487
During the late rainy season, dissolved oxygen is also important in structuring
fish assemblages. But, for the late dry season, both salinity and dissolved oxygen
were responsible for it. In the Paranaguá Estuary, seasons are also responsible for
defining salinity gradients and habitat movements. Environmental instability during
the late rainy season induces estuarine fish to move outwards in search of greater
salinity stability in the middle and lower portions, rather than favouring the freshwater species to move upstream (Figs. 16.5 and 16.6) (Barletta et al. 2008). The
main channel of the Paranaguá Estuary supports inflow of marine waters even during high river discharges and marine fishes remain within its bounds until the late
rainy season (Barletta et al. 2008). This corroborates the proposed model for tropical and subtropical estuarine fish movement patterns worldwide, where the salinity
ecocline induces the fish movement in different estuarine portions (Barletta et al.
2005; Barletta and Blaber 2007). However, if natural or anthropogenic effects, such
as dredging processes, modify the estuarine dynamics of current it will cause consequences on fish assemblage composition and therefore for fisheries practices
(Barletta et al. 2016; Blaber 2000, 2002, 2013).
16.3 Estuarine Ecocline
16.3.1 Influence of Estuarine Ecocline on Fish Fauna
of the Western Atlantic Estuaries
Being estuarine ecocline zones of gradual changes between river-dominated to
marine-like waters, these systems result from the intrusion of coastal waters (function of tidal amplitude, channel depth, etc.) and freshwater inputs (Barletta and
Dantas 2016) (Figs. 16.7 and 16.8). Turbulence zones mix these two different water
bodies, producing boundaries that result in a suite of faunal communities along the
salinity ecocline (Barletta and Dantas 2016). The fluctuation of the estuarine ecocline is strongly influenced by seasonal changes in freshwater flow and diel tidal
cycles, forcing faunal communities to adapt, in terms of quali-quantitative variables
or living strategies, to the different time scales of these modifications (Barletta et al.
2008; Dantas et al. 2010; Watanabe et al. 2014; Ferreira et al. 2016) (Figs. 16.2,
16.4, 16.6, 16.7, and 16.8). At a local scale, each estuary exhibits its own morphology and climatic distinctions, resulting in different abiotic demands through space
and time for a variety of organisms that depends on estuaries for their ecological and
biological requirements.
Estuarine-dependent fish species (Able 2005; Potter et al. 2013) are distributed
according to their physiological abilities to withstand variations in the abiotic environment during different lengths of time during their life cycles (Elliott et al. 2007;
Lima et al. 2015) (Figs. 16.7 and 16.8). It defines functional groups of species as
estuarine, freshwater and marine guilds; as well as migratory taxa, as anadromous,
catadromous, amphidromous and freshwater/marine migrant groups (Elliott et al.
16 Estuarine Ecoclines and the Associated Fauna: Ecological Information as the Basis…
During the late rainy season, dissolved oxygen is also important in structuring
fish assemblages. But, for the late dry season, both salinity and dissolved oxygen
were responsible for it. In the Paranaguá Estuary, seasons are also responsible for
defining salinity gradients and habitat movements. Environmental instability during
the late rainy season induces estuarine fish to move outwards in search of greater
salinity stability in the middle and lower portions, rather than favouring the freshwater species to move upstream (Figs. 16.5 and 16.6) (Barletta et al. 2008). The
main channel of the Paranaguá Estuary supports inflow of marine waters even during high river discharges and marine fishes remain within its bounds until the late
rainy season (Barletta et al. 2008). This corroborates the proposed model for tropical and subtropical estuarine fish movement patterns worldwide, where the salinity
ecocline induces the fish movement in different estuarine portions (Barletta et al.
2005; Barletta and Blaber 2007). However, if natural or anthropogenic effects, such
as dredging processes, modify the estuarine dynamics of current it will cause consequences on fish assemblage composition and therefore for fisheries practices
(Barletta et al. 2016; Blaber 2000, 2002, 2013).
16.3 Estuarine Ecocline
16.3.1 Influence of Estuarine Ecocline on Fish Fauna
of the Western Atlantic Estuaries
Being estuarine ecocline zones of gradual changes between river-dominated to
marine-like waters, these systems result from the intrusion of coastal waters (function of tidal amplitude, channel depth, etc.) and freshwater inputs (Barletta and
Dantas 2016) (Figs. 16.7 and 16.8). Turbulence zones mix these two different water
bodies, producing boundaries that result in a suite of faunal communities along the
salinity ecocline (Barletta and Dantas 2016). The fluctuation of the estuarine ecocline is strongly influenced by seasonal changes in freshwater flow and diel tidal
cycles, forcing faunal communities to adapt, in terms of quali-quantitative variables
or living strategies, to the different time scales of these modifications (Barletta et al.
2008; Dantas et al. 2010; Watanabe et al. 2014; Ferreira et al. 2016) (Figs. 16.2,
16.4, 16.6, 16.7, and 16.8). At a local scale, each estuary exhibits its own morphology and climatic distinctions, resulting in different abiotic demands through space
and time for a variety of organisms that depends on estuaries for their ecological and
biological requirements.
Estuarine-dependent fish species (Able 2005; Potter et al. 2013) are distributed
according to their physiological abilities to withstand variations in the abiotic environment during different lengths of time during their life cycles (Elliott et al. 2007;
Lima et al. 2015) (Figs. 16.7 and 16.8). It defines functional groups of species as
estuarine, freshwater and marine guilds; as well as migratory taxa, as anadromous,
catadromous, amphidromous and freshwater/marine migrant groups (Elliott et al.
16 Estuarine Ecoclines and the Associated Fauna: Ecological Information as the Basis…