Talking about the weather …

September is here.  When I visited this site two months ago we were in the midst of the heatwave and the samples I collected from the Wear at Wolsingham were different to any that I have seen at this location before, dominated by small green algae (see “Summertime blues …”).   As I drove to Wolsingham this time, I could see the first signs of autumn in the trees and the temperatures are more typical of this time of year.   We have had rain, but there has not been a significant spate since April and this means that there has been nothing to scour away these unusual growths and return the river to its more typical state.

That does not mean, however, that there have been no changes in the algae on the submerged stones.  Some of these differences are apparent as soon as I pick up a stone.  Last month, there was a thin crust on the surface of the stones; that is still here but now there are short algal filaments pushing through, and the whole crust seems to be, if anything, more consolidated than in July, and I can see sand grains amidst the filaments.   Biofilms in healthy rivers at this time of year are usually thin, due to intense grazing by invertebrates, so I’m curious to know what is going on here this year.

A cobble from the River Wear at Wolsingham, showing the thick biofilm interspersed with short green filaments.   Note, too, the many sand grains embedded in the biofilm.  The bare patch at the centre was created when I pulled my finger through it to show how consolidated it had become.  The cobble is about 20 centimetres across.

Many of the organisms that I can see when I peer at a drop of my sample through my microscope are the same as those I saw back in July but there are some conspicuous differences too.   There are, for example, more desmids, some of which are, by the standards of the other algae in the sample, enormous.   We normally associate desmids with soft water, acid habitats but there are enough in this sample to suggest they are more than ephemeral visitors.   And, once I had named them, I saw that the scant ecological notes that accompanied the descriptions referred to preferences for neutral and alkaline, as well as nutrient-rich conditions.  Even if I have not seen these species here before, others have seen them in similar habitats, and that offers me some reassurance.    In addition to the desmids, there were also more coenobia of Pediastrum boryanum and Coelastrum microporum compared to the July sample.

A view of the biofilm from the River Wear at Wolsingham on 1 September 2019. 

There were also more diatoms present than in my samples from July – up from about 13 percent of the total in July to just over 40 per cent in September.   The most abundant species was Achnanthidium minutissimum, but the zig-zag chains of Diatoma vulgare were conspicuous too.  The green filaments turned out to be a species of Oedogonium, not only a different species to the one I described in my previous post but also with a different epiphyte: Cocconeis pediculus this time, rather than Achnanthidium minutissimum.   I explained the problems associated with identifying Oedogonium in the previous post but, even though I cannot name the species, I have seen this form before (robust filaments, cells 1.5 to 2 times as long as broad) and associate it with relatively nutrient-rich conditions.  That would not normally be my interpretation of the Wear at Wolsingham but this year, as I have already said, confounds our expectations.   I did not record any Cladophora in this sample but am sure that, had I mooched around for longer in the pools at the side of the main channel, I would have found some filaments of this species too.

Desmids and other green algae from the River Wear at Wolsingham, 1 September 2019.  a. Closterium cf. acerosum; b. Closteriumcf. moniliferum; c. Cosmarium cf. botrysis; d. Closterium cf. ehrenbergii; e. Coelastrum microporum; f. Pediastrum boryanum.   Scale bar: 50 micrometres (= 1/20th of a millimetre).  

It is not just the differences between months this year that I’m curious about.  I did a similar survey back in 2009 and, looking back at those data, I see that my samples from August and September in that year had a very different composition.   There was, I remember, a large spate in late July or early August, and my August sample, collected a couple of weeks later had surprised me by having a thick biofilm dominated by the small motile diatom Nitzschia archibaldii.   My hypothesis then was that the spate had washed away many of the small invertebrates that grazed on the algae, meaning that there were few left to feed on those algae that survived the storm (or which had recolonised in the aftermath)..   As the algae divided and re-divided, so they started to compete for light, handing an advantage to those that could adjust their position within the biofilm.   This dominance by motile diatoms was, in my experience of the upper Wear, as uncommon as the assemblages I’m encountering this summer, though probably for different reasons.

