Processing of decomposing fruits by macroinvertebrates in a Central Amazonian stream food web

Abstract Food webs in small, forested streams rely heavily on litterfall for energy, but the role of fruitfall remains understudied. We conducted a field experiment comparing the decomposition of two fruits with hard pericarps ( Astrocaryum vulgare and Bactris gasipaes ) and five with soft pericarps ( Genipa americana , Mangifera indica [non-native], Mauritia flexuosa , Syzygium cumini [non-native], and Talisia esculenta ). Whole and cut fruits were incubated in fine- and coarse-mesh litter bags for 62 days to simulate undamaged and vertebrate-damaged fruitfall. We expected that fruits with thin pericarps or cut fruits would decompose faster than hard-pericarp fruits, because both macroinvertebrates and microbes could access the soft tissue. This expectation was partially confirmed; cut fruits generally decomposed faster and supported higher invertebrate richness, while hard-pericarp fruits resisted decomposition regardless of treatment. In the whole fruit experiment, 785 invertebrates were recorded, dominated by Endotribelos (Diptera: Chironomidae; 96%). Abundance was highest in S. cumini and lowest in A. vulgare , with higher values in coarse-mesh bags. A. vulgare had 17× more remaining mass than other fruits, with no mesh-size effects, indicating strong resistance to decomposition. In the cut-fruit experiment, 2715 invertebrates from 14 families were recorded, with A. vulgare again showing the highest remaining mass (34× more than other species). The remaining mass did not differ between mesh types, emphasizing microbial activity. Richness was highest in G. americana and A. vulgare and lowest in M. indica . Intact pericarps limited invertebrate access, as richness increased in cut fruits. Both whole and cut fruits can complement leaf litter as an energy source in Amazonian stream food webs.