Leaves as “crackers”, biofilm as “peanut butter”: Exploratory use of stable isotopes as evidence for microbial pathways in detrital food webs

Laboratory experiments have shown benthic macroinvertebrates to be capable of consuming heterotrophic organisms which develop on decomposing terrestrial leaves. Questions remain, however, as to whether these microbial biofilms represent a significant energy source to macroinvertebrates within the natural environment compared to that supplied by leaf substrates themselves. A compilation of literature data on field measurements of stable nitrogen isotope ratios for herbivorous macroinvertebrates suggests that assimilation of microbial biofilms may be the principle means by which allochthonous organic matter enters freshwater detrital food webs.