Stoneflies Consume Methane as Energy
December 05, 2017
Stoneflies, (Order: Plecoptera), are among the largest insects in any river community, and are of significant importance to fresh water fly fisherman wanting to target the big trout that prefer to eat them. However, some species of stoneflies present a biological contradiction, in that the larval forms of these typically abundant insects mature under the stony beds of river systems that offer little in the way of food sources. This paucity of resource is an environmental condition known as Oligotrophy, and is seen in many lakes, especially at high latitudes. The $64,000 question of groundwater ecologists for decades has been, "How are these insects thriving in this kind of environment?".
Researchers from the University of Montana, working in cooperation with the Rocky Mountain Biological Laboratory in Gothic, CO have recently published stunning new data that sheds light on fundamental organic processes in rivers, with potential implications for broader ecological policy. The summary finding – conducted by UM Ph.D. researchers Amanda DelVecchia and Jack Stanford, along with Xiaomei Xu from the University of California at Irvine – was hosted by the open access online journal Nature Communications. In it, the scientists have come to the conclusion that the majority of the organic carbon in the bodies of these stoneflies comes from an unusual and almost alien source: Methane.
Suspecting that an alternative basis for organic processes was in play with stonefly biology, the scientists used carbon dating techniques to identify the source of the carbon -- a fundamental building block for life as we know it -- that was being utilized and incorporated at a molecular level in the tissues of the insects. What they found was surprising, to say the least. Methane (with a molecular designation of CH4), present in the margins of the river bottoms, was being broken down by bacteria and the stoneflies were likely consuming this bacteria, thus ingesting the carbon that came from the methane. This was determined by radiocarbon dating of the carbon isotopes bound in the methane present in the ambient environment of the river bottom and comparing it to overall carbon in the bodies of the stoneflies. They matched.
As reported in followup coverage by UMT.edu, "The millennial-aged methane carbon could have come from organic matter deposited during the retreat of the last glaciation 7,000-10,000 years ago, or the ancient carbon could have come from a shale methane source, as the Kishenehn shale formation underlies the floodplain. Either methane source was likely consumed by bacteria first before being directly or indirectly consumed by the stoneflies themselves."
In my work reporting for Fly Fisherman, I am frequently challenged in understanding and interpreting scientific advances that are germane to our sport. The concept that the UM research presents is no exception, and is sufficiently big enough that I needed assistance to get my head wrapped around it. I caught up with DelVeccia by email after first making contact with her doing field sampling on the East River near Crested Butte, CO, not far from RMBL's base of operations. I asked if she could help clarify my thinking.
"The dated carbon is whatever carbon is in the sample - it includes everything. So for the methane samples, it is the carbon in the methane. For the stoneflies, it is all the carbon in their bodies BUT the majority of the carbon in their bodies is coming from methane and we know that because we measured carbon isotopes. So to express the bottom line to your readers, the stoneflies are getting millennial aged carbon from methane that has millennial aged carbon and we used a combination of radiocarbon dating and stable isotopes to figure that out."
What this means is that stoneflies, given no optional sources, have evolved to take advantage of what would probably be considered in accepted science as a completely alternative energy source for a nutrient base. Nature does provide other examples of life prospering in inhospitable environments, as in the case of deep sea dwelling and cave fish, or organisms flourishing near undersea volcanic vents, and the UM finding may help to shed light on these apparent biological contradictions.
As with all good science, the research raises more questions than it answers. If bacteria that are capable of converting methane resources to available carbon that can drive rich ecologies are susceptible to being affected by environmental pollutants, are agents like heavy metals or pesticides putting fundamental life webs at risk? This presents crucial information that needs to be considered at the policy level in the impacts of industrial activity.
The future health of our outdoor resources will depend on understanding the complex interactions of nature and mans impact on it. Readers should please consider supporting the work of the Rocky Mountain Biological Laboratory in it's ongoing and groundbreaking research.