Damp days in search of desmids …

Seatoller, in Borrowdale, is the wettest place in England, so we should not have been surprised by the persistent drizzle that accompanied us as we set off hunting for desmids last week.  The combination of Borrowdale’s hard volcanic rocks and a damp climate combine to create ideal habitats for bog-loving desmids and I had intelligence that Dock Tarn, on the fells above Borrowdale, was a hot spot of desmid diversity.   Getting there, however, was no easy task.  Though just a couple of kilometres from Stonethwaite on the map, there were an awful lot of contour lines awfully close together between the beginning and end of our walk.   The footpath zig-zagged through ancient woodland clinging to a steep hillside until we emerged onto the moorland above.  We then made our way across a plateau covered with heather moorland until we saw the tarn stretching away into the mist in front of us.

You know you are in good desmid habitat when there is water percolating into your body from both ends: rain dripping down from the hood of your cagoule and dampness seeping in through your shoes.  They are organisms that love marshy, boggy conditions, especially in areas where the water is as soft as it is here.   The alternative to damp feet would be to either climb up from Borrowdale in Wellingtons or waders or carry them up that steep hillside in a rucksack.   However, I suspect that the mud at the bottom of the tarn was too soft and deep for Wellington boots and lugging waders up that hillside would have been hard work so damp feet was the price I had to pay.   I leaned out as far as I could from the shore to grab some of the sedge stems which had a visible coating of attached algae, and also squeezed the peaty water from a few handfuls of Sphagnum that I pulled from a boggy pool.  That would have to do on this particular morning as the rain was now soaking through my trousers and, in any case, there were places I needed to be later that morning.   I shoved the bottles containing my samples into my rucksack and followed the path back down the hillside.

Epiphytic algae growing around a sedge stem in the outflow of Dock Tarn, Cumbria, July 2017.   The width of the stem plus epiphytes is about half a centimetre.

Dock Tarn is one of a number of sites identified as an “Important Plant Area” (IPA) on the basis of the rich desmid flora, largely due to work over the years by David Williamson.   It qualifies as an IPA on four criteria: the presence of threatened species, high diversity, a long history of study and because it represents a “threatened habitat”.   David Williamson has recorded over 50 species from this location, 13 of which are candidates for a “potential Red Data List”.   A few of these are illustrated in the figures below.   One of the species in the first image, Haplotaenium minutum, belongs to a genus only recently separated from Pleurotaenium, which looks very similar to the untrained eye (the difference lies in the structure of the ridges on the chloroplast).  Looking at these long cylindrical cells serves to emphasise just how much dexterity Chris Carter needed to produce his Hilda Canter-Lund prize winning image.  Images in the second plate include two more species of the genus Xanthidium, which we met in “Desmids on the defensive …”.

Dock tarn desmids: a. Netrium digitus var. latum; b. Tetmemorus brebissonii; c. Haplotaenium minutum.  Scale bar: 25 micrometres ( = 1/40^th of a millimetre). 

The desmids in the lower plate, in particular, show one of their key characteristics very clearly: their cells are divided into two distinct lobes (“semicells”) joined by an isthmus (the word desmid comes from the Greek desmos, meaning “bond”).  The image of Staurastrum manfeldtii var. productum also shows a number of bacteria growing on the cell: these are probably growing within the mucilage that desmids secrete around themselves whilst there are distinct pyrenoids in the two Xanthidium species.  Their predilection for soft water means that they need the carbon-concentrating mechanisms that these contain if they are to thrive.   Not all desmids live in water as soft as this, and some are able to use inorganic bicarbonate to fuel their photosynthetic engine, but there will be little or no bicarbonatae in a habitat such as Dock Tarn.   I wrote about these carbon concentrating mechanisms in algae from Ennerdale Water (see “Concentrating on carbon …”) and the two filamentous algae that featured in that post, Mougeotia and Spirogyra, both belong to the same class within the green algae as the desmids (Conjugatophyceae or Zygnemtetophyceae).

There will be more about desmids on this blog over the next few months in preparation for a the weekend of 15-17 September when I am organising a joint meeting of the British Phycological Society and Quekett Microscopical Club in Windermere.  We’ll be visiting some other Lake District tarns known to be rich in desmids during this weekend and have Dave Johns and Allan Pentecost on hand, amongst others, to offer expert advice on what we find.  There are still a few places left, so hurry up to book your place.  I haven’t done a great job of selling the Cumbrian climate in this post but we have the use of the Freshwater Biological Association facilities, including a laboratory and the library, so no one need get damper than they want.   See you there…

More desmids from Dock Tarn: d. Euastrum cuneatum; e. Xanthidium cristatum var. uncinatum; f. Xanthidium antilopaeum; g. Staurastrum manfeldtii var. productum.   Scale bar: 25 micrometres
( = 1/40^th of a millimetre). 

