My most recent visit to the River Ehen stimulated me to continue my explorations of what the subaquatic microbial worlds would look like in close up. Before showing my latest creation, here’s a view of my working space which, as befits my positon in the no-man’s land between art and science, is neither a “laboratory” nor a “studio”. My microscope is on the right of the desk, with a monitor for displaying specimens at the back. To the left is the bookcase where I keep my identification guides, within easy reach. The desk has been cleared of clutter to make space for my watercolour pad, paints and pencils. The main attraction of my study for painting is the good natural light, which floods through the south-facing window.
My study / studio / laboratory.
I have usually worked out a rough design for a painting in a sketchbook before I have started, working both from direct observations down the microscope or photographs, with occasional dips into my books to check features or dimensions. I then build up the picture gradually, starting with the foreground, and then slotting the other organisms into the spaces around the individuals at the front of the picture. Working with watercolour and gouache means that I have bursts of activity, followed by pauses whilst a wash dries, then another burst. Or, to put it another way, I get on with real work (the stuff I get paid for doing) and take occasional breaks to add the next piece of detail to my picture. The one I have shown here has taken about five days from start to finish, with painting slotted around other activities.
The finished picture is below. I’ve written much about the River Ehen over the past eighteen months or so and have been constantly surprised at how much variation we have seen in the algal communities over that time. Each time I visit, I pick up a stone covered in green algae from the stream bed but when I look at these apparently identical growths under the microscope, I se that several different species have appeared and disappeared over the course of the study. Back in winter 2013, these communities were dominated by Spirogyra (see “The River Ehen in February”); other times of the year, the most abundant alga has been Bulbochaete (see “The River Ehen in August”). Just a few kilometres downstream, we saw completely different algae again (see “At last a red alga that really is red …”). The structure of the communities when green algae predominated has, however, always been similar: the green filaments form a distinct layer over the top of a diatom-dominated understory. This is what I have tried to capture in this picture. I have also added some filaments of the cyanobacterium Calothrix sp (see “Looking is not the same as seeing …”).
The River Ehen in September 2014. The biofilm on stones has an understory of diatoms including Tabellaria flocculosa and Fragilaria tenera (right foreground) below a “canopy” of Bulbochaete. Other algae living in the biofilm include the cyanobacterium Calothrix (left foreground). Both Calothrix and Bulbochaete have long hairs, which release enzymes to capture phosphorus bound to organic particles suspended in the water. The Bulbochaete filaments are about 10-15 micrometres (1/100th – `/67th of a millimetre) across.
The presence of both Bulbochaete and Calothrix at the same location tells an interesting story. If you look back through my earlier posts, you’ll see that the long hairs characteristic of Bulbochaete and some other algae we’ve seen in the Ehen are thought to be adaptations that allow these species to thrive in situations where phosphorus is very scarce. But Calothrix also has the capacity to fix nitrogen, which is a useful adaptation when nitrogen is the scarcest nutrient. We know that nutrient levels in the River Ehen are low but the presence of both types of adaptation simultaneously suggests the organisms may be subject to both phosphorus and nitrogen limitation, perhaps reflecting short term oscillations in the relative availability of each over the year.
We’ve now got heaps of data telling us what species of algae are present, and how much algae there are over the courseof a year. What we have done is akin to lifting up the bonnet of a car and naming all the parts of the engine. Our next task is to try to work out what all these different parts are doing (interpreting the role of hairs is part of this) and then, more importantly, to work out why the River Ehen’s engine doesn’t seem to be running as smoothly as we think it should. I’ll come back to this in a future post.