Limnology in Action: Bug Pickin’

“Alright. Who is ready to get messy?”

Students sift through trays of sediment and plants, picking out aquatic invertebrates

Zach Lawson’s question is greeted with incredible enthusiasm. It is all-hands-on-deck in the wet lab and, today, everyone is sorting bugs.
Ten undergraduate students crowd around two small tables, armed with small plastic sampling bottles and metal tweezers. They meticulously sift through plastic tubs of sand, muck and aquatic plants, looking for any small movements in the water. Suddenly, spotting the slightest flicker, a hand strikes, snatching up a very tiny red worm-like creature. The student yells “I have a diptera!” and Lawson quickly walks over to inspect and label the specimen. The students work for hours, leaving no leaf or rock unturned, and soon the lab is filled with bottles of invertebrates.
Samples of the zooplankton and zoobenthic communities in Crystal Lake are one of the many series of data Zack Lawson and Eric Brown and their team collect. They are the leaders of the Crystal Lake Mixing Project, a large-scale lake manipulation experiment that is being conducted to try and eliminate invasive rainbow smelt from the lake.
The project is in its first official “mixing” year, as last summer was spent building and installing the system. The study is one of the first of its kind, therefore, Lawson and Brown are leaving nothing undocumented; they want to know everything that is going on in the lake.  “A big, whole-lake manipulation like this, it is our responsibility to monitor the ecosystem and the changes that could happen,” says Brown. This includes collecting data on water clarity, aquatic plants, water temperature, and fish and zoobenthic populations.
The zoonet captures zooplankton from the water column.

Today the team is focusing on collecting zoobenthos, invertebrate organisms that live on the lake floor, in order to look at quantitative population representation in Crystal Lake. By taking these samples throughout the summer, the team can document any changes in the populations or food web as the lake is warmed and mixed.
The morning starts in a whirlwind of preparation. Two boat teams are dispatched to the lake: a sampling group, and another with certified divers. Once out on the lake, the sampling crew, led by Lawson, gets underway immediately. First they take a sample of the zooplankton in the water column using a Wisconsin 400 micron zoonet. This tool is able to collect the very small “animals” in the lake, and filter the water out. Two different sized nets are used, one to collect all zooplankton, and a larger net to collect predators.
Ekman Dredge- Used for collecting zoobenthos and sediments off the bottom of the lake.

Next Lawson takes out an Ekman Dredge, a heavy tool that is sent down to the bottom of the lake, and takes a sediment sample by clamping shut. Hard. “Be careful, that will take off your finger,” warns Lawson.
In the other boat, four of the crew get their diving gear prepared. Once in the water, they swim to the bottom and use a lake vacuum (a PBC tube attached to a scuba tank) to suck up sand, muck, plants and insects into mesh bags. The group does this three times at four different depths in the lake, taking a total of twelve samples.

Both boats finish sampling and head back to the lab, where the crew of eager undergraduates are waiting. Everyone pulls apart plants and turns over rocks and sand but, despite all the help, it is slow work trying to pick up all the little insects and larvae crawling and swimming in the tubs.

A large Burrowing Mayfly is found among the sand of one sample.

Hours go by, and plastic containers are finally starting to be filled with various “critters.” They are mostly larvae, the juvenile stages for many different fly species.
It takes about four hours but, finally, the crew has sifted through every grain of sand and looked under every macrophyte leaf. This entire process will be repeated at the beginning of each month this summer and fall, until the lake is too cold or frozen to dive. The insects and zooplankton collected won’t be analyzed until the winter months, when Crystal Lake is frozen and the scientists do all of their work in the laboratory.
Brown and Lawson supervise labeling and preserving the specimens.

With this data, the research team can look at how the whole-lake manipulation affects native populations. Besides researching how to eradicate an invasive species, Lawson sees this experiment as an opportunity to gain more insights into population dynamics and ecology.
The key to excellent science is to consider every possible outcome. While scientists may not be able to predict what the outcome will be, they will certainly imagine how they will be able to view it, which is why recorded observations are so important. The Crystal Lake Mixing Project is completely dedicated to collecting all data they possibly can in order to fully observe the range of effects within Crystal Lake during the eradication process and contribute to our growing knowledge of limnology.

All summer long, Trout Lake Station outreach assistant, Ali Branscombe will be bringing you stories from the field. Join Ali as she follows researchers slogging through wetlands, boarding boats, and wrangling fish, bringing you – Limnology in Action.