many options for functional guilds, such as one for habitat
preference and another relating to position inhabited
within the water column (Elliott and Dewailly, 1995),
Elliott et al. (2007) proposed three groups of functional
guilds. The first is the Estuarine Use Functional Group,
which defines the overall ecological use of an estuary by
a given species and is composed by eight categories:
marine stragglers, marine migrants, estuarine species,
anadromous, catadromous, amphidromous, freshwater
stragglers, and freshwater migrants. The second is the
Feeding Mode Functional Group, which defines the primary method of feeding used by a given species and is
composed by seven categories: planktivorous,
detritivorous, herbivorous, piscivorous, benthophagous,
hyperbenthophagous, and opportunistic. The third is the
Reproductive Mode Functional Group that indicates
how, and in some cases where, an estuarine species reproduces, being composed of three main categories: viviparous, ovoviviparous, and oviparous. To explore possible
fundamental similarities and differences in estuarine
fishes in tropical, subtropical, and temperate estuaries
from different zoogeographic regions, it is necessary to
compare their fish assemblages, not only taxonomically,
but also in terms of their ecological structure and resource
use in different habitats of the estuary during different time
scales. Based on this information, Barletta and Blaber
(2007) made a comparison between Caeté (Northern
South America) and Embley (Northern Australia) estuaries. They found important taxonomic differences between
the two estuaries. The Neotropical fish species of the
upper Caeté Estuary have no equivalents in the Embley
Estuary, and the diverse chondrichthyan fauna of the
Embley have no equivalents in the Caeté Estuary. On the
other hand, the more ubiquitous families Engraulidae,
Sciaenidae, Ariidae, Carangidae, Haemulidae, and
Clupeidae, which were characteristic of the main channel
and mangrove tidal creeks of the Caeté Estuary, showed
70 % similarity with the main channel of the Embley
Estuary.
Environmental influence on fish assemblages
Estuaries are important ecosystems for marine fisheries,
and diverse authors have emphasized that fish landings
around the world consist of species that spend part of their
lives in estuarine waters (Blaber, 2000; Barletta et al.,
2003, 2005, 2008; Barletta-Bergan et al., 2002a;
Barletta-Bergan et al., 2002b). Estuarine and shallow
marine waters in tropical (Blaber, 2000; Barletta et al.,
2005), subtropical (Jaureguizar et al., 2004; Barletta
et al., 2008), and temperate (Thiel et al., 1995) regions
are important areas for feeding, mating, spawning, and
nursery habitat for many fish species. The species composition of estuarine fish assemblages is dictated by
a combination of biotic and abiotic variables, particularly
competition for space and food, and tolerance to diel and
seasonal changes in salinity, turbidity, and temperature
(Blaber, 2000; Barletta et al., 2003, 2005, 2008).
Some species occur in specific habitats such as tidal
marshes (Mathieson et al., 2000; Akin et al., 2003),
seagrass beds (Dorenbosch et al., 2006), mangrove forests
(Barletta et al., 2000; Hindell and Jenkins, 2004), mangrove tidal creeks (Barletta et al., 2003; Krumme et al.,
2005), and the main channel of the estuary (Barletta et al.,
2005, 2008). Others species use these habitats and areas
of the estuary (upper, middle, and lower) at various life
stages and when environmental conditions allow (Thayer
et al., 1987; Barletta et al., 2005, 2008; Dantas et al., 2010).
In tropical estuaries, seasonal fluctuations of salinity
are a major factor determining larval abundance (Morais
and Morais, 1994; Barletta-Bergan et al., 2002a;
Barletta-Bergan et al., 2002b), and juvenile and adult biomass and density (Barletta et al., 2000, 2005, 2008; Dantas
et al., 2010), mainly due to the effects of large fluctuations
of freshwater inputs during the year (Figures 1, 2, and 3).
