480
16.1 Introduction
An ecocline can be defined as a “gradation from one ecosystem to another when
there is no sharp boundary between the two” containing relatively heterogeneous
faunal communities influenced by progressive changes between the two systems
(Attrill and Rundle 2002; Barletta and Dantas 2016). To these boundaries, it is usually attributed environmental grades as upper, middle and lower reaches. Each of
these habitats can actually shift horizontally, moving seaward and back according to
rainfall patterns (Barletta et al. 2005, 2008) or upstream human interventions
(Morita and Yamamoto 2002; Dallas and Barnard 2009; Barletta et al. 2016).
Estuarine ecocline have been always defined as the strongest forcing structuring
faunal populations and communities within estuarine ecosystems (Bolton 1979;
Calder and Maÿal 1998; Barletta and Blaber 2007). A study in the estuary of the
Silver Burn, Castletown, Isle of Man, U.K., demonstrated that Pilayella littoralis
(brown algae, Phaeophyta) presented a gradual transition from moderately to markedly euryhaline populations according to the salinity regimes of the sampling sites
(Bolton 1979). Another study regarding hydroids (Cnidaria – Clytia gracilis, Obelia
bidentata, Garveia franciscana) distribution patterns along the ecocline of a small
estuary of northeast Brazil (Formoso River), demonstrated that changes in hydroid
species composition were attributed primarily to differences in salinity characteristics from one site to another (Calder and Maÿal 1998).
Therefore, estuarine ecocline produces boundaries that result in a suite of faunal
communities along the gradient, changing seasonally in terms of quali-quantitative
variables or living strategies. Estuarine ecocline can also set physico-chemical conditions that determine the bioavailability or sinking of dissolved oxygen, and the
concentration of pollutants (plastic debris, metals, emerging pollutants) (Lima et al.
2014; Costa and Barletta 2015; Costa et al. 2009; Reis et al. 2016) and microbiological contaminants (from sewage, urban runoff and animal farming) throughout
the salinity ecocline (Costa and Barletta 2016).
Considerable information on estuaries and their fish fauna are available for the
South American Atlantic border (Barletta et al. 2010; Blaber and Barletta 2016;
Costa and Barletta 2016). However, to compile and interpret this body of literature
turning it into useful managerial information is a daunting task for anyone, but a
most needed step to prompt well-informed decision-making. This is especially
complex if transitions among environments need to be considered, as is the case of
the Western Atlantic, which extends from Equatorial to Sub-tropical regimes (Beck
et al. 2001; Costa and Barletta 2016). Estuaries along this latitudinal gradient are
transitional themselves, and provide a variety of habitats for fishes, at all life stages,
that take advantages of available resources, especially the high productivity and
shelter, to complete their life cycles (Able 2005). These systems can be characterized by high densities of few species (catfishes, croakers, drums); larval fishes and;
smaller fishes (anchovies, herrings, sardines) that are trophic links to fishes of commercial and subsistence interest (Barletta-Bergan et al. 2002a, b; Dantas et al. 2012;
Ferreira et al. 2016; Lima et al. 2015, 2016; Ramos et al. 2016).
M. Barletta et al.
16.1 Introduction
An ecocline can be defined as a “gradation from one ecosystem to another when
there is no sharp boundary between the two” containing relatively heterogeneous
faunal communities influenced by progressive changes between the two systems
(Attrill and Rundle 2002; Barletta and Dantas 2016). To these boundaries, it is usually attributed environmental grades as upper, middle and lower reaches. Each of
these habitats can actually shift horizontally, moving seaward and back according to
rainfall patterns (Barletta et al. 2005, 2008) or upstream human interventions
(Morita and Yamamoto 2002; Dallas and Barnard 2009; Barletta et al. 2016).
Estuarine ecocline have been always defined as the strongest forcing structuring
faunal populations and communities within estuarine ecosystems (Bolton 1979;
Calder and Maÿal 1998; Barletta and Blaber 2007). A study in the estuary of the
Silver Burn, Castletown, Isle of Man, U.K., demonstrated that Pilayella littoralis
(brown algae, Phaeophyta) presented a gradual transition from moderately to markedly euryhaline populations according to the salinity regimes of the sampling sites
(Bolton 1979). Another study regarding hydroids (Cnidaria – Clytia gracilis, Obelia
bidentata, Garveia franciscana) distribution patterns along the ecocline of a small
estuary of northeast Brazil (Formoso River), demonstrated that changes in hydroid
species composition were attributed primarily to differences in salinity characteristics from one site to another (Calder and Maÿal 1998).
Therefore, estuarine ecocline produces boundaries that result in a suite of faunal
communities along the gradient, changing seasonally in terms of quali-quantitative
variables or living strategies. Estuarine ecocline can also set physico-chemical conditions that determine the bioavailability or sinking of dissolved oxygen, and the
concentration of pollutants (plastic debris, metals, emerging pollutants) (Lima et al.
2014; Costa and Barletta 2015; Costa et al. 2009; Reis et al. 2016) and microbiological contaminants (from sewage, urban runoff and animal farming) throughout
the salinity ecocline (Costa and Barletta 2016).
Considerable information on estuaries and their fish fauna are available for the
South American Atlantic border (Barletta et al. 2010; Blaber and Barletta 2016;
Costa and Barletta 2016). However, to compile and interpret this body of literature
turning it into useful managerial information is a daunting task for anyone, but a
most needed step to prompt well-informed decision-making. This is especially
complex if transitions among environments need to be considered, as is the case of
the Western Atlantic, which extends from Equatorial to Sub-tropical regimes (Beck
et al. 2001; Costa and Barletta 2016). Estuaries along this latitudinal gradient are
transitional themselves, and provide a variety of habitats for fishes, at all life stages,
that take advantages of available resources, especially the high productivity and
shelter, to complete their life cycles (Able 2005). These systems can be characterized by high densities of few species (catfishes, croakers, drums); larval fishes and;
smaller fishes (anchovies, herrings, sardines) that are trophic links to fishes of commercial and subsistence interest (Barletta-Bergan et al. 2002a, b; Dantas et al. 2012;
Ferreira et al. 2016; Lima et al. 2015, 2016; Ramos et al. 2016).
M. Barletta et al.