Testing the Role of Sediment-Mediated Interactions between Tadpoles and Armored Catfish in a Neotropical Stream

In Neotropical streams, benthic sediment affects community structure and may impose energetic costs for some species yet to be a resource for others. This study tested the hypothesis that removal of benthic sediment through ingestion by Rana palmipes (Ranidae), a detritivorous tadpole, facilitated the growth of Ancistrus triradiatus (Loricariidae), an algivorous armored catfish. We hypothesized that sediment removal by Rana would reduce energetic costs to respiration or digestion encountered by Ancistrus when grazing on periphyton and increase available periphyton biomass. Growth of Ancistrus was measured in a Venezuelan piedmont stream in enclosure cages in which the presence of Rana and ambient sediment levels were manipulated. Benthic sediment accumulation differed significantly between treatments. Growth of Rana was greater when sediments were present than when sediments were removed. However, there was no effect of sediment removal on Ancistrus growth. Total biomass of periphyton did not differ between treatments, because epipelic diatoms were abundant in benthic sediments and presumably compensated for any negative effects of shading by sediments on total periphyton biomass. Organic-rich sediment in this system provides a net energetic benefit to Rana. The consequences of sediment for Ancistrus are less clear, but we found no evidence of a net cost. If interspecific facilitation by Rana occurs, it is likely limited to systems where sediment is organic-poor or to species for which costs of organic-rich sediment exceed benefits.