Of microbes and mountains …

I spent a few anxious days last week watching the weather forecast in anticipation of fieldwork.   It was not clear from the forecast whether there would be enough rain to lift river levels to a point where I could not safely collect samples or if, rather than rain, there would snow, which may make the roads slippery but would, at least, mean that river levels were low.  The best I thought I could expect was to be working in near freezing conditions amidst flurries of snow, so it came as an unexpected surprise to find clear skies and sunshine even if April water temperatures were still bitingly cold.   The photograph at the top of the post shows Wastwater, looking towards Scafell Pike and Great Gable on a cold but still April morning, but the focus is on the River Irt, about 500 metres or so downstream from the outfall from the lake.   The landscape overlooking the lake is spectacular but, on a different scale, the subaquatic landscape that I see when I peer at the bed of the River Irt through my aquascope, is equally spectacular, albeit on a vastly smaller scale. 

Underwater landscape in the River Irt, April 2021, with green algae (a.), mosses mixed with Cyanobacteria (b.) and diatoms (c.).   The foreground of the picture frame is about a metre in width.

The flocs of green algae are mostly composed of Spirogyra whilst the mosses and cyanobacteria combos in the background are the same as those that I wrote about in “Tangled up under blue skies” a couple of months back.   The diatoms in the front foreground are the most intriguing.   Here, as at several other locations, we could see and feel distinct biofilms on rocks, but our measurements of chlorophyll concentrations were nearly always very low.  The answer became clear when I looked at some of the biofilm under my microscope: the dominant diatom in these biofilms was a long-stalked form of Gomphonema; probably the same one that I wrote about in “Diatoms and the space-time continuum” a few years back.   The biofilm that covered the patches where other algae and mosses were not dominant was composed mostly of the polysaccharide stalks, with the photosynthetic cells forming a surface layer.  From the point of view of any subaquatic grazer, this roughly equates to a piece of bread with a thin smear of marmite on top.   However, the tangled mass of stalks also works well as a means of trapping organic and inorganic particles that are in transit through this part of the river, and most of the invertebrates that live on stream beds are not particularly fussy about precisely what is on the menu.   I have no data to back this up, but my hunch is that these diatoms make a bigger contribution to the diet of these bugs through these trapped particles than they do through the energy that they have created from trapped sunlight.  

Gomphonema on long stalks, along with a few Achnanthidium, from the River Irt, April 2021.  Scale bar: 10 micrometres (= 1/100th of a millimetre).  

With samples from the River Irt safely packed into the cool box, our field work was finished and, as it had already spilled into the weekend, we felt no compunction about heading back to explore the mountains that loomed over Wastwater.   Our target today was Great Gable, a steep pull up from Wasdale, but a climb that rewarded us with striking views of the lake and the famous screes.   Having started our walk with blue skies and cotton wool clouds, it also gave us a panoramic view of the changing weather as clouds blew in and showers fell along the west Cumbrian coastal plain.   We encountered a few flurries of snow as we approached the summit of Great Gable, but not enough to obscure a view which extended to Windermere to the east, Skiddaw, Helvellyn and Blencathra to the north-east and Crummock Water and the Liza valley to the north.  Somewhat to my surprise, Ennerdale Water was not quite visible from the summit.

The view back along Wasdale towards Wastwater from the flank of Great Gable, April 2021.

We made a steep descent to Styhead Tarn, then followed the track back to Wasdale, passing a group of intrepid mountain cyclists on the way up variously pushing and carrying their bikes.  We could still see showers in the distance but the snow flurries we encountered on the way up did not seem to have come to much.  Consequently, it was a surprise to us when, having driven out of Wasdale and back to our accommodation in Ennerdale, we saw the flanks of the hills around Great Gable to be covered with snow.   Last April, we were basking in unseasonably warm weather at the start of the first lockdown; a year on there is snow, and not just on the high fells either.   Nature continually surprises us, on a whole range of scales, from the minute to the enormous.  That’s what keeps pulling us back.

