et al., 2000; Cresswell and Semeniuk, 2011), and various crustacean-polychaete-mollusc assemblages in tropical, subtropical, and temperate environments, again, with
different species in the various biogeographic regions
(Wolff, 1983; White, 1989; Semeniuk et al., 2000;
Brearley, 2005). For instance, western hemisphere mangroves have different species than eastern hemisphere
mangroves (Tomlinson, 1986), and their composition,
structure, and physiognomy change with climate and latitude (Tomlinson, 1986; Cresswell and Semeniuk, 2011;
Semeniuk and Cresswell, 2013).
Estuarine tidal flat biota comprise plants, resident
fauna, invading and temporary fauna, and microbiota.
The plants of tidal flats can be categorized into four main
groups, viz., mangroves, saltmarsh, seagrass, and algae.
Mangroves occupy the interval between MSL and MHWS
but, in more humid and tropical climates, occupy the interval between MSL and EHWS. Saltmarsh occupies the
interval between MSL and EHWS, but depending on climate, freshwater seepage, and tidal range, saltmarsh can
more narrowly occupy the interval between MHWS and
EHWS. Seagrass and algae generally occur in lower parts
of the tidal flat and extend to subtidal zones.
Within a given biogeographic region, the composition
of tidal flat biota, in site-specific locations, is related to
tidal zones (inundation frequency), substrate type, substrate moisture, and salinity, commonly resulting in species zonation (Bridgewater, 1975; Wolff, 1983;
Semeniuk, 1985; White, 1989; Pennings and Callaway,
1992; Emery et al., 2001; Pennings et al., 2005; Silvestri
et al., 2005; and Semeniuk and Cresswell, this volume,
see Species Zonation). Mangrove and saltmarsh emergent
vegetation conspicuously exhibit species zonation
(Semeniuk et al., 1978; Tomlinson, 1986; Adam, 1990;
Cresswell and Semeniuk 2011).
There is a specialized and often unique fauna associated
with mangroves, saltmarsh, and seagrass. For instance,
in mangroves, there is a biogeography-specific and
climate-specific mangrove-associated infauna of crustacea and polychaetes; an epifauna of crustacea (crabs, barnacles), insects, and vertebrates; and a canopy fauna of
avifauna, reptiles, insects, and mammals (bats) (MacNae,
1968; Semeniuk et al., 1978; Hutchins and Saenger,
1987; Johnstone, 1990; Kathiresan and Bingham, 2001).
Similarly in saltmarshes, there is a biogeography-specific
and climate-specific saltmarsh-associated fauna, but also
a partitioning of fauna relative to position of tidal levels
and salinity. Adam (1990) uses several approaches to categorizing saltmarsh fauna: taxonomically, ecologically
(e.g., marine, freshwater, and terrestrial affinities), trophically, subhabitat occupied, and residence status. For
instance, for a given biogeographic and climate setting,
saltmarsh may have an infauna of crustacea, other arthropods, molluscs, polychaetes, and meiofauna; an epifauna
of crustacea, other arthropods, molluscs, insects, and vertebrates; and a foliage-associated fauna of avifauna, reptiles, mammals, gastropods, and insects (Adam, 1990).
The resident fauna of tidal flats outside of the zone of
mangroves and saltmarsh, as macrofauna, can be diverse
and complex in composition and its internal dynamics.
Examples of compositional variability and complex
dynamics are provided by Beukema (1976, 1981),
Virnstein (1977), Bell and Coull (1978), Quammen
(1982), Reise (1982, 1991, 2000), Ambrose (1984), Bottom (1984), Tsuchiya and Nishihira (1986), Dittmann
(1990, 1995, 1996, 2000, 2002), Nehls and Thiel (1993),
Jones et al. (1994), Thiel and Dernedde (1994), Vargas
(1988), Ragnarsson and Raffaelli (1999), Attrill
et al. (2001), Dittmann and Vargas (2001), Hagberg et al.
(2004), Reichert and Buchholz (2006), Büttger
et al. (2008), and Buschbaum et al. (2009). In the first
instance, such fauna can be categorized as epifauna
TIDAL FLAT
669
depending on sediment supply and local hydrodynamics.
The tidal parts of flood-tidal deltas tend to be underlain
by sand and have marine salinities. The tidal parts of
intra-estuarine riverine deltas can be brackish to freshwater,
varying between the seasons (and even marine water during
the dry season) and, depending on the nature of the delta,
can be underlain by sand, muddy sand, or mud (see Estuarine Deltaic Wetlands and Deltas). The crests and flanks of
middle-of-estuary shoals reside in water that varies from
marine at seaward parts of the estuary to brackish/freshwater in riverine parts of an estuary. Again, depending on sediment supply, the tidal flats can be underlain by sand,
muddy sand, or mud. The tidal parts of protected lagoons,
leeward of spits, tend to be in seaward parts of the estuary
(though they can occur widely) and, as such, waters usually
are marine salinity. Their substrates are sandy. However, if
there is abundant mud in suspension in the estuarine waters,
the low-energy protected leeward zone results in mud accumulation and the tidal flats are mud floored.
