These effects are much more pronounced in the longer
valleys of Scotland’s eastern coast, with their limited
number of firths, than in the shorter and much deeper valleys
of the narrower western coasts with their extraordinary
proliferation of fjords.
The current hierarchy of the water network is dictated
by glacial erosion since the magnitude of the current
interfluvial structures and the proximity of the heads of
glaciers to the coast have limited the transformative action
of fluvial geodynamic activity (Figure 1). Within these
common traits, firths are further characterized by longer
and more structured fluvial networks, greater abundance
of fluvial sediment, and much smaller average gradient
in the valleys as a whole. These factors result in shallower
depths all along the basin, even in the coastal platform,
where the oldest glacial deposits have been incorporated
in littoral processes to accentuate the current silting
processes in the firths.
Bibliography
Duck, R. W., McManus, J., and Diez, J. J., 1995. Comparative study
of two largely unfilled estuaries: the Eden estuary (Scotland) and
the Ria de Foz (Spain). Netherlands Journal of Aquatic Ecology,
29(3–4), 203–210.
Firth, C. R., Collins, P. E. F., and Smith, D. E., 1997. Coastal
Processes and Management of Scottish Estuaries: IV - The Firth
of Forth. Scottish Natural Heritage Review, No 87.
McManus, J., Diez, J. J., Duck, R. W., Escobar, V., Anderson, J. M.,
Esteban, V., and Paz, R., 1993. Comparison of Scottish Firths
and Spanish Rias. Bulletin of the International Association of
Engineering Geology, 47, 127–132.
Cross-references
Coastal Bays
Fjord
Ria
FISH ASSEMBLAGES
Mario Barletta and David Valença Dantas
Laboratório de Ecologia e Gerenciamento de
Ecossistemas Costeiros e Estuarinos, Departamento de
Oceanografia, Universidade Federal de Pernambuco,
Recife, PE, Brazil
Definition
Fish Assemblage. A fish assemblage is simply a suite of
species whose individuals are collected in the same area
at the same time.
Introduction
There are no strict limits on the spatial or temporal scale of
a fish assemblage (Miller, 2002). It may be an assemblage
in a single season and region (e.g., a fish assemblage of an
estuarine main channel during the late rainy season) or at
specific times and locations (e.g., fish assemblages among
different estuaries in South America). Research on fish
assemblages has sought to understand where, why, and
when they occur and how these spatial and temporal distributions relate to patterns in reproduction, recruitment, and
foraging. The seasonal variation in proportion and abundance of freshwater and marine fish species in fish assemblages in estuarine habitats is a result of both the seasonal
variation of environmental gradients (e.g., salinity, temperature, turbidity) and a suite of biological variables,
including reproduction and recruitment (Blaber, 2000;
Barletta et al., 2005, 2008; Dantas et al., 2010, 2012). In
tropical estuaries, seasonal fluctuations of salinity are
a major factor determining larval abundance (BarlettaBergan et al., 2002a; Barletta-Bergan et al., 2002b), juvenile and adult density, and biomass of fishes (Blaber,
2000; Barletta et al., 2005, 2008), mainly due to the effects
of large fluctuations of freshwater inputs during the year.
Factors such as geology, geomorphology, and more immediate environmental factors as salinity and temperature
affect fish distributions, species richness, and fisheries
catch (Mahon et al., 1998; Mathieson et al., 2000; Araújo
and Azevedo, 2001; Roy et al., 2001; Thiel et al., 2003). In
addition, broadscale comparisons of tropical estuaries
across zoogeographic realms indicate possible significant
differences in the fish assemblage use of various estuarine
habitats, as well as differences in the patterns of species
composition (Blaber, 2000). For example, the relative proportions of freshwater and marine species using estuaries
may differ (Blaber, 2000; Barletta et al., 2003, 2005,
2008). An understanding of the roles and relative importance of different habitats within estuaries to fish is necessary for both effective management and conservation
(Elliott and Hemingway, 2002).
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
grounds, migration routes, and refuge areas for many fish
species, including resident fish assemblages (Blaber,
2000; McLusky and Elliott, 2004; Barletta et al., 2010;
Dantas et al., 2012). The study of estuarine fish assemblage structure and functioning is important for understanding the ecological characteristics of estuaries, as
well as for classifying species for use in management of
anthropogenic impacts in estuaries (McLusky and Elliott,
2004; Elliott et al., 2007).
Recently, studies have concentrated on the functional
analysis of finfish assemblage structure in which the species present are assigned to groupings or guilds, each of
which denotes certain attributes (Elliott et al., 2007).
A guild is a group of species that exploit the same class
of environmental resources in a similar way (Root,
1967). Hence, guilds have been used to provide information on functioning, hierarchical structure, and connectivity and to simplify complex ecosystems (McLusky and
Elliott, 2004; Barletta and Blaber, 2007). While there are
FISH ASSEMBLAGES
317
valleys of Scotland’s eastern coast, with their limited
number of firths, than in the shorter and much deeper valleys
of the narrower western coasts with their extraordinary
proliferation of fjords.
