Carbon from littoral producers is the major source of energy for bottom-feeding fish in a tropical floodplain

Abstract

Bottom-feeding fish show great variation in trophic morphology, resulting in a wide array of feeding habits exploiting from periphyton in littoral habitats to ingesting larger amounts of litterfall from terrestrial habitats. Nevertheless, it has been proposed that, in temperate aquatic systems, the energetic demands from bottom-feeding fish are supplied by primary production from phytoplankton in pelagic habitats. Thus, we aimed to determine which of several energy sources support bottom-feeding fish in tropical aquatic systems, where primary producers are diverse. We performed samplings in the Parana River floodplain from primary producers in littoral (periphyton), pelagic (phytoplankton) and terrestrial habitats (riparian vegetation). Using simultaneous signatures of C and N isotope ratios, we analysed the possible origin of available energy in muscles of nine different bottom-feeding fish species. We verified that seven of the nine fish species had the highest contribution of carbon from a littoral source compared to other energy sources, independent of trophic category. The importance of periphyton may be related to the high abundance of substrates (such as macrophytes) that are available in the littoral zone of tropical aquatic systems. Finally, we suggest that the actual carbon dynamics among bottom-feeding fish and primary producers is species-specific, varying within the same trophic guild, and therefore, it is possible to refute the assumption that each trophic guild is specialised for a distinct carbon source.