Stroud Research pinpoints warmer water as significant threat to mayflies

New research by Stroud Water Research Center has disproved a common hypothesis for why mayflies, which are frequently used as indicators of stream health, display poorer growth when stream temperatures rise as a result of climate change or lack of tree shade.

“Cold-blooded aquatic species like mayflies metabolize oxygen faster in warmer temperatures, so it was thought that the increased demand for oxygen exceeded the supply, which in turn resulted in poorer outcomes,” explained Research Scientist David Funk of Stroud Water Research Center.

He and fellow scientists Bernard Sweeney and John Jackson, also from the Stroud Center, tested the theory by raising two different mayfly species in high-oxygen environments across a range of temperatures.

Surprisingly, despite plenty of oxygen, the mayflies failed to thrive in the hotter waters.

So Funk investigated what would happen in a reduced-oxygen environment. Instead of struggling, the mayflies adapted, growing larger gills to compensate.

The bottom line– “researchers observed substantial ability for aquatic insects to compensate for oxygen depletion at high temperatures but little, if any, ability to actually compensate for high temperatures,” according to Diane Huskinson, at Stroud Water Research Center.

“This puts greater emphasis on establishing scientifically sound thermal limits to protect the aquatic insects– and life in general– of our streams and rivers and to have sound policies– local, state, federal– in place to keep streams and rivers from warming any further, e.g., good sound restrictions on deforesting streams, raising temperatures due to thermal warming from dams and power plants, and of course warming associated with climate change,” Huskinson said.

The scientists’ findings are the subject of a peer-reviewed article and accompanying feature article in the internationally acclaimed Journal of Experimental Biology, which has previously published the work of Nobel prize winners.

The Chester County-based Stroud Center seeks to advance knowledge and stewardship of freshwater systems through global research, education, and watershed restoration.

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