In an estuary located at the eastern Amazon (northern Brazil), the estuarine-dependent species, which use the main
channel, are ordered along a large-scale spatial gradient,
when relatively stable hydrological conditions create a
well-defined salinity gradient in the estuary during the late
dry season (Barletta et al., 2005). Moreover, during the
late rainy season, freshwater runoff increases, salinity
drops, and the estuary then becomes more suitable for
Neotropical freshwater species (Figure 1). Salinity and
distance from the estuary mouth are the most important
environmental variables structuring the fish assemblages
in this estuary (Barletta et al., 2005). As an example, studies conducted in other Neotropical estuaries in South
America (Barletta et al., 2005, 2008; Dantas et al., 2012)
suggest that, for the marine catfish species Cathorops
spixii (Agassiz) (Figure 4) and C. agassizii (Eigenmann
and Eigenmann) (Figure 5), the salinity gradient influences the seasonal distribution not only of adults but also
all of their different ontogenetic stages along the estuarine
ecocline (upper, middle, and lower estuary). Moreover,
the seasonal fluctuations in salinity (late dry and late
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 importance of this habitat as nursery for C. spixii and
C. agassizii juveniles is determined by the seasonal environmental gradient conditions along the estuarine ecocline
(Dantas et al., 2012).
In the temperate La Plata River Estuary (Uruguay–
Argentina), salinity has a stronger influence on the spatial
structure of the fish assemblages than temperature, and the
pattern of seasonal fish species distribution in the La Plata
Estuary reflects the seasonal discharge of this river
(Jaureguizar et al., 2004). On a large spatial scale, the
strong physical environment gradient along La Plata Estuary creates a gradual change in the fish composition from
fresh and shallow to marine and deeper waters that define
the riverine, estuarine, and coastal shelf fish assemblages
(Anganuzzi, 1983; Jaureguizar et al., 2004; Lorenzo
Pereiro, 2007). The riverine fish assemblages occupy the
inner part of the La Plata Estuary, characterized by
318
FISH ASSEMBLAGES
preference and another relating to position inhabited
within the water column (Elliott and Dewailly, 1995),
Elliott et al. (2007) proposed three groups of functional
guilds. The first is the Estuarine Use Functional Group,
which defines the overall ecological use of an estuary by
a given species and is composed by eight categories:
marine stragglers, marine migrants, estuarine species,
anadromous, catadromous, amphidromous, freshwater
stragglers, and freshwater migrants. The second is the
Feeding Mode Functional Group, which defines the primary method of feeding used by a given species and is
composed by seven categories: planktivorous,
detritivorous, herbivorous, piscivorous, benthophagous,
hyperbenthophagous, and opportunistic. The third is the
Reproductive Mode Functional Group that indicates
how, and in some cases where, an estuarine species reproduces, being composed of three main categories: viviparous, ovoviviparous, and oviparous. To explore possible
fundamental similarities and differences in estuarine
fishes in tropical, subtropical, and temperate estuaries
from different zoogeographic regions, it is necessary to
compare their fish assemblages, not only taxonomically,
but also in terms of their ecological structure and resource
use in different habitats of the estuary during different time
scales. Based on this information, Barletta and Blaber
(2007) made a comparison between Caeté (Northern
South America) and Embley (Northern Australia) estuaries. They found important taxonomic differences between
the two estuaries. The Neotropical fish species of the
upper Caeté Estuary have no equivalents in the Embley
Estuary, and the diverse chondrichthyan fauna of the
Embley have no equivalents in the Caeté Estuary. On the
other hand, the more ubiquitous families Engraulidae,
Sciaenidae, Ariidae, Carangidae, Haemulidae, and
Clupeidae, which were characteristic of the main channel
and mangrove tidal creeks of the Caeté Estuary, showed
70 % similarity with the main channel of the Embley
Estuary.
