Tag Archives: freshwater creatures

Nature

Freshwater Jellyfish: Cute, and They Don’t Sting

Students frequently confront teachers of biology with a variety of organisms: snakes captured under porches, wild birds rescued and nurtured at home, preying mantises temporarily housed in glass jars, occasional pet hamsters brought to school in their wire cages, and—occasionally—creatures one doesn’t see regularly.  That was the case when a boy lugged a large bucket of water into the classroom one September day.  His question was the kind I welcome the most: What are these?

highlake
Location of High Lake, East Bay Township, Grand Traverse County, Michigan. Image courtesy of Google Maps, September 2016.

I looked inside the bucket, at first not seeing a thing as I focused on the bottom of the bucket.   Then I saw them, swimming in the water column, tens of white, almost transparent disks, each one the size of a penny, swimming—is that too strong a word?—keeping themselves from sinking to the bottom.  Astounded because I had never seen them before, I croaked out, “Do you know what you’ve found?  Freshwater jellyfish!  They’re rare…where did you get them?   The boy, proud of his accomplishment, replied, High Lake.  High Lake!  High Lake had freshwater jellyfish! I wondered if I should report this finding to the University of Michigan.

Since that time much has been learned about freshwater jellyfish.  The source I had used concerning these organisms, Pennak’s Freshwater Invertebrates of the United States (1953) was outdated even at the time my classroom adventure occurred.  The book emphasized how rare the animals were, having been found at only fifty locations throughout the country.  As I read about them today I get a different impression about their origin, frequency and distribution across the lower 48 states.

Craspedacusta sowerbyi, a freshwater jellyfish native to China that is now a world-wide invasive species. Image courtesy of OpenCage (opencage.info) [CC BY-SA 2.5 (http://creativecommons.org/licenses/by-sa/2.5)], via Wikimedia Commons
Craspedacusta sowerbii, a freshwater jellyfish native to China that is now a world-wide invasive species. Image courtesy of OpenCage (opencage.info) [CC BY-SA 2.5 (http://creativecommons.org/licenses/by-sa/2.5)], via Wikimedia Commons
They are not native to North America, having gotten here from China most likely with shipments of tropical fish and aquarium plants.  Fifteen years ago High Lake was one of the earliest lakes affected by that introduction.  They are not rare:  freshwater jellyfish are found in bodies of water in almost all of the states east of the Mississippi River as well as many more out west.  Outside of the United States they are now found in North and South America, Australia, and New Zealand, almost always in temperate locations.  Alas, my excitement at finding rare fauna has cooled considerably.

Another invasive species!  I anxiously turned to Wikipedia to read about its effects on local ecosystems: What foul deeds is it performing on our freshwater lakes?  At present it is not clear what harm they are doing.  They do not seem to disrupt the major feeding relationships among the animals we care about, the fish, birds, and mammals.  Certainly they feed upon near-microscopic members of the zooplankton–the animals that feed small fish–and occasionally upon minnows themselves, but their presence seems benign—at least so far.

The development of Jellyfish. This image is taken from the book "Das Meer" (The Sea), by Matthias Jacob Schleiden. Top are medusae, or jellyfish; bottom are polyps. In the middle polyps strobilate (divide horizontally) to form medusae. Image courtesy of Matthias Jacob Schleiden (1804-1881) - Schleiden M. J. "Die Entwicklung der Meduse". In: "Das Meer". Verlag und Druck A. Sacco Nachf., Berlin, 1869.NOAA photo library, Public Domain, https://commons.wikimedia.org/w/index.php?curid=2051
The development of Jellyfish. This image is taken from the book “Das Meer” (The Sea), by Matthias Jacob Schleiden. Top are medusae, or jellyfish; bottom are polyps. In the middle polyps strobilate (divide horizontally) to form medusae. Image courtesy of Matthias Jacob Schleiden (1804-1881) – Schleiden M. J. “Die Entwicklung der Meduse”. In: “Das Meer”. Verlag und Druck A. Sacco Nachf., Berlin, 1869.NOAA photo library, Public Domain, https://commons.wikimedia.org/w/index.php?curid=2051

The fluttering disks I saw in the bucket represented the medusa stage of the jellyfish, the sexual stage in the life cycle, the stage that produces eggs and sperms.  However, the creature usually prefers the ease of asexual reproduction—a statement supported by the observation that all of the medusae in a lake might be male or else female, never a mixture of the two genders.

