Isotopic profile and mercury concentration in fish of the lower portion of the rio Paraíba do Sul watershed, southeastern Brazil

Adélia R M Rocha,Ana Paula M Di Beneditto,Cristina Maria M De Souza,Inácio A Pestana

doi:10.1590/1982-0224-20150047

Adélia R M Rocha, Ana Paula M Di Beneditto + Show 2 more

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https://doi.org/10.1590/1982-0224-20150047

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Abstract

ABSTRACT The aim of this study was to evaluate the isotopic profile and mercury (Hg) concentrations in fish (carnivores, omnivores and detritivores) in the lower portion of the rio Paraíba do Sul watershed, southeastern Brazil. Carbon (δ13C) isotopic analyses revealed that pelagic and benthonic sources are part of the feeding of the fish from the different guilds (-14.0 to -24.8 ‰). The benthic sources are usually enriched in δ13C (-16.9‰, from watershed runoff) compared to pelagic sources because the phytoplankton, important primary producer that supports several pelagic chains, has δ13C signature lighter (-23.9‰). The nitrogen (δ15N) isotopic signatures indicated that most guilds were at the same trophic position (10.0 to 15.5 ‰), except for pelagic omnivorous fish, which had a lower trophic position. Niche overlap was observed among pelagic and demersal carnivorous fish, demersal omnivorous fish, and demersal detritivorous fish. The lower isotopic niche breadth of pelagic carnivorous fish reveals the specialized resource use by this guild. Hg concentrations (ng g-1 dry weight) differed significantly between demersal carnivorous fish (185.3 dry weight; 27.8 wet weight) and demersal omnivorous fish (277.9 dry weight; 41.7 wet weight) and between pelagic omnivorous fish (197.2 dry weight; 29.6 wet weight) and demersal omnivorous fish due to (1) differences in food sources: guilds that fed on bottom resources were more affected by contamination because the sediment is an important Hg accumulator in the study area, and (2) because of its trophic positions. Considering that the fish consumed prey of similar trophic positions, the guilds did not show a well-defined food hierarchy. Therefore, in this study, there was no clear relationship between Hg and δ15N.

Highlights

Trophic dynamics between sympatric species can be understood from their isotopic compositions (BeneditoCecílio et al, 2000; Post, 2002; Layman et al, 2007)
The 22 fish species sampled were grouped into the following trophic guilds: 10 carnivorous fish (6 pelagic and 4 demersal), 9 omnivorous fish (4 pelagic and 5 demersal), and 3 demersal detritivorous fish (Table 1)
Pelagic omnivorous fish showed the lowest Trophic position (TP) value (2.68), which was significantly different for remaining trophic guilds ( p < 0.001) (Table 1)

Summary

Introduction

Trophic dynamics between sympatric species can be understood from their isotopic compositions (BeneditoCecílio et al, 2000; Post, 2002; Layman et al, 2007). Δ13C values are used to trace the origin of the different food sources (DeNiro & Epstein, 1978; Vander Zanden et al, 1997; Fry, 2008), whereas δ15N values are useful to evaluate the species’ trophic position, considering the fractionation along the food chain (Minagawa & Wada, 1984; Post, 2002). Trophic transfer is the main Hg source for consumer organisms, which is verified by the positive relationship between Hg concentration and δ15N values along the links of the food chains (Di Beneditto et al, 2012, 2013).

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