Other algae from the River Wear at Wolsingham, September 2018.    The upper image shows Diatoma vulgare and the lower image is Oedogonium with epiphytic Cocconeis pediculus.   Scale bar: 20 micrometres (= 1/50th of a millimetre).

I suspect that it is the combination of high temperatures and low flows (more specifically, the absence of spates that might scour away the attached algae) that is responsible for the present state of the river.  This, along with my theory behind the explosion of Nitzschia archibaldii in August 2009, both highlight the importance of weather and climate in generating some of the variability that we see in algal communities in rivers (see “How green is my river?”).   The British have a reputation for talking about the weather.   I always scan the weather forecasts in the days leading up to a field trip, mostly to plan my attire and make sure that I will, actually, be able to wade into the river.  Perhaps I also need to spend more time thinking about what this weather will be doing to the algae I’m about to sample.

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Desmid diversity …

Back in September, I wrote about a joint British Phycological Society and Quekett Microscopical Club field weekend looking at desmids in the Lake District (see “Desmid Masterclass”, “Lessons from School Knott Tarn” and “Different tarn, different desmids …”).  Dave John sent some of the samples that we collected to David Williamson, the UK’s leading expert on desmids but, at 92, too frail to join us, and he has now sent back some fine drawings illustrating the range of desmids that he encountered.

Two of the tarns (Long Moss Tarn, Kelly Hall Tarns) are already recognised as Internationally Important Plant Areas (IPAs) for desmids because of their desmid diversity and containing internationally very rare desmids (based largely on David Williamson’s records) so their diversity is not a complete surprise to us.  Nonetheless, David found a total of 129 desmid taxa in the three tarns, whilst another desmid specialist, Marien van Westen, identified almost 160 desmids in another set of samples from the same tarns.

The drawings are arranged in three plates, one for each tarn.   Desmids identified by David Williamson from the three tarns are illustrated.  The desmids have been numbered and the captions prepared by David John who is analysing the findings and comparing them with surveys dating back to the 1970s.   David Williamson has drawn the taxa at different scales to roughly balance the arrangement on the collage, and adjusted the sizes so important details are visible.   No details of the chloroplasts are given since all samples had been preserved in formalin.  A few of the desmids, particularly those that are very long, have not been included in the plates.

Desmids from Long Moss Tarn (SD 292 936), September 2017.   Long Moss Tarn is shown in the photograph at the top of this post.

Desmids from Kelly Hall Tarn (SD 289 933), September 2017.

Desmids from School Knott Tarn (SD 427 973), September 2017.

