Carbon sources of Amazonian fisheries

Variation in the seasonal and spatial isotopic composition of plant C-4 (aquatic macrophytes) and C-3 (forest, C-3 aquatic macrophytes and algae), and that of fish [Prochilodus nigricans Agassiz, Mylossoma duriventre (Cuvier), Colossoma macropomum (Cuvier), Semaprochilodus insignis (Schomburgk) and S. taeniurus Steindachner] in the Amazon floodplain were analysed to test whether the fisheries deliver plant carbon to the population of Manaus in the same proportion as it is available in the floodplain. The contribution of C-4 plants was significantly lower in C-13 during the season of high water levels and increased toward the west of the basin. Mylossoma duriventre and C. macropomum changed delta(13)C levels, while the delta(13)C of P. nigricans and C. macropomum shifted spatially. The contribution of C-4 to the fisheries yield was small. C-3 plants (excluding phytoplankton) also contributed less than expected. This was explained by the importance of detritivores to the yield of the fisheries and the dependence of these species on algal carbon.