F

FIDDLER CRABS

Judith S. Weis
Department of Biological Sciences, Rutgers University,
Newark, NJ, USA

Definition
Fiddler crabs are small (up to
5 cm across) ocypodid
crabs found worldwide in temperate and tropical estuaries.
They live along bay beaches and brackish intertidal salt
marshes, mangroves, mud flats, lagoons and swamps.

Description
There are about 100 named species of fiddlers, all in the
genus Uca (Figure 1). They are semiterrestrial and live
in the intertidal zone where they dig burrows, which are
used for protection. The name “fiddler” is probably Fiddler Crabs, Figure 1 Courtesy Wikimedia.
derived from the enlarged claw of males, which they wave
to attract females during the mating season and to warn
intruders who come too close to their burrow. Unlike most
intertidal organisms, they are active in the air during low unfold when they molt. Newly molted crabs with soft
tide and inactive in their burrows during high tide. They shells are vulnerable and generally hide in their burrows
feed by processing sediments and eating detritus and until their new shell hardens.
microalgae in the sediments. Their behaviors have been
the subject of considerable study by biologists. Like all Cross-references
crabs, they molt in order to grow. If they have lost legs Blue Crabs
or claws, they can regenerate them and the new one will Soldier Crabs (Mictyridae)

M.J. Kennish (ed.), Encyclopedia of Estuaries, DOI 10.1007/978-94-017-8801-4,

© Springer Science+Business Media Dordrecht 2016
316 FIRTH

FIRTH Genesis
Both the terms firth and fjord are generally applied to
J. Javier Diez1 and Efren M. Veiga2 water bodies resulting from the flooding of glacial valleys.
1
Research Group on Marine, Coastal and Port In general, intrusion of the sea into glacial valleys stems
Environment and Other Sensitive Areas, Department of from two factors: Quaternary eustasy and tectonic sinking
Land and Urban Planning and Environment, Universidad of grabens along the fractured plate margin borders. The
Politécnica de Madrid, Madrid, Spain latter is greater on the western facade. Isostatic rebound
2
Civil Engineering: Land & Urban Management and due to the present interglacial period seems to have had
Environment, Universidad Politécnica de Madrid, Escuela a greater effect on firths. There is a conceptual symmetry
de Caminos, Canales y Puertos, Madrid, Spain with the term ria, which also refers to coastal flooding
but of river valleys. Both kinds of estuaries have equiva-
lent characteristics but different typologies (McManus
et al., 1993; Duck et al., 1995).
Synonyms The flooded valleys of both firths and fjords are created
Flooded glacial valley and carved out by glacial action, which produces their
depth and breadth; these features are also evident in
subaerial segments, even if the rivers that drain them are
Definition subsequently able to rejuvenate the relief. Some show
a certain hydrological hierarchy of glacial origin that
The term firth is a modification of the more general endows the coast with its typical irregular morphological
term fjord and is used to refer to the estuary formations and multi-lobed nature. In general, they receive river
along Scotland’s eastern coast. Firths are shallower, flows at their heads. Some that formed more recently are
longer, and more heavily silted than fjords. They also act steeper, but they are always limited in length.
as sediment traps for littoral drift and show evidence of Glacial flows have a huge abrasive and erosive effect on
significant infilling (Firth et al., 1997). There are strong the sides and floors of valleys. Once the glaciers retreat, both
analogies with the term bay used for other geographical their moraine deposits and the valley’s abraded surfaces are
areas of glacial origins, such as along the northeast coast highly prone to weathering and erosion, which means that
of North America. the supply of sediment to the outlet can be enormous.

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Firth, Figure 1 Firth of Forth Drainage Basin.

 FISH ASSEMBLAGES 317

These effects are much more pronounced in the longer different estuaries in South America). Research on fish
valleys of Scotland’s eastern coast, with their limited assemblages has sought to understand where, why, and
number of firths, than in the shorter and much deeper valleys when they occur and how these spatial and temporal distri-
of the narrower western coasts with their extraordinary butions relate to patterns in reproduction, recruitment, and
proliferation of fjords. foraging. The seasonal variation in proportion and abun-
The current hierarchy of the water network is dictated dance of freshwater and marine fish species in fish assem-
by glacial erosion since the magnitude of the current blages in estuarine habitats is a result of both the seasonal
interfluvial structures and the proximity of the heads of variation of environmental gradients (e.g., salinity, tem-
glaciers to the coast have limited the transformative action perature, turbidity) and a suite of biological variables,
of fluvial geodynamic activity (Figure 1). Within these including reproduction and recruitment (Blaber, 2000;
common traits, firths are further characterized by longer Barletta et al., 2005, 2008; Dantas et al., 2010, 2012). In
and more structured fluvial networks, greater abundance tropical estuaries, seasonal fluctuations of salinity are
of fluvial sediment, and much smaller average gradient a major factor determining larval abundance (Barletta-
in the valleys as a whole. These factors result in shallower Bergan et al., 2002a; Barletta-Bergan et al., 2002b), juve-
depths all along the basin, even in the coastal platform, nile and adult density, and biomass of fishes (Blaber,
where the oldest glacial deposits have been incorporated 2000; Barletta et al., 2005, 2008), mainly due to the effects
in littoral processes to accentuate the current silting of large fluctuations of freshwater inputs during the year.
processes in the firths. Factors such as geology, geomorphology, and more imme-
diate environmental factors as salinity and temperature
Bibliography affect fish distributions, species richness, and fisheries
Duck, R. W., McManus, J., and Diez, J. J., 1995. Comparative study catch (Mahon et al., 1998; Mathieson et al., 2000; Araújo
of two largely unfilled estuaries: the Eden estuary (Scotland) and and Azevedo, 2001; Roy et al., 2001; Thiel et al., 2003). In
the Ria de Foz (Spain). Netherlands Journal of Aquatic Ecology, addition, broadscale comparisons of tropical estuaries
29(3–4), 203–210. across zoogeographic realms indicate possible significant
Firth, C. R., Collins, P. E. F., and Smith, D. E., 1997. Coastal differences in the fish assemblage use of various estuarine
Processes and Management of Scottish Estuaries: IV - The Firth habitats, as well as differences in the patterns of species
of Forth. Scottish Natural Heritage Review, No 87.
McManus, J., Diez, J. J., Duck, R. W., Escobar, V., Anderson, J. M., composition (Blaber, 2000). For example, the relative pro-
Esteban, V., and Paz, R., 1993. Comparison of Scottish Firths portions of freshwater and marine species using estuaries
and Spanish Rias. Bulletin of the International Association of may differ (Blaber, 2000; Barletta et al., 2003, 2005,
Engineering Geology, 47, 127–132. 2008). An understanding of the roles and relative impor-
tance of different habitats within estuaries to fish is neces-
Cross-references sary for both effective management and conservation
(Elliott and Hemingway, 2002).
Coastal Bays
Fjord
Ria
Estuarine fish guilds
The fish assemblages inhabiting estuaries worldwide have
common features (Blaber, 2000; Elliott and Hemingway,
2002; Barletta and Blaber, 2007). Estuaries are nursery
FISH ASSEMBLAGES grounds, migration routes, and refuge areas for many fish
species, including resident fish assemblages (Blaber,
Mario Barletta and David Valença Dantas 2000; McLusky and Elliott, 2004; Barletta et al., 2010;
Laboratório de Ecologia e Gerenciamento de Dantas et al., 2012). The study of estuarine fish assem-
Ecossistemas Costeiros e Estuarinos, Departamento de blage structure and functioning is important for under-
Oceanografia, Universidade Federal de Pernambuco, standing the ecological characteristics of estuaries, as
Recife, PE, Brazil well as for classifying species for use in management of
anthropogenic impacts in estuaries (McLusky and Elliott,
Definition 2004; Elliott et al., 2007).
Fish Assemblage. A fish assemblage is simply a suite of Recently, studies have concentrated on the functional
species whose individuals are collected in the same area analysis of finfish assemblage structure in which the spe-
at the same time. cies present are assigned to groupings or guilds, each of
which denotes certain attributes (Elliott et al., 2007).
Introduction A guild is a group of species that exploit the same class
There are no strict limits on the spatial or temporal scale of of environmental resources in a similar way (Root,
a fish assemblage (Miller, 2002). It may be an assemblage 1967). Hence, guilds have been used to provide informa-
in a single season and region (e.g., a fish assemblage of an tion on functioning, hierarchical structure, and connectiv-
estuarine main channel during the late rainy season) or at ity and to simplify complex ecosystems (McLusky and
specific times and locations (e.g., fish assemblages among Elliott, 2004; Barletta and Blaber, 2007). While there are
318 FISH ASSEMBLAGES