Key

1-Actinotaenium diplosporum; 2-Actinotaenium turgidum;  3-Bambusina borreri;  4-Closterium acerosum var. borgei; 5-Closterium angustatum;  6-Closterium archerianum var. pseudocynthia;  7-Closterium archerianum; 8-Closterium attenuatum;  9-Closterium baillyanum var. alpinum; 10-Closterium baillyanum; 11-Closterium closterioides; 12-Closterium costatum; 13-Closterium dianae var. arcuatum; 14-Closterium dianae var. minus;  15-Closterium didymotocum; 16-Closterium incurvum; 17-Closterium intermedium; 18-Closterium kuetzingii;  19-Closterium lunula; 20-Closterium navicula;  21- Closterium setaceum; 22-Closterium striolatum; 23-Cosmarium amoenum; 24-Cosmarium anceps; 25-Cosmarium binum; 26-Cosmarium brebissonii; 27-Cosmarium contractum;  28-Cosmarium davidsonii; 29-Cosmarium debaryi;  30-Cosmarium depressum; 31-Cosmarium formosulum; 32-Cosmarium hostensiense; 33-Cosmarium incrassatum var. schmidlei; 34-Cosmarium margaritatum; 35-Cosmarium margaritiferum; 36-Cosmarium monomazum var. polymazum;  37-Cosmarium obtusatum;  38-Cosmarium ornatum; 39-Cosmarium ovale;  40-Cosmarium pachydermum; 41-Cosmarium pachydermum var. aethiopicum; 42-Cosmarium perforatum var. skujae; 43-Cosmarium portianum; 44-Cosmarium punctulatum;  45-Cosmarium quadratum; 46-Cosmarium quadrum; 47-Cosmarium subochthodes var. majus; 48-Cosmarium subtumidum var. groenbladii;  49-Cosmarium subundulatum; 50-Cosmarium tetragonum var. ornatum ; 51-Cosmarium tetraophthalmum; 52-Cosmarium variolatum;  53-Cosmocladium tuberculatum; 54-Desmidium aptogonum; 55-Desmidium swartzii; 56-Docidium baculum; 57-Euastrum ampullaceum; 58-Euastrum ansatum;  59-Euastrum bidentatum var. speciosum; 60-Euastrum gemmatum; 61-Euastrum luetkemulleri; 62-Euastrum oblongum; 63-Euastrum pectinatum; 64-Euastrum pulchellum; 65-Euastrum verrucosum; 66-Gonatozygon aculeatum; 67-Gonatozygon brebissonii; 68-Groenbladia undulata; 69-Haplotaenium minutum;  70-Hyalotheca dissiliens;  71- Micrasterias americana var. boldtii; 72-Micrasterias compereana; 73-Micrasterias crux-melitensis; 74-Micrasterias denticulata; 75-Micrasterias furcata; 76-Micrasterias pinnatifida;  77-Micrasterias radiosa; 78-Micrasterias rotata; 79-Micrasterias thomasiana; 80-Micrasterias truncata; 81-Netrium digitus; 82-Netrium digitus var. latum; 83-Netrium interruptum;  84-Penium exiguum; 85-Penium margaritaceum; 86-Pleurotaenium coronatum var. robustum;  87-Pleurotaenium ehrenbergii; 88-Pleurotaenium truncatum; 89-Sphaerozosma filiforme; 90-Staurastrum arachne;  91-Staurastrum arctiscon; 92-Staurastrum bieneanum; 93-Staurastrum boreale var. robustum; 94-Staurastrum cristatum; 95-Staurastrum dilatatum; 96-Staurastrum inconspicuum; 97-Staurastrum kouwetsii; 98-Staurastrum lapponicum; 99-Staurastrum maamense; 100-Staurastrum polytrichum; 101-Staurastrum productum; 102-Staurastrum quadrangulare; 103-Staurastrum striolatum; 104-Staurastrum teliferum; 105-Staurastrum tetracerum; 106-Staurodesmus convergens; 107-Staurodesmus convergens var. wollei; 108-Staurodesmus cuspidatus var. curvatus; 109-Staurodesmus megacanthus; 110- Xanthidium antilopaeum; 111-Xanthidium antilopaeum var. laeve; 112-Xanthidium antilopaeum var. polymazum; 113-Xanthidium cristatum.

Taking desmids to the next dimension …

Participants at the British Phycological Society / Quekett Microscopical Club field weekend at the Freshwater Biological Association, September 2017.  Scale bar: one metre (= 1,000,000 micrometres).

A theme that has run through this blog over the years has been that what you see down a microscope is often a highly distorted view of reality and at the end of our weekend of desmid hunting, Chris Carter gave a talk that also made this point, using desmids as a case study.  In essence, we had spent much of Saturday and Sunday morning peering down microscopes at three-dimensional objects that appeared, as a result of the very shallow depth of field that is characteristic of high magnification images, two dimensional.   We were then matching these to two-dimensional representations in the Floras and identification guides that we had to hand.  Dave explained a few tricks that experts use, such as applying gentle pressure to a coverslip with a fine needle, to turn desmids in order to see them from other angles but, mostly, we were restricted to very flattened views of desmids.

Chris has tackled this problem from several directions over the years, including experiments with anaglyphs (see “Phworrrrhhh …. algal sex in 3D!“) as well as the very careful manipulation of a long, cylindrical Pleurotaenium that won the Hilda Canter-Lund prize earlier this year.   He has also produced a number of plates with desmids laid out almost as if on an engineer’s drawing board, with front, top and side views.   Several of these are on Algaebase, but one example is reproduced below.  Microscopists learn to use the fine-focus control to appreciate the depth of the objects that they are examining and Chris also shows how it can reveal the nature of surface ornamentation on different parts of the cell.  The temptation, given a series of photos such as these (excluding the side view) would be to use “stacking” software to produce a single crisp image.  This is appropriate in some situations but you are, in truth, just producing a crisp two-dimensional image rather than offering any insights into the true shape of the cell.