Wrote this whilst listening to:  Déjà vu, by Crosby, Stills, Nash & Young.

Cultural highlights:   The film The Mauritanean, about the longest serving prisoner at Guantanamo Bay.  

Currently reading:  Spring Has Not Been Cancelled: David Hockney in Normandy, by Martin Gayford.  Reflections on landscape painting by an undisputed master.

Culinary highlight: probably has to be the sandwiches we ate on the way up Great Gable, mostly because of the spectacular views that accompanied them.

Snow over the fells to the south of Ennerdale Water: Heather’s photo taken on the evening of 10 April after our ascent of Great Gable (just out of frame).

A multicoloured rock stop …

Our route to Cassop Pond is rural but certainly not natural.   That’s the way with much of County Durham’s landscapes: the economic history of the area is based around extractive industries and those parts that were not mined for coal were most likely quarried. That’s particularly the case in the immediate vicinity of our house, overlooked by the scarp face of the Permian limestone.  There is a large working quarry beside the footpath we follow but, even when we have left that behind, it took some time to realise that another path we followed, overhung by trees on both sides to form a natural tunnel, was an ancient, long-abandoned wagonway.  This leads to the edge of Cassop Vale, where there are also signs of quarrying but, en route, passes through what is either another abandoned quarry or a man-made cutting for the wagonway.  Or both.  Why not get a return from the back-breaking endeavours of flattening out the route that rock-laden wagons will have to take?  

Splashes of colour on the exposed rock in the cutting also drew our attention.  Some of this was the orange-yellow of the alga Trentepohlia aurea that I have written about before (see “Fake Tans in the Yorkshire Dales”).  However, there were also patches with a brick-red colour that, under the microscope resolved into a different species, Trentepohlia umbrina (see “Cassop Vale, Febrary 2021”).   Above there are blackish patches of Gloeocapsa alpina (see “The mysteries of Clapham Junction …”) and, if you look closely, you’ll see some green patches too (see “Little round green things …”).  That’s at least four different terrestrial algae within about a metre of one another.

The quarry / cutting bordering the wagonway near Cassop Vale (NZ 3369 3820).   The image on the right shows a close-up of the exposed limestone.   a. orange patches of Trentepohlia aurea; b. brick-red patches of T. umbrina; c. black patches of Gloeocapsa alpina.

I confess to having walked along this footpath several times without ever really noticing what was right in front of my eyes.  That brings to mind a quotation from Henry David Thoreau: “It’s not what you look at that matters, it’s what you see”.   Seeing is a process that is as much to do with the brain as it is to do with patterns of light falling on the retina.   And, at the same time as I notice that there are four species of algae on this outcrop, I have to acknowledge that there is so much more to this narrow track than I have realised.  I am aware of the rich diversity of limestone plants, largely because Heather points them out.   We notice several of the birds, either by sight or by their song and she is getting better at spotting and naming butterflies.  Then there are the fungi: the larger ones on trees we notice but we read Merlin Sheldrake’s Enchanted Lives recently and this made us conscious of the rich diversity of this group – and their many important roles in ecosystems.  

Gloeocapsa alpina from the rock face near Cassop Vale.   Scale bar: 10 micrometres (= 100th of a millimetre).  

Our local countryside, in other words, offers us both a sense of stability, via nature’s predictable rhythms, but also the opportunity to encounter the unexpected.   The unexpected arises from two directions.   The first is an intrinsic capacity for nature to change and surprise us – for a species of plant or bird to disappear or another to appear at a location for the first time.  But there is also a capacity that lies more with us, as observers, than with the habitat itself.  That is for us to notice details that had been there all along but which we had overlooked, perhaps because we were rushing along, perhaps because we lacked the awareness that allowed the patterns that fell on our retinas to make the necessary connections in our brain.   Noticing that we’ve noticed something that we should have noticed before is doubly important, especially when this happens in our own backyards, because it makes us realise how little we know, even about the habitats we think we know best.

Wrote this whilst listening to: various live sets on YouTube by P.J. Harvey.

