River Bugs

Anya Nova Metcalfe is an ecologist with the USGS Grand Canyon Monitoring & Research Center in Flagstaff, Arizona. Her research investigates aquatic food webs in the large and regulated rivers of the Colorado River Basin. More than anything, Anya really likes learning about bugs. She is interested in understanding how the life cycles and natural histories of aquatic invertebrates structure riverine communities. Through her work with USGS, Anya has collaborated with river runners, anglers, educational groups, non-profits, and federal partners to document aquatic insect communities on the Green, Colorado, Yampa, Gunnison, Dolores, and San Juan Rivers. Anya’s happy place is out on the water and she makes sure to visit these rivers frequently. She received a Master of Science in Biology from Northern Arizona University and a Bachelor’s degree in Environmental Science/Adventure Education from Prescott College.

Publications

USGS

Community Science

Aquatic insects can be used as bio-indicators of how a river’s ecosystem is doing.  In the case of the Colorado River through the Grand Canyon, these insects are being severely affected by the Glen Canyon Dam.  We talk with ecologist and bug lover Anya Metcalfe about her research with aquatic invertebrates in the Grand Canyon and how this might help sustain the weakening food web within this river corridor.

Science Moab:  In terms of an insect’s life cycle, can you explain what that means?

Metcalfe:  Life cycles describe the different forms and phases that an animal goes through during its life. With insects, most have three life stages, an egg, a larva and an adult. Others, like butterflies, have a fourth life stage where they pupate before they become an adult. My favorite aquatic insects are caddisflies. Those are like butterflies of the river as they’ve got four life stages. This is something that’s really cool about aquatic insect life cycles is that most of the time, they’ll start with those first three life stages in the river, and as adults, they’ll sprout wings and fly off into a whole new terrestrial world. This is interesting from a food web perspective, because while they’re in the river, they’re really important food for fish. Then once they emerge as adults, they also become important prey for lizards, spiders, birds and bats and they’re fueling food webs both in and out of the water.

Science Moab:  Specifically, you’re studying the aquatic insects in the Colorado River through the Grand Canyon. How are these insects being affected by the fact that they’re below a very large dam?

Metcalfe:  So the pre-dam Colorado River is very warm and turbid with a lot of suspended sediment, and it fluctuated in temperature with the seasons of the year. It also used to flood from 1000 cubic feet per second (CFS) up to 80,000 CFS.  Now we have a cold, clear, fairly fairly “stable” river.  it’s fairly stable throughout the whole year on a big picture because there are no natural floods, but there are hydro peaking flows, where water is released from the dam in response to peak power demand. So you can have these artificial tides in the river where the water is going up and down throughout the day in response to power needs.  Since you don’t get a tide in a natural river ecosystem, we’ve been finding evidence that these hydro peaking operations are having an effect on aquatic insect populations. Many aquatic insects lay their eggs pretty close to the shore on rocks and submerged vegetation, they’re not expecting that the river is going to drop out on them in an hour. So what we found is that aquatic insects are laying their eggs and then the tide is dropping, and those eggs are being exposed to dry air, so those eggs are drying up. So that’s a really interesting pattern that we found and attributed to the hydro peaking operations.

Science Moab:  How is that affecting fish and other critters that eventually would eat these insects? How are those populations doing?

Metcalfe:  A lot of research has been done on fish in the Grand Canyon reach of the Colorado River. What people are finding in a number of ways ranging from complex population models to directly measuring fish fat to going out and fishing and paying attention to what they’re catching is that fish are hungry. Down in the Grand Canyon, we’re just seeing skinny fish and drastic swings in fish populations. Much of it has been attributed to low food availability. These fish are relying on aquatic insects and sometimes there’s just not enough around to eat. This applies both to native, many of them endangered fish like the Humpback Chub, and also to the rainbow trout up at Lee’s Ferry.

Science Moab:  What research is being done to help address this problem with food shortages?

Metcalfe:  The relationship between insect populations and hydro-peaking is really exciting  because hydro-peaking is a problem that’s manageable since it’s human created in the first place. With those findings, the Glen Canyon Dam adaptive management program, they decided that it was worth running an experiment to see if less hydro peaking might lead to more aquatic insects and therefore help those food webs in the Grand Canyon.  So we’ve been calling them bug flows. From 2018 to 2020, there was an experiment where from May to August each year, there was no hydro peaking on the weekends. So kind of giving the bugs a weekend off from the water going up and down and drying out their eggs. We hope that those two days a week might lead to an increase in aquatic insect production, both in numbers and also in diversity.  Across those three years, we found that natural processes improved in the Grand Canyon so we saw a huge iincrease in caddisflies more than anything else. So that was a really exciting outcome.