Abstract
Fish otoliths store geochemical and isotopic signatures that can be used as proxies for environmental conditions in ecological investigations. We investigated the δ13C and δ18O of otoliths of four freshwater fish species (Astronotus ocellatus, Serrasalmus brandtii, Plagioscion squamosissimus, and Cichla ocellaris) from the Moxotó Reservoir in the São Francisco River, Brazil. The enriched δ13C signatures that distinguish A. ocellatus from other species could be caused by dissolved inorganic carbon (δ13CDIC) in reservoir waters. Macrophytes growing along the reservoir margins would favor photosynthetic uptake of 12C, leading to enriched δ13CDIC incorporated into the otoliths of those fish. Otolith δ18O signatures appear to reflect water column preferences, in which species preferentially inhabiting surface waters (such as S. Brandtii) show more enriched values (due to high surface evaporation ratios), while bottom water species show depleted δ18O values. Our results represent the first investigation of the isotopic compositions of fish otoliths in freshwater environments in the São Francisco River, and shed light on the interpretation of isotopic information stored in otoliths and how they can be used to infer the ecological strategies of freshwater fish.
Highlights
Stable isotopes have been used in recent decades to examine interactions between living organism and their surrounding environments, to identify and elucidate gaps in our ecological knowledge, and to track environmental changes in ecosystems (e.g., Rundel et al 1989, Thompson et al 2005)
The carbon isotopic compositions of the species analyzed in this study (Fig. 2) varied from −8.48 to −3.89‰ for S. brandtii, which was similar to the values observed for C. ocellaris, with its δ13C values varying from −8.58 to −4.88‰
The δ13C signature of the species A. ocellatus was statistically distinct from the others, whereas P. squamosissimus was similar to C. ocellaris, but statistically distinct from S. brandtii; the latter was more similar to C. ocellaris (Table I)
Summary
Stable isotopes have been used in recent decades to examine interactions between living organism and their surrounding environments, to identify and elucidate gaps in our ecological knowledge, and to track environmental changes in ecosystems (e.g., Rundel et al 1989, Thompson et al 2005). The application of stable isotopes in ecological studies has helped to increase our understanding of complex processes in many different ecosystems (e.g., carbon flux and food chain relationships) and highlight the importance of this approach as a tool for ecological investigations (Thompson et al 2005, Dawson & Siegwolf 2007). Teleost fish otoliths are hard, long-lived structures composed of calcium carbonate (mostly aragonite and calcite) with well-defined growth bands that can serve as natural archives of past environmental conditions and the life histories of those fish (Radtke et al 1996). During a fish’s life, calcium carbonate is deposited or
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