Cultural highlights:   Brilliant new film, Munari, about a Korean family’s attempts to farm in a remote corner of Arkansas.   Little House on the Prairie, but with Asian, rather than European settlers.  

Currently reading:  Lila, by Marilynne Robinson.  

Culinary highlight: homemade samosas, eaten al fresco on Stannage Edge, Derbyshire with daughter and partner: our first face-to-face meeting this year.

Structural engineering with diatoms …

I’ve been looking at shallow, calcareous lakes in two very different locations over recent weeks: on the Shetland Islands north of Scotland and in Greece.   Climatically, they are different worlds but there are surprising similarities in the diatoms that I find in the two habitats: many species are common to both but, even when the species are not identical, genera that are not widespread in other habitats are well represented in these lakes in both the Shetlands and Greece.   There must be something about these lakes that makes them attractive to a few genera over almost all other possible habitats despite the differences in climate.   

One of the genera that falls into this category is Epithemia, which I also find in my local calcareous pond (see “Working their passage …”); another is Rhopalodia, a relative of Epithemia and a third is Mastogloia, the subject of this post.   Mastogloia has a very unusual structure.   If you focus carefully on the top of the valve, you see striae and a raphe; if you then adjust the focus very slightly a series of chambers (“partecta”) will come into view, arranged in a row along each side of the valve.  They look a little like a row of cabins along the two sides of a boat.

Mastogloia (probably M. lacustris) from Limni Trichonida in Greece, December 2020.   Seven focal planes of the same frustule, seen in girdle view showing how the organisation of the partecta on girdle bands on either side of the cell.   The image at the top of the post shows Mastogloia species from the Shetland Islands: a., b., c., d., g.: M. baltica; e., f.: M. dansei; h., i. M. elliptica; j. M. dansei.  g. – k. from Carter & Bailey Watts (1980).  Scale bars: 10 micrometres (= 100th of a millimetre).

When seen from the side, rather than from above, we see that Mastogloia cells are, typically, rather deep so, pushing our nautical metaphor just a little further, they are rather ungainly.   Although they have raphes and are, in theory, capable of movement, these are not going to be found darting around like species of Nitzschiaand Navicula, constantly adjusting their position in relation to light and other resources.  Instead, Mastogloia have a very different set of priorities, with the partecta playing a key role in enabling these.

We see the partecta as empty chambers because we usually look at diatoms after they have been treated with oxidising agents that remove all organic matter.  When viewed live, however, Mastogloia are often seen surrounded by extracellular strands, capsules and tubes and it is assumed that these are secreted from pores which are, in effect, the “portholes” associated with the partecta.   The empty “cabins” we see under the microscope are, in fact, busy little slime factories.  A lot of different extracellular structures have been described, particularly from the many marine representatives of this genus, and most seem to be designed to keep the cell in one place, rather than to help it adjust position. 

For the freshwater species, calcareous habitats offer some particular challenges to organisms: the porous nature of the rock means that there is often a high risk of drying out, high calcium carbonate concentrations lead to the precipitation of calcite.  In the process, phosphorus is also removed from the water, trapped in the calcite crystals.  Evelyn Glaiser and colleagues suggested that this combination of characteristics favoured organisms that produced a lot of extracellular polysaccharides.  Firstly, the strands act to bind inorganic particles and the microbial life into dense aggregations and slows rates of desiccation.  Second, this dense moist matrix will provide not just organic matter but also microbes that can break it down to recycle nutrients for the diatoms and other organisms to use.   Third – not mentioned by Evelyn Glaiser and colleagues but touched upon in “A journey to the headwaters of the River Coquet” and other posts – the algae themselves may contribute to this recycling via enzymes present in their extracellular polysaccharides. 

A schematic view of a Mastogloia cell with polysaccharide strands emerging from pores and tangled around mineral particles. 

