Flow increases tolerance of heat and hypoxia of an aquatic insect

Abstract

Recent experiments support the idea that upper thermal limits of aquatic insects arise, at least in part, from a lack of sufficient oxygen: rising temperatures typically stimulate metabolic demand for oxygen more than they increase rates of oxygen supply from the environment. Consequently, factors influencing oxygen supply, like water flow, should also affect thermal and hypoxia tolerance. We tested this hypothesis by measuring the effects of experimentally manipulated flows on the heat and hypoxia tolerance of aquatic nymphs of the giant salmonfly (Plecoptera: Pteronarcys californica ), a common stonefly in western North America. As predicted, stoneflies in flowing water (10 cm s −1 ) tolerated water that was approximately 4°C warmer and that contained approximately 15% less oxygen than did those in standing water. Our results imply that the impacts of climate change on streamflow, such as changes in patterns of precipitation and decreased snowpack, will magnify the threats to aquatic insects from warmer water temperatures and lower oxygen levels.

Going with the flow – how a stream insect,Pteronarcys californica,exploits local flows to increase oxygen availability

“…Our results corroborate field observations of caddisflies and stoneflies, showing that individuals occur more frequently in high-flow microhabitats when bulk flows were low or temperatures high (Kovalak, 1976;Kovalak, 1979;Genkai-Kato et al, 2005). Taken together, these results support the idea that interactions among temperature, oxygen, and flow strongly influence aquatic ectotherm metabolism, performance, and survival (Pörtner, 2007;Rubalcaba et al, 2020;Verberk et al, 2016a b;Harrison et al, 2018;Frakes et al, 2021). In addition, they suggest that aquatic insects exploit mosaics of flow to increase ratios of oxygen supply:demand in nature.…”

“…For water-breathing ectotherms like aquatic insects, the challenge is to extract sufficient oxygen to fuel metabolism, despite low levels of environmental oxygen supply Woods & Moran, 2020). This oxygen problem is complicated further by variation in temperature and water velocity (Woods, 1999;Jacobsen, 2003;Verberk et al, 2011;Frakes et al, 2021;Verberk et al, 2016b). Warmer water modestly increases rates of oxygen supply but raise organismal demand even more (Woods, 1999;Woods & Moran, 2008;Verberk et al, 2011;Verberk & Atkinson, 2013).…”

“…This oxygen problem is complicated further by variation in temperature and water velocity (Woods, 1999; Jacobsen, 2003; Verberk et al, 2011; Frakes et al, 2021; Verberk et al, 2016b). Warmer water modestly increases rates of oxygen supply but raise organismal demand even more (Woods, 1999; Woods & Moran, 2008; Verberk et al, 2011; Verberk & Atkinson, 2013).…”

“…When boundary layers are thin, as in fast-flowing and turbulent water, oxygen diffuses over shorter distances between the water column and respiratory tissues, increasing supply rates (Pinder & Feder, 1990; Hall & Ulseth, 2019). Thus, aquatic ectotherms can tolerate deeper hypoxia and warmer temperatures when water velocities are sufficiently high (Frakes et al, 2021).…”

Future of Freshwater Ecosystems in a 1.5°C Warmer World

“…Threats to freshwater organisms posed by rising water temperatures and associated declines in dissolved oxygen will be exacerbated by climate change impacts on flow regimes (Frakes et al, 2021). Because impacts on water quality and flow regimes will be more or less commensurate to global warming, prospects for freshwater biodiversity are considerably improved under scenarios in which temperature rise is limited to 1.5 °C.…”