many options for functional guilds, such as one for habitat Some species occur in specific habitats such as tidal
preference and another relating to position inhabited marshes (Mathieson et al., 2000; Akin et al., 2003),
within the water column (Elliott and Dewailly, 1995), seagrass beds (Dorenbosch et al., 2006), mangrove forests
Elliott et al. (2007) proposed three groups of functional (Barletta et al., 2000; Hindell and Jenkins, 2004), man-
guilds. The first is the Estuarine Use Functional Group, grove tidal creeks (Barletta et al., 2003; Krumme et al.,
which defines the overall ecological use of an estuary by 2005), and the main channel of the estuary (Barletta et al.,
a given species and is composed by eight categories: 2005, 2008). Others species use these habitats and areas
marine stragglers, marine migrants, estuarine species, of the estuary (upper, middle, and lower) at various life
anadromous, catadromous, amphidromous, freshwater stages and when environmental conditions allow (Thayer
stragglers, and freshwater migrants. The second is the et al., 1987; Barletta et al., 2005, 2008; Dantas et al., 2010).
Feeding Mode Functional Group, which defines the pri- In tropical estuaries, seasonal fluctuations of salinity
mary method of feeding used by a given species and is are a major factor determining larval abundance (Morais
composed by seven categories: planktivorous, and Morais, 1994; Barletta-Bergan et al., 2002a;
detritivorous, herbivorous, piscivorous, benthophagous, Barletta-Bergan et al., 2002b), and juvenile and adult bio-
hyperbenthophagous, and opportunistic. The third is the mass and density (Barletta et al., 2000, 2005, 2008; Dantas
Reproductive Mode Functional Group that indicates et al., 2010), mainly due to the effects of large fluctuations
how, and in some cases where, an estuarine species repro- of freshwater inputs during the year (Figures 1, 2, and 3).
duces, being composed of three main categories: vivipa- In an estuary located at the eastern Amazon (northern Bra-
rous, ovoviviparous, and oviparous. To explore possible zil), the estuarine-dependent species, which use the main
fundamental similarities and differences in estuarine channel, are ordered along a large-scale spatial gradient,
fishes in tropical, subtropical, and temperate estuaries when relatively stable hydrological conditions create a
from different zoogeographic regions, it is necessary to well-defined salinity gradient in the estuary during the late
compare their fish assemblages, not only taxonomically, dry season (Barletta et al., 2005). Moreover, during the
but also in terms of their ecological structure and resource late rainy season, freshwater runoff increases, salinity
use in different habitats of the estuary during different time drops, and the estuary then becomes more suitable for
scales. Based on this information, Barletta and Blaber Neotropical freshwater species (Figure 1). Salinity and
(2007) made a comparison between Caeté (Northern distance from the estuary mouth are the most important
South America) and Embley (Northern Australia) estuar- environmental variables structuring the fish assemblages
ies. They found important taxonomic differences between in this estuary (Barletta et al., 2005). As an example, stud-
the two estuaries. The Neotropical fish species of the ies conducted in other Neotropical estuaries in South
upper Caeté Estuary have no equivalents in the Embley America (Barletta et al., 2005, 2008; Dantas et al., 2012)
Estuary, and the diverse chondrichthyan fauna of the suggest that, for the marine catfish species Cathorops
Embley have no equivalents in the Caeté Estuary. On the spixii (Agassiz) (Figure 4) and C. agassizii (Eigenmann
other hand, the more ubiquitous families Engraulidae, and Eigenmann) (Figure 5), the salinity gradient influ-
Sciaenidae, Ariidae, Carangidae, Haemulidae, and ences the seasonal distribution not only of adults but also
Clupeidae, which were characteristic of the main channel all of their different ontogenetic stages along the estuarine
and mangrove tidal creeks of the Caeté Estuary, showed ecocline (upper, middle, and lower estuary). Moreover,
70 % similarity with the main channel of the Embley the seasonal fluctuations in salinity (late dry and late
Estuary. rainy) define the nursery role for C. spixii and
C. agassizii in the middle estuary (Barletta et al., 2005,
2008; Dantas et al., 2012) (Figures 4 and 5). The impor-
Environmental influence on fish assemblages tance of this habitat as nursery for C. spixii and
Estuaries are important ecosystems for marine fisheries, C. agassizii juveniles is determined by the seasonal envi-
and diverse authors have emphasized that fish landings ronmental gradient conditions along the estuarine ecocline
around the world consist of species that spend part of their (Dantas et al., 2012).
lives in estuarine waters (Blaber, 2000; Barletta et al., In the temperate La Plata River Estuary (Uruguay–
2003, 2005, 2008; Barletta-Bergan et al., 2002a; Argentina), salinity has a stronger influence on the spatial
Barletta-Bergan et al., 2002b). Estuarine and shallow structure of the fish assemblages than temperature, and the
marine waters in tropical (Blaber, 2000; Barletta et al., pattern of seasonal fish species distribution in the La Plata
2005), subtropical (Jaureguizar et al., 2004; Barletta Estuary reflects the seasonal discharge of this river
et al., 2008), and temperate (Thiel et al., 1995) regions (Jaureguizar et al., 2004). On a large spatial scale, the
are important areas for feeding, mating, spawning, and strong physical environment gradient along La Plata Estu-
nursery habitat for many fish species. The species compo- ary creates a gradual change in the fish composition from
sition of estuarine fish assemblages is dictated by fresh and shallow to marine and deeper waters that define
a combination of biotic and abiotic variables, particularly the riverine, estuarine, and coastal shelf fish assemblages
competition for space and food, and tolerance to diel and (Anganuzzi, 1983; Jaureguizar et al., 2004; Lorenzo
seasonal changes in salinity, turbidity, and temperature Pereiro, 2007). The riverine fish assemblages occupy the
(Blaber, 2000; Barletta et al., 2003, 2005, 2008). inner part of the La Plata Estuary, characterized by
 FISH ASSEMBLAGES 319

Fish Assemblages, Figure 1 Movement of fish assemblages induced by the seasonal fluctuations of salinity in the Caeté Estuary
(eastern Amazon).

freshwater and shallow depths. The estuarine fish assem- juveniles of fresh-brackish-water adventitious visitors
blage occupies the mixohaline waters of the La Plata Estu- are found in the intertidal mangrove creeks during the
ary, and its ichthyofauna is dominated by euryhaline flood tide (Barletta et al., 2003). Another strategy has been
species of marine origin. The species composition shows observed for fish species such as Myrophis punctatus,
a gradient to the mouth, where estuarine resident species Gobionellus smaragdus, and Kryptolebias spp. They
predominate and, to a lesser degree, occasional freshwater remain in the intertidal mangrove forest when it is not
species, marine species, either stragglers or migrants, and flooded (Figure 6). Barletta et al. (2000) identified three
estuarine migrants (Barletta et al., 2010). different strategies of use of this habitat during low tide
In the intertidal mangrove creek habitats of an estuarine by these species. The first group (G1) includes fish species
ecosystem in the northern Brazilian coast, fishes utilize the that remain in crabholes until the next flood tide; the sec-
intertidal areas in different ways (Barletta et al., 2000, ond group (G2) consists of fish species that remain buried
2003; Barletta-Bergan et al., 2002b). Some fishes remain or attached to Rhizophora mangle roots; and the third
in the intertidal area at low tide, while others avoid this group (G3) is comprised of species which remain in the
area during the low tide, using the habitat only when it is water streams (Figure 6). Independent of this fish assem-
submerged. Two distinct fish assemblage patterns can be blage variability, it is clear that seasonal variations in envi-
observed in the intertidal mangrove creeks in this region. ronmental gradients are the most important factor
Estuarine residents, marine seasonal migrants, and marine influencing the fish assemblage composition and structure
juvenile migrants represent the first fish assemblage, and in estuarine habitats (Barletta et al., 2010). In addition to
marine juvenile migrants and marine adventitious visitors the abiotic parameters (e.g., salinity, water temperature,
form the second fish assemblage. This pattern is strongly dissolved oxygen, and turbidity) that influence fish assem-
influenced by the seasonal fluctuation of abiotic parame- blage characteristics, it is the combination of particular
ters, mainly salinity. During the late rainy season, the features of each estuarine system (e.g., climate, geology,
freshwater runoff increases, salinity decreases, and geomorphology, latitude) that make them ever so valuable.
320 FISH ASSEMBLAGES

Fish Assemblages, Figure 2 Movement of fish assemblages induced by the seasonal fluctuations of salinity in Goiana Estuary
(tropical semiarid of northeast Brazil).

Estuarine habitat roles channel, mudflats, and intertidal mangrove forest, at both
Estuaries in the tropical (Blaber, 2000; Barletta et al., high and low tides. The mangrove forest along the north-
2005; Dantas et al., 2012), subtropical (Jaureguizar et al., ern coast of South America is not flooded during low tide
2004), and temperate regions (Thiel et al., 1995) act as (tidal range, 5–7 m). Nevertheless, many fish species
breeding, mating, nursery, and feeding grounds for many remain in the mangrove forest during this time. Tidal
fish species. Estuarine habitat use depends on behavior strategies are described for fish species that lin-
a combination of the seasonal variation of abiotic factors ger in mangrove forests during low tide, using this habitat
(e.g., salinity, turbidity, temperature) and biotic factors for protection from predation and for food resources
(e.g., competition for food and space) (Blaber, 2000). (Barletta et al., 2000).
For example, mangrove intertidal creeks (Barletta et al., Estuaries support resident fish assemblages that are
2000, 2003), main channels (Barletta et al., 2005, 2008; functionally important as an intermediate trophic level
Dantas et al., 2012), and seagrass beds (Dorenbosch for many consumers. The production and seasonal occur-
et al., 2006) provide different habitat for each fish species rence of fishes vary with salinity, hydrology, and nutrient
in a fish assemblage, depending on the ontogenetic phase status in the estuary, and many species are adapted to these
of the species and the environmental conditions of specific salinity fluctuations and are resident within estuarine hab-
sites during different times scales. In mangrove estuaries, itats. Other species remain in estuaries only during certain
the controlling marine influence is the tide, and periods of their life cycles and when the conditions are
up-estuary is the seasonal fluctuation of freshwater river favorable (Blaber, 2000; Barletta et al., 2010).
flow (Barletta et al., 2010). Fish assemblages can be Estuaries are frequently referred to as nursery areas for
described by their biomass, density, and number of spe- fishes (Beck et al., 2001). Ichthyoplankton can originate
cies, and these variables change in the estuary main either from within the estuary or from adjacent marine and
 FISH ASSEMBLAGES 321

Fish Assemblages, Figure 3 Movement of fish assemblages induced by the seasonal fluctuations of salinity in Paranaguá Estuary
(tropical to subtropical transition zone, south Brazil).

freshwater environments (Barletta-Bergan et al., 2002a). systems enables the transference of organisms, organic
Juvenile fish use the different estuarine habitats as feeding matter, and nutrients to nearshore coastal waters
grounds and refuge (Krumme et al., 2005; Dantas et al., (Blaber, 2000; Barletta-Bergan et al., 2002a; Barletta-
2013). The structure and seasonal dynamics of the fish lar- Bergan et al., 2002b; Barletta et al., 2003, 2005). Studies
vae and juvenile fish assemblages clearly reflect the impor- of estuarine fish assemblages show that they undergo large
tance of the main channel (Barletta-Bergan et al., 2002a; seasonal fluctuations in biomass and density, and
Barletta et al., 2005) and mangrove forest (Barletta-Bergan estuarine-dependent species are ordered along a large-
et al., 2002b; Barletta et al., 2003) of the estuary as fish nurs- scale spatial gradient, when relatively stable hydrological
ery habitats (Barletta and Blaber, 2007). conditions create a well-defined salinity gradient in the
estuary (McLusky and Elliott, 2004; Barletta et al., 2005,
2008; Vilar et al., 2013). Understanding connectivity
Estuarine connectivity among estuarine habitats and populations of freshwater,
Estuaries are transitional zones between marine and estuarine, and marine fish is vital for studying population
freshwater systems, and the connection of these dynamics, managing fish stocks, designing marine
322 FISH ASSEMBLAGES

Fish Assemblages, Figure 4 Idealized model of the movement patterns of different ontogenetic phases of Cathorops spixii in the
main channel (upper (U), middle (M), and lower (L)) of Neotropical estuaries along the western Atlantic coasts for each season (early
dry, late dry, early rainy, and late rainy).

