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XIV Reunião de Trabalho de Especialistas em Mamíferos Aquáticos da América do Sul (RT) 8º Congresso da Sociedade Latinoamericana de Especialistas em Mamíferos Aquáticos (SOLAMAC) Florianópolis (SC), 24 a 28 de outubro de 2010
INSIGHTS ON TROPHIC RELATIONSHIP OF DELPHINIDS FROM SOUTHEAST BRAZILIAN COAST DETERMINED BY CARBON AND NITROGEN STABLE ISOTOPIC RATIOS Bisi, T. L.1,2,3; Dorneles, P. R.1,2; Lailson-Brito, J.2; Lepoint, G.4; Azevedo, A. F.2; Malm, O.1; Das, K.4 1
Laboratório de Radioisótopos, Instituto de Biofísica/UFRJ, Rio de Janeiro, Brasil, tbisi@yahoo.com.br
2
Laboratório de Mamíferos Aquáticos e Bioindicadores "Profa. Izabel Gurgel" (MAQUA), Faculdade de Oceanografia/UERJ, Rio de Janeiro, Brasil 3
Programa de Pós-Graduação em Ecologia/UFRJ, Rio de Janeiro, Brasil
4
Centre MARE, Laboratoire d’Oceanologie, Université de Liége, Belgique
Carbon and nitrogen stable isotope measurements constitute a useful tool to access potential primary sources and trophic levels of marine organisms. In order to investigate trophic distinctions among delphinids that occur in marine environments from Rio de Janeiro State, carbon and nitrogen stable isotope ratios (δ13C and δ15N) were measured in muscle samples from 10 species, including delphinids that inhabit estuarine (Sotalia guianensis, n=19), continental shelf (Stenella frontalis, n=9; Tursiops truncatus,n=6; Steno bredanensis, n=3; Pseudorca crassidens, n=2; and Delphinus delphis, n=1) and oceanic environments (Lagenodelphis hosei, n=10; Stenella attenuata, n=2; Stenella longirostris, n=1; and Grampus griseus n=1). As lipids have been shown to be depleted in 13C relatively to the diet, they were extracted from samples using repeated rinses with 2:1 chloroform:methanol mixture prior to analysis. Stable isotope measurements were performed on a V.G. Optima Isotope Ratio Mass Spectrometer (IR-MS) coupled to an N-C-S elemental analyzer (Carlo Erba). Carbon isotopic ratios varied significantly among the groups (ANOVA test F2,51=190.45; p<0.05) and the values ranged from -14.44‰ to -12.27‰ in estuarine dolphins, from -16.07‰ to -14.22‰ in continental shelf (CS) species and from -17.26‰ to -15.76‰ in oceanic delphinids. Our findings probably reflected differences among the three groups regarding not only the feeding grounds, but also the species/size preyed. The oceanic species, for instance, were significantly depleted in δ13C (Tukey HSD test p<0.05), which reflected the offshore contribution to food intake. The δ15N values varied significantly among the groups as well (ANOVA test F2,51=16.48; p<0.05). Estuarine and CS species showed the highest average δ15N values, 14.44‰ (min-max=12.22-16.18) and 14.27‰ (min-max=11.57-16.69), respectively whereas oceanic delphinids showed the lowest values, 12.30‰ (min-max=10.04-13.76). Considering the species separately, S. attenuata and L. hosei showed the lowest mean nitrogen isotopic ratios, 11.27‰ and 12.62‰, respectively. S. guianensis, T. truncatus and P. crassidens showed the highest values, 14.44‰, 14.81‰ and 15.30‰, respectively (Tukey HSD test p<0.05). These nitrogen-related findings are probably a result of a combination of factors, such as size and trophic level of the prey ingested by each predator species. As extreme examples are the ingestion of small mesopelagic myctophid fish by L. hosei, as well as the possible predation on other marine mammals by P. crassidens. This study brought new insights on feeding ecology of delphinid species that inhabit Rio de Janeiro region. Keywords: trophic ecology, stable isotopes, Delphinidae
Financial support: CAPES (fellowship), “Pensa Rio” Program/FAPERJ (Proc. E-26/110.371/2007), APQ12009/1 - FAPERJ (Proc. E26-110.858-2009), Universal/CNPq (480701/2009-1) and Cetacean Society International grant.
Sociedade Latinoamericana de Especialistas em Mamíferos Aquáticos – SOLAMAC