236
from deep pelagic regions, such as Fraser’s dolphin (−12.8‰), showed the most
13
C-depleted δ
13
C values. In the sub Antarctic region, Riccialdelli et al. (2010) also
showed that isotopic carbon values clearly reflect the inshore-offshore decreasing
gradient of δ
13
C (France 1995; Clementz and Koch 2001). On the other hand, δ
15
N
values also showed this gradient and evidenced the relative trophic level of the species in their habitats. Bottlenose dolphins and killer whales, for example, had high
trophic levels within coastal sub tropical species (Botta et al. 2012), while Pale’s
and hourglass dolphins occupied high trophic positions among the sub Antarctic
dolphin species (Riccialdelli et al. 2010).
Stable isotopes were also used as evidence of putative ecotypes of some odontocetes in the SAO (Riccialdelli et al. 2010, 2012; Botta et al. 2012; Ott et al. 2016).
Two putative ecological stocks of Risso’s dolphins were recognized in sub Antarctic
waters based on significant differences in δ
13
C and δ
15
N values from bone samples
(Riccialdelli et al. 2010, 2012). Both groups were associated to the southern
Argentina continental shelf break, one inhabiting northern areas and the other foraging in higher latitudes. In the SAO off southern Brazilian waters, Botta et al. (2012)
found isotopic evidence for the existence of more than one putative ecotype of bottlenose dolphins and false killer whales.
In tropical SAO, two studies used stable isotopes as ecological tracers of the
trophic structure of food webs that sustain coastal small cetaceans. Furthermore,
both studies also analyzed trace-metals, mercury (Hg) (Bisi et al. 2012; Kehrig et al.
2013) and selenium (Se) (Kehrig et al. 2013) in order to understand their distribution throughout the food web. In southern Rio de Janeiro state, Bisi et al. (2012)
used SIA and total Hg of several components of the biota, including the Guiana
dolphins, to investigate the structure of food webs of Sepetiba, Guanabara and Ilha
Grande bays. Individuals from Guanabara bay had the lowest δ
15
N values, suggesting the contribution of atmospheric nitrogen fixation by cyanobacteria in the region.
Considering the range of δ
15
N found in Guiana dolphins from the three bays, results
corroborate the stomach content analyses, indicating that the species feed on prey of
different trophic levels. Contrary to what was observed in Guanabara bay, some
prey showed higher δ
15
N than dolphins in Sepetiba and Ilha Grande bays. These
locations have high biodiversity, and dolphins there seem to be feeding upon a wider
range of taxa, especially those of lower trophic levels, in comparison to the former.
A similar pattern was observed in a coastal region under the influence of the Paraiba
do Sul river. Stable nitrogen isotopes of Guiana dolphins, fish, cephalopods, crustaceans and mesoplankton revealed five trophic positions along this food web, with
Guiana dolphins and the largehead hairtail (Trichiurus lepturus) occupying the top
of the trophic web (Kehrig et al. 2013). Hg web magnification was higher than Se,
being positively correlated with δ
15
N values. These studies emphasized the useful
application of stable isotopes as tracers for disentangling the complex trophic structure of tropical food webs. Furthermore, the combined use of these tracers provides
important information about biomagnification processes that could affect
top-predators.
E. Seyboth et al.
from deep pelagic regions, such as Fraser’s dolphin (−12.8‰), showed the most
13
C-depleted δ
13
C values. In the sub Antarctic region, Riccialdelli et al. (2010) also
showed that isotopic carbon values clearly reflect the inshore-offshore decreasing
gradient of δ
13
C (France 1995; Clementz and Koch 2001). On the other hand, δ
15
N
values also showed this gradient and evidenced the relative trophic level of the species in their habitats. Bottlenose dolphins and killer whales, for example, had high
trophic levels within coastal sub tropical species (Botta et al. 2012), while Pale’s
and hourglass dolphins occupied high trophic positions among the sub Antarctic
dolphin species (Riccialdelli et al. 2010).
Stable isotopes were also used as evidence of putative ecotypes of some odontocetes in the SAO (Riccialdelli et al. 2010, 2012; Botta et al. 2012; Ott et al. 2016).
Two putative ecological stocks of Risso’s dolphins were recognized in sub Antarctic
waters based on significant differences in δ
13
C and δ
15
N values from bone samples
(Riccialdelli et al. 2010, 2012). Both groups were associated to the southern
Argentina continental shelf break, one inhabiting northern areas and the other foraging in higher latitudes. In the SAO off southern Brazilian waters, Botta et al. (2012)
found isotopic evidence for the existence of more than one putative ecotype of bottlenose dolphins and false killer whales.
In tropical SAO, two studies used stable isotopes as ecological tracers of the
trophic structure of food webs that sustain coastal small cetaceans. Furthermore,
both studies also analyzed trace-metals, mercury (Hg) (Bisi et al. 2012; Kehrig et al.
2013) and selenium (Se) (Kehrig et al. 2013) in order to understand their distribution throughout the food web. In southern Rio de Janeiro state, Bisi et al. (2012)
used SIA and total Hg of several components of the biota, including the Guiana
dolphins, to investigate the structure of food webs of Sepetiba, Guanabara and Ilha
Grande bays. Individuals from Guanabara bay had the lowest δ
15
N values, suggesting the contribution of atmospheric nitrogen fixation by cyanobacteria in the region.
Considering the range of δ
15
N found in Guiana dolphins from the three bays, results
corroborate the stomach content analyses, indicating that the species feed on prey of
different trophic levels. Contrary to what was observed in Guanabara bay, some
prey showed higher δ
15
N than dolphins in Sepetiba and Ilha Grande bays. These
locations have high biodiversity, and dolphins there seem to be feeding upon a wider
range of taxa, especially those of lower trophic levels, in comparison to the former.
A similar pattern was observed in a coastal region under the influence of the Paraiba
do Sul river. Stable nitrogen isotopes of Guiana dolphins, fish, cephalopods, crustaceans and mesoplankton revealed five trophic positions along this food web, with
Guiana dolphins and the largehead hairtail (Trichiurus lepturus) occupying the top
of the trophic web (Kehrig et al. 2013). Hg web magnification was higher than Se,
being positively correlated with δ
15
N values. These studies emphasized the useful
application of stable isotopes as tracers for disentangling the complex trophic structure of tropical food webs. Furthermore, the combined use of these tracers provides
important information about biomagnification processes that could affect
top-predators.
E. Seyboth et al.