An unexpected source of invertebrate community recovery in intermittent streams from a humid continental climate

Abstract

Intermittent streams are naturally dominant landscape features of Mediterranean and arid regions, but also occur more and more in humid climates, such as in the Czech Republic. Organism abilities to cope with drying (i.e. resistance forms) have been quantified in naturally intermittent streams from Mediterranean and arid regions, in which long‐term flow intermittence patterns have promoted physiological adaptations. In contrast, the capacity of aquatic communities to persist without requiring resistance adaptations under recent intermittent flow regimes in more humid climates is virtually unexplored, along with its contribution to community recovery upon rewetting. Here, we addressed the ability of aquatic invertebrates devoid of specific desiccation‐resistance forms (e.g. cysts or eggs) to cope with climate change‐induced flow intermittence from rivers in continental climate. Owing to the high relative air humidity, the importance of riparian cover and the short duration of drying events, we expected taxonomically and functionally rich communities to persist in the dry streambed during phases with no surface water and to contribute to community recovery upon flow resumption. To explore these ideas, we collected invertebrate communities in the riverbeds before, during and after drying from 10 intermittent rivers in the Czech Republic. We quantified the pool of organisms remaining alive in the dry riverbeds and determined its taxonomic and functional contribution to the recovery of benthic communities upon rewetting. Of the organisms collected, 83%, belonging to 22 taxa, were able to survive during the dry phase without producing desiccation‐resistance forms. This pool of organisms contributed substantially both taxonomically and functionally to the quick recovery of benthic communities. The exponential decrease in taxonomic and functional richness implies an initial quick loss of sensitive taxa, while a pool of less sensitive taxa persisted long in the dry riverbeds, hence contributing to the fast community recovery upon rewetting. Survival rates of active aquatic macroinvertebrates devoid of specific desiccation‐resistance adaptations have rarely been quantified. Probably promoted by benign environmental conditions prevailing on dry riverbeds in this study, their survival demonstrated the need to protect communities in dry riverbed and their adjacent riparian environments so that assemblages can recover rapidly from short periods without river flow. Riparian forest management along intermittent streams from continental climates could help conserve the value of dry streambeds as a source of resilience for riverine communities.

Fragmentation promotes the role of dispersal in determining 10 intermittent headwater stream metacommunities

“…Arscott et al., 2010). In contrast, in intermittent rivers with abundant refuges during the dry phases, such as braided systems with alluvial hyporheic zones underneath (Vander Vorste et al., 2016), streams with disconnected pools during the dry period (Bonada, Rieradevall, & Prat, 2007), or streams that maintain a high sediment moisture due to high riparian shading (Pařil et al., 2019), community recovery is generally much quicker and occurs within 3–4 weeks. Headwater streams generally lack hyporheic zones, and their relatively small size can preclude the maintenance of pools or humid conditions in their dry riverbeds (Finn, Bonada, Múrria, & Hughes, 2011).…”

Drying in newly intermittent rivers leads to higher variability of invertebrate communities

“…The effects of drying were stronger in RD than in HD networks despite potentially milder conditions during drying events in the RD networks considered here and/or differences in drying duration and timing of post‐drying sampling. For example, dry riverbeds in RD networks remain with relatively high sediment moisture, up to 12% (Pařil, Polášek, et al, 2019), while sediment moisture in HD dry riverbeds is typically lower than 7% (Datry et al., 2012). Such conditions have recently been shown to favour the persistence of invertebrates in the dry riverbed of these RD streams, even for those lacking the physiological adaptations to cope with drying that are generally found in IRs (Pařil, Polášek, et al, 2019).…”

“…We only considered biological traits that may be related to drying (i.e. lifespan, resistance forms, Crabot et al, 2020; Datry, Larned, Fritz, et al, 2014; Pařil, Polášek, et al, 2019). Selected traits characterise life‐cycle features, resilience and resistance features, physiology, morphology, and reproduction and feeding behaviour.…”

“…When no wet refuge is left, only desiccation‐resistant taxa remain, including resistant eggs, larvae, or adults (Strachan et al., 2015; Stubbington et al, 2017). In IRs with suitable sediment structure and sufficient moisture, an invertebrate seedbank of active and dormant invertebrates surviving in sediments can thus be a crucial source of recolonisation (Pařil, Polášek, et al, 2019; Stanley et al., 1994; Stubbington & Datry, 2013; Tronstad et al., 2005). Other taxa cannot persist during drying, and their recovery after drying instead relies on resilience via spatial dispersal (Bogan, Chester, et al, 2017; Chester & Robson, 2011).…”

“…In rivers exposed to such recent flow intermittence (FI), taxa without adaptation could undergo stochastic extinctions following drying events (Chase, 2007). However, the natural responses of aquatic communities to drying are still poorly understood in these systems (Pařil, Polášek, et al, 2019; Strachan et al., 2015), which hinders our capacity to assess how climate change will affect riverine biodiversity globally.…”