The underwater world of Ennerdale Water …

I’ve tried to capture the world of microscopic benthic algae many times but never, until now, attempted the same effect with plankton.   The picture below illustrates the problem that I face: whereas the benthic flora are organised with, for the most part, a clear three-dimensional structure and known dependencies amongst organisms (species A, for example, being epiphytic on species B), plankton are randomly distributed in a very dilute solution.   My picture  below, which is based on four phytoplankton samples collected by the Environment Agency in the summers of 2014 and 2016.

A representation of the phytoplankton of Ennerdale Water with cells of Rhodomonas and Kephyrion depicted at a realistic density (c. 1000 – 2000 cells per millilitre).

I had to address two issues in producing this image, which is based on four phytoplankton samples collected by the Environment Agency in the summers of 2014 and 2016: depicting the phytoplankton cells at approximately the correct density and making sense of the list of names that appeared on the list.  Ennerdale Water is a very nutrient-poor lake and cell concentrations during the summer are in the order of 1000 to 2000 per millilitre.  That sounds a large number until you consider the scale at which we are working.   For simplicity, I assumed spherical cells of about 20 micrometres diameter (= 1/50th of a millimetre) at a density of 1000 cells/ml.    That equates to one cell per micrometre which is 1 mm x 1 mm x 1 mm.   Using these assumptions, each cell is 50 diameters distant from its nearest neighbour, which means the foreground of a picture should contain only two small cells and a lot of blue paint.

Next, I need to know what algae to paint and the problem here is that 85 per cent of the cells in the Environment Agency phytoplankton analyses were described as “picoplankton < 2 micrometres diameter” or “nanoplankton 2-20 micrometres diameter” (the latter divided into flagellates and non-flagellates).  There are, apparently, big difficulties in naming many of the cells found as preservation with Lugol’s Iodine coupled with the long time in storage before analysis can lead to loss of useful diagnostic features.   Cells in the nanoplankton category can, in theory, belong to any one of a number of groups of algae but If I focussed just on those organisms that could be named, I see that the Cryptophyta Rhodomonas lacustris var nannoplanctica (formerly R. minuta var. nannoplanctica) predominates, followed by Chrysophytes, of which Kephyrion is the most abundant.   So these are the two cells that I have put in the foreground.

I subsequently turned up a paper from 1912 by the father and son team of William and George West who looked at the phytoplankton of Ennerdale Water and a number of other lakes in the Lake District and Scotland.  The range of taxa that they found was quite different to that recorded in these recent surveys with samples dominated by desmids and almost no Chrysophytes or Cryptophytes recorded at all. That may, in part, be due to differences in methods – they collected samples using a “silken tow net”, which would probably have missed the very small Chrysophyta and Cryptophyta (an earlier paper by them tells us of the size of the nets but not the mesh itself) .  Some desmids that they found were found in the recent surveys but in much smaller quantities and it is possible that this was partly an artefact of the differences in sampling technique.  The idea of comparing count data from old papers with modern records is appealing but, in most cases, separating genuine changes in composition from differences introduced by sampling and analytical methods is always difficult.

Excuse these ramblings … there is, as you can see, not a lot of pictorial interest in the underwater world of an oligotrophic lake.   If you want excitement, tune into Blue Planet II, David Attenborough’s latest series for the BBC You will find sex and violence galore there.  The underwater world of Ennerdale Water is a quieter, more serene and certainly less televisual place.  Maybe that’s not such a bad thing …

References

Lund, J.W.G. (1948) A rarely recorded but very common British alga, Rhodomonas minuta Skuja. British Phycological Bulletin, 2:3, 133-139.

West, W. & West, G.S. (1909). The British freshwater phytoplankton, with special reference to the desmid-plankton and the distribution of British desmids.   Proceedings of the Royal Society of London Series B 81: 165-206.

West, W. & West, G.S. (1912).  On the periodicity of the phytoplankton of some British lakes.  Journal of the Linnaean Society, Botany 40: 395-432.

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What a difference a storm makes …

I was back at Croasdale Beck last week and noticed a rather dramatic change to the meander just upstream from our regular sampling spot.   If you look at the photograph that heads the post “A tale of two diatoms …”, you’ll see the stream flowing around this meander.  Now, however, it has cut a new, shorter channel that bypasses the meander altogether.   We visited the stream just a few days after Storm Ophelia had passed through although, judging by the grass growing on the gravel of the abandoned meander, it was not necessarily this particular event that reshaped the stream.