The current hierarchy of the water network is dictated
by glacial erosion since the magnitude of the current
interfluvial structures and the proximity of the heads of
glaciers to the coast have limited the transformative action
of fluvial geodynamic activity (Figure 1). Within these
common traits, firths are further characterized by longer
and more structured fluvial networks, greater abundance
of fluvial sediment, and much smaller average gradient
in the valleys as a whole. These factors result in shallower
depths all along the basin, even in the coastal platform,
where the oldest glacial deposits have been incorporated
in littoral processes to accentuate the current silting
processes in the firths.
Bibliography
Duck, R. W., McManus, J., and Diez, J. J., 1995. Comparative study
of two largely unfilled estuaries: the Eden estuary (Scotland) and
the Ria de Foz (Spain). Netherlands Journal of Aquatic Ecology,
29(3–4), 203–210.
Firth, C. R., Collins, P. E. F., and Smith, D. E., 1997. Coastal
Processes and Management of Scottish Estuaries: IV - The Firth
of Forth. Scottish Natural Heritage Review, No 87.
McManus, J., Diez, J. J., Duck, R. W., Escobar, V., Anderson, J. M.,
Esteban, V., and Paz, R., 1993. Comparison of Scottish Firths
and Spanish Rias. Bulletin of the International Association of
Engineering Geology, 47, 127–132.
Cross-references
Coastal Bays
Fjord
Ria
FISH ASSEMBLAGES
Mario Barletta and David Valença Dantas
Laboratório de Ecologia e Gerenciamento de
Ecossistemas Costeiros e Estuarinos, Departamento de
Oceanografia, Universidade Federal de Pernambuco,
Recife, PE, Brazil
Definition
Fish Assemblage. A fish assemblage is simply a suite of
species whose individuals are collected in the same area
at the same time.
Introduction
There are no strict limits on the spatial or temporal scale of
a fish assemblage (Miller, 2002). It may be an assemblage
in a single season and region (e.g., a fish assemblage of an
estuarine main channel during the late rainy season) or at
specific times and locations (e.g., fish assemblages among
different estuaries in South America). Research on fish
assemblages has sought to understand where, why, and
when they occur and how these spatial and temporal distributions relate to patterns in reproduction, recruitment, and
foraging. The seasonal variation in proportion and abundance of freshwater and marine fish species in fish assemblages in estuarine habitats is a result of both the seasonal
variation of environmental gradients (e.g., salinity, temperature, turbidity) and a suite of biological variables,
including reproduction and recruitment (Blaber, 2000;
Barletta et al., 2005, 2008; Dantas et al., 2010, 2012). In
tropical estuaries, seasonal fluctuations of salinity are
a major factor determining larval abundance (BarlettaBergan et al., 2002a; Barletta-Bergan et al., 2002b), juvenile and adult density, and biomass of fishes (Blaber,
2000; Barletta et al., 2005, 2008), mainly due to the effects
of large fluctuations of freshwater inputs during the year.
Factors such as geology, geomorphology, and more immediate environmental factors as salinity and temperature
affect fish distributions, species richness, and fisheries
catch (Mahon et al., 1998; Mathieson et al., 2000; Araújo
and Azevedo, 2001; Roy et al., 2001; Thiel et al., 2003). In
addition, broadscale comparisons of tropical estuaries
across zoogeographic realms indicate possible significant
differences in the fish assemblage use of various estuarine
habitats, as well as differences in the patterns of species
composition (Blaber, 2000). For example, the relative proportions of freshwater and marine species using estuaries
may differ (Blaber, 2000; Barletta et al., 2003, 2005,
2008). An understanding of the roles and relative importance of different habitats within estuaries to fish is necessary for both effective management and conservation
(Elliott and Hemingway, 2002).
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
grounds, migration routes, and refuge areas for many fish
species, including resident fish assemblages (Blaber,
2000; McLusky and Elliott, 2004; Barletta et al., 2010;
Dantas et al., 2012). The study of estuarine fish assemblage structure and functioning is important for understanding the ecological characteristics of estuaries, as
well as for classifying species for use in management of
anthropogenic impacts in estuaries (McLusky and Elliott,
2004; Elliott et al., 2007).
Recently, studies have concentrated on the functional
analysis of finfish assemblage structure in which the species present are assigned to groupings or guilds, each of
which denotes certain attributes (Elliott et al., 2007).
A guild is a group of species that exploit the same class
of environmental resources in a similar way (Root,
1967). Hence, guilds have been used to provide information on functioning, hierarchical structure, and connectivity and to simplify complex ecosystems (McLusky and
Elliott, 2004; Barletta and Blaber, 2007). While there are
FISH ASSEMBLAGES
317