References

Coesel, P.F.M. (1994). On the ecological significance of a cellular mucilaginous envelope in planktic desmids. Algological Studies 73: 65-74.

Kiemle, S.N., Domozych, D.S. & Gretz, M.R. (2007). The extracellular polymeric substances of desmids (Conjugatophyceae, Streptophyta): chemistry, structural analyses and implications in wetland biofilms. Phycologia 46: 617-627.

Spijkerman, E., Maberly, S.C. & Coesel, P.F.M. (2005).  Carbon acquisition mechanisms by planktonicdesmids and their link to ecological distribution. Canadian Journal of Botany 83: 850–858.

 

Hilda Canter-Lund competition 2016 second prize winner

A short while ago I wrote about Tiffany Stephens winning entry for the 2016 Hilda Canter-Lund prize.   Following that, the Council of the British Phycological Society agreed that a second prize, of equal value, would also be awarded, starting this year, which means that I am very pleased to announce that Petr Znachor’s image of summer phytoplankton from the Řìmov Rservoir in the Czech Republic will also be honoured by the society.

The rationale for the decision is that Hilda Canter-Lund was primarily a photographer of the microscopic world, yet five of the seven winners of the competition to date have either been of images of macroalgae or (in the case of the 2009 winner) a seascape in which an algal bloom is prominent.  I suspect that there are a number of reasons for this, but the greater technical challenges facing anyone who wishes to photograph the microscopic world plays a key role.  The first prize is awarded based on a vote by members of the BPS Council; the second prize, by contrast, will be awarded at the judge’s discretion, but for an image in a contrasting style.   This year, as Tiffany Stephens won with an image of the macroalga Durvillaea antarctica, the award goes to Petr Znachor but there is no reason why, in future years, a microalgal image may get the most votes, in which case a macroalgal image will get the other prize.

Petr’s image shows summer phytoplankton in the eutrophic Řìmov Rservoir dominated by the desmids Cosmarium and Staurastrum. It was taken during examination of a sample that was collected as part of a long-term monitoring program and concentrated with 20 µm plankton net.  He used an Olympus BX51 microscope with Nomarski contrast lighting and an Olympus DP70 camera.

Petr Znachor received his Ph.D. from the University of South Bohemia (Czech Republic) in 2003. He is currently a research associate at the Institute of Hydrobiology where his research focuses on phytoplankton ecology and, in particular, the ecology of reservoirs and analyses of long-term time series of data. Ever since he first looked through a microscope he was astonished by the myriad beautiful shapes and colours of phytoplankton existing in a single drop of water. He hopes that his pictures raise awareness of the importance of these tiny organisms.

As do we.

More from Loughrigg Fell

As I do not pretend to great expertise on the desmids, I sent photographs of the specimens I collected during my visit to Loughrigg (see “A visit to Loughrigg Fell”) to Dave John who, in turn, passed them to David Williamson, to confirm their identities.   David Williamson co-authored the most comprehensive work on British desmids currently available, so I’m pleased to have his views on these specimens. To be honest, I was a little disappointed that I found so few desmids at a location from which so many had been recorded in the past. But then I am not a desmid expert, and may not have been looking in the best places.

Desmids from the margins of Lily Tarn, Loughrigg Fell, Cumbria, May 2015. a. Netrium digitus var. latum; b. Closterium dianae; c. Closterium dianae var. minus; d. Closterium directum (e. shows an entire cell of C. directum, photographed at lower magnification). Scale bar: 25 micrometres (= 1/40^th of a millimetre).

I also found several cells of Eremosphaera viridis in squeezings from submerged Sphagnum at the edge of Lily Tarn.   At first, I thought that this was a colony of small cells but it is, in fact, a single large cell containing numerous small chloroplasts around the edge, giving it a very distinctive appearance. Like the desmids, it is a member of the Chlorophyta, or green algae, but it belongs to a different order, the Chlorellales rather than the Zygnemetales. That means that they are as different to one another as a rat is to a human.   By contrast, Euglena mutabilis, which we met in the previous post, is as different from a desmid as a human is from a slug.

I can recommend the desmids to anyone interested in microscopy.   They are, in many ways, much more amenable to amateur study than the diatoms. Desmids are generally about an order of magnitude larger than diatoms, which means that you can study them with a medium-power objective, rather than an expensive oil-immersion objective.   There is, in addition, a good English-language guide available whereas much of the key literature on diatoms is in German.   There are also plenty of sources of information available online. The only drawback with desmids is that their habitats are less widespread. Alternatively, I could put a positive spin onto this and remind you that a fascination with desmids will take you to some of our most spectacular landscapes.

