and every common bush afire with God,
but only he who sees takes off his shoes,
the rest sit around and pick blackberries.”
— Elizabeth Barrett Browning
Did you know there are JELLYFISH in Bays Mountain Lake? Today our Nature Study class visited Bays Mountain in Kingsport, Tennessee, to learn about freshwater jellyfish. We even convinced a good-natured naturalist to take us on a barge ride around the lake to investigate! How in the world did they get there, you ask? Read on…..
Although we call them freshwater jellyfish, some argue that the Craspedacusta sowerbii is more closely related to the Hydra family than a “true” jellyfish, so many naturalists and scientists just call them Freshwater Jellies. The main difference between jellies and “true” jellyfish is the presence of a velum — a think circular membrane around the cap that helps propel the jelly forward. Freshwater jellies are transparent, gelatinous, umbrella-shaped creatures with a whorl of stringy tentacles around the edge of their bodies. Microscopic barbs called nematocysts run along the tentacles to help capture food and protect the jelly from predators. Luckily for us, jellies are quite small — adults are the size of a quarter — and their stings can’t even penetrate our skin.
Jellies have no head or skeleton, and contain no special organs for respiration or excretion. Their bodies are 99% water. Their large, flat reproductive organs are the only parts of the freshwater jelly that are not translucent, and this makes them easy to spot on sunny days when they tend to surface in large groups called “blooms.” They eat tiny microscopic animals called zooplankton that are found floating in the water. When they come into contact with prey, stinging cells in the jelly’s tentacles paralyze the organisms and then sway about moving the captured prey its mouth which is in the middle of the underside. The bell (body or umbrella part) of the jelly goes through several contractions to move the prey into the mouth and digestive cavity. The primary predators of freshwater jellies are crayfish and turtles.
Freshwater jellies have a multi-stage life cycle that includes two forms — the polyp and the medusa. The medusa form is more familiar, and it is during this adult stage that jellies reproduce sexually and fertilized eggs that develop into larvae detach from the medusa and drift away. This larvae form, now called polyps, will also reproduce — but it will do so asexually by dividing from one another. This is called “budding,” and the buds will then develop into adult medusa and the cycle repeats. During the winter the polyps contract and become “resting bodies” that are capable of surviving the cold temperatures. They are circular and fairly flat with no hooks or burrs, but there does seem to be some adhesive property which allows them to become attached to surfaces. Some scientists believe that the resting bodies are one way in which the jellyfish are transported — on aquatic plants, by aquatic animals, or on the feet of birds. When conditions become favorable and temperatures rise, the resting bodies develop into polyps and the life cycle continues.
Freshwater jellyfish can be found all over the world, but are not native to the United States. There are two schools of thought on their origins. Some believe they originated in the upper Yangtze River basin in China, and were first observed in the western world in water lily ponds in London’s Regents Park in the late 1800’s — having presumably arrived as polyps on the plants imported from China. Others say they originated in South America and made their way to the US in the bilge water of ships. However they got here, jellies spread rapidly and are now found all over the US in every state except North and South Dakota, Montana, Wyoming, Alaska and Hawaii. Why might this be? (Too cold in most of these places, and Hawaii just doesn’t have enough fresh water)
I asked the class how jellies might have gotten into Bays Mountain Lake. They can enter a body of water in many ways — in the water of bait buckets, through flooding from another site, on boat propellers. But we decided the most probable answer may be that they were carried in on the feet of migrating birds during the “resting body” stage of development.
The appearance of jellies is sporadic and unpredictable. Often they will appear in a body of water in large numbers even though they were never reported there before. The following year they may be absent and may not reappear for several years. It’s also possible for jellies to appear once and never appear in that body of water again. In some lakes they appear almost every single year. Why this difference? What triggers the appearance of medusa in certain places and at certain times? Temperature seems to play some role in triggering the medusa stage, which is why there is a freshwater jellyfish season, typically from August to September when water temperatures are highest.