protected areas, and determining the patterns of habitat use estuarine fish assemblages. Throughout the world, estuar-
by fish assemblages (Blaber et al., 2000; Gillanders, 2002; ies and adjacent coastal waters support numerous ecolog-
Barletta et al., 2010). ical and socioeconomic activities, but estuaries in
Many fish species use different habitats within estuar- particular are among the most modified and threatened
ies, tidal marshes (Mathieson et al., 2000; Akin et al., of aquatic environments (Blaber et al., 2000). Human
2003), seagrass beds (Dorenbosch et al., 2006), mangrove activities can drastically change the hydrological patterns
forests (Barletta et al., 2000; Hindell and Jenkins, 2004), of estuarine systems and can directly affect the connection
mangrove tidal creeks (Barletta et al., 2003; Krumme between estuarine habitats, potentially impacting many
et al., 2005), and the main channel of the estuary ecological functions of these habitats for fish assemblages
(Blaber, 2000; Barletta et al., 2005, 2008), only during (Barletta et al., 2010).
a specific ontogenetic stage. These habitats are considered
areas of feeding, mating, spawning, and nursery use for
many fish species during a specific life stage, and the con- Fisheries and estuarine habitats conservation
nectivity between these areas is very important to these Coastal systems, including coastal lagoons (Mar Chiquita,
species can complete their life cycles (McLusky and Central Argentina; Rocha, Uruguay), estuaries (Caeté,
Elliott, 2004). The connectivity between habitats of an northern Brazil; Paranaguá, south Brazil; Embley, North-
estuarine ecosystem is dictated not only by geomorpho- ern Australia; La Plata, Uruguay–Argentina), and bays
logical factors but also by the environmental fluctuation (Samborombón Bay at La Plata Estuary, Anegada Bay in
of abiotic parameters, such as salinity, temperature, turbid- southern of Buenos Aires Province, Argentina), provide
ity, and dissolved oxygen, which also influence the con- critical habitats for many commercial and recreational fish
nection between the habitats and movement patterns of species (feeding, mating, spawning, and nursery grounds)
 FISH ASSEMBLAGES 323

Fish Assemblages, Figure 5 Idealized model of the movement patterns of different ontogenetic phases of Cathorops agassizii in the
main channel (upper (U), middle (M), and lower (L)) of Neotropical estuaries along the western Atlantic coasts for each season (early
dry, late dry, early rainy, and late rainy).

and are characterized by wide variability of environmental Monitoring and knowledge of the effects of small-scale
conditions (Barletta et al., 2010). These systems also sup- and large-scale patterns in abiotic and biotic conditions, as
port human activities, such as fishing and environment well as fisheries activities, are necessary for a more com-
use. Fisheries are an integral part of human societies in plete understanding of fish and fisheries dynamics and,
the coastal zone and are directly related and dependent therefore, their effective management (Blaber et al.,
on estuarine productivity (Blaber, 2000; Barletta et al., 2000; Barletta et al., 2010). Moreover, understanding the
2010). They can be divided into four main sectors: (1) sub- variations of fish assemblages in estuarine ecosystems at
sistence (fishers consume their catch or give it away but do different spatial and temporal scales can provide valuable
not sell it); (2) artisanal (fishers sell part of their catch but insights for fisheries management and nature conserva-
also retain part for their own consumption); (3) commer- tion. The high spatial heterogeneity and the different fish
cial (all catch is sold); and (4) recreational (fishing is car- fauna assemblages need a habitat-based classification of
ried out as a sport or leisure pastime and not primarily estuarine landscape features employing readily obtainable
for producing food or income) (Blaber et al., 2000). Tradi- quantitative data for geophysical and oceanographic char-
tional fisheries have a long history and form part of the acteristics (Barletta et al., 2010). This categorization could
human culture in estuarine communities. They may also provide data that correlate fish assemblages, or key spe-
have a long-standing and complex interrelationship with cies, to specific estuaries or coastal sectors. This would
the environment and in the tropics and subtropics are offer the necessary aid to regional fisheries management
increasingly regarded as part of the overall ecology systems and provide a framework for research, monitor-
(Blaber et al., 2000). Implementing conservation strate- ing, and conservation of the estuarine ecosystem.
gies is essential in order to protect natural resources, Barletta et al. (2010) indicated that seasonal and annual
including fishes and their habitats. variability in the southwest Atlantic coastal system
324 FISH ASSEMBLAGES

Fish Assemblages, Figure 6 Idealized cross sections through a typical intertidal mangrove forest in the coastal plain, indicating fish
group distribution strategies during low tide. A1 and A2 represent the main tidal channel; B1 and B2 represent the very small creeks in
the intertidal mangrove forest. Cross section 1: intertidal mangrove forest during high tide; cross section 2: intertidal mangrove forest
during low tide; cross section 3: intertidal mangrove creek during low tide (B2 situation – vertical scale exaggerated). Cross section
3 represents the three different ecological strategies developed by fish to reduce interspecific competition in the intertidal mangrove
forest during low tide. The first strategy (Group 1 – G1) includes fish species that stay in crabholes until the next flood tide. Group two
(G2) represents the fish species that stay buried or attached to Rhizophora mangle roots. The third group (G3) represents the species
that stay in the water stream (Modified from Barletta et al., 2000).

influences various fish biological behaviors (migration, (salinity 0.08  0.02) and shallow depths (7.88 
spawning, mating, and bottom fidelity), as well as the sea- 1.53 m). Its ichthyofauna forms part of the Paranoplatense
sonal and interannual coastal habitat use, that determine fish community and shows a high affinity for the Paraná
fish catchability and susceptibility. On a large spatial and Uruguay River basins (Cousseau, 1985). It is mainly
scale, the strong physical environmental gradient along dominated by freshwater and anadromous species. The
the southwest Atlantic coastal system creates a gradual anadromous species, during spring and early summer,
change in the fish composition from fresh and shallow extends up the La Plata River and its basin to spawn.
to marine and deeper waters that define the riverine, The estuarine fish assemblage occupies the mixohaline
estuarine, and coastal shelf fish assemblages (Anganuzzi, waters of the La Plata Estuary, and its ichthyofauna is
1983; Jaureguizar et al., 2004; Lorenzo Pereiro, 2007). dominated by euryhaline species of marine origin. The
The riverine fish assemblages occupy the inner part species composition shows a gradient to the mouth where
of the La Plata River characterized by freshwater estuarine resident species predominate and, to a lesser
 FISH ASSEMBLAGES 325

degree, occasional freshwater species, marine species, The information on estuarine fish community structure
either stragglers or migrants, and estuarine migrants. The and functioning is important to understanding the ecolog-
fish assemblages can be described in relation to biomass, ical services of estuaries and is also important to classify
density, and number of species and the seasonal fluctua- and categorize estuarine fauna as an aid to understanding
tions of environmental variables (salinity, water tempera- and managing the effects of human activities on estuaries
ture, and dissolved oxygen). (McLusky and Elliott, 2004; Elliott et al., 2007). Tradi-
In tropical estuaries from the western Atlantic Ocean, tional fisheries have a long history and comprise part of
these variables change in the estuarine main channel and the human culture of estuarine communities. They may
intertidal mangrove forest at both high and low tides also have a long-standing and complex interrelationship
(Barletta et al., 2010). The estuary then supports with the environment and in the tropics and subtropics
a resident fish community that is functionally important have become part of the overall ecology (Blaber et al.,
as an intermediate trophic level for many consumers. 2000). Implementing conservation strategies is essential
The production and seasonal occurrence of fishes appear to protect natural resources, including fishes and fish
to vary with salinity, hydrology, and nutrient status in the habitats.
estuary, all of which are controlled by both freshwater
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Others stay in the estuary only during a certain period of spatial variations in fish and macrocrustacean assemblage struc-
their life and when conditions are appropriate. Estuaries ture in Mad Island Marsh estuary, Texas. Estuarine, Coastal and
are frequently referred to as nursery areas for both fishes Shelf Science, 5, 269–282.
and invertebrates (Beck et al., 2001). Anganuzzi, A., 1983. Estructure de la comunidad de peces del área
Intertidal mangrove areas are also considered essential costera bonaerense. MSc thesis, Argentina, Universidad
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Araújo, F. G., and Azevedo, M. C. C., 2001. Assemblages of
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Johnson, 1995; Barletta et al., 2003). The northern Brazil- of fishes. Estuarine, Coastal and Shelf Science, 52, 729–738.
ian coast (tropical and humid) houses the largest continu- Barletta, M., and Blaber, S. J. M., 2007. Comparison of fish assem-
ous mangrove estuarine belt in the world and constitutes blage and guilds in tropical habitats of the Embley (Indo-West
56.6 % of the mangroves in South America (7,592 km2) Pacific) and Caeté (Western Atlantic) estuaries. Bulletin of
(Souza Filho, 2005). South of the mouth of the Amazon Marine Science, 80(3), 647–680.
Barletta, M., Saint-Paul, U., Barletta-Bergan, A., Ekau, W., and
River, more than 30 estuaries fringe
650 km of Schories, D., 2000. Spatial and temporal distribution of
mangrove-dominated coastline, and many fish species Myrophis punctatus (Ophichthidae) and associated fish fauna
use intertidal creeks for tidal migrations between man- in a Northern Brazilian intertidal mangrove forest.
grove habitats and adjacent subtidal areas, the main chan- Hydrobiologia, 426, 65–74.
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connection between mangrove and adjacent estuarine 2003. Seasonal changes in density, biomass and diversity of
estuarine fishes in tidal mangrove creeks of the lower Caeté Estu-
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ing fishes and fish habitats, decision makers need to plan a tropical estuary. Journal of Fish Biology, 66, 1–28.
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A fish assemblage is simply a suite of species whose indi- Agostinho, A. A., Almeida-Val, V., Val, A., Torres, R. A.,
viduals are collected in the same area and at the same time. Jimenes, L. F., Giarrizzo, T., Fabré, N. N., Batista, V.,
There are no strict limits on the spatial or temporal scale of Lasso, C., Taphorn, D. C., Costa, M. F., Chaves, P. T.,
Vieira, J. P., and Corrêa, M. F. M., 2010. Fish and aquatic habitat
a fish assemblage (Miller, 2002). It is correct to speak of conservation in South America: a continental overview with
the assemblage in a single season and region or at specific emphasis on Neotropical systems. Journal of Fish Biology, 76,
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sought to understand why they occur in the places and at Barletta-Bergan, A., Barletta, M., and Saint-Paul, U., 2002a. Struc-
the times they do and how these spatial and temporal dis- ture and seasonal dynamics of larval and juvenile fish in the
tributions relate to patterns in breeding, nursery area, mangrove-fringed estuary of the Rio Caeté in North Brazil. Estu-
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relative importance to fish of different habitats within munity structure and temporal variability of Ichthyoplankton in
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and conservation (Elliott and Hemingway, 2002). 33–51.
326 FJORD