Eremosphaera viridis from submerged Sphagnum at the margin of Lily Tarn, Loughrigg Fell, Cumbria, May 2015. Scale bar: 25 micrometres (= 1/40^th of a millimetre).

Reference

Brook, A.J. & Williamson, D.B. (2010): A Monograph on some British Desmids. Ray Society, London.

Back to the bog

The microscopic world of an Upper Teesdale Sphagnum bog revisited, with diatoms and desmids living on and in the spaces between Sphagnum leaves and diatoms The chlorophyllose cells are about ten micrometres in diameter (1/100^th of a millimetre) whilst the desmid in the foreground (Cosmarium ralfsii) is about 100 micrometres (1/10^th of a millimetre) across.

I showed my first attempt at portrayal of the microscopic life of a Sphagnum bog a few weeks ago (see “Swimming with desmids …“) but, at the same time, I felt that there were a few elements that could be improved, so here is my second effort. The first time I tackle a new subject, there are usually technical issues to address and, perhaps, the outcome was not quite as naturalistic as I would have liked. Not that I, or anyone else, really has a great insight into “natural” in this particular context, but then none of us have seen dinosaurs hunting in Jurassic forests, but that hasn’t stopped people producing “naturalistic” illustrations.   In my first picture, just capturing the underside of a Sphagnum leaf in something approaching linear perspective and including two desmids seemed like progress. This time, there are two Sphagnum leaves plus a couple of diatoms – a single cell of Eunotia implicata on the underside of one leaf, plus a couple of cells of Tabellaria flocculosa on the other leaf. Both of these specimens were present when I made my initial observations of the Sphagnum leaves back in December.

One additional issue that the composition of this picture raised, is that the morphology of the upper surface of a Sphagnum leaf differs from that of the lower surface. This relates to the relative size of the chlorophyllose and hyaline cells (see the schematic diagram in Swimming with desmids ...). There were moments, I promise you, when I interrupted my meditations on Sphagnum morphology to wonder if I should go and get a life.

My justification, if any is needed, is that peering down a microscope and compiling data about the species present without sometimes contemplating the organisms in their natural state seems like an equally bizarre way of spending one’s life. I write this post having peer-reviewed a paper for the journal Limnology and Oceanography this afternoon. The work was quite interesting but, at the same time, I felt that it was a very sterile, technical study that had abstracted the real world into long lists of diatom species and then processed these using complicated statistical methods, without giving much sense of a real understanding of the ecosystems that they were studying.

Swimming with desmids …

My sampling trip to Upper Teesdale in search of desmids (see “Hunting for desmids in Upper Teesdale”) has now yielded another picture, this time figurative rather than semi-abstract.   I have tried to depict the world inside a Sphagnum bog so have shown two desmids underneath a canopy of Sphagnum leaves.   The Sphagnum leaves have a characteristic structure, with chlorophyllose cells alongside water-filled “hyaline” cells. The desmids live, in effect, inside a glass-roofed conservatory although I have probably conveyed an overly bright impression of the subaquatic world of the bog.   The reality is that the slow decay of Sphagnum yields brown humic materials that create an altogether murkier environment.

The microscopic world of an Upper Teesdale Sphagnum bog, with desmids living in the space underneath Sphagnum leaves.   The chlorophyllose cells are about ten micrometres in diameter (1/100^th of a millimetre) whilst the desmid in the foreground (Cosmarium ralfsii) is about 100 micrometres (1/10^th of a millimetre) across.

I’ve tried to illustrate the structure of a Sphagnum leaf in the diagram below.   Compare this with the photograph in “More from Upper Teesdale” (showing the view from above) the leaf to get an idea of how the leaf is constructed.   It also demonstrates why Sphagnum moss is capable of absorbing so much water: two-thirds or more of the leaf is composed of empty space and there is even a convenient pore to let the water in.

A schematic cross-section through a leaf of Sphagnum showing the arrangement of hyaline and chlorophyllose cells.   The chloropyllose cells are about 10 micrometres (1/100^th of a millimetre) across.

My illustration of the microscopic world of a Sphagnum bog is a step outside my comfort zone, as I tried to combine the various elements together from separate microscopic images.   Microscopy tends to flatten perspective, partly because specimens are squashed onto microscope slides but also because of the focal length of the lenses involved.   Added to this was the problem of depicting the sinuous chlorophyllose cells in an approximation of single-point perspective.   Almost as soon as I had finished the picture, I was thinking about how I could be improving the next version. Striving towards realism is, itself, an ongoing mind experiment that offers tantalising glimpses of an otherwise hidden world.

