The duration of channel drying affects survival of Gammarus pulex (Amphipoda: Gammaridae) within subsurface sediments: an experimental flume study

Field studies have demonstrated that benthic fauna use hyporheic sediments during drying events in temporary rivers, but the factors influencing the survival of fauna in subsurface sediments remain poorly quantified. Laboratory mesocosm experiments were conducted to determine how the length of drying events (1, 7, 14 and 21 days) influenced the survivorship of Gammarus pulex (L.) (Amphipoda: Gammaridae). The water level was reduced to 5 cm below the substrate surface during drying experiments and held at 5 cm above the sediment surface during control experiments. The results demonstrate that G. pulex survivorship was reduced with increasing length of the experiment, particularly in the drying treatment compared to the control treatment. We show that G. pulex can persist in subsurface sediments for up to 21 days during surface drying. In view of interacting climatic drivers and water resource pressures that are increasing the spatial and temporal occurrence of streambed drying, our results have important implications for stream management. Our results also highlight the utility of mesocosm-based studies for elucidating the abiotic controls of macroinvertebrate survival during stream drying events.