Peter Coesel (82) skillfully catches a blob of bladderwrack out of the water with the handle of his umbrella. “Let’s see if there is anything here.” We are standing in the Leijeskamp Nature Reserve in Bussum, our feet sinking into bog moss. An excellent site for finding desmidiaceae or desmids. “You can see from the plants that grow here—the oat ranunculus, the hedgehog ranunculus, the marsh deer hay—that it’s a moderately acidic environment, Blacksmith please.”
Squeeze bladderwrack onto a plastic jar. “We’ll look at this under a microscope later, hopefully it will contain beautiful specimens.” Squeeze the plant and put the lid on the jar. “This is the most efficient way to collect shakes. Because they are relatively large—compared to other microalgae they are really giants—they often sink and wind up among the aquatic plants.”
For fifty years, Coesel (emphasis on the last “e”) has been an expert in the field of desmids in the Netherlands. He has long retired, but continues to do two days of research at the University of Amsterdam (UvA), and his standard work, Scattered Plants. Desmids of the Lowlands Co-written with Koos Meesters in 2007, it will be reprinted this year. “At the time, we described about five hundred lowland species in it, but dozens have been added since then.”
When is algae dark?
“It depends on which family the species belongs to. There are about ten thousand species of green algae or green algae all over the world: single-celled organisms that, like land plants, have a green color because of the pigment chlorophyll. Within those green algae, you have two families that are distinguished by their shapes replica, f Mesotaeniaceae and the desmidiaceae. These are the malicious ones.
the desmidiaceae It has a constriction in the middle, and the waist divides the two halves of the cell. This is where cell division takes place. The two halves diverge, between which a new piece arises, which splits in two and adds a new half for each “half-cell”. Repeated division sometimes occurs afterwards, giving rise to a whole row of cells, with the older halves on the outside. Then the cells separate from each other, so that the algae become unicellular again.”
Some are shaped like boomerangs, others look like military trophies
desmid refers to other algae being unsightly…
“Wrong. They are just less symmetrical. Honestly, I’m not happy with the name either. It’s very reminiscent of aquarium fish, which are bred for their beauty. I prefer to call them desmides. And sometimes you hear the name jewers, because the shape is like an old yoke, in which buckets were carried “.
How did your fascination with desmids arise?
“When I first looked at them under a microscope, I was immediately captivated by their beauty. When viewed with the naked eye, they look at best insignificant green dots less than a millimeter in size, but you see a lot of detail under the lens. Some are boomerang-shaped, others Looks like military trophies… Algae from the last group, the genus Micrasterias, called Knight’s Crosses in Dutch. Described by Jacob Heymans, son of Eli Heymans, in 1916 Already lyrical as “delicious, elegant, green stars”. He wrote, “This comparatively small genus—twenty species at most can be expected in our country—already contains so many elegant shapes, that a person who has ever begun to smell them can never tire of them.”
“Thanks to a talk by Jakob Heymans, I also came into contact with desmids for the first time. It was really the pioneer in the Netherlands. Later, when I got a permanent appointment at the UvA, I wanted to do research on deciduous weeds. But such algae take up a lot of space if you like.” In trying it out in the lab, I then thought of algae – much smaller and therefore easier to grow. Moreover, she appealed to me that not much was known about them. I am an old-school scientist, preferring to research one subject from as many angles as possible – taxonomy, physiology Organs, reproduction … – and it was possible here. I never ventured into DNA research on my own. These technologies appeared when I was already retired. “
In fact, you can find Desmides almost anywhere in the world, including subantarctic islands
From Bussum we continue to Science Park at UvA, where the microscope that Coesel has been using for decades is located. In his bag is the freshly filled jar with two water samples collected earlier. “If you keep it in the fridge, and it doesn’t have a lot of bacteria in it, it will stay good for a long time.”
He immediately hits the mark with his Laegieskamp monster: Coesel spontaneously depicts a large, slyly sly, looking gherkin with a narrow waist. „Acinotainium turgidum”, he sees immediately. A little later, in a boomerang-like sample, firmly: „Closterum calosporum. ”
Coesel himself no longer does much fieldwork, but he’s still active in the working group he created, with dozens of skilled amateur biologists. “They take beautiful pictures, and I benefit from them, too. Since my eyes can now no longer make out all the details with a microscope, but with these pictures, the identification works well.”
Is the Netherlands a good likable country?
“If you look at per unit surface area, the Netherlands is much richer than average, thanks to the diversity of its landscapes: from the shaky peat bogs of Overijssel to the peat lakes of Utrecht and the Finn Brabant. But in fact, you can find desmides almost anywhere in the world,” he says. Even the Antarctic islands including, as long as there is fresh or brackish water and if there is not too much pollution. The nitrogen crisis is also a disaster for the fugitives.
It is unbelievable how much life can be found in a single drop of trench water.
“Yes, and very beautiful! Look, in the water from the second jar you see Micrasterias truncata, the cross of the round order. Heimans actually wrote that a graceful contour line could be a nice design for a badge. And you know what’s so cute? Used NJN, Dutch Young Society for the Study of Nature Micrasterias truncata Actually as a slogan! By the way, desmids are often a source of inspiration: in the visitor center at Oisterwijkse Bossen en Vennen, flickering lamps hang from the ceiling.”
Finally, Coesel found one of the most impressive defenders in the third sample: Micrasteria crux melitensisMaltese cross. “This species could thrive in a lot of places, if it weren’t so dirty and so rich in nutrients. So it is, like many other desmids, an excellent indicator of water quality. Truly a beauty.”
I’ll hang it up for you if I can!
A version of this article also appeared in the newspaper on August 14, 2023.
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