489
maintain fulfil trophic and biological functions. Many marine/freshwater migratory
taxa enter estuaries sporadically, especially as juveniles, only to take advantage of
shelter from predators and food abundance. Some are highly euryhaline and move
through the full length of the system (Elliott et al. 2007). In tropical and subtropical
estuaries of the western Atlantic, salinity-dominated ecocline is a major driver influencing spatial and temporal distribution of fish and other fauna. Changes in fish
sizes, diversity and abundance are strong indicatives of environmental variability
into a particular habitat and are associated to seasonal movements of these habitats
due to river flow switches from the dry to the rainy season and back (Barletta et al.
2005, 2008; Dantas et al. 2012; Lima et al. 2015; Ramos et al. 2016).
The management and conservation of estuaries (and consequently of its
resources) should take into account the overlapping of environmental variables and
life cycles of key species for different estuarine reaches and seasons (Figs. 16.7 and
16.8). Abrupt changes in climatic patterns or in the river flow regime will induce
abrupt changes in the estuarine ecocline trends and fish communities will respond
to these changes by modifying assemblage structures. In the Paranaguá Estuary, for
example, during dredging operations, the upper estuary is deepened and alterations
in the geomorphology of the system is responsible to the intrusion of a greater
amount of coastal waters upstream, resulting in changes in fish community (Barletta
et al. 2016). These concepts need to be taken as the basis of descriptors of reference
conditions for regional coastal systems, considering the resilience of the system,
including when under anthropogenic interference (Barletta et al. 2010).
Also important to note, is that tropical and subtropical estuaries usually have a
greater diversity and complexity of habitats, including main channel, flood plain,
intertidal creeks and surrounding mangrove forest (Fig. 16.9a–c) (Reis et al. 2016).
The connectivity of these habitats guarantee that estuarine-dependent fishes complete their life cycle by accessing all the resources and using all the protection they
need. Patterns of estuarine use can differ during the ontogenetic development of fish
species. Larval, juvenile, sub-adult and adult stages of the same species respond
differently to seasonal fluctuations of estuarine ecocline, as well as in the use of
available effective habitats (Barletta-Bergan et al. 2002a, b; Barletta and BarlettaBergan 2009; Ferreira et al. 2016; Lima et al. 2015). This trait is suggested to be a
strategy to avoid competition and predation during the earlier, critical stages. The
estuarine ecocline defines spatial and temporal patterns in community diversity and
structure, population abundance, periods of reproduction and temporary nursery
habitats for juveniles of many socio-economically important fish species (Dantas
et al. 2010; Ferreira et al. 2016; Ramos et al. 2014, 2016).
16 Estuarine Ecoclines and the Associated Fauna: Ecological Information as the Basis…
maintain fulfil trophic and biological functions. Many marine/freshwater migratory
taxa enter estuaries sporadically, especially as juveniles, only to take advantage of
shelter from predators and food abundance. Some are highly euryhaline and move
through the full length of the system (Elliott et al. 2007). In tropical and subtropical
estuaries of the western Atlantic, salinity-dominated ecocline is a major driver influencing spatial and temporal distribution of fish and other fauna. Changes in fish
sizes, diversity and abundance are strong indicatives of environmental variability
into a particular habitat and are associated to seasonal movements of these habitats
due to river flow switches from the dry to the rainy season and back (Barletta et al.
2005, 2008; Dantas et al. 2012; Lima et al. 2015; Ramos et al. 2016).
The management and conservation of estuaries (and consequently of its
resources) should take into account the overlapping of environmental variables and
life cycles of key species for different estuarine reaches and seasons (Figs. 16.7 and
16.8). Abrupt changes in climatic patterns or in the river flow regime will induce
abrupt changes in the estuarine ecocline trends and fish communities will respond
to these changes by modifying assemblage structures. In the Paranaguá Estuary, for
example, during dredging operations, the upper estuary is deepened and alterations
in the geomorphology of the system is responsible to the intrusion of a greater
amount of coastal waters upstream, resulting in changes in fish community (Barletta
et al. 2016). These concepts need to be taken as the basis of descriptors of reference
conditions for regional coastal systems, considering the resilience of the system,
including when under anthropogenic interference (Barletta et al. 2010).
Also important to note, is that tropical and subtropical estuaries usually have a
greater diversity and complexity of habitats, including main channel, flood plain,
intertidal creeks and surrounding mangrove forest (Fig. 16.9a–c) (Reis et al. 2016).
The connectivity of these habitats guarantee that estuarine-dependent fishes complete their life cycle by accessing all the resources and using all the protection they
need. Patterns of estuarine use can differ during the ontogenetic development of fish
species. Larval, juvenile, sub-adult and adult stages of the same species respond
differently to seasonal fluctuations of estuarine ecocline, as well as in the use of
available effective habitats (Barletta-Bergan et al. 2002a, b; Barletta and BarlettaBergan 2009; Ferreira et al. 2016; Lima et al. 2015). This trait is suggested to be a
strategy to avoid competition and predation during the earlier, critical stages. The
estuarine ecocline defines spatial and temporal patterns in community diversity and
structure, population abundance, periods of reproduction and temporary nursery
habitats for juveniles of many socio-economically important fish species (Dantas
et al. 2010; Ferreira et al. 2016; Ramos et al. 2014, 2016).
16 Estuarine Ecoclines and the Associated Fauna: Ecological Information as the Basis…