Staurastrum furcatum from Botswana, photographed by Chris Carter.

Another technique that can be used to generate three-dimensional images is, of course, scanning electron microscopy.  However, this is beyond the budget for anyone outside a major institution.  This has helped greatly get a better understanding of the morphology of diatoms, in particular, but the third dimension comes at a price.   Scanning electron micrographs take us to an opaque, monochrome world, purged of the vivid colours that the microscopic world usually offers us.

Chris’ pièce de résistance, however, was a three-dimensional model of a Staurastrum, produced by the 3D printing company Shapeways and loosely-based on various pictures of S. furcatum and presented to him as a 70th birthday present by his son.  The main point is to demonstrate the symmetry and gross features of a typical Staurastrum rather than to be a taxonomic blueprint. The designers were very helpful but it does hint at what is possible with modern technology.

Chris Carter’s three-dimensional model of Staurastrum.  It is about six centimetres across.   You can buy your own copy from Shapeways by following this link …

The missing ingredient in this recipe is imagination.  Or, to be more precise, the viewer’s imagination as Chris has clearly demonstrated that he is not lacking in that department.  Once you have a sense of the three-dimensional form of a Staurastrum, you be able to use that knowledge every time you look at a two-dimensional image of a desmid through a microscope.   Seeing, as Ernest Gombrich reminds us in his great book Art and Illusion, is as much about using prior experiences to interpret the raw data collected by our optic nerves as it is about the patterns of light that stimulate our retinas.   Just as a child can look at a two-dimensional image of a cat in a book and match this to the real creatures that he or she encounters, so knowing about Staurastrum’s third dimension helps us to interpret the flat shapes that we see.

At a more basic level, all identification is a matter of matching the objects we see either to schemata stored in our memory or to patterns in books.  This, in turn, helps us to understand why the microscopic world seems so strange and mysterious to those who do not study it.  It all comes down to having (or not having) the prior experiences that generate recognition.   At one level, there are gasps of astonishment as people with none of these schemata in their memories encounter the beauty of desmids for the first time.  And then there is Frans Kouwets, another speaker at the meeting , who is busy cataloguing 750 different species of one genus, Cosmarium.   And in between there are the rest of us …

Frans Kouwets explains his fascination with Cosmarium to the British Phycological Society / Quekett Microscopical Club field meeting at the Freshwater Biological Association in September 2017.

Different tarn, different desmids …

Geoff and Chris, two of our band of desmid hunters, chose to stay in the FBA’s brand new holiday apartments and, rather than cross the lake to join us on Saturday morning they headed out to Moss Eccles Tarn, in the area between Esthwaite Water and Windermere.   One of Dave’s first dips into one of their samples yielded an almost pure monoculture of another filamentous desmid, Spherozosma vertebratum which presented some beguiling abstract patterns on my computer monitor.

Spherozosma vertebratum from Moss Eccles Tarn, September 2017.   Scale bar: 25 micrometres (= 1/40th of a millimetre).

Curiously, after our first encounter with Spherozosma vertebratum we did not see it in any of our other dips into the Moss Eccles samples although there were plenty of other desmids on display.   The most abundant of these was Staurastrum productum and, usefully, there were examples showing both apical and side views.   The three arms are distinctive (and distinguish it from relatives such as S. arachne which have five) and you can also see the knobbly “verrucae” on the spines as well as a broad mucilaginous envelope around the cells.

Staurastrum productum in side (left) and apical (right) views.  Images photographed from a computer monitor so apologies for their poor quality.  Scale bar: 25 micrometres (= 1/40th of a millimetre).

Another desmid with spines and mucilage was quite common.  This was Staurodesmus bulnheimii.  Spines slow the rate of sinking so are associated with several genera of predominately planktonic desmids.   The star-shaped arrangement of colonies of the diatom Asterionella formosa play a similar role (see “Little bugs have littler bugs upon their backs to bite ‘em”).   There were also several cells  of a small Cosmarium species, including some that had recently divided and the image shows how one cell has split down the central isthmus and a new semicell is growing back on each of the two daughter cells.   Finally, I have included an illustration of Micrasterias radiosa.  To the uninitiated this may look little different to M. compereana, illustrated in the previous post, but if you look closely you will see that the incisions between the lobes are much deeper in M. radiosa.