Mastogloia, in other words, is not just part of the structure of biofilms in in shallow calcareous lakes and ponds, it actively creates these.   In the Florida Everglades it is a keystone species, around which thick microbial mats form and within which, in turn, other species, some unique to these ecosystems, are found.   It does this through diverting energy and resources to produce extracellular polysaccharides and because the scant nutrients mean that more competitive algae are kept out.   However, if this delicate balance is disrupted and nutrients become more widely available, then Mastogloia is out-competed, the mats lose the structural integrity that Mastogloiaimparts, and the biodiversity associated with them disappears.   A classic ecological cascade: for want of a nail, the shoe is lost and so on …

References

Carter, J.R. & Bailey-Watts, A. (1981).  A taxonomic study of diatoms from standing waters in Shetland.  Nova Hedwigia 33: 513-629.

Glaiser, E., La Hée, J.M., Tobias, F.A.C. & Wachnicka, A.H. (2016).  Mastogloia smithii var. lacustris Grun.: a structural engineer of calcareous mats in karstic subtropical wetlands.  Proceedings of the Academy of Natural Sciences of Philadelphia 160: 99-112.

Hain, M.K., Winsborough, B.M., Davis, J.S. & Golubic, S. (1993).   Extracellular structures produced by marine species of Mastogloia.  Diatom Research 8: 73-88. 

Some other highlights from this week:

Wrote this whilst listening to: The Go-Betweens, an Australian indie band from the early 1980s.  There has been press coverage of a new book about one of their members and this reminded me of the one occasion I saw them whilst a student in London in 1982 or 1983.   I remember that the venue was full of goths hoping to see another band on the bill, The Dancing Did, who did not show up for some reason.  I found their sole album, And Did Those Feet, on Spotify too: 

Cultural highlights:   Watched the new film Ammonite about Mary Anning.   It plays fast and loose with history (see “It all started here …”) but is well-acted.  Charlotte Murchison, the character played by Saoirse Ronan, lived for a while in Barnard Castle, about 30 kilometres from Durham.

Currently reading:  Persepolis by Marjane Satrapi, autobiographical graphic novel about growing up in Iran during and after the 1979 revolution.

Culinary highlight:  Normandy-style galettes followed by a chocolate and ginger cheesecake.

The Natural History of Upper Weardale

A very short post this week, having been knocked for six by my first dose of the Covid vaccine.  I’m going to use it to publicise The Natural History of Upper Weardale, a new book published by Durham Wildlife Trust that provides an accessible insight into the geological, geomorphological, climatic, ecological and human influences that have shaped the dale.  I contributed to the chapter on freshwater life and Heather wrote (and illustrated) the chapter on the plants of Weardale.  You can buy it (and its companion volume, The Natural History of Upper Teesdale) from the DWT website.

At some point in the not-too-distant future, you’ll also be able to access the book via the Living Uplands website.  The Upper Teesdale book is already here, with the individual chapters all downloadable as pdfs.  Weardale and Teesdale both have their own individual characters and putting the chapters of the two books alongside each other helps to understand the reasons behind this.   No-one would readily associate the northern Pennines with volcanoes, but it is two igneous rocks that are largely responsible for the differences between the two dales.   Whin Sill outcrops much more in Teesdale and is responsible for the dramatic waterfalls at High Force and Cauldron Snout which have no counterparts in Weardale, whilst the “Weardale Granite” was responsible for the mineral veins and associated mining activity which, though present in both dales, is more widespread and obvious in Weardale.    

David Attenborough said: “no-one will protect what they don’t care about; and no one will care about what they have not experienced”, and Buddha said: “true love is born from understanding”.  I hope this book helps people to understand Weardale better and, with this understanding, to have better experiences in Weardale.  That will give us a firm foundation for conserving and protecting this beautiful landscape.  

Some other highlights from this week:

Wrote this whilst listening to:  Lana Del Rey’s new album Chemtrails Over the Country Club.  And some vintage Mahavishnu Orchestra with John McLaughlin.

