Using stable isotopes derived trophic position to improve mass-balanced food web models

OCAMPO REINALDO, MATÍAS; BOTTO, FLORENCIA; STORERO, LORENA P.; GONZÁLEZ, RAÚL; IRIBARNE, OSCAR

Viña del Mar

Conferencia; 11th International Conference on the Applications of Stable Isotope Techniques to Ecological Studies (IsoEcol 2018); 2018

Pontificia Universidad Católica de Valparaiso

Food web modelling has become an important research field in marine ecology and a tool for decision making in fisheries management. The ?Ecopath with Ecosim? approach (EwE) is widely used to represent tropic relationships among different groups or species within a given assemblage. However, with fish, these models are usually based on stomach content analyses and bibliographic data about diets in similar environments (with its associated biases and drawbacks), and usually ?similar? species are pooled together into homogeneous or functional groups in order to have an average representation of their diet and trophic connectivity. In this study, a published EwE model of San Matías Gulf demersal community associated to hake was analysed and the trophic levels (TL) of its functional groups were calculated. On the other hand, using stable isotopes data and a Bayesian modelling approach (by means of the tRophicPosition package in R) the individual trophic position (TP) of several species of the demersal community were calculated. The objective was to compare the results of these modelling approaches in order to detect differences in the TL/TP of the species within each functional group. The range of estimations of TL by EwE was wider (2.02 ; 4.64) than the estimations of TP by stable isotopes (3.32 ; 4.49). The highest TL estimated was for the large Argentine hake (TP=4.02, TL=4.64), while the highest TP estimated was for the Angular angel shark (TP=4.49, TL=3.62). On the other hand, within functional groups of lower TL, estimations of TP were higher than estimations of TL values, while in functional groups of higher TL, the estimated TP were lower than the estimated TL values. Also, as expected due to the methodology used to pool species together in EwE, there was a variability in the estimated TP within some functional groups (e.g. medium-sized sharks, flounders), while others showed homogeneous estimations of TP (e.g. small rays, squids, hakes). Our results show that stable isotopes can provide useful information to improve the models developed with EwE, in order to achieve a better understanding of the ecosystem.