One sample from Moss Eccles Tarn kept me busy for half the morning and this account describes only part of the diversity.   Note how the differences between this and the School Knott Tarn sample are not just in the genera and species present but also in the life-forms I found.  The School Knott sample was from a Sphagnum squeezing whilst the Moss Eccles sample was from a plankton net.  That explains why I saw more spine-bearing desmids in the latter.  If I had looked at a plankton sample from School Knott and a Sphagnum squeezing from Moss Eccles, I might have found a different balance of life-forms between the two tarns.   But time was running out and I had to move on …

More desmids from Moss Eccles Tarn, September 2017: a. Staurodesmus bulnheimii; b. Cosmarium quadrifarium var. hexastichum; c. Euastrum cf. gemmatum.   Scale bar: 25 micrometres (= 1/40th of a millimetre).

Micrasterias radiosa from Moss Eccles Tarn, September 2017.   Scale bar: 25 micrometres (= 1/40th of a millimetre).

Lessons from School Knott Tarn …

As not everyone could join us on our excursion on Friday afternoon, we repeated the exercise on Saturday morning, heading to a small tarn just a short walk from Windermere and Bowness.   Despite its proximity to two of the busiest towns in the Lake District, there were very few other people around to disturb our peace whilst we collected samples.   As at Kelly Hall and Long Moss Tarns, Dave had his plankton net out, but we also explored a boggy region at one end, finding more patches of Sphagnum but also extensive growths of Utricularia minor (Lesser Bladderwort), one of a small number of aquatic carnivorous plants.   Dave was particularly pleased by this find as he associates this particular plant with rich hauls of desmids.

It was tempting to linger in the sunshine beside School Knott Tarn but the green tinge of the water that dripped out of the Sphagnum squeezings in particular was enough to lure us towards the Freshwater Biological Association’s laboratories in order to start examining our samples.

Utricularia minor (Lesser Bladderwort) from School Knott Tarn, near Windermere, September 2017.   Several of the spherical bladders which trap small invertebrates are visible on the plant.

My selection of photographs below shows just a part of the diversity that we encountered during our microscopic examinations.  I was using a borrowed set-up and the images are all from photographs of the desmids displayed on computer monitor, which is far from ideal.   Some of the larger desmids – one large Closterium species in particular – were too large to fit onto the screen and have had to be omitted from this account.  There were also a number of cells of Eremosphaera (see “More from Loughrigg Fell”) and some Cyanobacteria (Merismopedia was quite common) so this is a very partial description of our microscopical adventures in School Knott Tarn.

The first two desmids, Spirotaenia condensata and Cylindrocystis gracilis, belong to a group of desmids called “saccoderm desmids”.  These are more closely related to filamentous green algae of the Zygnemetaceae that are old friends of this blog (see “Concentrating on Carbon, for example) and, in fact, we could think of these genera as being unicellular analogues of their filamentous cousins.   Spirotaenia, with its helical chloroplast, for example, recalls Spirogyra whilst Cylindrocystis’ two star-shaped chloroplasts is reminiscent of Zygnema.  Mesotaenium, which we did not see in this sample, has a plate-like chloroplast similar to that in Mougeotia.

The next two illustrations both show species of Micrasterias.  Of these, M. compereana generated a vigorous discussion amongst our experts. This would have been described as M. fimbriata using the latest British floras but a paper has been published recently which uses molecular data to demonstrated the need to split the species. Finally, we have representatives of Euastrum and Haplotaenium, two genera that we also met at Dock Tarn (see “Damp days in search of desmids …”) although the species are different.   Haplotaenium differs from Pleurotaenium in the number and form of the chloroplasts and also because it lacks a terminal vacuole.