Cultural highlights:  Unusual low-key Canadian film Mouthpiece and, whilst crashed out with post-vaccination blues, the 2018 film about a dysfunctional all female punk rock band, Her Smell

Currently reading:  Matt Haig’s Midnight Library, having finished Penelope Fitzgerald’s The Bookshop.  More time than usual for reading this week. 

Culinary highlight:  Persian New Year feast of tahdig served with cauliflower roasted with harissa and tahini.

Tangled up under blue skies …

We were in the Lake District at the turn of the month to collect some of our regular samples and measurements and our reward for some very cold water and slightly higher river levels than was ideal was a day of cloudless, still weather with some inviting vistas of the peaks.   That invitation will, however, have to wait, as we have work to do and, having dragged our eyes away from the distant view of Great Gable, we peered at the algae in the littoral zone of Wastwater and then made our way to the two sites on the River Irt, which flows out from the lake.

I wrote about one of these sites after our visit in December (see “As old as the hills …”) and was intrigued to see how the situation that I described there had changed over the intervening two months.   The cyanobacterial growths that I described back in December were, if anything, more prolific now, and whilst I was puzzling over their identity then, I am now almost certain (having shown the material to Brian Whitton) that it is Tolypothrix distorta var. penicillatus.  Last time, I saw enough double false branches to suspect a species of Scytonema; this time, the branches were almost all single and the general habit of the plant also pointed to T. distorta var. penicillatus.   

These growths were still associated with an acrocarpous moss (probably Racomitrium aciculare), presumably gaining some support and protection from stems and leaves.  The key difference this time, however, was that the Tolypothrix itself seemed to have been colonised by other organisms.  In addition to some very small cyanobacterial cells (guessing Chamaesiphon – see “More from the River Ehen”), there were also a few longer filaments (likely Heteroleibleinii – see “River Ehen … again”) as well as a few diatoms (mostly Fragilaria gracilis).  Those earlier posts also highlight the relationship between Tolypothrix and aquatic mosses and were written at approximately the same time of year.  

Tolypothrix distorta var. penicillatus at Cinderdale Bridge in the River Irt, March 2021.  Scale bar: 10 micrometres (= 1/100th of a millimetre).   The photograph at the top of the post shows the view along Wastwater towards Great Gable.

I’ve tried to capture this relationship in a painting, with Tolypothrix filaments entangled around Racomitrium aciculare leaves (note the characteristic wavy outline of the cells) .  The false branches typically have a heterocyst (cell responsible for nitrogen fixation) at the base, and then run almost parallel to the main filament for some time. The epiphytes grow on the thick colourless sheath.  Compare the images in this post with those taken in December to see just how the abundance of epiphytes has changed in two months.    

This is the second post in a row in which I’ve mused about the relationship between bryophytes and algae.   When I was writing about Riccia fluitans and Epithemia, I speculated that the liverwort may gain some nitrogen from the relationship and the same possibility must exist for Tolypothrix and Racomitrium.   In both cases, we are probably looking at an arrangement that is too loose for the term “symbiosis” to be appropriate but general proximity of organisms in environments where resources are scarce must lead to mutual benefits.  I would go further and suggest that patchy distributions of algae is a common property of nutrient-poor streams, and these patches are often composed of more than one species.  So it is fair to speculate that they may gain both physical support and opportunities to share nutritional and other benefits too.   It would, alas, also be very difficult to prove.

A depiction of Tolypothrix distorta var. penicillatus growing amidst filaments of the moss Racomitrium aciculare in the River Irt, Cumbria, March 2021.  

Once we had packed away our samples from the Irt our fieldwork was finished.  The sky was, however, still blue, the wind still absent, and the fells tempting.  Our only constraint was the limited amount of daylight left to us.   Rather than attempt anything too ambitious, we drove to the Honister Pass, between Buttermere and Borrowdale, parked at the slate mine at the top and headed up the steep fell to the south.  Our car had done half the climbing for us and we were on Grey Knott and striding through the rough grassland towards Brendreth within an hour of parking.  The views down the Ennerdale and Buttermere valleys were quite spectacular, with the lakes shimmering in their respective valleys. Forgive me if I end the post with a couple of memories of those very special views.  