Students of Greek mythology might remember the word “medusa”, a monster with a hideous female face surrounded by venomous snakes, its visage so terrible that humans would be turned to stone upon beholding it.  The jellyfish medusa, thankfully, does not possess that power.  It is named after the many tentacles that hang from its margin, a reminder of the monster’s snakes.  Indeed, like the snakes,  it does possess venom—in tiny darts called “nematocysts”—but these are not robust enough to penetrate our skin.  They cannot “sting” us like their relatives, the Portuguese Man of War.

How does the jellyfish reproduce without sex?  It spends much of its life under water in the form of a polyp, a tiny but not microscopic form without tentacles that pinches off the little caps that become the medusa.  Sometimes it does not even bother with that, simply budding off a new polyp from its side.  Boaters and swimmers may not even see medusae in the water for years at a time.  The animal produces them when he/she is ready.

That bucket of water from High Lake did open my eyes to something I did not know existed, even if it proved not to be the rarity I had imagined.  It made me aware of another living form I had never heard of.  Does stimulating my curiosity add to the value of an organism?  If so, I have come to value the freshwater jellyfish.

Richard Fidler is co-editor of the Grand Traverse Journal.

Nature

A Kiss of Death: The Life of the Sea Lamprey

There are few animals in the world that get less respect than lampreys.  They are ugly, lacking fins and the grace of a recognizable face.  They are slimy.  They are deemed inedible, at least in the United States.  They parasitize fish we like to eat.  They are the animals we love to hate, and yet…

Image of sea lampry mouth parts. Photo courtesy of I, Drow male, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=1999560
Image of lamprey mouth parts. Photo courtesy of I, Drow male, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=1999560

My encounters with lampreys have been few, but always interesting.  There was the time my fish class went to a lamprey weir many years ago, and allowed them to suck onto the palms of students’ hands.  Lacking jaws, that is all they could do—give us an intense rubbery kiss.  Perhaps it was the time of year or else the disgusting nature of mammal skin, but they did not try to bore into our flesh to suck our blood as they might do with the Lake Trout.  It was hard to detach, its body not offering traction for the other hand to pull it off (scraping turned out to be the best method).

"Sea lamprey traps often produce by-catch. This native silver lamprey was found in the trap and released back into the St. Mary's River." Photo and caption courtesy of Joanna Gilkeson, US Fish and Wildlife Service, Midwest, https://flic.kr/p/oqQWi3
“Sea lamprey traps often produce by-catch. This native silver lamprey was found in the trap and released back into the St. Mary’s River.” Photo and caption courtesy of Joanna Gilkeson, US Fish and Wildlife Service, Midwest, https://flic.kr/p/oqQWi3

Earlier that day we had gone upstream with a box sieve, a wooden frame with a wire screen affixed to the bottom, to capture immature lampreys.  We would plunge it into a muddy bank and swish it around in the water to wash out the mud and silt.  What was left were—among other invertebrates—many several-inch long young lampreys.  Many, if not most, were native to Michigan, not having invaded by way of the St. Lawrence Seaway as the parasitic sea lamprey did.

Our native lampreys seem content to wallow in the mud, straining out organisms from the water with gill filaments.  They transform into adults, mate, lay eggs, and die, much as salmon do.  The sea lamprey goes one step farther, leaving its stream for the Great Lakes, feeding off fish such as Lake Trout for one year or more, finally returning to a stream to lay eggs and die.

Because lampreys return to streams to spawn and die, they can be controlled by several methods.  The simplest of these is to erect a dam to keep them from migrating upstream where they may find gravel beds for spawning and muddy banks for nurturing the young larvae.  The Union Street dam serves this purpose in Traverse City.  Unlike Brown Bridge dam upstream, it will not be removed, in part, because of this useful function.  Another method of controlling sea lampreys is to poison them periodically with poisons that work only on lampreys.  It is necessary to use these chemicals once every several years because the larvae spend so much time buried on mud, feeding on microscopic organisms.

Oddly, we humans are related to these creatures.  While lacking a jaw and a skeleton made of bone, lampreys have a nerve cord running along its back, a larval rod-like structure in its back that evolved into a backbone, and gill slits towards the mouth.  We all have those features as embryos, but they change into other things as we develop.  Our gill slits morph into a jaw and the structures in our necks, and our dorsal nerve cord lies within a bony column of vertebrae.

Lampreys and their kin are the ancestors of the dominant groups that we know today: the bony fish, amphibians, birds, reptiles, and mammals.  They are evolutionary throwbacks, relics of a time that preceded the appearance of more modern vertebrates.

