242
The understanding about the feeding ecology of the southern elephant seal
(Mirounga leonina) has also improved through the use of SIA. The δ
13
C and δ
15
N
composition of the vibrissae of individuals from Peninsula Valdés, Argentina, and
one male from Malvinas/Falkland Islands, revealed that males presented a great
between- groups variability in isotopic composition (up to 6‰ δ
13
C and 7‰ δ
15
N),
indicating considerable differences in their main prey item and in their trophic
level (Lewis et al. 2006). Males where considered as specialist foragers with but
variable preferences between groups. The authors attributed this variation to intra
and interspecific competition near the breeding site. Females, on the other hand,
presented a consistent diet (feeding behavior), with a considerable contribution of
invertebrates.
Although δ
18
O are much less used than δ
13
C and δ
15
N in ecological studies, it was
employed to investigate the relationship of sea surface temperature (SST) changes
in the past and with the sealing of South American fur seal (Saporiti et al. 2013).
The oxygen-isotope values used was not from this marine mammal species, but
from the bivalves Aulocomya atra atra and Mytilus edulis. The shell of these organisms assimilates variations in the oxygen-isotope ratio of the water during their
biomineralization, and then their δ
18
O can be used as a proxy to SST values from the
past (Dettman et al. 1999). No relationship was found between fur seals’ densities
and the δ
18
O values in the bivalves’ band shells. Then, the fluctuations in the number
of the seals were attributed to variations in the primary productivity during the second half of the Holocene, because it is related to the availability and quality of food
to the fur seals.
Assuming that the bone apatite also registers δ
18
O of the animals’ diet, it was
used to evaluate the overlap of the areas used by South American sea lion (Otaria
byronia = flavescens), from southern Brazil and from Patagonia and Tierra del
Fuego, in Argentina (Zenteno et al. 2013). The δ
18
O values differed significantly
from one region to another, with Patagonia individuals presenting the higher ones.
This result was expected, once tissues tend to be enriched in
18
O as temperature
declines (Kim and O’Neil 1997) and reveal that they have restricted dispersal movements between the three areas. In addition, it was also found was that the variability
of the δ
18
O values of juveniles of both sexes was wider than for adults, suggesting
that they disperse during this earlier life stage.
9.2.3 Sirenia
The application of SIA for ecological studies in sirenians from the southwestern
South Atlantic, is restricted to only one study on Antillean manatee (Trichechus
manatus manatus) (Ciotti et al. 2014). Values of δ
13
C and δ
15
N were obtained from
samples of bones and teeth at different positions of the manatee’s mandible. One
interesting characteristic of manatee dentition is the continuous tooth replacement,
in which the new tooth emerges in the distal part and moves towards the frontal part
of the arcade, allowing for a chronological analysis of the isotopic composition.
E. Seyboth et al.
The understanding about the feeding ecology of the southern elephant seal
(Mirounga leonina) has also improved through the use of SIA. The δ
13
C and δ
15
N
composition of the vibrissae of individuals from Peninsula Valdés, Argentina, and
one male from Malvinas/Falkland Islands, revealed that males presented a great
between- groups variability in isotopic composition (up to 6‰ δ
13
C and 7‰ δ
15
N),
indicating considerable differences in their main prey item and in their trophic
level (Lewis et al. 2006). Males where considered as specialist foragers with but
variable preferences between groups. The authors attributed this variation to intra
and interspecific competition near the breeding site. Females, on the other hand,
presented a consistent diet (feeding behavior), with a considerable contribution of
invertebrates.
Although δ
18
O are much less used than δ
13
C and δ
15
N in ecological studies, it was
employed to investigate the relationship of sea surface temperature (SST) changes
in the past and with the sealing of South American fur seal (Saporiti et al. 2013).
The oxygen-isotope values used was not from this marine mammal species, but
from the bivalves Aulocomya atra atra and Mytilus edulis. The shell of these organisms assimilates variations in the oxygen-isotope ratio of the water during their
biomineralization, and then their δ
18
O can be used as a proxy to SST values from the
past (Dettman et al. 1999). No relationship was found between fur seals’ densities
and the δ
18
O values in the bivalves’ band shells. Then, the fluctuations in the number
of the seals were attributed to variations in the primary productivity during the second half of the Holocene, because it is related to the availability and quality of food
to the fur seals.
Assuming that the bone apatite also registers δ
18
O of the animals’ diet, it was
used to evaluate the overlap of the areas used by South American sea lion (Otaria
byronia = flavescens), from southern Brazil and from Patagonia and Tierra del
Fuego, in Argentina (Zenteno et al. 2013). The δ
18
O values differed significantly
from one region to another, with Patagonia individuals presenting the higher ones.
This result was expected, once tissues tend to be enriched in
18
O as temperature
declines (Kim and O’Neil 1997) and reveal that they have restricted dispersal movements between the three areas. In addition, it was also found was that the variability
of the δ
18
O values of juveniles of both sexes was wider than for adults, suggesting
that they disperse during this earlier life stage.
9.2.3 Sirenia
The application of SIA for ecological studies in sirenians from the southwestern
South Atlantic, is restricted to only one study on Antillean manatee (Trichechus
manatus manatus) (Ciotti et al. 2014). Values of δ
13
C and δ
15
N were obtained from
samples of bones and teeth at different positions of the manatee’s mandible. One
interesting characteristic of manatee dentition is the continuous tooth replacement,
in which the new tooth emerges in the distal part and moves towards the frontal part
of the arcade, allowing for a chronological analysis of the isotopic composition.
E. Seyboth et al.