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Elliott, M., and Hemingway, K. L., 2002. Fishes in Estuaries. changes and ecological guild classification of the ichthyofaunas
Oxford: Blackwell Science. of large European estuaries – a comparison between the Tagus
Elliott, M., Whitfield, A. K., Potter, I. C., Blaber, S. J. M., Cyrus, (Portugal) and the Elbe (Germany). Journal of Applied Ichthyol-
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Gillanders, B. M., 2002. Connectivity between juvenile and adult fish assemblages in Brazilian estuaries. Marine Ecology Pro-
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Environmental factors structuring fish communities of Rio de Ichthyofauna
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nurseries for commercial species. Marine Ecology Progress Department of Geological Sciences, University of
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Lorenzo Pereiro, M. I., 2007. Estructura de la comunidad de peces Delaware, Newark, DE, USA
demersales en el Rı́o de la Plata y su frente oceánico. PhD thesis,
Argentina, Universidad Nacional de Mar del Plata.
Mahon, R., Brown, S. K., Zwanenburg, K. C. T., Atkinson, D. B.,
Buja, K. R., Clafin, L., Howell, G. D., Monaco, M. E., O’Boyle, Synonyms
R. N., and Sinclair, M., 1998. Assemblage and biogeography of Fiord
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Definition Benn, D. I., and Evans, D. J., 2010. Glaciers and Glaciation.
Hodder Education.
A fjord is a sea inlet that has inundated a trough formed by Bennett, M., and Glasser, N., 2009. Glacial Geology: Ice Sheets and
glacial erosion. Like the glaciers that formed the troughs, Landforms, 2nd edn. Hoboken: Wiley.
fjords range in length from a few to hundreds of kilome- Bronge, C., 1996. The excavation of the Storglasiären trough during
ters and are common in the modern and past glaciated por- the Quaternary. Geografiska Annaler, 78, 163–169.
tions of the Arctic, Antarctic, South America, northwest Farmer, D. M., and Freeland, H. J., 1983. The physical oceanogra-
Europe and Scandinavia, northern North America, and phy of fjords. Progress in Oceanography, 12, 147–219.
Farmer, D. M., and Huppert, H. E., 1979. The oceanography of
New Zealand. fjords. Nature, 280, 273–274.
Harbor, J. M., 1995. Development of glacial-valley cross sections
Origin and morphology under conditions of spatially variable resistance to erosion. Geo-
morphology, 14, 99–107.
Although troughs erode rapidly under glacial conditions, Harbor, J. M., and Wheeler, D. A., 1992. On the mathematical
many fjords are erosionally complex, palimpsest fea- description of glaciated valley cross sections. Earth Surface Pro-
tures that formed over the course of multiple glacial epi- cesses and Landforms, 17, 477–485.
sodes (Nesje and Whillans, 1994; Bennett and Glasser, Holtedahl, H., 1967. Notes on the formation of fjords and fjord–
2009). Because glacial erosion is dependent on ice thick- valleys. Geografiska Annaler, 49A, 188–203.
ness, erosion rates are highest on the valley floors, James, L. A., 1996. Polynomial and power functions for glacial
resulting in the common steep-sided U-shaped valley valley cross-section morphology. Earth Surface Processes and
Landforms, 21, 413–432.
forms. These cross-sectional profiles can be described Nesje, A., and Whillans, I. M., 1994. Erosion of Sognefjord,
mathematically by empirical power-law functions or Norway. Geomorphology, 9, 33–45.
second-order polynomials (Harbor and Wheeler, 1992; Yingkui, L., Gengnian, L., and Zhijiu, C., 2001. Longitudinal vari-
Harbor, 1995; James, 1996; Amerson et al., 2008). How- ations in cross-section morphology along a glacial valley: a case-
ever, profile asymmetry is common due to both the phys- study from the Tien Shan, China. Journal of Glaciology, 47,
ical characteristics of the underlying bedrock and 243–250.
subsequent erosional and depositional processes after
inundation (Augustinus, 1992; Nesje and Whillans, Cross-references
1994; Augustinus, 1995). The longitudinal profile of Coastal Bays
a fjord depicts the erosional and depositional characteris- Firth
tics of the formative glacier system with the deepest ero-
sion and subsequent inundated water depths, coinciding
with the area of maximum ice discharge (Yingkui et al.,
2001). Reduced bedrock erosion and/or moraine deposi- FLOCCULATION
tion near the terminus of the past glacier extent results in
a shallow sill near the mouth of the fjord. The sills and
overdeepened troughs allow fjords to accumulate Dorothy Joyce D. Marquez
a unique sedimentary archive of past marine and glacial Nannoworks Laboratory, National Institute of Geological
conditions (Benn and Evans, 2010). This same bathy- Sciences, University of the Philippines Diliman,
metric juxtaposition also causes extreme currents and Quezon City, Philippines
inhibits exchange of bottom waters between the fjord
and adjacent sea (Farmer and Huppert, 1979; Farmer Synonyms
and Freeland, 1983). The seasonal and annual mixing of Aggregation; Coagulation
terrestrial and oceanic waters, coupled with various sea
ice and glacier inputs at high latitudes, yields complex Definition
temperature, salinity, and density gradients both vertically Flocculation is a process of contact and adhesion whereby
and between the head and the mouth of the fjord (Farmer dispersed particles are held together by weak physical
and Huppert, 1979; Farmer and Freeland, 1983). interactions.

Bibliography Introduction
Amerson, B., Montgomery, D. R., and Meyer, G., 2008. Relative Flocculation has been widely used in water and wastewa-
size of fluvial and glaciated valleys in central Idaho. Geomor- ter treatment applications mainly for clarification and
phology, 93, 537–547. reduction of suspended solids, respectively. Recently, it
Augustinus, P. C., 1992. The influence of rock mass strength on gla- has also been used as a cost-effective method for
cial valley cross-profile morphometry: a case study from the harvesting microalgae for biomass for production of
Southern Alps, New Zealand. Earth Surface Processes and food, feed, fuel, or chemicals (Vandamme et al., 2013).
Landforms, 17, 39–51.
Augustinus, P. C., 1995. Glacial valley cross-profile development: Aside from these applications, in situ flocculation has
the influence of in situ rock stress and rock mass strength, with also been studied for years to understand sediment trans-
examples from the Southern Alps, New Zealand. Geomorphol- port in different aquatic environments. In this regard,
ogy, 14, 87–97. Eisma (1986) defined flocculation as a natural process
328 FLOCCULATION

by which suspended particles are brought together into collide and flocculate (Day et al., 1989). pH is a measure
larger units called flocs. of acidity or alkalinity which can either increase (e.g., salt
Flocculation or floc formation depends on the physical influences) or decrease (organic matter load) due to the
collision between suspended matter and their adhesion ionic composition of the system. It has been reported in
(Alldredge and Jackson, 1995; Hansen et al., 1995). some experiments that changes in surface charge due to
Droppo (2001) described flocs as heterogeneous, compos- pH variations affect floc stability (Wilén et al., 2000).
ite structures composed of an active biological compo- Another factor called bridging occurs when the loops
nent, a nonviable biological component, inorganic and tails of a polymer adsorbed to one particle
particles, and water held within or flowing through pores. become attached to one or more other particles
Because of the diverse origins of flocs, their characteristics (Droppo et al., 2005). Divalent cations such as Ca2+
are highly variable (Alldredge and Silver, 1988). These and Mg2+ can in some cases act as chemical bridging
can also be viewed as individual microecosystems with agents between negative charges of the polymers and neg-
autonomous and interactive physical, chemical, and bio- ative charges on the particle surface, enhancing the attrac-
logical functions or behaviors operating within the floc tion and sticking properties of electronegatively charged
matrix (Droppo et al., 1997). Microflocs are dense, particles and polymers (Simon et al., 2002).
quasi-spherical, resistant to turbulent mixing, and small Flocculation can be biologically mediated by either par-
with sizes ranging from 100 to 160 mm (Verney et al., ticulate or dissolved organic matter. Organic matter is
2009). Under favorable conditions, microflocs collide adsorbed at the surface of sediment particles, giving it a
with each other, flocculate, and form macroflocs (Simon negative charge. Sticky organic compounds (transparent
et al., 2002; Verney et al., 2009). Macroflocs are formed exopolymer particles) produced in the water column by
from microflocs up to several millimeters and can rapidly phytoplankton, bacteria, and macrophytes also promote
disintegrate back into microflocs. aggregation and sedimentation of particles (Passow,
2002).
Factors affecting flocculation Summary and conclusion
Flocs are formed within the water column or on the sur- Diverse studies on flocculation have been conducted
face of a bed by a variety of complicated physical, phys- through the years. These studies lead to better understand-
icochemical, and biological means (Droppo, 2001; ing of the factors affecting flocculation at given environ-
Simon et al., 2002). The physical mechanisms that bring mental conditions. Moreover, applications of
particles together in the ocean are Brownian motion, fluid flocculation studies can be valuable to society such as in
shear, and differential settlement (Mccave, 1984; water and wastewater treatment, management of harmful
Alldredge and Silver, 1988; Simon et al., 2002). algal blooms, and siltation control.
Brownian motion dominates interactions of fine particles
(less than 8 mm). Differential settlement should dominate
coagulation between similarly sized particles between Bibliography
1 and 100 mm in surface waters. It is important for sinking Alldredge, A. L., and Jackson, G. A., 1995. Aggregation in marine
of particles in the water column and in slack water in tid- systems – preface. Deep-Sea Research Part II-Topical Studies in
ally affected shallow seas and estuaries (Simon et al., Oceanography, 42(1), 1–7.
2002). McCave’s (1984) calculations indicate that colli- Alldredge, A. L., and Silver, M. W., 1988. Characteristics, dynam-
sions of small particles with larger ones resulting in ics, and significance of marine snow. Progress in Oceanography,
20(1), 41–82.
floc formation should be controlled primarily by shear. Chen, M. S., Wartel, S., Van Eck, B., and Van Maldegem, D., 2005.
Shear collides similarly sized particles and leads to scav- Suspended matter in the Scheldt estuary. Hydrobiologia,
enging of small particles by large ones more effectively 540(1–3), 79–104.
than differential settling. In agreement, a study Day, J. W., Hall, C. A., Kemp, W. M., and Alejandro, Y., 1989. Estu-
conducted by Chen et al., (2005) in Scheldt reported that arine Ecology. New York: Wiley-Interscience.
floc formation in the estuary was rather controlled by cur- Droppo, I. G., 2001. Rethinking what constitutes suspended sedi-
ment. Hydrological Processes, 15(9), 1551–1564.
rent velocity and the suspended matter concentration Droppo, I. G., Leppard, G. G., Flannigan, D. T., and Liss, S. N.,
than salinity. 1997. The freshwater floc: a functional relationship of water
Flocs are composed of biological components, inor- and organic and inorganic floc constituents affecting suspended
ganic particles, and water that carry with them negative sediment properties. Water Air and Soil Pollution, 99(1–4),
surface charge, hence, are affected by varying pH and 43–53.
salinity. Salinity is used by oceanographers as a measure Droppo, I. G., Leppard, G. G., Liss, S. N., and Milligan, T. G. (eds.),
2005. Flocculation in Natural and Engineered Environmental
of the total salt content of seawater. Clay particles which Systems. Boca Raton, Florida: CRC Press.
are usually negatively charged have a high cationic Eisma, D., 1986. Flocculation and deflocculation of suspended mat-
adsorption capacity. Interparticle forces then become ter in estuaries. Netherlands Journal of Sea Research, 20(2/3),
attractive at increased salinities, causing particles to 183–199.
 FLUSHING TIME 329