Searching for jellyfish can be a fruitless venture, but the best time of year is NOW, and they are most likely to be found in calm bodies of water, which they prefer to rocky, fast-flowing rivers and streams. After walking across the dam and peering into the deepest part of the lake (which is what jellies usually prefer) we were unable to locate a single specimen. So Ranger Bob (sans the ponytail and facial hair he has sported for years) graciously treated us to a long ride on the barge so we could explore further. While we didn’t encounter any jellies (none of the naturalists we spoke with have seen them this year), we did see beaver dams, water lilies and lots of dragonflies. Definitely time well spent!
“It would be well if all we persons in authority, parents and all who act for parents, could make up our minds that there is no sort of knowledge to be got in these early years so valuable to children as that which they get for themselves of the world they live in. Let them once get touch with Nature, and a habit is formed which will be a source of delight through life. We are all meant to be naturalists, each in his degree, and it is inexcusable to live in a world so full of the marvels of plant and animal life and to care for none of these things.” — Charlotte Mason (I.61)
What an adventure we had today! We started out in a sunny field full of wildflowers and grasshoppers and ended up soaked to the skin but oh-so-joyful! Our Nature Study class met beside a meandering stream at a friend’s farm to learn about an amazing aquatic insect: The Water Strider.
Also known as “Jesus Bugs,” water striders literally walk on water! They use something called the “surface tension” of the water to their advantage. Water molecules are attracted to each other and like to stay together, especially on the surface where there is only air above. Since there are no water molecules above the surface for them to hold onto, the molecules at the surface cling extra tightly to the molecules beside them and under them — so tight, in fact, that a “skin” seems to form on the surface. Water striders walk on this thin membrane. Here’s a cool slow-motion video of them in action: https://www.youtube.com/watch?v=RphuMEUY3Og
But water striders have another secret for walking on water — their legs! The legs have tiny hairs that repel water and trap air. By repelling water, the tiny insects stand on the water’s surface and the trapped air allows them to float and move easily — almost as if they were skating!
And finally, water striders are very, very lightweight. So much so that they are able to float. Lily pads and twigs float because the water is pushing up on them, but a rock dropped into the water sinks rapidly because it’s so heavy for its size that it overcomes the “push” of the water.
Using a large bowl filled with water, I asked the class to predict from their size, weight and shape whether these items would sink or float: Paper clip, straight pin, bottle cap, coin, cotton ball, rubber band. Only the bottle cap and cotton ball floated (and the cotton ball sank when it finally became saturated).
Using the surface of the water like a trampoline, water striders can jump into the air to avoid predators or catch prey! Jumping requires a large amount of force on the starting surface. Easy enough on terra firma, right? But jumping on water is much more difficult because too much force will break the surface tension. Recently mechanical engineers from Seoul National University have developed a robotic insect that can jump on water, too. Researchers say this technology could someday be used in surveillance missions. Watch! https://www.youtube.com/watch?v=Z83l347rh6E
Water striders can live for many months, and adults can overwinter by crawling inside a plant stem when it gets too cold.
Like all insects, water striders have six legs, and each set has a different use. I asked the students to observe water striders in the stream and try to determine to what use the insects puts each set of legs. (They use their front legs to catch and hold prey, their middle legs to row, and their hind legs to steer.)
If there is time, observe what water striders eat and how they eat it. (Water striders are carnivorous and use their piercing mouth parts to inject a chemical that liquifies the prey’s internal structure so they may then suck them dry. They will eat whatever falls into the water (other insects, worms, honeybees) and use their front legs to find food by sensing ripples made by struggling prey, then grab and hold it while they drink its life juices. Here’s a not-gross video of water striders catching and enjoying a meal: https://www.youtube.com/watch?v=SVoG0Uy_uQ8
Try to determine what preys on water striders. (fish, frogs, salamanders)
A violent thunderstorm with dangerous lightning caused our class to be cut short, but some of the students recorded their observations at home.
