Fine sediment reduces vertical migrations of Gammarus pulex (Crustacea: Amphipoda) in response to surface water loss

Abstract

Surface and subsurface sediments in river ecosystems are recognized as refuges that may promote invertebrate survival during disturbances such as floods and streambed drying. Refuge use is spatiotemporally variable, with environmental factors including substrate composition, in particular the proportion of fine sediment (FS), affecting the ability of organisms to move through interstitial spaces. We conducted a laboratory experiment to examine the effects of FS on the movement of Gammarus pulex Linnaeus (Crustacea: Amphipoda) into subsurface sediments in response to surface water loss. We hypothesized that increasing volumes of FS would impede and ultimately prevent individuals from migrating into the sediments. To test this hypothesis, the proportion of FS (1-2 mm diameter) present within an open gravel matrix (4-16 mm diameter) was varied from 10 to 20% by volume in 2.5% increments. Under control conditions (0% FS), 93% of individuals moved into subsurface sediments as the water level was reduced. The proportion of individuals moving into the subsurface decreased to 74% at 10% FS, and at 20% FS no individuals entered the sediments, supporting our hypothesis. These results demonstrate the importance of reducing FS inputs into river ecosystems and restoring FS-clogged riverbeds, to promote refuge use during increasingly common instream disturbances.

Do benthic invertebrates use hyporheic refuges during streambed drying? A manipulative field experiment in nested hyporheic flowpaths

“…The rapid reduction in surface flow within the lateral channels informed the duration of the experiment because under natural conditions, invertebrates would have to migrate rapidly to avoid substrate drying after channel disconnection. Nevertheless, this duration, such as the short time between sampling periods (several hours), was in accordance with the possible rapid movements of the fauna, as reported in other sampling designs (Gayraud, Philippe, & Maridet, 2000;Holomuzki & Biggs, 2000;Palmer et al, 1992;Sherman & Coull, 1980;Stubbington, Hoggan, & Wood, 2017;Vadher, Stubbington, & Wood, 2015).…”

“…The channel was adjacent to a larger control channel (≈31-m width), which received the diverted water ( Figure 1b). Water flow in the control channel was not significantly affected by the impact channel diversion because its width and its discharge were much higher than those of the side channel , 1992;Sherman & Coull, 1980;Stubbington, Hoggan, & Wood, 2017;Vadher, Stubbington, & Wood, 2015). …”

Direct observations of the effect of fine sediment deposition on the vertical movement of Gammarus pulex (Amphipoda: Gammaridae) during substratum drying

“…This reflects the high clogging potential of 0.5-1 mm compared to 0.125-0.5 mm particles and the ability of larger particles to bridge the interstitial spaces between grains, blocking pathways within the subsurface and reducing sediment porosity/permeability (Boulton et al, 1998;Bo et al, 2007;Vadher et al, 2015). The high clogging potential of the 0.5-1 mm particles was clearly exhibited in this study as this size fraction completely clogged the surface of mesocosms (bridging the majority of surface interstitial pathways) forming a physical barrier (Gibson et al, 2009) through which G. pulex could not penetrate.…”

“…Consequently, a growing number of field experiments have demonstrated the deleterious effects of increased fine sediment content within the subsurface on faunal community structure and function within lotic systems (Richards & Bacon, 1994;Bo et al, 2007;Larsen et al, 2011;Buendia et al, 2013;Jones et al, 2015). The direct effects of surface (Navel et al, 2010;Vadher et al, 2015) and subsurface (Mathers et al, 2014) clogging/colmation on the vertical movement of macroinvertebrates has, however, only been characterised and quantified more recently, using ex situ experiments. These have demonstrated that sedimentation has a limiting and deleterious effect on macroinvertebrate vertical movements within subsurface sediments (Navel et al, 2010;Mathers et al, 2014;Vadher et al, 2015).…”

“…The direct effects of surface (Navel et al, 2010;Vadher et al, 2015) and subsurface (Mathers et al, 2014) clogging/colmation on the vertical movement of macroinvertebrates has, however, only been characterised and quantified more recently, using ex situ experiments. These have demonstrated that sedimentation has a limiting and deleterious effect on macroinvertebrate vertical movements within subsurface sediments (Navel et al, 2010;Mathers et al, 2014;Vadher et al, 2015).…”