With all these tidal flats, except generally for the floodtidal delta, if there is both sand and mud available, the sand
and mud commonly are partitioned in different parts of the
environment because of hydrodynamic processes, and as
such, there can be depth-related mud tidal flats grading
to sand tidal flats.
Biota of tidal flats within estuaries
There are various factors that influence the structure and
composition of biota that inhabit a tidal flat. These include
biogeography and climate, inundation frequency, substrates, moisture, salinity, hydrochemistry, herbivory, and
predation (Verwey, 1954; Paine, 1974; Lubchenco, 1978;
Semeniuk, 1983; Reise, 1985; Reise et al., 1994; Reise,
2000; Cronin et al., 2010).
Biogeography and climate are major determinants of
the composition of biota of tidal flats in estuaries. The
range of biota includes mangroves and their associated
fauna in tropical and subtropical environments, rushes,
sedges, samphire, and other saltmarsh plants and their
associated fauna in tropical, subtropical, and temperate
environments, with different species in the various biogeographic regions (Tomlinson, 1986; Adams, 1990;
Pen et al., 2000; Cresswell and Semeniuk, 2011), and various crustacean-polychaete-mollusc assemblages in tropical, subtropical, and temperate environments, again, with
different species in the various biogeographic regions
(Wolff, 1983; White, 1989; Semeniuk et al., 2000;
Brearley, 2005). For instance, western hemisphere mangroves have different species than eastern hemisphere
mangroves (Tomlinson, 1986), and their composition,
structure, and physiognomy change with climate and latitude (Tomlinson, 1986; Cresswell and Semeniuk, 2011;
Semeniuk and Cresswell, 2013).
Estuarine tidal flat biota comprise plants, resident
fauna, invading and temporary fauna, and microbiota.
The plants of tidal flats can be categorized into four main
groups, viz., mangroves, saltmarsh, seagrass, and algae.
Mangroves occupy the interval between MSL and MHWS
but, in more humid and tropical climates, occupy the interval between MSL and EHWS. Saltmarsh occupies the
interval between MSL and EHWS, but depending on climate, freshwater seepage, and tidal range, saltmarsh can
more narrowly occupy the interval between MHWS and
EHWS. Seagrass and algae generally occur in lower parts
of the tidal flat and extend to subtidal zones.
Within a given biogeographic region, the composition
of tidal flat biota, in site-specific locations, is related to
tidal zones (inundation frequency), substrate type, substrate moisture, and salinity, commonly resulting in species zonation (Bridgewater, 1975; Wolff, 1983;
Semeniuk, 1985; White, 1989; Pennings and Callaway,
1992; Emery et al., 2001; Pennings et al., 2005; Silvestri
et al., 2005; and Semeniuk and Cresswell, this volume,
see Species Zonation). Mangrove and saltmarsh emergent
vegetation conspicuously exhibit species zonation
(Semeniuk et al., 1978; Tomlinson, 1986; Adam, 1990;
Cresswell and Semeniuk 2011).
There is a specialized and often unique fauna associated
with mangroves, saltmarsh, and seagrass. For instance,
in mangroves, there is a biogeography-specific and
climate-specific mangrove-associated infauna of crustacea and polychaetes; an epifauna of crustacea (crabs, barnacles), insects, and vertebrates; and a canopy fauna of
avifauna, reptiles, insects, and mammals (bats) (MacNae,
1968; Semeniuk et al., 1978; Hutchins and Saenger,
1987; Johnstone, 1990; Kathiresan and Bingham, 2001).
Similarly in saltmarshes, there is a biogeography-specific
and climate-specific saltmarsh-associated fauna, but also
a partitioning of fauna relative to position of tidal levels
and salinity. Adam (1990) uses several approaches to categorizing saltmarsh fauna: taxonomically, ecologically
(e.g., marine, freshwater, and terrestrial affinities), trophically, subhabitat occupied, and residence status. For
instance, for a given biogeographic and climate setting,
saltmarsh may have an infauna of crustacea, other arthropods, molluscs, polychaetes, and meiofauna; an epifauna
of crustacea, other arthropods, molluscs, insects, and vertebrates; and a foliage-associated fauna of avifauna, reptiles, mammals, gastropods, and insects (Adam, 1990).
The resident fauna of tidal flats outside of the zone of
mangroves and saltmarsh, as macrofauna, can be diverse
and complex in composition and its internal dynamics.
Examples of compositional variability and complex
dynamics are provided by Beukema (1976, 1981),
Virnstein (1977), Bell and Coull (1978), Quammen
(1982), Reise (1982, 1991, 2000), Ambrose (1984), Bottom (1984), Tsuchiya and Nishihira (1986), Dittmann
(1990, 1995, 1996, 2000, 2002), Nehls and Thiel (1993),
Jones et al. (1994), Thiel and Dernedde (1994), Vargas
(1988), Ragnarsson and Raffaelli (1999), Attrill
et al. (2001), Dittmann and Vargas (2001), Hagberg et al.
(2004), Reichert and Buchholz (2006), Büttger
et al. (2008), and Buschbaum et al. (2009). In the first
instance, such fauna can be categorized as epifauna
TIDAL FLAT
669