Temporary pools provide stability to fish assemblages in Amazon headwater streams

Temporal variations in the environment may function as disturbances that affect population processes and change the structure and composition trajectories of communities. The presence of refuges may buffer such variations and also support the recovery of communities after disturbances. In this study, we tested the effect of temporary pools as seasonal refuges for the ichthyofauna in upland forest streams in the Brazilian Amazon. We sampled environmental characteristics and fish in five occasions over one seasonal cycle in eight stream stretches and their adjacent temporary pools in Reserva Ducke, Manaus. We recorded 27 fish species, 13 of which occurred in both habitats and represented 81% of the total fish abundance in the stream-pool system (3695 records of fish, 54% made in pools). During rainy periods, fish abundance in pools was higher than in the channels. Total number of records varied inversely among habitats over time with a reduction in the pools and an increase in the channels as the pools gradually desiccated. The number of species exhibited a similar pattern. When data from pools and channels were pooled, representing the entire flood zone, fluctuations in all the measured variables along the time were smoothed. The variability in fish assemblage composition was associated with variability in the volume of water in the entire system. These results indicate that temporary pools are an important habitat component of upland forest streams, providing resources and spatial refuges for the fish during rainy periods, and regulating the stability of these communities.