388
Stable Isotope Analysis (SIA) has had a great impact over many areas of research,
since it offers significant advantages in comparison to traditional methods, such as,
avoiding sacrifice of extinction endangered species, allowing the comprehension of
complex diet networks over large space and time scale, it is cheaper than traditional
methods, it enables open sea and deep-water species studies, beyond diet reconstruction of extinct species, what was simply impossible by stomach content
analysis. Furthermore, contrary to the traditional analysis of stomach content, stable
isotope analysis is not challenged by empty stomachs, and permits a more effective
use of collected individuals for different analysis (Vander Zanden et al. 1998).
Stable isotopes use in marine fish studies has a long history. Harrod et al. (2005)
examined stable isotope analysis to evaluate the ecological plasticity of eels. Cunjak
et al. (2005) demonstrated the use of isotopes as a tracking element of fish movement, combined with use the telemetry and mark-recapture data.
Schlacher et al. (2005) analyzed the relationships between waste water pollution
and isotopes in fish, in this study, he observed that δ15N signatures obtained from
estuarine fish muscles were effective indicators of nitrogen derived from sewage
pollution, since all analyzed fish showed high values of δ15N.
Through the pioneering researches of Smith and Epstein (1971), Minson et al.
(1975), and Haines (1976), it was possible to verify that the isotopic signatures
(expressed as δ) of the consumers were similar to the isotope signatures of associated plants. Therefore, the analysis of stable isotopes proved to be a useful tool to
rebuild diets, characterize trophic relationships, clarify patterns of resource allocation, and construct food webs. As a consequence, the number of studies using this
tool in trophic ecology has increased exponentially in the past years.
Based on trophic niche width, isotope variation indicates higher amplitude in the
diet and its consistency, while low variation can be attributed to a large population
and little consistency, or high amplitude combined with a low population (Vander
Zanden et al. 2000). A higher isotopic variability is directly related to a greater diet
range, while a low variability can reflect a low diet variety used by a population
(Vander Zanden et al. 2000).
Although few studies have used stable isotope analysis to assess diet variability
within and between populations, some researchers have suggested that the change
in isotopic variability offers a promising tool for studying dietary variation at a
population level (Paterson et al. 2006; Syvaranta and Jones 2008).
For a long time muscles (usually white muscles) were used in stable isotope
studies, but it was confirmed that the use of tissues that do not require fish sacrifice,
such as tissues from scales and fins, can be substituded for muscular tissue. Thus a
new moment in the study of stable isotopes arises, using now fish tissues obtained
through non-lethal procedures. These sampling methods can be used to investigate
rare and endangered species, as well as it allows the analysis of fish scales from
scientific collections (Kelly et al. 2006).
Scales can better represent the carbon sources of a fish diet since they are not
influenced by lipid dynamics. However, scales seem to be less sensible to short-term
changes in diet when compared to muscles, therefore, they should only be used to
M. Hostim-Silva et al.
Stable Isotope Analysis (SIA) has had a great impact over many areas of research,
since it offers significant advantages in comparison to traditional methods, such as,
avoiding sacrifice of extinction endangered species, allowing the comprehension of
complex diet networks over large space and time scale, it is cheaper than traditional
methods, it enables open sea and deep-water species studies, beyond diet reconstruction of extinct species, what was simply impossible by stomach content
analysis. Furthermore, contrary to the traditional analysis of stomach content, stable
isotope analysis is not challenged by empty stomachs, and permits a more effective
use of collected individuals for different analysis (Vander Zanden et al. 1998).
Stable isotopes use in marine fish studies has a long history. Harrod et al. (2005)
examined stable isotope analysis to evaluate the ecological plasticity of eels. Cunjak
et al. (2005) demonstrated the use of isotopes as a tracking element of fish movement, combined with use the telemetry and mark-recapture data.
Schlacher et al. (2005) analyzed the relationships between waste water pollution
and isotopes in fish, in this study, he observed that δ15N signatures obtained from
estuarine fish muscles were effective indicators of nitrogen derived from sewage
pollution, since all analyzed fish showed high values of δ15N.
Through the pioneering researches of Smith and Epstein (1971), Minson et al.
(1975), and Haines (1976), it was possible to verify that the isotopic signatures
(expressed as δ) of the consumers were similar to the isotope signatures of associated plants. Therefore, the analysis of stable isotopes proved to be a useful tool to
rebuild diets, characterize trophic relationships, clarify patterns of resource allocation, and construct food webs. As a consequence, the number of studies using this
tool in trophic ecology has increased exponentially in the past years.
Based on trophic niche width, isotope variation indicates higher amplitude in the
diet and its consistency, while low variation can be attributed to a large population
and little consistency, or high amplitude combined with a low population (Vander
Zanden et al. 2000). A higher isotopic variability is directly related to a greater diet
range, while a low variability can reflect a low diet variety used by a population
(Vander Zanden et al. 2000).
Although few studies have used stable isotope analysis to assess diet variability
within and between populations, some researchers have suggested that the change
in isotopic variability offers a promising tool for studying dietary variation at a
population level (Paterson et al. 2006; Syvaranta and Jones 2008).
For a long time muscles (usually white muscles) were used in stable isotope
studies, but it was confirmed that the use of tissues that do not require fish sacrifice,
such as tissues from scales and fins, can be substituded for muscular tissue. Thus a
new moment in the study of stable isotopes arises, using now fish tissues obtained
through non-lethal procedures. These sampling methods can be used to investigate
rare and endangered species, as well as it allows the analysis of fish scales from
scientific collections (Kelly et al. 2006).
Scales can better represent the carbon sources of a fish diet since they are not
influenced by lipid dynamics. However, scales seem to be less sensible to short-term
changes in diet when compared to muscles, therefore, they should only be used to
M. Hostim-Silva et al.