Some other highlights from this week:

Wrote this whilst listening to:  Omega, debut album by jazz saxophonist Immanuel Wilkins.  And Julio Iglesias singing Begin the Beguine at the funeral of an elderly aunt.

Cultural highlights:  My Donkey, My Lover and I: a French comedy set in the Cévennes.  

Currently reading:  Lightseekers, by Femi Kayode, a crime novel set on a Nigerian university campus.

Culinary highlight:  definitely not the food I encountered on the journey to and from the funeral I mentioned above.   I am now definitely inoculated against fast food chain burgers for several months at least. 

The Liza Valley and Ennerdale Water from near the summit of Brandreth, March 2021.  
Buttermere and Crummock Water taken from between Grey Knott and Brandreth.  March 2021. 

Working their passage …

My February visit to Cassop Pond was a warmer experience than my January visit, though copious rain meant that the footpaths we followed to reach the reserve were extremely muddy.  I’ve been gazumped in my endeavour to bring you the phycological riches we encountered on this trip by Heather, who has already mentioned the two species of Trentepohlia that we noticed growing on the wall of an abandoned quarry in her post about the visit.  However, I still managed to find plenty to amuse me in the pond itself. 

On first glance, the pond still does not look very prepossessing.  The ice that had covered the pond during our January visit had gone, but there were still few signs of life above the water level.  It is only when we look below the surface that we find evidence of activity.   Standing at the edge of a marshy area, churned up by the herd of highland cattle who roam the reserve, I can see greenish flocs which, from a distance, they look like filamentous algae.  Up close, however, they are a tangle of narrow, branched strap-like fronds.   This is Riccia fluitans, one of just two free-floating liverworts found in Britain (the other one, Ricciocarpus natans, is also found here, but that’s a story for another day).   In my photograph, you’ll also see a few leaves of Lemna minor, duckweed.  That will become way more prolific later in the year.  Today, Riccia fluitans is the star of the show.

Flocs of the liverwort Riccia fluitans floating just below the surface in Cassop Pond, February 2021.
A close-up of the floc of Riccia fluitans in Cassop Pond.  Each frond is about a millimetre wide.

When we move in even closer and peer at Riccia fluitans through a microscope, the reason for its buoyancy becomes clear: there are a number of floatation chambers.  This, in turn, creates the impression that the cells that contain chloroplasts are forming sinuous bands along the thallus.   I had never thought of chloroplasts as being particularly heavy, but many aquatic plants are parsimonious in the way that they deploy their photosynthetic arsenal.  We saw this in the moss Sphagnum (see “Back to the bog”) and also, last year, in Potamogeton polygonifolius (see “The dark side of the leaf …”)

The thallus of Riccia fluitans viewed under a microscope, showing the mix of green photosynthetic cells and empty cells which help it to remain close to the surface. The thallus is about half a millimetre across.

One other characteristic that Riccia fluitans shares with Potamogeton polygonifolius (and, for that matter, Lemna minor: see “Cassop”) is that it carries passengers.   Cranking up the magnification on my microscope, I can just make out the outlines of several cells of the diatom Epithemia.  I’ll write more about the diatoms from Croft Kettle at a later date but Epithemia is an interesting find here because it is a diatom that is capable of nitrogen fixation (see “More about Croft Kettle”).  I’ve recorded Epithemia from Cassop Ponds in the past, but never noticed its affinity for Riccia fluitans before.   Rooted plants can draw on nitrogen in the sediments to meet their needs; however, free-floating plants depend on what can be acquired from the water.  We also know now that many aquatic organisms are quite leaky so an alga that has a trick like nitrogen fixation up its sleeve may be serving as a food bank for the host organism.   It might just be that the buoyancy that Riccia fluitans provides is a quid pro quo for these nutrients.   This looks like being a mutually beneficial relationship: this small corner of nature being less “red in tooth and claw” than “you scratch my back, I’ll scratch yours” …

Epithemia species just visible on the lower surface of Riccia fluitans from Cassop Pond.  The two cells at the centre of the image are each about a tenth of a millimetre long. 

