243
Variations in the isotopic values of teeth suggest temporal differences in the contributions of macroalgae and seagrasses during the life of some individuals. In addition, interindividual variations were related to differences in the use of the feeding
area. Individuals with lower variations in the isotope values were assumed to have
higher site fidelity, while those with more variable values, were associated to more
mobile animals.
9.3 Trace Elements
This method is based on the connection between the concentrations of chemical
elements in tissues of an organism to the environment where it lives. The most common elements used for the application of this technique are barium (Ba) and strontium (Sr). Considering that their bioavailability are, respectively, negatively and
positively correlated to the salinity of aquatic environments (Jacquet et al. 2005),
they can be used as biochemical tracers to track animals habitat use (e.g. Elsdon and
Gillanders 2005; Albuquerque et al. 2012).
In this case, the use of inert tissues, as tooth and bones, are very useful, because
they have marks that can be related to the age of the animal, and then to a period of
life in which it used habitats with different biogeochemical characteristics. To our
knowledge, among marine mammals, just cetaceans have already been studied
using this technique. Botta et al. (2015) used Ba/Ca and Sr/Ca ratios in teeth from
dolphins stranded or incidentally killed in fishing gear in Brazil and Uruguay. Two
of the species (the Amazon River dolphin, Inia geoffrensis, and tucuxi, Sotalia fluviatilis) were typical of freshwater environments and other two (franciscana and
Guiana dolphin), from marine coastal regions subject to different degrees of freshwater discharge. Ba/Ca results well represented the salinity gradient and this ratio
was considered useful as natural marker for habitat use in marine mammals.
9.4 Final Considerations
Some advantages of the SIA method can be recognized considering the studies presented here and the contribution of them to different species knowledge and conservation. Compared to the traditional method of gastro-intestinal content, the main
advantages of stable isotope to be considered are: (i) the resolution of the pathways
in the food web if the pathways are well distinguished by δ
13
C values; (ii) the possibility of indicate the nutritional roles of prey items, as stable isotopes are a result
of the diet absorved and not consumed by the predator; (iii) the estimation of the
trophic level of the organisms, if the basal isotope composition of the food web is
known (e.g. Polunin and Pinnegar 2002); and (iv) the possibility of following ontogenetic changes and individual consistency and specialization through longitudinal
analysis of chronologically ordened structures such as teeth and vibrissae.
9 Using Chemical Elements to the Study of Trophic and Spatial Ecology in Marine…
Variations in the isotopic values of teeth suggest temporal differences in the contributions of macroalgae and seagrasses during the life of some individuals. In addition, interindividual variations were related to differences in the use of the feeding
area. Individuals with lower variations in the isotope values were assumed to have
higher site fidelity, while those with more variable values, were associated to more
mobile animals.
9.3 Trace Elements
This method is based on the connection between the concentrations of chemical
elements in tissues of an organism to the environment where it lives. The most common elements used for the application of this technique are barium (Ba) and strontium (Sr). Considering that their bioavailability are, respectively, negatively and
positively correlated to the salinity of aquatic environments (Jacquet et al. 2005),
they can be used as biochemical tracers to track animals habitat use (e.g. Elsdon and
Gillanders 2005; Albuquerque et al. 2012).
In this case, the use of inert tissues, as tooth and bones, are very useful, because
they have marks that can be related to the age of the animal, and then to a period of
life in which it used habitats with different biogeochemical characteristics. To our
knowledge, among marine mammals, just cetaceans have already been studied
using this technique. Botta et al. (2015) used Ba/Ca and Sr/Ca ratios in teeth from
dolphins stranded or incidentally killed in fishing gear in Brazil and Uruguay. Two
of the species (the Amazon River dolphin, Inia geoffrensis, and tucuxi, Sotalia fluviatilis) were typical of freshwater environments and other two (franciscana and
Guiana dolphin), from marine coastal regions subject to different degrees of freshwater discharge. Ba/Ca results well represented the salinity gradient and this ratio
was considered useful as natural marker for habitat use in marine mammals.
9.4 Final Considerations
Some advantages of the SIA method can be recognized considering the studies presented here and the contribution of them to different species knowledge and conservation. Compared to the traditional method of gastro-intestinal content, the main
advantages of stable isotope to be considered are: (i) the resolution of the pathways
in the food web if the pathways are well distinguished by δ
13
C values; (ii) the possibility of indicate the nutritional roles of prey items, as stable isotopes are a result
of the diet absorved and not consumed by the predator; (iii) the estimation of the
trophic level of the organisms, if the basal isotope composition of the food web is
known (e.g. Polunin and Pinnegar 2002); and (iv) the possibility of following ontogenetic changes and individual consistency and specialization through longitudinal
analysis of chronologically ordened structures such as teeth and vibrissae.
9 Using Chemical Elements to the Study of Trophic and Spatial Ecology in Marine…