Gammarus pulex (Crustacea: Amphipoda) avoids increasing water temperature and intraspecific competition through vertical migration into the hyporheic zone: a mesocosm experiment

Abstract

The saturated interstices below and adjacent to the riverbed (i.e., the hyporheic zone) can be a refuge for biota during low flows, flow cessation and river drying. Prior to complete drying, organisms are constrained by abiotic and biotic factors (e.g., water temperature, competition) and may respond through vertical migration into the hyporheic zone. However, it remains unclear when temperature and competition become harsh enough to trigger migration. Furthermore, potential consequences of using the hyporheic zone, which is often food-limited, on the survival, effects on ecosystem function and physiology of organisms are unknown. We tested the hypotheses that (1) Gammarus pulex, a widespread detritivore, migrates into the hyporheic zone to avoid increasing surface water temperature and intraspecific competition and (2) that these factors would reduce their survival, leaf mass consumption and energy stores. Using 36 mesocosms, three temperature (15, 20, 25°C) and species density levels (low, medium, high) were manipulated in a factorial design over 15 days. Increasing temperature to 25°C and a threefold increase in density both caused G. pulex to vertically migrate, and the interaction of these factors was additive, rather than antagonistic or synergistic. Importantly, survival, leaf consumption and glycogen content were reduced in high temperature and density treatments, suggesting tradeoffs between tolerating harsh surface conditions and limitations of inhabiting the hyporheic zone. Identifying that the hyporheic zone is used by G. pulex to avoid high water temperature and intraspecific competition is a key finding considering the global-scale increases in temperature and flow intermittence.

Drying duration and stream characteristics influence macroinvertebrate survivorship within the sediments of a temporary channel and exposed gravel bars of a connected perennial stream

“…A range of studies have examined the effect of dry periods and flow permanence (perennial, intermittent and ephemeral streams) on community structure, often demonstrating that different dry phase duration controls community composition (e.g. Feminella, 1996;Bonada, 2007b;Arscott et al, 2010;Datry, 2012;Storey, 2016); although knowledge regarding the effects of stream drying on individual populations remains limited (but see Vander Vorste et al, 2017). In a number of studies amphipod crustaceans have been identified as keystone species and where suitable subsurface sediments exist can migrate from benthic to subsurface habitats (e.g.…”

Mesocosm experiments reveal the direction of groundwater–surface water exchange alters the hyporheic refuge capacity under warming scenarios

“…Typical consequences include geographical range shifts in animal and plant communities (Holzinger, Hülber, Camenisch, & Grabherr, ; Root, Price, Hall, & Schneider, ; Walther et al., ), habitat loss or fragmentation (Mantyka‐Pringle, Martin, & Rhodes, ) and altered food‐web interactions (Kratina, Greig, Thompson, Carvalho‐Pereira, & Shurin, ; Ledger et al., ; Woodward, Dybkjær, et al., ). As most aquatic animals are ectotherms, they are highly sensitive to temperature increases (Daufresne, Lengfellner, & Sommer, ; Daufresne, Roger, Capra, & Lamouroux, ; Sibly & Atkinson, ; Vander Vorste, Mermillod‐Blondin, Hervant, Mons, & Datry, ). So changes to river thermal regimes alter freshwater community diversity and composition (Brown, Hannah, & Milner, ; Datry et al., ; Leigh et al., ).…”

“…The hyporheic zone (HZ), defined as the saturated interstices below and adjacent to river channels (White, ) in which groundwater and surface water mix (Krause, Hannah, Fleckenstein, et al., ), can provide a refuge for river animals (Palmer, Bely, & Berg, ; Stubbington, ; Vander Vorste, Mermillod‐Blondin, Hervant, Mons, Datry, et al., ). Refuges, sensu Sedell, Reeves, Hauer, Stanford, and Hawkins (), can favour the survival of many riverine species including invertebrates and fish, particularly in a context of global change (Keppel et al., ; Ledger & Milner, ).…”

“…Refuges, sensu Sedell, Reeves, Hauer, Stanford, and Hawkins (), can favour the survival of many riverine species including invertebrates and fish, particularly in a context of global change (Keppel et al., ; Ledger & Milner, ). Because the HZ is characterised by reduced daily and annual temperature amplitudes compared with surface water (Hannah, Webb, & Nobilis, ; Krause, Hannah, & Blume, ), it is a potential refuge for surface river invertebrates during adverse thermal conditions (Palmer et al., ; Stubbington, ; Vander Vorste, Mermillod‐Blondin, Hervant, Mons, Datry, et al., ). Surface and HZ habitats are vertically interconnected by upwelling (exfiltration) and downwelling (infiltration) fluxes of water, solutes and invertebrates (Boulton, Findlay, & Marmonier, ; Brunke, Gonser, Brunke, Gonser, & Gonser, ).…”

“…Therefore, the HZ represents a potential thermal refuge for surface invertebrates when surface temperatures become unfavourable. Early signals of the amphipod Gammarus pulex actively using the HZ to avoid exposure to elevated temperatures (Vander Vorste, Mermillod‐Blondin, Hervant, Mons, Datry, et al., ; Wood, Boulton, Little, & Stubbington, ) or desiccation (Vadher, Stubbington, & Wood, ; Vander Vorste, Mermillod‐Blondin, Hervant, Mons, Forcellini, et al., ) have been detected in natural systems. Hence, the HZ may mitigate the negative effects of climate warming on invertebrate resilience and associated ecosystem processes, such as organic matter decomposition (Kawanishi, Inoue, Dohi, Fujii, & Miyake, ; Stubbington, ; Vander Vorste, Mermillod‐Blondin, Hervant, Mons, Datry, et al., ).…”