Patterns of flow, leaf litter and shredder abundance in a tropical stream

The seasonal dynamics of leaf litter and associated consumers (shredders) in tropical streams are not well documented. We investigated the occurrence of litter (density and age composition) and shredders through late dry, wet and early dry seasons in an Australian rainforest stream. Leaf litter packs of varying density and leaf age covered most of the stream bed in the late dry season, but a one-in-one-year flood removed a substantial proportion of the sparse packs and much of the intermediate-aged litter, with green litter becoming more prevalent. Shredder abundances declined accordingly, but recovery was rapid, demonstrating substantial resilience to the disturbance. In a 36-day field experiment using fine- and coarse-mesh bags, green litter was decomposed more rapidly than intermediate and aged litter by both microbes and shredders, an unexpected and important result, given the abundance of green litter in the study stream. The resilience of shredders to moderate flood, their ability to process green leaves and their continued presence across seasons contribute to seasonal consistency in detrital-based food webs in the study stream except, perhaps, after extreme floods. This study demonstrates the need to consider the temporal changes in litter composition and decomposition in determining the nature of trophic processes in streams.