Desmids from Sphagnum squeezings from School Knott Tarn, September 2017: a. Spirotaenia condensata; b. Cylindrocystis gracilis; c. Micrasterias compereana; d. Micrasterias crux-meltensis; e. Euastrum oblongum; f. Haplotaenium rectum.  Scale bar: 25 micrometres (= 1/40th of a millimetre).

Four more desmids are illustrated on the lower plate.   Of these, we have seen Netrium digitus in Dock Tarn and the illustration there is better than this one, showing the undulating nature of the chloroplast margins quite clearly.   The desmid below this, Closterium closterioides caused some confusion at first.   We usually associate Closterium with lunate (moon-shaped) cells (see “More from Loughrigg Fell”) but this species is straight, sending me towards the section on Netrium in my Flora.  However, Netrium lacks terminal vacuoles whereas this specimen has prominent vacuoles at both ends.   We also found a variety, C. closterioides var. intermedium, in the same sample.

The final desmid that I have illustrated is a filamentous form: Desmidium schwartzii.  In contrast to Hyalotheca dissilens (see “Desmids from the Pirin mountains”) there is no obvious mucilaginous sheath around this specimen, but this may be an anomaly of this population or an artefact of the microscopy set-up.   We are looking at the side view of a chain of cells but if we were to look at the end view of one cell it would be triangular in this particular species.  The chloroplast fills most of the cell and has projections running into the corners of the cells.  However, as the filaments of the cells are slightly twisted, these projections appear to shift in position from cell to cell, giving a helical appearance.  I’ve tried to illustrate this with a schematic diagram.

More desmids from Sphagnum squeezings from School Knott Tarn, September 2017: g. Netrium digitus; h. Closterium closterioides var. closterioides; i. C. closterioides var. intermedium; j. Desmidium schwartzii Scale bar: 25 micrometres (= 1/40th of a millimetre).

This short post gives some idea of the diversity in a single sample from a single Tarn.   Dave handed all the samples we collected over to David Williamson on his way back south and we’ll get a fuller list of their diversity in due course.  This one sample occupied me for the latter part of Saturday morning and all of the afternoon.   On Sunday, I moved on to look at another sample and I’ll write about that in another post very soon.

A schematic view of a chain of Desmidium cells, showing the arrangement of the chloroplast seen in apical view (k.) and the implications of slight twisting of the filament on appearance (l.).  Diagram adapted from John et al. (2011).

Reference

John, D.M., Whitton, B.A. & Brock, A.J. (2011). The Freshwater Algal Flora of the British Isles. 2nd Edition. Cambridge University Press, Cambridge.

Neustupa, J., Šťastný, J. & Škaloud, P. (2014). Splitting of Micrasterias fimbriata (Desmidiales, Viridiplantae) into two monophyletic species and description of Micrasterias compereana sp. nov.  Plant Ecology and Evolution 147: 405-411.

Desmid masterclass …

My chance encounter with desmids in the Pirin Mountains (described in the previous post) was serendipitous insofar as, less than a fortnight after my return from Bulgaria I find myself standing beside a soft water tarn in the Lake District noted for its rich desmid flora.  I’m here for a joint field meeting of the British Phycological Society and Quekett Microscopical Club and, having decided on a venue, realised that the location of the Freshwater Biological Association’s laboratory meant that desmids were the obvious focus of our investigations.

So, on Friday afternoon, a small convoy of vehicles made its way from the FBA, on the west side of Windermere, via Hawkshead and Coniston, to two small tarns for an initial collecting trip.  Dave John, our in-house desmid expert, had been directed to these by David Williamson, the UK’s leading expert on desmids (but, alas, too elderly and infirm to join us), who had recorded large numbers of desmids from both Kelly Hall Tarn and Long Moss Tarn.   Fortunately, the weather today was rather more amenable to sampling than my previous desmid-hunting trip in this part of the world (see “Damp days in search of desmids”).

The predilection of desmids for boggy areas means that there is always a risk of damp feet when –collecting samples, especially when grabbing a chance sample whilst out walking.   Last time, my problem was that footwear appropriate to getting to Dock Tarn was not really appropriate for getting into Dock Tarn; today, however, I could tramp the short distance from our vehicles in wellies.  Dave noted wryly that most of David Williamson’s best sites were close to car parks, and that many of the sites sampled by the Wests, writers of a significant desmid flora of Britain in the late 19th century, were similarly placed closed to train stations.   Such practicalities probably lie behind more of our decisions about where to sample than we care to admit.