Environmental influence on fish assemblages
Estuaries are important ecosystems for marine fisheries,
and diverse authors have emphasized that fish landings
around the world consist of species that spend part of their
lives in estuarine waters (Blaber, 2000; Barletta et al.,
2003, 2005, 2008; Barletta-Bergan et al., 2002a;
Barletta-Bergan et al., 2002b). Estuarine and shallow
marine waters in tropical (Blaber, 2000; Barletta et al.,
2005), subtropical (Jaureguizar et al., 2004; Barletta
et al., 2008), and temperate (Thiel et al., 1995) regions
are important areas for feeding, mating, spawning, and
nursery habitat for many fish species. The species composition of estuarine fish assemblages is dictated by
a combination of biotic and abiotic variables, particularly
competition for space and food, and tolerance to diel and
seasonal changes in salinity, turbidity, and temperature
(Blaber, 2000; Barletta et al., 2003, 2005, 2008).
Some species occur in specific habitats such as tidal
marshes (Mathieson et al., 2000; Akin et al., 2003),
seagrass beds (Dorenbosch et al., 2006), mangrove forests
(Barletta et al., 2000; Hindell and Jenkins, 2004), mangrove tidal creeks (Barletta et al., 2003; Krumme et al.,
2005), and the main channel of the estuary (Barletta et al.,
2005, 2008). Others species use these habitats and areas
of the estuary (upper, middle, and lower) at various life
stages and when environmental conditions allow (Thayer
et al., 1987; Barletta et al., 2005, 2008; Dantas et al., 2010).
In tropical estuaries, seasonal fluctuations of salinity
are a major factor determining larval abundance (Morais
and Morais, 1994; Barletta-Bergan et al., 2002a;
Barletta-Bergan et al., 2002b), and juvenile and adult biomass and density (Barletta et al., 2000, 2005, 2008; Dantas
et al., 2010), mainly due to the effects of large fluctuations
of freshwater inputs during the year (Figures 1, 2, and 3).
In an estuary located at the eastern Amazon (northern Brazil), the estuarine-dependent species, which use the main
channel, are ordered along a large-scale spatial gradient,
when relatively stable hydrological conditions create a
well-defined salinity gradient in the estuary during the late
dry season (Barletta et al., 2005). Moreover, during the
late rainy season, freshwater runoff increases, salinity
drops, and the estuary then becomes more suitable for
Neotropical freshwater species (Figure 1). Salinity and
distance from the estuary mouth are the most important
environmental variables structuring the fish assemblages
in this estuary (Barletta et al., 2005). As an example, studies conducted in other Neotropical estuaries in South
America (Barletta et al., 2005, 2008; Dantas et al., 2012)
suggest that, for the marine catfish species Cathorops
spixii (Agassiz) (Figure 4) and C. agassizii (Eigenmann
and Eigenmann) (Figure 5), the salinity gradient influences the seasonal distribution not only of adults but also
all of their different ontogenetic stages along the estuarine
ecocline (upper, middle, and lower estuary). Moreover,
the seasonal fluctuations in salinity (late dry and late
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 importance of this habitat as nursery for C. spixii and
C. agassizii juveniles is determined by the seasonal environmental gradient conditions along the estuarine ecocline
(Dantas et al., 2012).
In the temperate La Plata River Estuary (Uruguay–
Argentina), salinity has a stronger influence on the spatial
structure of the fish assemblages than temperature, and the
pattern of seasonal fish species distribution in the La Plata
Estuary reflects the seasonal discharge of this river
(Jaureguizar et al., 2004). On a large spatial scale, the
strong physical environment gradient along La Plata Estuary creates a gradual change in the fish composition from
fresh and shallow to marine and deeper waters that define
the riverine, estuarine, and coastal shelf fish assemblages
(Anganuzzi, 1983; Jaureguizar et al., 2004; Lorenzo
Pereiro, 2007). The riverine fish assemblages occupy the
inner part of the La Plata Estuary, characterized by
318
FISH ASSEMBLAGES