Abstraction and reality in Upper Teesdale

Just before Christmas I wrote about a visit to Upper Teesdale to collect desmids (see “Hunting for desmids in Upper Teesdale”) and mentioned that I was working towards a painting.   That painting is now finished and is reproduced below.   The style of this painting is quite to the other pictures I’ve been working on recently, drawing on ideas I explored during the final year of my Fine Art degree.   I was interested, during this period, in exploring the boundaries between figurative and abstract art and found algae to be an ideal resource for this investigation.   To me, they are living organisms with defined parameters yet they are beyond the boundaries of most people’s sense of reality.   “Most people” included my tutors and this led to some challenging discussions about just how far I could alter the shapes and colours I was using.   They felt that I was too rigid and unwilling to push my artistic experiments too far. In many ways they were right but there were also times when I felt that they were asking me to do the phycological equivalent of drawing a cow with five legs.

Upper Teesdale. 2015. 86 x 91 cm. Acrylic on canvas,

The picture shows five different desmids that I collected from Upper Teesdale in December.   To me, these organisms are as much a characteristic of the area as the more famous gentians (see “Blue skies and blue flowers in Upper Teesdale”) and to present them in an context that evokes abstract art emphasises the lack of familiarity that most of the visitors to this area has to these organisms.

The lower picture shows a close-up of some of the desmids in the picture, to show how the painting was built up as a series of washes of very dilute acrylic paint over a white ground, with the details of the desmid blocked out in stages using masking fluid. The result is a “negative” image of each of the desmids. The final stage of the painting was to use a syringe to add translucent trails of paint thinned with acrylic gloss medium to give a translucent effect that imparts some visual energy into the finished picture.

You can see more work on this general theme at http://www.martynkelly.co.uk/other_paintings.html.

Upper Teesdale. Detail.

 

Hunting for desmids in Upper Teesdale

Cronkley Fell from near Widdybank Farm, December 2014

We had Upper Teesdale to ourselves on Saturday morning, most fellow-walkers having been deterred, perhaps, by the strong westerly winds.   They missed some spectacular lighting as the weak December sun briefly broke through the clouds to light the Pennine fells.   The open fire in the bar of the Langdon Beck Hotel, and the bowl of hot soup, were very welcome when we finally completed our regular 13 kilometre loop.

As ever, my eyes are forever adjusting between the grand panoramic landscapes of Upper Teesdale, and the small scale botanical wonders all around us. Today, my primary interest was the desmids that inhabit the blanket bog and I diverted off the boardwalks that mark the Pennine Way’s course along the Tees to squeeze the brown water from handfuls of Sphagnum moss into my sampling tubes. The peaty-brown water that I collect usually contains a diverse assemblage of desmids, which I’m collecting to form the basis of a new painting.

I wrote about the desmids from Upper Teesdale last year (see “More from Upper Teesdale”) but since then I have upgraded the camera on my microscope and also purchased focus stacking software (see “Now … with added depth of field …”) that makes a repeat visit worthwhile.   Many of the desmids I found were the same as those in my sample from March last year, though there were a couple of strangers and the long moon-shaped cells of Closterium striolatum did not fit neatly into a single field of view.   However, a quick scan of the slide revealed half a dozen abundant species and a few that were represented by just occasional specimens as well as plenty of diatoms, other green algae and protozoans.

Squeezing Sphagnum to collect desmids in Upper Teesdale, December 2014.   The photo doesn’t really capture the reality of the 30 km/hour winds and associated wind-chill.

When I look at desmids, I’m way out of my comfort zone, but there is something about their symmetrical, often intricate outlines that is beguiling and makes me want to continue scanning the slide in search of more.   This particular sampling trip is the first step of the research for a new painting and, like diatoms, the desmids have a beauty that transcends the limits of objective science. That’s my agenda for this painting: to use the microscopic life of Upper Teesdale’s boggy pools as the counterpoint to the rugged, panoramic beauty of the landscape itself.   I could use pictures of desmids from the books I have on my shelves, but I like my pictures to have a direct link with a particular place and time. It is veracity that, perhaps, few will appreciate, but without this the end-product would just be a collection of abstract shapes.

Upper Teesdale desmids. a. Netrium oblongum; b. Micrasterias oscitans (var. mucronata); c Eurastrum didelta; d. Desmidium cf. aptogonum; e. Cosmarium ralfsii.; f. Micrasterias truncata.   Scale bar: 50 micrometres (1/20^th of a millimetre).