Behavioral response of the freshwater cyclopoid copepod Eucyclops serrulatus to hydropeaking and thermopeaking in a laboratory flume

Abstract

The generation of electricity by hydropower plants meets the requirements for intermittent energy demand and for the production of renewable energy. However, the hydropower plant operation has important consequences for the biotic compartment of the river reaches downstream. Intermittent release of water causes sudden variations in discharge that increase bed shear stress and dislodge benthic organisms. Release from high-elevation reservoir can also affect the thermal regime of the river by causing sharp variations in water temperature. Because the hydrodynamic and thermal waves separate while propagating downstream, the benthic community is exposed to two distinct stressors that affect taxa differently based on their sensitivity and adaptations. We investigated separately the effects of a sudden variation in discharge or in water temperature on the small-scale swimming behavior of a widespread species of cyclopoid copepod in a laboratory flume that allows the tracking of organisms both in the water column and in a transparent sediment bed. We gradually varied the discharge or the temperature of the water to mimic the artificial changes caused by hydropower plants. We tracked copepods in three dimensions and quantified the kinematics of their motion. Copepods increased substantially their counter-current swimming effort in response to increasing flow velocity. This behavioral response seems to occur above a threshold in flow velocity of approx. 40 mm/s. It results in a substantial reduction in their downstream transport and hence opposes drift. Copepods reacted differently to warm and cold variations in temperature. Decreasing temperature resulted in a substantially lower counter-current swimming effort, which may therefore increase drift. Rising temperature had no clear effect on their behavior. Our study highlights the importance of understanding the behavioral traits that mediate the response of stream invertebrates to disturbances in the hydraulic and thermal regimes of their environment.

Beneath the surface: Application of transparent super absorbent polymer substrates to track faunal activity within the sediment layer

“…Prior to experiments, SAP substrates were placed in a bucket of deionised water and left overnight to swell to their maximum size (containing 90% water at this point and soft in texture). All efforts were made to ensure that the experimental sediment layer was densely packed to mitigate differ- This experimental setup has been used to successfully observe the swimming behaviour of benthic copepods within the water column of a small volume (~1 L) of the flume (Sidler et al, 2017(Sidler et al, , 2018 but to date has not been tested to observe organisms within deeper sediment layers. Here we also stitch together several camera views as described below to observe fauna in the sediment layer of the whole experimental flume area.…”

“…Experiments were conducted in a custom‐made recirculating acrylic glass flume (dimensions 179 cm long by 27.5 cm wide by 49.5 cm high; Figure S1; following Sidler, Michalec, Detert, & Holzner, 2017; Sidler et al., 2018). The sediment layer consisted of SAP spheres derived from polyacrylamide with a diameter of 8–12 mm (M2 Polymer Technologies, 2020), which were kept in place using an acrylic frame and butterfly netting (mesh size 8 mm).…”

“…Water temperatures were allowed to fluctuate under ambient air temperatures (20.2 ± 0.3°C). This experimental setup has been used to successfully observe the swimming behaviour of benthic copepods within the water column of a small volume (~1 L) of the flume (Sidler et al., 2017, 2018) but to date has not been tested to observe organisms within deeper sediment layers. Here we also stitch together several camera views as described below to observe fauna in the sediment layer of the whole experimental flume area.…”

“…Within freshwater ecology, several methods have been employed that seek to study the response of organisms to biotic and abiotic cues. These include: the deployment of passive integrated transponder tags and radio telemetry that enable monitoring of invertebrate and vertebrate movements (Barbin Zydlewski, Haro, Whalen, & McCormick, 2001; Cooke et al., 2013); experimental observations of avoidance behaviours and locomotion levels to predation and competition (Alexander & Covich, 1991; Haddaway, Vieille, Mortimer, Christmas, & Dunn, 2014), and abiotic stresses (Conroy et al., 2018; Wood, Toone, Greenwood, & Armitage, 2005) and; flume studies to observe small scale movement patterns and responses to flow variations (Lancaster et al, 2006; Sidler, Michalec, & Holzner, 2018). However, all of these methods have focussed on quantifying the activity of freshwater biota within the water column / surface sediments, whilst studies investigating activity within the sediment layer are rare.…”

The Influence of the Recording Time in Modelling the Swimming Behaviour of the Freshwater Inbenthic Copepod Bryocamptus pygmaeus

“…In zooplankton ecology, trajectory analysis has gained increasing impetus over past decades thanks to the advent of computer-assisted video analysis tools, allowing users to adopt a more quantitative, objective and consistent approach to describe behavioural parameters (e.g., speed, percentage of activity, area exploitation, thigmotaxis, phototaxis, chemotaxis and encounter probability) [2][3][4]. This quantitative approach also gave the possibility to explore and statistically analyse the behavioural alterations induced by the exposure to specific compounds [5,6], increasing salinity [7,8] or temperature fluctuations [9]. With few exceptions, nowadays tracking analysis relies on digital video-based recording permitting a frame-by-frame software encryption of the animal movement pattern into a grid of pixels.…”