12 Instream refuges are places where invertebrates persist during disturbances due to 13 reduced adverse impacts. During droughts, low flows may be accompanied by 14 elevated temperatures, and potential refuges including subsurface sediments and 15 spring-fed headwaters are therefore characterized by hydrological and thermal 16 stability. This study examined invertebrate use of benthic and interstitial habitats 17 (analogous to the hyporheic zone) in a groundwater-dominated, perennial

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... 18 spring during a supra-seasonal drought. Although exceptionally high air temperatures 19 occurred as flow declined, environmental conditions in the spring were relatively 20 stable, and refuge-seeking vertical migrations into interstitial habitats did not coincide 21 with peak temperatures. However, maximum benthic abundance of two amphipods 22 (Gammarus pulex and Crangonyx pseudogracilis) occurred shortly after the period of 23 elevated temperatures. It is suggested that this temporary increase in the abundance of 24 these mobile taxa reflected upstream migrations triggered by a combination of refuge-25 seeking behaviour and thermally-stimulated activity. In addition, the spring provided 26 a passive refuge for many lotic invertebrate taxa. A conceptual model is presented, 27 which illustrates the potential contribution of multiple refuges to invertebrate 28 persistence in drought-impacted ecosystems. 29 30