Sea lampry adhered to lake trout. Image available in Public Domain, https://commons.wikimedia.org/w/index.php?curid=2760638
Sea lamprey adhered to lake trout. Image available in Public Domain, https://commons.wikimedia.org/w/index.php?curid=2760638

The kiss of a lamprey is singularly unrewarding, both for that animal and for us.  To an appropriate fish it is the kiss of death, since many fish die as their blood is drained out.  It is a kiss of death: Is that the reason we cannot love these animals—they plague our sleep with night terrors?  Are we remembering our ancestral past when, as fish, we felt the sucking disk attach to our side, the creepy sensation that spelled our doom?  Should we let down our fears as the Europeans have done to feast upon these animals?  I don’t know—you go first.

However, should any readers be inspired to extend their range of culinary skill, I offer this recipe for the preparation of sea lampreys.  It was taken from the Middle Ages, so cooking methods will seem a bit unorthodox.  However, the success of the preparation may explain why King Henry I of England died from eating a surfeit of lampreys.  He could not hold himself back from eating them all.

Nature

“I vant to suck your blood”: Encountering Leeches in Northern Michigan

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A naturalist must cope with whatever Nature deals out.  Once when I took a course in invertebrates, I had to walk through shallow, warm ponds in the middle of summer, an action that would surely attract leeches (known by some as bloodsuckers).  Sure enough, after traipsing through one particularly muddy body of water, I looked down to discover that one had attached to my leg.  It was not only attached, but was apparently feeding: it wouldn’t let go.

When one’s life blood is being sucked out by a predator, one does not always behave rationally.  Not entertaining the notion of spraying an offensive chemical on the animal so it would let go on its own, I used my fingernails to scrape it off.  Not a good idea.  The wound bled and bled, taking twenty minutes or so to stop.  Thus, I learned about the anti-coagulant properties of leech saliva: leech bites don’t readily stop bleeding because the creature injects hirudin, an chemical that prevents the blood from clotting.

The wound didn’t hurt—I am told the clever leech employs an anesthetic as well as an anti-coagulant.  It would never do to annoy a mammal to the point it would forcibly remove the animal feeding off it.: better to feed quietly and drop off to browse, sated with food and satisfied for any number of months to come.

This predator leech—the word “predator” is more appropriate than “parasite” since it feeds for only minutes instead of days and months—was Macrobdella decora, the American medicinal leech, the red-bellied leech.  As its name implies, it sports an attractively decorated array of red spots, a possible design pattern for a necktie or a scarf.  The animal is a distant relative of the earthworm with its concentric rings that encircle its body, marking off no fewer than 34 segments.

While the practice of leeching, using leeches to bleed patients, has fallen into disfavor since the nineteenth century, it still is occasionally employed in modern medicine whenever it is necessary to increase circulation to a blood-starved part of the body such as a newly reattached finger that has been accidently cut off, for example.  I remember distinctly that in our own Munson hospital not too many years ago, a young girl had a finger reattached and submitted to treatment with leeches.  “It’s kissing my finger,” she would tell visitors.  Indeed, in a way, it was.

Most leeches do not feed upon mammals, preferring frogs, fish, and, especially, snapping turtles.  Some do not attack large animals at all, being satisfied with earthworms and smaller creatures found in water.  One of the largest leeches to be found in the area, its body extending a full six inches or more, seldom feeds on humans or their pets–the horse leech, Haemopis marmorata.  I have observed this creature in Lime Lake, Leelanau County, where it can be seen rapidly scudding across the marly bottom, fully as capable of swimming as a fish.

Haemopis sanguisuga, or horse leech. Image courtesy of H. Krisp, Wikimedia Commons.
Haemopis sanguisuga, or horse leech. Image courtesy of H. Krisp, Wikimedia Commons.

Horse leeches sometimes are found on mud at the edge of the water.  If they are grabbed to use for bait—as bass or walleye fishermen will occasionally do—they will readily try to climb out of the bucket, unlike other more docile species.  

Leeches are given a bad rap.  They seldom bite, they do not spread disease, they have medical uses, and they make good bait.  However, the idea of having our blood sucked does not go down well with us.  We despise things that do that–mosquitoes, black flies, or biting midges—and we cut them no slack.  Perhaps, we should, though, with leeches. After all, they do us little harm–much less than mosquitoes—and at least one of them, Macrobdella decora, looks terrific!

Richard Fidler is co-editor of Grand Traverse Journal.

Header image courtesy of Tim Eisele at “The Backyard Arthropod Project”, American Medical Leech.