Croasdale Beck is an unruly tributary of the River Ehen, rising on the fells above Ennerdale Water and tumbling down across rough grazing land and some semi-improved pasture (as in the picture above) before joining the Ehen in Ennerdale Bridge.   This is not the first time that we have seen conspicuous changes in the channel after a storm.  The magnitude of the flood is illustrated by the hydrograph below, which went off-scale for a period, as the discharge exceeded 3000 mega litres per day (300 MLD is the approximate limit for safe wading, in my experience).   I noticed that there was much less green algae present than we usually record at this time of year, although the diatom film was still quite thick.   Some of the stones that I picked up to sample had the slimy biofilm on the underside, suggesting that they had been recently rolled by the flooded river.   Croasdale Beck has no lake to buffer the rise and fall of the floodwaters and a huge amount of energy is carried down in a short period of time as the water surges downstream.

By the time we had arrived, the floodwaters had subsided and the sheep were contentedly grazing the surrounding land.  The stream itself was almost back to base flow (in contrast to the River Ehen which was still only just wadable).  Only the meander looked different …

The hydrograph for the River Ehen, as the aftereffects of Storm Ophelia make their way downstream.

Buffers for duffers …

In Ecology in the hard rock café I wrote about the challenges of living in an aquatic world where carbon – one of the raw materials for photosynthesis – was in short supply.   What I did not write about in that post is that this carbon also gives freshwater some useful additional properties.   In brief, rainwater is not pure water, but absorbs carbon dioxide from the atmosphere.  This, in turn, makes rainwater slightly acidic and, when it falls onto rocks, this weak acid dissolves the minerals from which the rock is made.  This adds two other forms of carbon to the water – bicarbonate and carbonate (the latter, particularly, from limestone).

Each of these three types of carbon in freshwater can convert to either of the other two types, with the speed of the reaction depending on the balance between the forms (the “law of mass actions”).  In essence, the reactions proceed until equilibrium is obtained, and this equilibrium, in turn, depends upon the pH of the solution.  These processes are summarised in the diagram below.

Relationship between pH and the proportion of inorganic carbon as free carbon dioxide (or carbonic acid, H2CO3 – orange line), bicarbonate (HCO3 – green line) and carbonate (CO32- – blue line).

The chemistry behind this is not easy to explain but a consequence is that any attempt to shift the pH (e.g. by adding acid) causes an automatic adjustment in the balance between the different forms of carbon.  Some of the hydrogen ions that could make the water acid are, instead , bound up as bicarbonate, and the pH, as a result, does not change.  The greater the quantity of inorganic carbon in the sample, in other words, the greater the capacity of the water to resist changes in pH.   The carbonate, bicarbonate and free carbon dioxide together act as a “buffer”, a chemical shock absorber.   Think of it as equivalent to the responsible use of a credit card or savings account to defer the cost of an unexpected bill (a car repair, for example) so that your current account does not go overdrawn.

Because life largely evolved in well-buffered marine systems, the enzymes that run our cells generally work best within a narrow range of pH (approximately 6-9).   Cells – unicellular life forms in particular – get stressed if pH strays outside this range, so the greater the buffering capacity, the easier it is for cells (life at high pH can bring additional complications, but we don’t have time to go into those here).  “Alkalinity”, as I mentioned in the earlier post, is the measure that ecologists use to assess the strength of the buffer system in a lake or river.  The principle of the measurement is straightforward: we add a dilute acid very slowly and watch what happens to the pH.   At first, nothing happens but, as soon as the water’s natural buffering capacity has been exceeded, pH drops rapidly.

I have a small portable alkalinity titration kit which involves adding drops of bromophenol blue indicator to a sample of stream or lake water.  This gives the water a blue colour when the pH is greater than 4.6.  As the pH falls, the solution becomes colourless and, eventually, turns yellow.   If you look at the graph above you will see that, at pH 4.6 most of the bicarbonate (HCO3) has been converted to carbon dioxide so the buffering capacity is pretty much non-existent.  This means that I can use the quantity of acid that is needed to make the bromophenol blue change colour as a measure of the buffering capacity of the water.

Alkalinity titrations beside Ennerdale Water (see top photograph) using a Hanna HI 3811 alkalinity test kit.  The right hand image shows acid being added to the water sample with a 1 ml pipette.  The blue colour shows that pH has not yet dropped below 4.6.