Once by the edge of the Kelly Hall Tarn, Dave gave us a demonstration of sampling desmids, starting with David Williamson’s preferred method using a plankton net.   There are two options – either casting a net attached to a piece of rope, then drawing it back through the water  or using a small plankton net attached to a telescopic handle.   Dave’s has a mesh of 33 micrometres (1/30th of a millimetre) which is fine for relatively large algae such as desmids.   He took care to avoid disturbing the bottom, in order to collect only phytoplankton but also pulled the through patches of submerged plants in order to dislodge the algae that live around their stems and leaves.  With care, it is also possible to brush the net gently against the bottom, dislodging some of the heavier desmids that typically sit just on the surface of the bottom sediments.  Too much disturbance will mean that the net quickly clogs with fine sediment particles.

Dave John demonstrating how to sample desmids with a plankton net at Kelly Hall Tarn, Cumbria, September 2017.

From Kelly Hall Tarn it was a short uphill walk to Long Moss Tarn for our second demonstration.   There is usually a part of the perimeter of tarns in this part of the world that is marshy, often dominated by Sphagnum.  The hummocks of Sphagnum were of no great interest except as stepping stones to the edge but, once there, we could see the semi-aquatic Sphagnum cuspidatum living at the margins of the lake (moss cognoscenti describe S. cuspidatum as looking like “drowned kittens”).   Dave took a handful of this soft, damp moss, flicked it a couple of times to remove surplus water, then gently squeezed it, catching the water that oozed out of the moss in a small sampling bottle.   Holding this up to the light, we could see a distinct green tinge which brought a big smile to Dave’s face, anticipating the rich haul of desmids that awaited us.

Dave John demonstrating how to collect desmids by squeezing Sphagnum at Long Moss Tarn, Cumbria, September 2017.

A patch of Sphagnum cuspidatum at Kelly Hall Tarn: perfect desmid habitat.

Kelly Hall Tarn had one further attraction for me.   It is perched on a hillside overlooking Coniston Water and from a small knoll a couple of hundred metres from the tarn I had a wonderful view southwards down the lake.  In the middle distance I could see Peel Island which was the inspiration for “Wild Cat Island” in Arthur Ransome’s Swallows and Amazons, a book that I read and re-read many times as a child.   At the north end of the lake you will find Bank Ground Farm, which was the setting for “Holly Howe” in the book and which, I notice, still offers accommodation and can be booked via Airbnb.   Finally, on this theme, the Steamboat Museum in Windermere has the original “Amazon”, the sailing dinghy that is the centre of many of the adventures.

Enough of these digressions.   We now have samples from two tarns and the next post will start to explore the contents of these and other samples that we collected.

The view down Coniston Water from Long Moss Tarn.  Peel Island is in the centre of the picture.

 

 

Desmids from the Pirin mountains

Our travels in southern Bulgaria took us south from Rila Monastery to Bansko, on the edge of the Pirin Mountains and, from here, via a chair lift and a rather more strenuous walk than we had expected to Popovo Lake  situated in a corrie overlooked by rugged mountains soaring up to over 2800 metres.

The outflow from the lake cascades over the lip of the corrie and down the hillside to a series of smaller lakes, before merging with some other small streams to form the Mesta river which flows south from Bulgaria and through northern Greece to the Aegean Sea.   The footpath that took us back from Popovo took a gentler route down the hillside but brought us close enough to the first of this series of lakes for the bright green areas at the margins to pique our interest.  Getting closer, we found ourselves on soft, yielding Sphagnum bog, more familiar to us from the moorlands of northern England (see, amongst other posts, “Back to the bog“) than in southern Europe.   A lot of the rock that we had passed on our hike up from the chair lift terminus had been granite, so the water around us would clearly have been soft enough for Sphagnum and, I guess, the marshy land was testimony to a higher level of precipitation than the cloudless skies that we encountered suggested.

