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half underwater half above water photo of clear stream in summer

Under the Microscope

Do they look like willow leaves or maple leaves? Does it have two tails or three tails? What shape are the gills? Are there branching gills on the abdomen segment six?

You may have thought we were trying to identify a tree or a shrub when you first started reading this. And then, maybe a salamander? We were actually identifying aquatic insects or macroinvertebrates. Liz Metzger and I (Carrianne) have been collecting aquatic macroinvertebrates from eight river sites across the watershed. We are comparing their populations at stream restoration sites, on degraded reaches, and at reference reaches, which represent nearly perfect, functioning sections of the river. Over the winter, we spent long hours working through the identification of several hundred insects that we collected last summer.

What are aquatic macroinvertebrates?

If we look specifically at the word, macro-invertebrate, we can break it apart to understand what it means. Macro refers to something large, in this case, something large enough for us to see with our naked eye (versus micro or something we might need a microscope to see). Invertebrate refers to an animal without a backbone. These can include insects, spiders, mollusks, and crustaceans. Therefore, our aquatic macroinvertebrates are small critters in these categories that live in aquatic or watery environments. In this part of the world, we have several groups of animals that belong in this category. Examples include dragonflies, mayflies, stoneflies, caddisflies, true flies, and aquatic beetles. In most cases, this group includes the larval or immature stages of insects that spend part of their life underwater in streams, lakes, ponds, and rivers.

What can aquatic macroinvertebrates tell us about river health?

Each species of aquatic macroinvertebrate has unique habitat requirements. Some require cold water while others like warm water. Some need lots of oxygen and others can tolerate low oxygen. Some require the most frigid, cleanest, freshest waters available, while others can tolerate slow water, and others can even tolerate different pollution levels or sedimentation in their habitats. Each species has habitat preferences for different river substrates, including boulders, cobble, gravel, and sand. Others are adapted to mud and clay. By understanding the habitats these insects occupy and consulting existing research, we can determine the overall health of each habitat by looking at the whole community of aquatic macroinvertebrates. We also measure water quality and habitat type to predict what species of insects might be present in specific locations.

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How are we using aquatic macroinvertebrates to study our river habitats?

Our biodiverse habitats team has been using studies of aquatic macroinvertebrate populations and community dynamics to compare river health at several study sites in the region. We are comparing insect populations at our river restoration sites, at sites that are unrestored and very degraded, and reference sites that are as healthy and functioning as can be. This information will help us understand whether the macroinvertebrate populations change at our restoration projects over time from the types of species you see at an unrestored, degraded site to species that you might find instead in the reference reaches.

Caddisfly larvae, Trichoptera (A); Stonefly nymph, Plecoptera (B); mayfly nymph, Ephemeroptera (C). Pictures by Jan Hamrsky, Dave Huth, and Bob Henricks.

How quickly can stream macroinvertebrate populations change?

Stream macroinvertebrates have strict habitat requirements, but they are very well adapted to changing conditions and disturbance. For example, if they get knocked off the rock when you cross a stream on a hike, they are dislodged and drift downstream. Unless they get eaten by a trout, they'll settle into a new habitat as soon as they land. On a broad scale, if a large area of streambed were disturbed like several rocks being moved at once by flooding or ice, the disturbed area can be re-colonized as quickly as a few hours to a few days. We can use data about aquatic insects as indicators of change or ecological uplift at our restoration sites over a short time period because their populations can change so quickly.

How do we collect aquatic insects and identify them?

As part of our three-year research study, Liz and Carrianne are using kick-nets to sample aquatic insects at each of our study sites. We place a standardized research net facing upstream and kick several rocks in front of it with our feet. We also use our hands to dislodge the insects from the substrate of the river. We take what we capture in our net, preserve them in alcohol, and identify them back at the lab using a microscope and identification books and keys. Later, we use the data on the number of each insect and each species or family group to calculate several different biodiversity indexes and compare populations at our different site types and across time. I began using taxonomic dichotomous keys for identification in college and learned about several families of aquatic insects in our region. It's been an exciting experience to re-immerse ourselves in this project. Over winter and early spring, Liz and I spent long hours staring into microscopes comparing identifications, our findings, and counting the bugs that we picked out of our samples. This is when we asked questions like: Do they look like willow leaves or maple leaves? Does it have two tails or three tails? What shape are the gills? Are there branching gills on abdomen segment six?

Liz and I (Carrianne) are hard at work identifying stoneflies using dissecting microscopes and taxonomic keys.

To date, we've identified several species of dragonflies and numerous species of caddisflies, mayflies, and stoneflies occupying these river habitats. The most exciting has been comparing the cases of caddisflies built out of stream materials like pebbles, sand, pine needles, and leaves. Also, a few of our true flies like craneflies and dobsonflies have truly creepy life stages. They look like Godzilla when you get called to look into the microscope lens and are not expecting it!

Godzilla! No, just a dragonfly larva.

The groups of insects are similar and so different at the same time. Often, the major difference is how each group of insects breathes underwater. Several have branching external gills, some that look like leaves and others that look like feathers. Others breathe from their tails. It has been breathtaking indeed to think about the metamorphosis and transformation these species undergo to become terrestrial adults. Perhaps you have found empty casings of aquatic insects on rocks and bridges and docks, or maybe you have lifted rocks and looked to see who was crawling around underneath them.

Getting to look at these creatures under the microscope once again has reminded me of the incredible diversity that we have right in our backyard and our watershed. Creatures coexist, carving out a little bit of habitat for themselves and it's incredible to see their adaptations to life underwater in a river that is sometimes hot and sometimes frozen, sometimes high and sometimes low. Rushing waters, with sweeping tumbling boulders, and our insects continue to thrive, adapt, and move on with their life cycles. It's a reminder to me as a biologist to adapt and keep learning. Here, changing seasons create entirely different work for us, no longer poring over whether the insect has branching or feathery gills, but instead spending the week collecting seeds for our new nursery, collecting these insects, or snorkeling for fish. We adapt, we move forward, and we continue to do good science that will inform restoration and decision-making for the community.

Story by Carrianne Pershyn, Biodiversity Research Manager. 

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