The sun was setting behind the Adirondacks on a clear summer evening and Lake Champlain was flat as a mirror. The only disturbance was the hum of a small motor propelling an aluminum boat. Rosie Chapina — a PhD student in the Rubenstein School of Environment and Natural Resources — had her net and other tools by her side as she sat on the hull, waiting to find the right spot. She was looking for large zooplankton; mysids, more specifically, a shrimp-like crustacean found in both fresh and brackish waters.
“At the end of the day, what people want is big fish, cool fish,” Chapina said. “But mysids are powerful in the sense that they’re a key species in the whole food web in Lake Champlain. We care about them because they’re a primary food source for many fish including juvenile lake trout.”
Chapina is studying mysids’ daily migration patterns. Every day, mysids circulate the depths of Lake Champlain and other fresh water bodies, feeding during the day and migrating near the surface at night. On Lake Champlain’s surface, the water is much warmer than the depths below. This temperature difference — a thermocline — allows for distinct habitats to form with different species of fish to thrive.
“Mysids migrate at night, they transfer nutrients from bottom to the top of lake,” Chapina said. “This transfer brings nutrients from one kind of habitat to another within the lake.”
Though some mysids don’t migrate at all, staying at the bottom of Lake Champlain all day and night.
“This is something we know when we think about population behavior,” Chapina said. “Some mysids exhibit partial migration. We can’t really track which ones migrate and which don’t, but we have different ways of looking at carbon and nitrogen signatures to see what they eat and where they are in the food web. I am conducting experiments to see how safe the benthic habitat is or to see if mysids are hiding in the sediment, which may be why they’re staying at the bottom.”
With mysids being incredibly small, ranging in size from 3 to 25 millimeters, it can be incredibly difficult to accurately track their migration patterns. But Chapina has some creative ways to find out just how these critters move throughout the day.
“I wish I could put trackers on them, like how researchers have put trackers on bumblebees,” Chapina said. “Instead, you can see them migrate by using high frequency sonar systems.” Previous researchers in Virginia have used a simple staining process — essentially dyeing organisms with a pigment — to differentiate live and dead zooplankton in water field samples.
Chapina also uses cameras, nets, and sediment sleds in the lake to track mysids.
“I deploy cameras all the way down to 120 meters. I’ve done it in Lake Champlain and in the Great Lakes,” Chapina said. Mysids are naturally distributed throughout North America in the Great Lakes and in northern lakes in Wisconsin, New York, and here in Vermont. “We also have a sled that is towed along the bottom of the lake for five minutes and collects everything. With cameras, nets, and the sled, we collect mysids in both the pelagic and the benthic zones.”
Chapina explained that there are several working theories about why some mysids migrate and some don’t. Ultimately, she said, some think the mysids are safer at the bottom of the lake where there may be fewer predators.
“Some researchers have surveyed mysids and fisheries and demonstrated a decline in mysids,” Chapina said. “But quite a large portion of mysid stay at the bottom. Researchers in the past weren’t assessing the numbers correctly because they didn’t know the mysids were staying in the benthic zone, where it’s possibly safer for larger mysids carrying embryos.”
Another dynamic at play in researching mysids’ migration is their sensitivity to both light and temperature. In a large walk-in refrigerator at ¶¶Ňő̽̽’s Rubenstein Ecosystem Science Laboratory on the Lake Champlain waterfront, a tank of mysid caught for research and observation could be ruined from the light of smart phone’s flash light.
“Mysids have a lower tolerance to temperature and light and so maybe smaller ones remain suspended in the water column but not the larger ones,” Chapina said. “It could also be the fact that it’s too warm because of climate change and warming water temperatures.”
Ultimately, Chapina is simply fascinated with the mysids of Lake Champlain.
“I think they’re cool and that’s why I’m researching them but it’s sometimes difficult,” Chapina said. “They’re important. If you think about how small they are and how quickly they migrate. An organism so small migrating up 100 meters in one night, through the water. It’s pretty impressive.”
Note: Technically, one could eat freshwater mysids; however, Chapina explained that mysids are essentially tasteless. Some people have attempted to make a kind of mysid dip — like a hummus — with little success.