Some other highlights from this week:

Wrote this whilst listening to: Kin Sonic by Congolese musicians Jupiter & Okwess.   

Cultural highlights:  The Martian, which is basically about growing potatoes in inhospitable environments.  “Fear my botany powers, Mars!”

Currently reading:  My Last Supper: One Meal, a Lifetime in the Making by Jay Rayner.  

Culinary highlight: Persian kababs in a meal box from Berenjak’s restaurant in London.  

Depths of imagination …

I’ve written many posts over the years about algae that grow in lakes, mostly based on samples I’ve collected whilst paddling around in the shallow littoral zone.   One feature that I have not previously mentioned is that the attached algal flora changes quite dramatically as you descend into the deeper parts of the lake.  These habitats have only been thoroughly explored since SCUBA diving became possible in the middle of the twentieth century.   Before then, what was known of underwater algae came from chunks of rock dredged up from depths in nets.  

This was the case in Lake Constance, which straddles the borders of Germany, Austria and Switzerland and, in particular, in the northern arm, the Überlinger See, where there are steep underwater cliffs composed of Molasse (a sedimentary sandstone/shale association).   Studies by Lauterborn and Zimmerman revealed crusts and mats smothering these cliffs and extending to great depths.   As you descended from the shallower, lighter water to the depths the composition shifted from predominately green algae to brown and red algae.  Zimmerman captured these changes in a sketch of the algae on a ledge on the cliff wall at about fifteen metres depth, showing the red alga Hildenbrandia rivularis tucked away in the shady recesses whilst Cladophora profunda (now regarded as a synonym of Aegagropila linnaei, which we met in “A load of balls …”) was more abundant on the lighter, more exposed faces.   The big interest, though, were the extensive growths of a freshwater brown alga, Bodanella lauterbornii.  

A reconstruction of the algal communities at approximately 15-20metres depth in Lake Constance at the time of Zimmermann’s survey in 1925.   a: Aegagropia linnaei; b: Bodanella lauterbornii; c: Hildenbrandia rivularis.   The foreground of the picture frame represents about 30 centimetres.   The picture at the top shows the surface of Lake Constance at the time of the modern survey (photo: Lydia King).   

The Phaeophyta – brown algae – are much more common in marine environments than in freshwaters.   A few species can be found but these form small, inconspicuous growths that are frequently overlooked.    Lauterborn and Zimmerman’s record of a rare brown algae in the depths of Lake Constance (it has only been recorded in three other lakes in Austria) came to light during the preparation of a Red List of algae in Baden-Württemberg and led to a search to see if it was still present.  

The study proved fruitless, with all the submerged cliffs covered not by algae but by extensive growths of invasive mussels, mostly zebra mussels, Dreissena polymorpha.  My illustration tries to convey the extent to which zebra mussels smother the surfaces but is still an underestimate, compared to the photographs taken by divers in this study, which show mussels filling all available spaces and often growing over each other.  Zebra mussels were first recorded in Lake Constance in the 1960s and it is possible that the algal assemblages described by Zimmerman were already declining at this point.   In the period since the original surveys, Lake Constance received considerable nutrient enrichment which would have boosted phytoplankton growth, in turn reducing the limited light available to the deep water algae yet further.  So we can envisage a two-stage decline: first gradual darkening of an already very shaded habitat followed by a coup de grace of mussels covering all available surfaces.   

An impression of Bodenella lauterbornii, based on illustrations in Zimmermann (1927) and Eloranta et al. (2011).  The filaments are about 11 – 15 micrometres (circa. 100th of a milllimetre) in diameter. 

