[CHEERY MUSIC INTRO].

In terms of surface area, Flathead Lake is the largest U. S. freshwater lake west of the Mississippi River.

It has its own stunning beauty, and many stories to tell. I decided to visit Flathead Lake for our invertebrate month here on Nature League because one of these incredible stories involves an invertebrate: the Mysis shrimp. Flathead Lake was a chunk of ice until about 15-20,000 years ago.

In the late 1800's, accounts of Flathead Lake detailed about 10 species of fish, so at this point fisheries managers saw an opportunity to stock Flathead Lake with a ton of fish that the public would enjoy fishing and eating. State and federal managers intentionally introduced about 25 fish species into the lake. One of these was the kokanee salmon, and people absolutely loved fishing and eating them.

That meant major money for the local economy, so fisheries managers figured, “We should make sure that the kokanee have plenty of food.” They introduced what they thought would be better food: the larger, freshwater shrimp Mysis. What happened over the next few years has become one of the most famous examples of a trophic cascade ever recorded. Between 1984 and 1989, kokanee in Flathead Lake went from over 300,000 individuals to 0.

See, the Mysis shrimp eat zooplankton, which are also invertebrates, but much smaller than the Mysis. These zooplankton were the original food for the kokanee, so the Mysis started directly competing with the kokanee for food. What's more, the kokanee couldn't even eat the Mysis, because Mysis hang out on the lake bottom during the day while kokanee feed near the surface.

The intended food for the kokanee didn't even cross their path! However, the introduced lake trout and lake whitefish feed on the bottom. Helloooo Mysis shrimp.

Instead of the preferred kokanee salmon eating the Mysis, the introduced lake trout and whitefish had an everyday buffet. Their populations skyrocketed, while kokanee disappeared. Fast forward to today, and Flathead Lake is dominated by three species introduced by humans: lake trout, lake whitefish, and Mysis shrimp.

But the coolest part, in my opinion, is that researchers at the Flathead Lake Biological. Station were able to monitor and study this entire process, and are still actively monitoring. Mysis shrimp and other invertebrates today.

For this field trip, we joined a crew for late night invertebrate sampling on Flathead Lake. But first a word... Not from our sponsors but from the dictionary.

Welcome to this month's Wild Word! Once a month on Nature League we'll look at the etymology, or origin and history, of words related to nature. This month's theme is invertebrates, so we're going to examine a word that is used when talking about the most speciose group of invertebrates.

The word is “insect”. Like our other Wild Words on Nature League, the word insect is a pretty common word. However, a true breakdown of the word helps inform us about the group of animals it describes.

You may have heard before that the “sect” part of “insect” derives from a root word meaning “six”. And that seems to make sense, because we think of insects as things with six legs. However, this isn't exactly correct.

The word “insect” can actually be traced back something a little bit different. “Insect” comes to us from Latin, and can be split into two parts. The prefix “in-” is a Latin word meaning “into”. So far so good.

But what about the “sect” part of the word “insect”? It's actually from a noun form of the Latin verb “sectare”, which means “to cut”. This is really straightforward word-wise, but in my opinion, the elegance is in how perfectly this denotation fits these organisms.

I mean, just look at them! As biologists long ago started using this term to describe this group of organisms, they were definitely recognizing that this was a unique body plan unlike anything else on Earth. So while a formal definition of “insect” is “any of a class of arthropods with well-defined head, thorax, and abdomen, only three pairs of legs, and typically one or two pairs of wings”, insect literally means “to cut into”.

Nothing like being named after what you look like, right? Though insects do in fact have many different defining traits, it's undeniable that they look cut into. Literally, they look insected.

And that, is pretty wild. The Mysis shrimp do a vertical migration daily when they feed, so we had to wait until it was pitch dark for them to come up from the bottom. This meant timing our trip for the new moon, and waiting to sample until late that night.

We sampled at three different depths, using a tow net. We used a red light, which is invisible to the Mysis shrimp but let us see what we were doing. At each depth, we took three different tow samples, and filtered them down into falcon tubes to take back to the lab.

The next morning we sat down with Dr. Jim Elser to chat about the sampling we did as well as the biostation itself. Then we got to check out some of our water samples under the microscope.

We saw all kinds of zooplankton, as well as Mysis. It's no wonder fisheries managers thought Mysis would be better food for the kokanee. These shrimp are massive compared to the other zooplankton.

The story of Mysis shrimp affecting an entire ecosystem is just one example of how tiny invertebrates can have massive effects. Places like the Flathead Lake Biological Station are monitoring these effects and discovering new things all the time. Flathead Lake is an amazing place to visit, and ridiculously beautiful on the surface...but what's even cooler are all of the stories unfolding underneath.

Thanks for joining us on this Nature League Field Trip. If you'd like to learn more about the trophic cascades and community interactions of Mysis shrimp in Flathead Lake, you can click on the links in the description below. We'll see you next week for an episode of De-Natured where I'll breakdown a study about another vertically migrating shrimp and how that might have an effect on the mixing of the oceans.