The first of the “Fish Popovski” lakes below Popovo Lake in the Pirin Mountains, southern Bulgaria, with the marshland area clearly visible in the foreground.

One of the pools in this bog attracted my attention: a mat-like portion of the substratum, had floated to the surface whilst still being loosely attached at one corner.   This is a good clue that the substratum is jam-packed with algae, doing a double job of binding the silty particles together into a cohesive whole and, at the same time, pumping out oxygen as a by-product of photosynthesis in order to make the mat buoyant.   I last wrote about this in 2013 when I found some mats of Oscillatoria limosa in my local river (see “More from the River Wear”).   The same phenomena seem to be at play here although, on closer investigation, it was desmids rather than Cyanobacteria which were responsible for the mat.   There were, in fact, far fewer filamentous algae in this particular mat, something that I quickly noticed as there was very little physical integrity to the mat, and it dissolved into a suspension of fine particles as soon as I tried to remove a piece.   Had I stayed until nightfall, I expect the mat would have gradually sunk again as the rate of photosynthesis declined and oxygen production ceased.

The desmid mat floating up from the bottom of the bog pool beside the first of the Fish Popovski lakes in the Pirin Mountains.

The most abundant desmids in the mat were Hyalotheca dissilens and Closterium baillyanum.  The former is a filamentous desmid, whose chains of cells are enclosed in a broad mucilage sheath and, whilst there were many fewer of these filaments than I have seen in more cohesive mats, I suspect that these played a role in trapping the other algae, plus organic and inorganic particulate matter to form the structure that I saw.  Closterium baillyanum, by contrast, has large, robust cells and, in this case, the cell wall has a distinct brown colour.  Other desmids that I found in my brief examination included Tetmemorus granulatus, which has cylindrical cells with a narrow incision in the broadly rounded apex (most clearly visible at the left-hand side of the illustration) and two species of Euastrum: E. humerosum and E. ansatum.  There were also a few large cells of Eremosphaera, a green alga though not a desmid (see “More from Loughrigg Fell”), and various assorted unicellular algae.  I’ll write about the diatoms in a separate post.

Some common desmids from the Pirin mountains: a. Hyalotheca dissilens; b. Closterium baillyanum prox.; c. Tetmemorus granulatus.  Scale bar: 25 mm (= 1/40th of a millimetre).

Unfortunately, the chloroplasts in these illustrations are not at their best.   My preference is always to keep algal samples fresh for as long as possible but, as I was moving around southern Europe in August I adopted my usual practice when travelling and added some vodka to the sample as a temporary preservative.   Nonetheless, Dave John, who identified the species, could find enough in the general morphology and cell wall characteristics to guide him.   Desmid species are considered to be cosmopolitan so he was able to use identification literature from Northwest and Central Europe in order to do this.   The search terms “desmid” and “Bulgaria” yielded no papers when I looked on Web of Science, so this looks like a relatively unexplored corner of Europe, as far as this group is concerned.   Having said that, all five of the species illustrated here are listed in the checklist of Romanian algae, and it is quite likely that there are local publications that have not made it onto the major bibliographic databases.

Incidentally, it was only after I had bought a miniature of vodka that I realised that I should have used this as an opportunity to buy a bottle of rakija, the local spirit.  For some reason, I had assumed that this was an ouzo-type spirit and that it would give the water an opaque milky-white appearance (caused by the lower solubility of essential oil of anise in water compared to alcohol).   Experimental studies later that same evening showed that the local rakija was closer to the Romanian ţuică, prepared from grapes, plums or apricots (the latter is especially good), and would have made a fine preservative.   I am older and wiser although, in the immediate aftermath of my experiment, that wisdom may not have been immediately apparent.

More desmids from the Pirin mountains: d. Euastrum humerosum; e. E. ansatum. Scale bar: 25 mm (= 1/40th of a millimetre).

Reference

Cărăuş, I. (2017). Algae of Romania.  A Distributional Checklist of Actual Algae.  Version 2.4.  Original print edition published by University of Bacău, Romania.  Latest version available online [https://www.researchgate.net/publication/285888477_The_algae_of_Romania]