Hansen, J. L. S., Timm, U., and Kiørboe, T., 1995. Adaptive of freshwater in the estuary (Vfw) to the total rate of fresh-
significance of phytoplankton stickiness with emphasis on the water input (Qfw):
diatom Skeletonema costatum. Marine Biology, 123(4),
667–676. V fw
IUPAC, 1997. Compendium of Chemical Terminology, 2nd edn. tfw ¼
(the “Gold Book”). Compiled by McNaught, A. D., and Qfw
Wilkinson, A. Oxford: Blackwell Scientific Publications.
XML on-line corrected version: http://goldbook.iupac. While Vfw increases as Qfw does, it does so more slowly,
org (2006) created by M. Nic, J. Jirat, B. Kosata; updates com- so that flushing time decreases as freshwater flow
piled by A. Jenkins. ISBN 0-9678550-9-8. doi:10.1351/ increases (Pilson, 1985).
goldbook.
McCave, I. N., 1984. Size spectra and aggregation of suspended
particles in the deep ocean. Deep-Sea Research Part
a-Oceanographic Research Papers, 31(4), 329–352. Measurement
Passow, U., 2002. Transparent exopolymer particles (TEP) in The freshwater content (Vfw), and therefore tfw, may be
aquatic environments. Progress in Oceanography, 55(3–4), determined by mass balance calculations from the estu-
287–333. ary volume, the volume-weighted average salinity in
Simon, M., Grossart, H. P., Schweitzer, B., and Ploug, H., 2002. the estuary, and the salinity outside the seaward boundary
Microbial ecology of organic aggregates in aquatic ecosystems.
Aquatic Microbial Ecology, 28(2), 175–211. (Pilson, 1985). This is termed the freshwater replacement
Vandamme, D., Foubert, I., and Muylaert, K., 2013. Flocculation as method.
a low-cost method for harvesting microalgae for bulk biomass Flushing time may also be estimated by introducing
production. Trends in Biotechnology, 31(4), 233–239. a conservative tracer, such as dye, at a constant concentra-
Verney, R., Lafite, R., and Brun-Cottan, J. C., 2009. Flocculation tion into the freshwater inflow until the mass or average
potential of estuarine particles: the importance of environ- concentration of tracer in the estuary at a given tide
mental factors and of the spatial and seasonal variability of
suspended particulate matter. Estuaries and Coasts, 32(4),
stage attains equilibrium. After termination of tracer input,
678–693. the spatially averaged concentrations will decrease
Wilén, B.-M., Lund Nielsen, J., Keiding, K., and Nielsen, P. H., approximately exponentially as tracer is flushed from the
2000. Influence of microbial activity on the stability of activated estuary. The time required for the concentration to attain
sludge flocs. Colloids and Surfaces B: Biointerfaces, 18(2), e1 times the initial concentration, often referred to as
145–156. the e-folding time, is an estimator of the flushing time.

Cross-references Applications
pH Flushing time is a useful indicator of the behavior of
Sediment Transport
Tides materials introduced into an estuary with freshwater.
For instance, the fraction of nitrogen entering the estuary
from the watershed that flows through the estuary to the
sea, and the fraction lost within the estuary to processes
such as denitrification and permanent burial in sedi-
FLUSHING TIME ments, may be estimated using the flushing time
(Dettmann, 2001). The turnover or mean transit time of
Edward H. Dettmann conservative materials introduced with freshwater are
U.S. Environmental Protection Agency, Office equal to the flushing time of freshwater, while those of
of Research and Development/NHEERL Atlantic nonconservative materials that are consumed by pro-
Ecology Division, Narragansett, RI, USA cesses in the estuary have shorter turnover times. See
Dettmann (2008) for details in an application to freshwa-
Synonyms ter lakes.
e-Folding time; Freshwater replacement time; Freshwater Flushing time, as described above, applies to an estuary
residence time, Freshwater transit time; Freshwater turn- as a whole. The concept of a flushing time may also be
over time applied to a portion of an estuary, e.g., in a box model
(Hagy et al., 2000).
Other concepts related to flushing time are sometimes
Definition used in describing material movement through an
The flushing time of an estuary is generally defined as the estuary. Examples are estuarine residence time, that is,
turnover time of freshwater in the estuary (tfw), that is, the residence time in the estuary of a conservative
the time required to replace the freshwater contained in substance introduced uniformly in concentration through-
the estuary with freshwater inflow. The flushing time of out the estuary, and pulse residence time (the residence
an estuary is calculated as the ratio of the volume time of a conservative substance introduced as an
330 FOOD CHAIN

instantaneous pulse in a limited portion of the estuary) organization, resource availability, habitat stability, and
(Hagy et al., 2000). ecosystem size.
Different hypotheses predict food-chain length to
Bibliography be determined by productivity alone (productivity
Dettmann, E. H., 2001. Effect of water residence time on annual
hypothesis) (Diehl and Feissel, 2001), ecosystem size
export and denitrification of nitrogen in estuaries: a model anal- alone (ecosystem-size hypothesis) (Kitching, 2000], or a
ysis. Estuaries, 24, 481–490. combination of productivity and ecosystem size
Dettmann, E. H., 2008. Turnover time. In Jørgensen, S. E., and Fath, (productive-space hypothesis). The productivity and
B. D. (eds.), Ecological Indicators, Encyclopedia of Ecology. productive-space hypotheses propose that food-chain
Oxford: Elsevier, Vol. 5, pp. 3639–3644. length should increase with increasing resource availabil-
Hagy, J. D., Sanford, L. P., and Boynton, W. R., 2000. Estimation of ity; however, the productivity hypothesis does not include
net physical transport and hydraulic residence times for a coastal
plain estuary using box models. Estuaries, 23, 328–340. ecosystem size as a determinant of resource availability.
Pilson, M. E. Q., 1985. On the residence time of water in Narragan- The ecosystem-size hypothesis is based on the relation-
sett Bay. Estuaries, 8, 2–14. ship between ecosystem size and species diversity,
habitat availability, and habitat heterogeneity (Menge
and Sutherland, 1987).

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Diehl, S., and Feissel, M., 2001. Intraguild prey suffer from enrich-
Mónica Lara Uc, Rafael Riosmena-Rodríguez and ment of their resources: a microcosm experiment with ciliates.
Juan M. Rodríguez-Baron Ecology, 82, 2977–2983.
Programa de Investigación en Botãnica Marina, Kidd, K. A., et al., 1998. Effects of trophic position and lipid on
Departamento Académico de Biología Marina, organochlorine concentrations in fishes from subarctic lakes in
Universidad Autónoma de Baja California Sur, La Paz, Yukon Territory. Canadian Journal of Fisheries and Aquatic
Sciences, 55, 869–881.
Baja California Sur, Mexico Kitching, R. L., 2000. Food Webs and Container Habitats.
Cambridge: Cambridge University Press.
Synonyms Kitching, R. L., 2001. Food webs in phytotelmata: ‘bottom-up’ and
Trophic levels ‘top-down’ explanations for community structure. Annual
Review of Entomology, 46, 729–760.
Menge, B. A., and Sutherland, J. P., 1987. Community regulation:
Definition variation in disturbance, competition, and predation in relation
Food chain refers to the transfer of energy (linear sequence to environmental stress and recruitment. American Naturalist,
of links) from the base to the top of a food web. The num- 130, 730–757.
ber of trophic levels is often called the food-chain length. Moore, J. C., et al., 1993. Influence of productivity on the stability
of real and model ecosystems. Science, 261, 906–908.
Oksanen, L., and Oksanen, T., 2000. The logic and realism of the
Description hypothesis of exploitation ecosystems. American Naturalist,
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subarctic grazing webs in relation to primary production.
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1999; Oksanen and Oksanen, 2000); key ecosystem gration of Pattern and Process. London: Chapman & Hall,
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and atmospheric carbon (C) exchange (Pace et al., Pace, M. L., et al., 1999. Trophic cascades revealed in diverse eco-
1999); and the bioconcentration of contaminants in top systems. Trends of Ecology and Evolution, 14, 483–488.
predators, including many fish that humans consume Persson, L., 1999. Trophic cascades: abiding heterogeneity and
(Spencer and Warren, 1996; Kidd et al., 1998). Conven- the trophic level concept at the end of the road. Oikos, 85,
385–397.
tional wisdom holds that food-chain length is deter- Persson, L., et al., 1996. Productivity and consumer regulation –
mined either by the dynamic stability of food webs or concepts, patterns, and mechanisms. In Polis, G. A., and
by the availability of limiting food resources (often Winemiller, K. O. (eds.), Food Webs: Integration of Pattern
represented as energy). Some recent studies strongly and Process. London: Chapman & Hall, pp. 396–434.
challenge this conventional wisdom (Post et al., 2000), Pimm, S. L., 1982. Food Webs. London: Chapman & Hall.
whereas others reframe the question to accommodate Post, D. M., et al., 2000. Ecosystem size determines food-chain
length in lakes. Nature, 405, 1047–1049.
functional definitions of food-chain length (Oksanen Power, M. E., et al., 1996. Disturbance and food chain length in
et al., 1996). These and other studies suggest a complex rivers. In Polis, G. A., and Winemiller, K. O. (eds.), Food Webs:
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processes, such as the history of community pp. 286–297.
 FOOD WEB/TROPHIC DYNAMICS 331

