Experimental dietary manipulations and concurrent use of assimilation-based analyses for elucidation of consumer-resource relationships in tropical streams

The relative contribution of autochthonous foods to consumer biomass in small tropical streams is unknown, but extrapolation of findings from temperate forest streams, where food webs are based on allochthonous resources, might be misleading. Experimental dietary manipulations were conducted to investigate the food used by the snail Brotia hainanensis (Pachychilidae), a generalist primary consumer common in Hong Kong streams, through the concurrent use of stoichiometry, stable isotope analysis (SIA) and fatty acid (FA) profiling. Juvenile B. hainanensis collected from the field were cultured under laboratory conditions and fed with conditioned leaf litter, periphyton or commercial fish-food flakes for 6 months and then compared with field-collected snails at the end of the trial. The results of the SIA and FA profiling showed that snails depended primarily on algal food. Prolonged feeding with leaf litter put B. hainanensis under elemental constraints and litter-fed snails deviated from strict stoichiometric homeostasis. Periphyton-fed, flake-fed and field-collected snails contained more total lipids and autochthonous FA biomarkers than litter-fed snails. The concurrent application of assimilation-based analyses allowed effective and accurate elucidation of consumer-resource relationships and, in the present study, confirmed the importance of autochthonous energy in a tropical stream food web. This approach will be useful for investigating complex trophic interactions. © CSIRO 2008.