All this talk of chemical equilibria seems to be a long way from the natural history that is the core business of this blog.  Yet, at the same time, these reactions describe natural phenomena every bit as real as the plants and animals that attract the interest of naturalists.   Geology and chemistry ultimately create the context within which biology flourishes, but it is rare to meet a chemist who can talk with a naturalist’s passion.  I think that this is partly because chemistry tends not to describe tangible features of the landscape but, instead, quickly gets lost in abstract equations.  However, it is also a matter of culture: chemists need clinical separation from the mud and filth to maximise precision, whilst ecologists feel the lure of the field.  There is, nonetheless, a very basic and necessary link between the chemistry and ecology of aquatic systems.   Geology may shape a landscape but chemistry is one of the key mediators that determines the types of plants that cloak the hills and vales.  We ignore it at our peril.

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.

The stresses of summertime …

One reaches a stage in an ecological career when your “niche” becomes the office not the field and you are expected to focus your hard-earned experience on data that others have collected.  That means that I spend more time than I wish – even in the summer – staring at computer screens and writing reports – and far too little time engaging directly with nature.   Today’s post is the result of a Saturday’s excursion around some of the more enigmatic parts of the Yorkshire Dales National Park (the enigma being, basically, that we spent most of our time in Cumbria, not Yorkshire).

The photograph above shows a steam locomotive hauling a train along the Settle to Carlisle railway as it makes its way through Mallerstang, the upper part of the Eden Valley.   It is a beautiful little valley, hidden away from the main tourist drags and the sight of a steam train imparted a sense that we were somehow detached, albeit briefly, from the modern world.   The river channel itself lies amidst the ribbon of woodland in the valley bottom.

The River Eden in Mallerstang (SD 778 985) with (right) a large pebble with a Cyanobacterial film.

Curious to see what kind of life thrives in such a heavily shaded stream, I hopped over a fence, pushed through some bankside vegetation, crouched down and lent out as far as possible to grab a few of the stones from the streambed.   As I would have expected in a stream in such a location, the slippery film on the stone surface was thin (this is the time of year when the algae and other microbes can barely grow fast enough to keep up with the voracious appetites of the invertebrates that inhabit the crevices among the rocks) but, when I held it up to the light, there was a distinct greenish tinge that piqued my curiosity.

Under the microscope, this green tinge revealed itself to be due to numerous filaments of a thin, non-heterocystous cyanobacterium (blue-green alga), similar to that which I see in the River Ehen (see “’Signal’ or ‘noise’?”).  There, Phormidium autumnale forms tough leathery mats whereas here there was no obvious arrangement of the filaments.   In fact, the filaments seemed to be randomly organised within a mass of organic matter that made photography difficult and the photograph below is of one that had glided into a clear space on the coverslip.   I was surprised that there were relatively few diatoms present but, amidst the clumps of cyanobacteria and organic matter, I could see cells of Gomphonema pumilum, though it was very definitely sub-dominant to the Phormidium.  That was not very easy to photograph either, and my images have been built-up using Helicon Focus stacking software.

Some of the algae living on stones in the upper River Eden, August 2017: a. Phormidium cf autumnale; b. and c.: Gomphonema cf pumilum.  Scale bar: 10 micrometres (= 100th of a centimetre). 

I have seen other streams where non-heterocystous cyanobacteria thrive during the summer months and suspect that their unpalatability relative to other algae may play a part in this.  This is partially induced by the proximity of grazers – a recent study suggested that filaments of Phormidium did not need to come into contact with the grazer itself, only to detect chemicals associated with the grazer in the ambient water.  This, in turn, can promote production of a tougher sheath, making the filaments less palatable.   I’m always a little surprised that aquatic invertebrates find diatoms, with their silica cell walls, palatable, but I see enough midge larvae greedily hoovering-up diatoms to recognise that they know something that I do not.

My brief visit to the upper River Eden reminds me that summer can be a tough time for stream algae.   Not only is this the time that the invertebrate larvae are scouring rock surfaces for algae to serve as the fuel that will catapult them into their brief adult phases, but also the trees are in full leaf, limiting the amount of energy that the algae can capture in order to power their own growth.   Not surprising, then, that so many algae – diatoms and other groups alike – are more prolific in the winter, when the invertebrates are not so active and there is less shade from marginal trees (see “Not so bleak midwinter?” and “A winter wonderland in the River Ehen”).   I’ll probably be sitting indoors staring at spreadsheets and writing reports this winter too, but I’ll still be looking for excuses to get out and explore nature’s hidden diversity.

Pendragon Castle, guarding the entrance to Mallerstang in the upper Eden Valley. 

Reference

Fiałkowska, E.  & Pajdak-Stós, A. (2014).  Chemical and mechanical signals inducing Phormidium (Cyanobacteria) defence against their grazers.   FEMS Microbiology Ecology 89: 659-669.

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 ( = 1/40th 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
( = 1/40th 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.