Schoener, T. W., 1989. Food webs from the small to the large. Definition
Ecology, 70, 1559–1589.
Spencer, M., and Warren, P. H., 1996. The effects of habitat size and The network of interconnected food chains in an ecosys-
productivity on food web structure in small aquatic microcosms. tem, wherein organisms that eat each other form
Oikos, 75, 419–430. a sequence of interconnecting links from the initial pro-
Sterner, R. W., et al., 1997. The enigma of food chain length: ducers of organic matter through the various consumers.
absence of theoretical evidence for dynamic constraints.
Ecology, 78, 2258–2262.
Description
Believed to have been initially depicted by the Muslim
Cross-references scientist al-Jāḥiẓ (nickname, meaning “google-eyed” for
Detritus Food Webs Abu ‘Uthman’ Amr ibn Bahr) in the ninth century
Food Web/Trophic Dynamics (Egerton, 2002), food chains communicate the procession
of energy from the origin of fixation by primary producers
through herbivores and successive levels of higher level
consumers. Early formulations by Sir Alistair Hardy
FOOD WEB/TROPHIC DYNAMICS (1924, Figure 1) and Charles Elton’s Animal Ecology
(1927 and subsequent volumes) amalgamated food chains
Charles A. Simenstad into food webs (Figure 2). Transfer of energy through the
School of Aquatic and Fishery Sciences, University of respective trophic levels from one part of an ecosystem to
Washington, Seattle, WA, USA another was further articulated by Lindeman (1942) in his
transformative ideas of trophic-dynamic relationships to
the process of ecological succession. Winemiller and Polis
Synonyms (1996) stated that, “With few exceptions (fossilization,
Food cycle; Food nexe; Trophic network mineralization), the ultimate fate of organisms is some

Food Web/Trophic Dynamics, Figure 1 The classical food web, based on Hardy (1924). Page 294 from Chamberlin, W.S., and T.D.
Dickey. 2008. Exploring the Ocean World. McGraw-Hill Higher Education; ISBN: 0073016543.
332 FOOD WEB/TROPHIC DYNAMICS

consumers
Sixth-level
Top predator

consumers consumers
Third-level Fourth-level Fifth-level
Carnivore

consumers
(tertiary)

Planltivore
Second-level
(secondary)
consumers

Zooplankton
consumers
First-level
(primary)
producers
Primary

Phytoplankton

Marine food chain Marine food web

Food Web/Trophic Dynamics, Figure 2 Food chains versus food webs. (a) The linear transfer of energy and matter can be depicted
in a simple food chain. In the open ocean, these chains become quite long. (b) Food webs included all of the possible pathways of
exchange of energy and materials among organisms. Food webs are especially useful where organisms feed at multiple trophic levels
during different stages of their life. Page 290 from Chamberlin, W.S., and T.D. Dickey. 2008. Exploring the Ocean World. McGraw-Hill
Higher Education; ISBN: 0073016543.

form of consumption by and assimilation into tissues of connectedness to (2) energy flow and (3) the strength of
other organisms, be they metazoans or microbes. The functional interactions among the connected species
structure, dynamics, and spatial relationships of the tro- (Figure 3). With revelations of contaminant biomagni-
phic networks derived from this basic observation are cer- fication (Suedel et al., 1994), the role of the “microbial
tain to affect the distribution and abundance of organisms loop” (Azam et al., 1983), emergence of intrinsic patterns
in very fundamental ways.” The dynamics of food webs (Pimm, 1982), and the use of elaborate ecological models
are now viewed from multiple perspectives. Paine (e.g., Ecopath, Ecosim and Ecospace; Pauly et al., 2000)
(1980) effectively articulated three synthetic characteriza- and geochemical biomarkers such as natural stable iso-
tions of both the structure and dynamics of food web links topes and fatty acids (e.g., Hanson et al., 2010) have
affecting community structure, from (1) static, topological greatly expanded our delineation and application of
 FOOD WEB/TROPHIC DYNAMICS 333

Food Web/Trophic Dynamics, Figure 3 Four conceptual and empirical approaches to characterizing trophic relationships (Modified
from Paine’s (1080; Food webs: linkage, interaction strength and community infrastructure; Journal of Animal Ecology 49: 666–685;
British Ecological Society, Blackwell Publishing LTD, John Wiley & Sons; ISBN: 0021-87980) example from rocky intertidal community.
The connectedness web (a) is based on observation, the energy flow web (b) on measurements and literature values, the stable
biomarker and bioenergetic web on measurements and modeling, and the functional web (d) on controlled experimental
manipulation. The size of arrows in (b) through (d) indicate strength of energy transfer or community interaction; the shaded arrows
in (c) implies less source transfer or net bioenergetic benefit to consumer.

complex food webs. An understanding of the cascading Lindeman, R. L., 1942. The trophic-dynamic aspect of ecology.
effects of functional interactions among species across Ecology, 23, 399–418.
communities and ecosystems remains at the core of tro- Paine, R. T., 1980. Food webs: linkage, interaction strength and
community infrastructure. Journal of Animal Ecology, 49,
phic dynamics. 667–685.
Pauly, D., Christensen, V., and Walters, C., 2000. Ecopath, ecosim,
and ecospace as tools for evaluating ecosystem impact of fisher-
Bibliography ies. ICES Journal of Marine Science, 57, 697–706.
Pimm, S. L., 1982. Food Webs. London: Chapman and Hall.
Azam, F., Fenchel, T., Field, J. G., Gray, J. S., Meyer-Reil, L. A.,
Suedel, B. C., Boraczek, J. A., Peddicord, R. K., Clifford, P. A., and
and Thingstad, F., 1983. The ecological role of water-column
Dillon, T. M., 1994. Trophic transfer and biomagnification
microbes in the sea. Marine Ecology Progress Series, 10,
potential of contaminants in aquatic ecosystems. Reviews of
257–263.
Environmental Contamination and Toxicology, 136, 21–89.
Egerton, F. N., 2002. A history of the ecological sciences, part 6:
Winemiller, K. O., and Polis, G. A., 1996. Food webs: what can they
Arabic language science: origins and zooplogical writings. Bul-
tell us about the world? In Polis, G. A., and Winemiller, K. O.
letin of the Ecological Society of America, 83, 142–146.
(eds.), Food Webs: Integration of Patterns & Dynamics. New
Elton, C. S., 1927. Animal Ecology. New York: Macmillan.
York: Chapman & Hall, pp. 1–22.
Hanson, C. E., Hyndes, G. A., and Wang, S. F., 2010. Differentia-
tion of benthic marine primary producers using stable isotopes
and fatty acids: implications to food web studies. Aquatic Bot-
any, 93, 114–122. Cross-references
Hardy, A. C., 1924. The herring in relation to its animal environ- Detritus Food Webs
ment. Fishery Investigations Series II, 7, 1–45. Food Chain
334 FOREDUNE

FOREDUNE Cross-references
Back Dune
Beach Processes
Michael J. Kennish Coastal Barriers
Department of Marine and Coastal Sciences, Coastal Landforms
School of Environmental and Biological Sciences, Estuarine Beaches
Rutgers University, New Brunswick, NJ, USA

Synonyms
Beach ridge; Frontal dune; Primary dune; Transverse dune FORESTED WETLAND HABITAT

Jamie A. Duberstein1 and Ken W. Krauss2

Definition 1
Baruch Institute of Coastal Ecology and Forest Science,
A foredune is a shore-parallel dune ridge that forms on Clemson University, Georgetown, SC, USA
2
the back beach of an ocean, estuary, or bay by aeolian U.S. Geological Survey, National Wetlands Research
depositional processes (Hesp, 1988; Nordstrom, 1992; Center, Lafayette, LA, USA
Nordstrom and Jackson, 1994).
Synonyms
Description Mangrove forest; Swamp; Tidal freshwater forested
As part of a dune system, the foredune is located closest to wetland; Tidal saltwater forested wetland; Tidal várzea
the water body. Vegetation in the backshore plays an
important role in the accumulation and retention of sand Definition
to form the dune ridge. Plant succession occurs as the dune A forested wetland (swamp) is a forest where soils are sat-
develops. Foredunes often exhibit different morphologies urated or flooded for at least a portion of the growing sea-
(from convex ridges to flat terraces) and variable ecologi- son, and vegetation, dominated by trees, is adapted to
cal characteristics (Hesp, 1988). As the foredune enlarges, tolerate flooded conditions.
it traps more windblown sand and hence can expand rather A tidal freshwater forested wetland is a forested wet-
rapidly. land that experiences frequent but short-term surface
There are two main types of foredunes: incipient and flooding via tidal action, with average salinity of soil
established types (Hesp, 2002). Incipient foredunes are porewater less than 0.5 g/l. It is known locally as tidal
new or embryo dunes formed by sand deposition within várzea in the Amazon delta, Brazil.
discrete vegetation (e.g., Ammophila, Ipomoea, and Spi- A tidal saltwater forested wetland (mangrove forest) is
nifex) from the immediate backshore to back-barrier flats a forested wetland that experiences frequent but short-
(Carter et al., 1992). They develop into established term surface flooding via tidal action, with average salin-
foredunes (up to 30–35 m in height) with the growth of ity often exceeding 3 g/l and reaching levels that can
larger and more mature vegetation, notably woody exceed seawater. Mangrove ecosystems are composed of
plants. A number of factors control the developmental facultative halophytes that generally experience better
process, including the plant species present, degree of growth at moderate salinity concentrations.
vegetation cover, sand supply, accretion rate, wave and
wind forces, storm erosion, extent of human impact and Introduction
use, as well as other elements (Hesp, 2002). Forested wetlands represent a globally diverse array of
types but are restricted to only a few true estuarine types.
The primary component differentiating various types of
Bibliography forested wetland habitat is the vegetation, which is domi-
Carter, R. W. G., Bauer, B. O., Sherman, D. J., Davidson-Arnott, nated by trees and shrubs. The specific composition of tree
R. G. D., Gares, P. A., Nordstrom, K. F., and Orford, J. D., and shrub species (i.e., the community) is mostly
1992. Dune development in the aftermath of stream outlet clo- influenced by the local hydrology (Mitsch and Gosselink,
sure: examples from Ireland and California. In Carter,
R. W. G., Curtis, T. G. F., and Sheehy-Skeffington, M. J. 2000). Because estuarine systems are dominated by the
(eds.), Coastal Dunes: Geomorphology, Ecology and Manage- oceanic processes of sea level and tidal action on one side
ment for Conservation. Rotterdam: Balkema, pp. 57–69. and the continental processes of river discharge and sedi-
Hesp, P., 2002. Foredunes and blowouts: initiation, geomorphology, ment load on the other, hydrologic characteristics within
and dynamics. Geomorphology, 48, 245–268. the estuary vary considerably. Depth, duration, and fre-
Hesp, P. A., 1988. Foredune morphology, dynamics, and structures. quency of flooding; salinity of the soil porewater; and
Journal of Sedimentary Geology, Special Issue on Aeolian
Sediments, 55, 17–41. regional climate all determine the type of forested wetland
Nordstrom, K. F., 1992. Estuarine Beaches. London: Elsevier. habitat. Estuarine forested wetlands are divided into tidal
Nordstrom, K. F., and Jackson, N. L., 1994. Aeolian processes and freshwater forested wetlands and mangroves, also known
dune fields in estuaries. Physical Geography, 15, 358–371. as tidal saltwater forested wetlands.
 FORESTED WETLAND HABITAT 335

