The hypothesis that leaf litter breakdown in Guinean streams is governed by microorganisms was confirmed, supporting the reported latitudinal shift in decomposers’ contribution to this process. The large body size of dominant macroinvertebrate decomposers (shrimps) only partially compensated for their very low densities. In contrast with other tropical regions mostly dominated by insect larvae, the functional consequences of global warming on these stream ecosystems may be less severe due to the lower sensitivity of crustaceans to temperature increase.