A few of us were able to wait out the storm and take a walk into the woods along the creek bank. In addition to a perfectly-preserved, bleached-out cricket exoskeleton, a mystery nut (which turned out to be an immature beechnut) and some nearly translucent, gelatinous, very slimy fungus (maybe snow fungus?), we found the most amazing deep aquamarine bracket fungus growing on a fallen log. What a treasure! It looked just like this (only much more of it):
WE LIVE ON A BLUE PLANET
THAT CIRLES AROUND A BALL OF FIRE
NEXT TO A MOON THAT MOVES THE SEA,
…AND YOU DON’T BELIEVE IN MIRACLES?
Today our Nature Study class went snorkeling in the Clinch River near Natural Tunnel State Park in Duffield, Virginia, to get up-close-and-personal with freshwater mussels. Rare and endangered species abound in the Appalachian and Smoky Mountains, and the Clinch River alone sustains 48 imperiled and vulnerable animal species — including 29 varieties of rare freshwater mussels. Because of this concentration of rare animals, the Clinch River has been identified as the number one hotspot in the US for imperiled aquatic species.
The Clinch is home to 45 species of freshwater mussels. Appalachian mussels have terrific names like PURPLE WARTYBACK, SHINY PIGTOE, MONKEYFACE, and PEARLYMUSSEL. Although they all look pretty much alike to the untrained eye, their astonishing diversity is one of the Clinch’s main claims to fame. For a bit of perspective, you’d have to explore every stream in Europe and temperate Asia to find as many species!
Mussels live in a variety of aquatic habitats, but all require areas where the running water has a high oxygen content and supplies a rich food source of organic particles. The constant flow of water also removes waste materials that would be toxic to the mussels, so they are important indicators of water quality. The best substrate (stream bed) for freshwater mussels is a combination of silt, sand, gravel or cobble with little sedimentation.
Adult mussels are sedentary, moving no more than a few feet along the bottoms of the rivers during their entire lifetime, and spending their time flushing water through their bodies and extracting microscopic organisms to eat. The young, however, experience a more adventurous beginning. Each species of mussel has a different species of host fish which it uses as its “nursery.” Female mussels trick fish into coming close by showing off fleshy appendages that act as bait. When a fish swoops close to eat the “bait” the mussel shoots her babies out into the water and they dash to latch onto the fish’s gills where they’ll spend the rest of their early childhood. After several weeks their small shells are formed and they drop off the host fish into the water and float down to the bottom of the stream where they will spend the rest of their lives.
Before the class donned goggles and snorkels, I suggested some things they might look for underwater:
After exploring the underwater habitat, we gathered to share observations and record these in our nature journals. I’ll share some of those entries with you soon, and hopefully some of my students (or their moms) will share comments and photos as well.
Life Cycle of a Mussel (short) https://www.youtube.com/watch?v=UD8sHa84M_Q
Mussels Luring Host Fish (mentions evolution) https://www.youtube.com/watch?v=I0YTBj0WHkU
“Planting” Mussels in the Clinch River https://www.youtube.com/watch?v=Uf0ZIoNnuiI
Among the Pond People — Clara D. Pierson (free online) http://www.mainlesson.com/display.php?author=pierson&book=pond&story=_contents
Wild Folk at the Pond — Carroll Lane Fenton
By Pond and River – Arabella Buckley (free online) http://www.mainlesson.com/display.php?author=buckley&book=pond&story=life
Pets from the Pond — Margaret Waring Buck
In Ponds and Streams — Margaret Waring Buck
One Small Square: Pond
Pond and Stream – Arthur Ransome (free online) http://www.gutenberg.org/files/40447/40447-h/40447-h.htm
DK Eyewitness Books: Pond and River
Pond Life (Golden Guides)
http://www.fws.gov/midwest/mussel/harvest.html (button industry)