On the patterns of biomass transfer in the benthic fauna of an amazonian black-water river, as evidenced by 32P label experiment

Abstract

Leaf litter colonised by aquatic decomposition fungi was labelled with Na2H32PO4 and placed in a submerged litter bank in the Central Amazonian river Tarumã-Mirim. Of a total of 540 animals subsequently collected and analysed, 17% were definitely labelled. The phase-spatial pattern of label indicated that most species, notably fish and shrimps, were territorial with a radius of movement rarely exceeding 1 m; while chironomids and other microfauna are virtually stationary. From the distribution of labelled individuals within the litter bank and the gradual buildup of label it seems the fish feed within the same small area over periods of several weeks. The appearance of label in the shrimps was more erratic. The 32P appeared to be firmly retained within the living cells throughout the experiment and passed via the foodchains previously established by analysis of gut contents. The observed predator/prey density and foraging pattern have important implications for competition theory and the maintainance of species richness. © 1991 Kluwer Academic Publishers.