Intense droughts affect temporal stability of Amazonian stream fish assemblages

Abstract

Abstract The frequency and duration of exceptionally intense droughts is increasing as a consequence of ongoing climate change in many regions of the planet. Lower rain fall in some regions and the increasing in the use of water resources by human populations is increasing the number of water bodies experiencing drying processes. Such changes in ecosystem dynamics have direct impacts on biological communities. Here, we investigated the temporal structure of fish assemblage in terra‐firme (i.e., non‐floodable) streams in the Eastern Brazilian Amazon by sampling over three seasonal cycles (2012, 2013, 2014). The research investigated the temporal dynamics of the ichthyofauna of streams that experienced temporary flow interruption in 2012; using the ichthyofauna of perennial streams (not interrupted by the effects of drought) as controls to determine the effects of flow cessation on the temporal structure of fish assemblages and their recovery after drought. The species composition of perennial streams remained stable over 3 years (2012, 2013, 2014), not differing between the dry and rainy periods. On by contrast, the species composition of the streams that temporarily dried changed after the flow interruption event. Responses to the temporary flow interruption were not uniform among species, with some increasing in abundance after the event while others decreased. The species whose abundance increased immediately after flow interruption tended to return to initial conditions in the third year of sampling, which might be related to low resource availability in those streams. Species whose abundance decreased tended to remain in low abundance, possibly as a result of local/regional rarity of these species, hindering population restoration processes. The dissimilarity in fish assemblage composition (based on the relative abundance of species) between sampling events revealed that the changes caused by the temporary flow interruption were significantly greater than the temporal changes recorded in perennial streams. Overall, the results indicated that intense drought events may alter fish species composition in terra‐firme streams and that such changes may persist for some years. Our results also provide evidence that the responses of fish species to flow regime change are not uniform, highlighting the need for a better understanding of the basic biology of fishes to predict the effects of increased climate disturbances more accurately in aquatic communities. Untangling the effects of natural cyclical factors from the effects deriving from unpredictable extreme events is crucial to better predict the impacts of global climate change on the structure of biological communities.