Limnetica 35

Shredder invertebrates are key organisms in the decomposition of leaves in streams. These organisms transform coarse organic matter into fine organic matter, incorporate carbon and nutrients into animal biomass and promote the recycling of terrestrial carbon. Despite their importance in headwater streams, the life history of this shredder taxa and their relationship with organic matter processing is unclear. The main objectives of this study were to evaluate leaf breakdown during two periods of the year and test whether differences in the Phylloicus larvae abundance alter organic matter processing.We incubated leaves of a common native species (Campomanesia xanthocarpa) in the same stream during March (autumn) and October (spring). Samples were collected after 7, 15 and 30 days. After 30 days of incubation, the remaining leaf mass was lower in autumn (30%) than in spring (53%). The breakdown rate (k) was –0.0449±0.0042 day–1 in autumn and –0.0180± 0.0003 day–1 in spring. The abundance of Phylloicus was also higher in autumn than in spring (11.1 ± 1.9 ind/litter bag versus 2.7 ±1.9 ind/litter bag). We observed a positive correlation between Phylloicus abundance and leaf mass loss in autumn (r = 0.74). Our results demonstrate that Phylloicus abundance differs with season and impacts the processing of particulate organic matter. Furthermore, this work highlights the importance of Phylloicus larvae and their contribution to leaf breakdown in subtropical streams.