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January 3 - Febuary 28, 2021

Meeting Abstract

P5-9  Sat Jan 2  Temperature and oxygen tolerance limits of an aquatic insect depend strongly on water flow Frakes, JI*; Birrell, JH; Shah, AA; Woods, HA; Univ. Montana; Univ. Montana; Univ. Montana; Univ. Montana

For aquatic insects, extracting sufficient oxygen from water is challenging, as molecules of oxygen move approximately 300,000 times slower and are ~33 times less abundant in water than in air. Interactions among abiotic factors, including temperature, oxygen concentration, and flow, influence supply and demand of oxygen to aquatic organisms. Although recent studies have focused on the joint effects of temperature and oxygen, they have largely ignored the effect of flow. Low flows generate thick boundary layers— regions of slow-moving fluid that form around solid objects in a liquid. The boundary layers that form around respiratory exchange surfaces of an aquatic insect, for example, can act as barriers to oxygen diffusion when they are thick, as in slow-moving water. Thus, flow should alter oxygen delivery to insects and should modify sensitivity to other abiotic factors like temperature and oxygen concentration. We tested this hypothesis by subjecting salmonfly nymphs to temperature and oxygen ramps with flow and without flow. We recorded two behavioral stress responses; loss of righting response and ventilatory ‘pushups’. We show that water flow velocity strongly influenced respiratory oxygen supply to an aquatic invertebrate (stonefly, P. californica), presumably by altering the rate of delivery. As predicted, the addition of flow (10 cm s-1) increased heat tolerance by ~4ºC and hypoxia tolerance by an average of 15% of oxygen levels at air saturation. Climate change is predicted to alter abiotic factors in streams worldwide. Our results indicate that warming paired with reduced oxygen concentrations and/or flow in streams may challenge many aquatic ectotherms.