Abstract
In the present study, we examined the effects of different drying conditions on the composition, structure and function of benthic invertebrate assemblages. We approached this objective by comparing invertebrate assemblages in perennial and intermittent sites along two intermittent Mediterranean streams with contrasting predictability, duration, and spatial patterns of drying: Fuirosos (high predictability, short duration, downstream drying pattern) and Rogativa (low predictability, long duration, patchy drying pattern). Specifically, we quantified the contribution of individual taxa to those differences, the degree of nestedness, and shifts in the composition, structure and function of benthic invertebrate assemblages along flow intermittence gradients. We observed greater effects of drying on the benthic invertebrate composition in Fuirosos than in Rogativa, resulting in a higher dissimilarity of assemblages between perennial and intermittent sites, as well as a lower degree of nestedness. Furthermore, a higher number of biotic metrics related to richness, abundance and biological traits were significantly different between perennial and intermittent sites in Fuirosos, despite a shorter dry period compared to Rogativa. At the same time, slightly different responses were detected during post-drying (autumn) than pre-drying (spring) conditions in this stream. In Rogativa, shifts in benthic invertebrate assemblages along increasing gradients of flow intermittence were found for three metrics (Ephemeroptera, Plecoptera and Trichoptera (EPT) and Odonata, Coleoptera and Heteroptera (OCH) abundances and aerial active dispersal. Furthermore, we demonstrated that combined gradients of dry period duration and distance to nearest perennial reach can generate complex, and different, responses of benthic invertebrate assemblages, depending on the flow intermittence metric. Our study advances the notion that special attention should be paid to the predictability, duration and spatial patterns of drying in intermittent streams in order to disentangle the effects of drying on benthic invertebrate assemblages, in particular in areas subject to high spatial heterogeneity and temporal variability in drying conditions.
Highlights
Intermittent streams that periodically cease to flow and dry out are a global phenomenon [1,2,3]
The present study–by comparing streams of different drying conditions–advances our understanding of the different responses of benthic invertebrate assemblages to drying; emphasizing that predictability, duration, and spatial patterns of drying will require major attention in order to disentangle the effects of drying dynamics on stream biota
Benthic invertebrate richness declines with increasing duration of drying and decreasing predictability of event timing along intermittent streams [35]
Summary
Intermittent streams that periodically cease to flow and dry out are a global phenomenon [1,2,3]. Flow intermittence is expected to increase worldwide due to global warming, land-cover changes, and increased water abstraction for human use [9,10,11]. The dry period has been shown to exert a strong selective pressure controlling the structure, composition and biological traits of benthic invertebrates [8, 26, 32,33,34]. Invertebrate assemblages in intermittent streams are characterized by biological traits, which increase their resistance against drying (e.g. eggs, coccons, diapauses) and their resilience after dry events (e.g. aerial dispersal mode) [26, 40,41,42]
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