Tidal freshwater forested wetlands storm surge or drought, are incorporated into the
These wetlands occur within floodplains of coastal rivers porewater, and when that happens, habitat change to
at the upper boundary of tidal influence, often just oligohaline (low salinity, 0.5–5.0 g/l) marsh can occur
upstream of tidal marshes. Larger areal distributions of (Brinson et al., 1985).
tidal freshwater forested wetlands are generally found in Tidal freshwater forested wetlands within the south-
areas that have large tidal ranges coupled with high river eastern United States vary more in the relative dominance
discharge (Conner et al., 2007). However, they are not and density of tree species, rather than presence or
restricted to these conditions and can occur in smaller absence, with some exceptions. The most common can-
watersheds. Conditions are favorable for this habitat type opy trees include swamp tupelo (Nyssa biflora), water
worldwide, but most published accounts describe condi- tupelo (Nyssa aquatica), baldcypress (Taxodium
tions in the southeastern United States. Studies outside distichum), pumpkin ash (Fraxinus profunda), Carolina
the United States have been limited to Central America ash (Fraxinus caroliniana), green ash (Fraxinus
and the Amazonian coast in South America, with limited pennsylvanica), and red maple (Acer rubrum). Shrub
descriptions (see Verhoeven et al., 2001; Struyf et al., species tend to vary more between river systems, but
2009) of willow (Salix spp.)-dominated tidal freshwater the most ubiquitous are hazel alder (Alnus serrulata)
forested wetlands in Europe. and wax myrtle (Morella cerifera). Atlantic white cedar
A frequently described characteristic of these wetlands (Chamaecyparis thyoides) is rare in tidal freshwater areas
includes the prominent development of microtopographic but can be found in isolated stands in the southeastern
patterning under purely freshwater conditions. This pattern- United States. It occurs in fairly monotypic stands along
ing is often called hummock and hollow topography the coast of North Carolina or as part of a diverse mix of
(Rheinhardt and Hershner, 1992) and is common in these hardwood species restricted to parts of Mississippi near
wetlands when occurring in non-stressed states (Conner the Alabama border (Conner et al., 2007). Swamps in
et al., 2007). Hollows are low-lying, flat areas that are Louisiana contain primarily baldcypress and water
mostly bare mud or contain herbaceous vegetation similar tupelo, but in other parts of the southeastern United
to tidal freshwater marshes. Hummocks are raised States, the diversity of trees and specific assemblages fol-
microsites that average 15–20 cm high and are roughly low a salinity and flood frequency gradient (Conner et al.,
1–10 m2 in size. Hollows are flooded during most flood 2007) with the most frequently flooded and most saline
tides and remain saturated within 20 cm of the surface stands consisting primarily of baldcypress in the canopy
nearly 100 % of the time. In contrast, hummocks with wax myrtle in the understory (Krauss et al., 2009).
typically flood less frequently, to lesser depths, and Central American and Amazonian tidal freshwater for-
remain saturated for shorter times, which increases ested wetlands are often managed for agriculture (e.g.,
oxygen penetration and affects nutrient availability cacao, assai), though some unmanaged landscapes still
(Courtwright and Findlay, 2011). As a result, hummocks exist. There are two general types of unmanaged tidal
often contain a greater diversity of tree and shrub species, freshwater forested wetlands in Central and South Amer-
especially in remote backswamp areas (Duberstein and ica: palm swamps and hardwood swamps. Tidal palm
Conner, 2009). swamps generally occur as low-diversity patches within
hardwood swamps, with virtual monocultures of the dom-
inant tree or palm species (Prance, 1979). Hardwood
Hydrology and community composition swamps in Central America also have very low diversity
Rivers flowing toward the ocean are impeded during (Ellison, 2004). Amazonian tidal várzea are dominated
flooding tides, first resulting in flow reversals within the by relatively few species as well but have higher total
channel and then rising water levels, often resulting in diversity than any other tidal freshwater forested wetland
overbank flooding onto the floodplain. The frequency, reported thus far in the scientific literature when left
depth, and duration of flooding are determined primarily unmanaged (see Almeida et al., 2004). Tidal palm swamps
by lunar- and wind-driven tides (Conner et al., 2007), in Honduras are dominated by the spiny palm (Bactris
and the salinity of the floodwater ranges from full-strength minor), whereas yolillo palm (Raphia taedigera) dominates
seawater (35 g/l) to completely fresh (<0.5 g/l) depending in Costa Rica and Amazonia. Amazon palm swamps can
upon the relative contributions of seawater versus fresh also be dominated by muriti (Mauritia flexuosa), assai
river water over multiple tidal cycles. However, floodwa- (Euterpe oleracea), or troolie (Manicaria saccifera). Hard-
ter over the soil surface in tidal freshwater forested wet- wood tidal swamps in Honduras are dominated by
lands typically has low salinity, thus keeping the soil dragonsblood tree (Pterocarpus officinalis) with coin vine
porewater fresh or nearly so. Storm surges can bring (Dalbergia ecastophyllum, a shrub) common in the under-
pulses of saline water into tidal freshwater forested wet- story. Tree species in tidal várzea vary widely between
lands, but high salinity floodwater usually leaves the stands and subregions, but perhaps the most common
floodplain relatively quickly, allowing for freshwater include baboonwood (Virola surinamensis), tornillo
flushing. Tidal freshwater forested wetlands have, by (Cedrelinga catenaeformis), silk cotton tree (Ceiba
definition, average annual soil porewater salinities pentandra), and pracuiba (Mora paraensis) (Prance, 1979).
<0.5 g/l; however, sometimes, salinity pulses, e.g., from Much like tidal freshwater swamps in the United States,
336 FORESTED WETLAND HABITAT

the differences in tree communities found between different and recolonization of previously used root channels (Reef
tidal várzea are attributed to slight differences in elevation et al., 2010); several Rhizophora species are well adapted
(Cattanio et al., 2002), which influences flooding. for low-nutrient conditions. Mangroves that do well in
high-nutrient conditions (e.g., Avicennia spp.) exhibit rapid
Climate change impacts growth, increased leaf area relative to stems and roots, thin-
ner leaves with lower tannin concentrations, and greater
Tidal freshwater forested wetlands are generally adapted
photosynthesis and growth relative to the amount of water
to tolerate short-term increases in salinity that arise from
used (i.e., water use efficiency) (Krauss et al., 2008).
storm surges and/or decreased river flow during droughts,
but their proximity to the coast also makes them prone to
the chronic salinization driven by sea-level rise and land Hydrology and community composition
subsidence (Conner et al., 2007). The conversion of habi-
Mangrove forests have a remarkable zonation pattern rel-
tat from tidal freshwater to oligohaline manifests at
ative to distance from open ocean water, with each zone
sustained average annual porewater salinity around 2 g/l
often dominated by a single tree species and frequently
as trees die off and tidal swamps convert to brackish
sharp (but dynamic) boundaries between zones (Smith,
marshes or open water (Hackney et al., 2007). Tidal fresh-
1992). This zonation pattern correlates with the frequency
water forested wetlands would be expected to respond to
and duration of tidal immersion, which directly affects the
rising sea levels and the expanded “reach” of tidal influ-
degree of waterlogging (i.e., soil saturation), availability
ence by migrating upstream (Krauss et al., 2009). How-
of nutrients, and salinity of the floodwater and soil
ever, the extent of their migration is limited in many
porewater (Ball, 1988).
places by the presence of levees built for flood control,
When a wetland is flooded, the oxygen available in the
human development, and/or agricultural production
soil and water column is quickly depleted, resulting in
(Doyle et al., 2010). By one modeling account, the extent
oxygen deficiencies. Roots require oxygen for respiration
of tidal freshwater forested wetlands in the southeastern
using normal aerobic metabolic pathways, and many
United States is expected to decrease by 24–34 % by
mangroves have structural adaptations to cope with
2100 (Craft et al., 2009). It is likely that this habitat type
oxygen deficiencies. Shallow root systems, extensive
is undergoing similar pressures globally with coastal
aerenchyma, and lenticels all increase the amount of
development and sea-level rise.
oxygen available to roots (Ball, 1988).
Oxygen availability also affects soil nutrient availabil-
Tidal saltwater forested wetlands (mangroves) ity. The availability of nitrogen and phosphorous, the
Mangroves are found in the intertidal zone (at the edge of two essential soil nutrients most widely linked to rates
continental land masses or islands) of low energy coasts. of plant growth, can change coincident with the amount
The hydrologic environment that mangroves occupy is sim- of time the soil is flooded (see Mitsch and Gosselink,
ilar to that of salt marshes, and the two habitat types are 2000). For instance, nitrogen that is bioavailable (able
dynamic with regard to their shared boundaries. However, to be taken up by the roots and used for growth; i.e.,
mangroves are more restricted globally due to their limited nitrate or NO3) reduces to biologically unavailable
cold tolerance. Mangrove forests are most pervasive in forms such as nitrite (NO2), nitrous oxide (N2O),
tropical climates where they can readily outcompete salt dinitrogen (N2), and/or ammonium (NH4+) with
marshes (Saintilan et al., 2009), but they are found in sub- prolonged flooding. Phosphorus can become less bioavail-
tropical and warm temperate climates as well. In total, there able under anaerobic conditions by precipitating out with
are approximately 73 species and/or hybrids of mangroves ferric iron, calcium, and aluminum, or binding onto clay
(Duke et al., 1998) found in 123 countries, occupying particles, organic peat, and ferric and aluminum hydroxides
roughly 13.7–15.2 M ha of intertidal, estuarine habitat and oxides. Because oxygen availability in the soil is
worldwide (Spalding et al., 2010). dependent upon flooding frequency and duration, the
Mangroves occupy a wide variety of soil types, ranging amount of bioavailable nitrogen and phosphorous varies
from coralline soils that can be very alkaline (pH 8.5) and along the tidal immersion gradient. In general, mangrove
nutrient deficient to highly organic soils that can be very growth is considered to be nitrogen limited in the anaerobic
acidic (pH 5.8) and nutrient rich (Alongi, 2009). However, sediments at positions closest to the open ocean, while the
many mangrove forests are located on soils that are nutrient availability of phosphorus limits mangrove growth
poor (Reef et al., 2010). Species distributions are often in more oxidized soils at positions more landward
related to nutrient availability, and trade-offs exist between (Boto and Wellington, 1983).
having morphological and physiological adaptations to tol- As facultative halophytes, mangroves are generally
erate low-nutrient environments and the ability to found in saline environments, but species exhibit a wide
outcompete for dominance in high-nutrient environments variety of growth responses to salinity. Optimal salinities
(Krauss et al., 2008). Adaptations best suited for low nutri- for growth range from 2 to 26 g/l (5–75 % seawater), but
ent conditions include the following: thick, carbon-rich most can also grow in freshwater (Krauss and Ball,
evergreen leaves, efficient nutrient resorption prior to leaf 2013). All mangroves accumulate ions for osmoregulation
fall, high biomass allocation to roots relative to shoots, but differ in the extent to which ions can be accumulated
 FORESTED WETLAND HABITAT 337

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Mangroves are very susceptible to shifts in distribution that tic composition and topographic variation in a tidal floodplain
will result from increasing temperatures and sea-level rise. forest in the Amazon estuary. Revista Brasileira De Botanica,
24, 419–430.
Rising air and ocean temperatures will likely increase man- Conner, W. H., Doyle, T. W., and Krauss, K. W. (eds.), 2007.
grove growth rates and may allow them to expand their Ecology of Tidal Freshwater Forested Wetlands of the
global distribution where they will encroach into salt marsh Southeastern United States. Dordrecht: Springer.
habitats (Traill et al., 2011). At the local scale, the effects of Courtwright, J., and Findlay, S. E. G., 2011. Effects of
sea-level rise will vary depending on a variety of microtopography on hydrology, physiochemistry, and vegeta-
co-occurring environmental factors including tidal range, tion in a tidal swamp of the Hudson River. Wetlands, 31,
sedimentation and accretion (i.e., increase in soil surface 239–249.
Craft, C., Clough, J., Ehman, J., Joye, S., Park, R., Pennings, S.,
elevation) rates, and local and regional subsidence. Biolog- Guo, H., and Machmuller, M., 2009. Forecasting the effects of
ical feedback mechanisms, which vary depending upon accelerated sea-level rise on tidal marsh ecosystem services.
species composition and growth rates, will also affect rela- Frontiers in Ecology and the Environment, 7, 73–78.
tive sea-level rise via sediment trapping and/or enhanced Doyle, T. W., Krauss, K. W., Conner, W. H., and From, A. S., 2010.
root growth (McKee, 2011). For instance, in many Austra- Predicting the retreat and migration of tidal forests along the
lian mangrove forests, the rate of accretion equals or northern Gulf of Mexico under sea-level rise. Forest Ecology
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2011). Given continued seedling recruitment and adequate lows by trees in tidal freshwater forested wetlands along the Savan-
growth, the potential for landward migration of mangroves nah River. Forest Ecology and Management, 258, 1613–1618.
into new intertidal areas is strong. However, many man- Duke, N. C., Ball, M. C., and Ellison, J. C., 1998. Factors influenc-
grove communities occur near prime real estate areas; ing biodiversity and distributional gradients in mangroves.
migration landward is restricted where human and natural Global Ecology and Biogeography Letters, 7, 27–47.
Ellison, A. M., 2004. Wetlands of Central America. Wetlands
barriers block their expansion. Ecology and Management, 12, 3–55.
Hackney, C. T., Avery, G. B., Leonard, L. A., Posey, M., and
Alphin, T., 2007. Biological, chemical, and physical characteris-
Summary tics of tidal freshwater swamp forests of the Lower Cape Fear
Tidal freshwater forested wetlands are found along rivers River/Estuary, North Carolina. In Conner, W. H., Doyle, T. W.,
at the uppermost extent of tidal influence, whereas man- and Krauss, K. W. (eds.), Ecology of Tidal Freshwater Forested
Wetlands of the Southeastern United States. Dordrecht: Springer,
groves are found nearest the ocean in the lowermost por- pp. 183–221.
tion of the intertidal zone. Both systems are regulated Krauss, K. W., and Ball, M. C., 2013. On the halophytic nature of
largely by hydrology. Tidal freshwater forested wetlands mangroves. Trees-Structure and Function, 27, 7–11.
will not persist where average annual porewater salinity Krauss, K. W., Lovelock, C. E., McKee, K. L., Lopez-Hoffman, L.,
exceeds 2 g/L, whereas mangroves can tolerate a wide Ewe, S. M. L., and Sousa, W. P., 2008. Environmental drivers in
range of salinities. However, mangroves are intolerant to mangrove establishment and early development: a review.
Aquatic Botany, 89, 105–127.
freezing, and the adaptations necessary for mangroves to Krauss, K. W., Duberstein, J. A., Doyle, T. W., Conner, W. H., Day,
survive in saline conditions often limit their growth rates R. H., Inabinette, L. W., and Whitbeck, J. L., 2009. Site condi-
and ability to outcompete salt marsh species. Rising tem- tion, structure, and growth of baldcypress along tidal/non-tidal
peratures associated with climate change will likely salinity gradients. Wetlands, 29, 505–519.
expand the range of mangroves globally, at the detriment Lovelock, C., Bennion, V., Grinham, A., and Cahoon, D., 2011. The
of salt marsh species in some cases. Sea-level rise is forc- role of surface and subsurface processes in keeping pace with sea
level rise in intertidal wetlands of Moreton Bay, Queensland,
ing the migration of both forested wetland habitats. Both Australia. Ecosystems, 14, 745–757.
forested wetland types have done this successfully, but McKee, K. L., 2011. Biophysical controls on accretion and eleva-
levees and other barriers (natural and anthropogenic) will tion change in Caribbean mangrove ecosystems. Estuarine,
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338 FRINGING REEF

Mitsch, W. J., and Gosselink, J. G., 2000. Wetlands, 3rd edn. Description
New York: Wiley.
Prance, G. T., 1979. Notes on the vegetation of Amazonia III. The Fringing reefs form close to shore, most often being shore
terminology of Amazonian forest types subject to inundation. attached, and are relatively thin veneers over non-reefal sub-
Brittonia, 31, 26–38. strate (Steers and Stoddart, 1977). Fringing reefs can form as
Reef, R., Feller, I. C., and Lovelock, C. E., 2010. Nutrition of a continuous reef flat projecting from the shoreline or may
mangroves. Tree Physiology, 30, 1148–1160. be backed by a shallow lagoon sometimes termed a boat
Rheinhardt, R. D., and Hershner, C., 1992. The relationship of channel (Guilcher, 1988). For a reef to be classed as fringing
below-ground hydrology to canopy composition in five tidal
freshwater swamps. Wetlands, 12, 208–216.
the lagoon, it should have a maximum depth of 10 m
Saintilan, N., Rogers, K., and McKee, K. L., 2009. Salt marsh- (Milliman, 1974). Fringing reefs represent the first evolu-
mangrove interactions in Australasia and the Americas. In tionary stage of Charles Darwin’s (1842) theory of coral
Gerardo, M. E. P., Wolanski, E., Cahoon, D. R., and Brinson, atoll evolution when the coral reefs establish on the shore-
M. M. (eds.), Coastal Wetlands: An Integrated Ecosystem line of a volcanic island in the open ocean. Gradual subsi-
Approach. Amsterdam: Elsevier, pp. 855–883. dence of the volcanic island leads to the fringing reef
Smith, T. J., III, 1992. Forest structure. In Robertson, A. I., and evolving into a barrier reef as vertical coral growth is
Alongi, D. M. (eds.), Tropical Mangrove Ecosystems.
Washington: American Geophysical Union, pp. 101–136. maintained on the reef crest. Eventually, the central island
Spalding, M., Kainuma, M., and Collins, L., 2010. World Atlas of sinks below the sea surface, leading to the formation of
Mangroves. London: Earthscan. a coral atoll. The growth and form of a fringing reef is
Struyf, E., Jacobs, S., Meire, P., Jensen, K., and Barendregt, A., 2009. strongly influenced by the available accommodation space
Plant communities of European tidal freshwater wetlands. In determined by the position of the antecedent surface on
Barendregt, A., Whigham, D. F., and Baldwin, A. H. (eds.), Tidal which the reef establishes in relation to sea level and the rate
Freshwater Wetlands. Leiden: Backhuys Publishers, pp. 59–70.
Traill, L. W., Perhans, K., Lovelock, C. E., Prohaska, A., Mcfallan, of sedimentation (Kennedy and Woodroffe, 2002). Fringing
S., Rhodes, J. R., and Wilson, K. A., 2011. Managing for change: reefs may grow vertically to the sea surface in a keep-up or
wetland transitions under sea-level rise and outcomes for threat- catch-up mode, having been established on a newly flooded
ened species. Diversity and Distributions, 17, 1225–1233. substrate during a period of rising sea level. Fringing reefs
Verhoeven, J. T. A., Whigham, D. F., van Logtestijn, R., and may also initiate at the same elevation as a stable sea surface,
O’Neill, J., 2001. A comparative study of nitrogen and phospho- prograding horizontally as a reef framework or over
rus cycling in tidal and non-tidal riverine wetlands. Wetlands, 21,
210–222.
non-reefal sediments. Progradation can be characterized by
progressive lateral accretion, but in some cases it may be
Cross-references episodic, occurring through the attachment of fore-reef coral
Climate Change
bommies or patch reefs onto the reef front. In some cases
Coastal Wetlands fringing reefs may establish just offshore of a landmass
Intertidal Zonation either as a framework deposit or on top of an accumulation
Mangroves of storm-deposited rubble (Kennedy and Woodroffe, 2002).
Marine/Freshwater Mixing
Nutrient Limitation
Pneumatophores Bibliography
Saltmarshes Darwin, C. R., 1842. The Structure and Distribution of Coral Reefs.
Tidal Freshwater Habitat London: Smith, Elder and Company.
Wetlands Guilcher, A., 1988. Coral Reef Geomorphology. New York: Wiley.
Kennedy, D. M., and Woodroffe, C. D., 2002. Fringing reef growth
and morphology: a review. Earth Science Reviews, 57, 255–277.
Milliman, J. D., 1974. Marine Carbonates. Berlin: Springer.
Steers, J. A., and Stoddart, D. R., 1977. The origin of fringing reefs,
FRINGING REEF barrier reefs, and atolls. In Jones, O. A., and Endean, R. (eds.),
Biology and Geology of Coral Reefs. New York: Academic
David M. Kennedy Press, pp. 21–57.
Department of Resource Management & Geography,
The University of Melbourne, Parkville, VIC, Australia
Cross-references
Definition Artificial Reef
A fringing reef is a shore-attached coral framework structure. Oyster Reef