The absence of the deep water algal assemblages from present day Lake Constance means that my painting of the 1920s-era Molasse cliffs is very much “imagined”, in the tradition of Henry de la Beche and his followers, as described in my previous post.   Wolfgang Schūtz, Lydia King and Marco Cantonati, who had collaborated on the recent resurvey thought that an artist’s impression of the Molasse cliffs then and now might be a useful addition to the English-language report of their work currently in preparation.  We had Zimmerman’s original diagram of the arrangement of algae on a rock crevice to work from but that gave us no idea of colour or of the lateral extent of the patches.  Did the Bodenella, for example, form isolated colonies or continuous mats?   I put together some sketches based on my own interpretations then the others critiqued these and I used their comments to produce new versions. After two or three iterations, we had an arrangement with which we all agreed.  Whether this is an accurate portrayal is another question: all we needed to agree was that was a plausible arrangement, given what we know of these organisms from our own experience. 

Our last encounter with Aegagropila linnaei in this blog was as balls of filaments in a lake in Ireland but it can alos be found forming mats or turfs of interwoven filaments on stones in streams, so I went with this growth form in the illustration.  Zimmerman’s diagram suggests it had a fringe of filaments trailing in the water but this is not my experience of A. linnaei in rivers, so I left them out.   You can decide: it’s a case of his artistic license versus mine.    

But what do we know of Bodenella lauterbornii, a rare, deep water brown alga?   None of us had seen it living so my colonies are based on another brown alga, Heribaudiella fluviatilis.  Microscopically, these look quite different, with Heribaudiella having tightly packed erect filaments composed of just a few cells whereas Bodenella seems, from illustrations, to have longer, more loosely-packed filaments.  However, one study has suggested that these species may be genetically identical so it is possible that the difference in growth form and habit is due to the habitat.   I’ve depicted it as being quite dark brown, suggesting more accessory pigments than you would find in algae closer to the surface, in order to harvest as much of the meagre light as possible.  That raises another point: both pictures are painted much brighter than would really be the case at fifteen metres depth.   At best, both would depict a spot of Caravaggio-esque brightness (the diver’s torch, in this case, rather than a candle) amid the stygian gloom of Lake Constance’s depths.   

An artistic impression of the same rock ledge portrayed above but in 2020 rather than in the 1920s, with zebra mussels (Dreissena polymorpha) occupying the habitats previously occupied by algae.

It is not exactly ichthyosaurs chasing plesiosaurs but the essence of this picture is the same as in Duria Antiquior: lost worlds are as likely to be a hundred years old as 100 million years old and the evidence we have rarely tells us the whole story.   A leap of imagination, seasoned with knowledge and experience, is always necessary to bring lost worlds to life.  

References

Eloranta, P., Kwandrans, J. & Kusel-Fetzmann, E. (2011).  Die Sūsswasserflora von Mitteleuropa 7: Rhodophyceae and Phaeophyceae.  Springer Spektrum, Heidelberg & Berlin.

Lauterborn, R. (1922): Die Kalksinterbildungen an den unterseeischen Felswänden des Bodensees und ihre Biologie.– Mitteilungen des badischen Landesvereins für Naturkunde und Naturschutz 8: 209-215.

McCauley, L.A.R., Wehr, J.D., 2007. Taxonomic reappraisal of the freshwater brown algae BodanellaEctocarpusHeribaudiella, and Pleurocladia (Phaeophyceae) on the basis of rbcL sequences and morphological characters. Phycologia 46: 429–439.

Schütz W., King L., Cantonati M. & Leist N. 2020. Algenbestände an den Molasse-Steilwänden des Überlinger Sees (Bodensee) – früher und heute. Carolinea 78: 5-18.

Zimmermann, W. (1927): Über Algenbestände aus der Tiefenzone des Bodensees. Zur Ökologie und Soziologie des Tiefseepflanzen. – Zeitschrift für Botanik 20: 1–28.

Wrote this whilst listening to: Ancient Heart by Tanita Tikaram, taking me back to the early 1990s.   

Cultural highlights:  More nostalgia: watched Shakespeare in Love on the iPlayer

Currently reading:  Washington Black by Esi Edugyan

Culinary highlight: Chocolate, lime and Sichuan pepper cake. 

It all started here …

This rather quaint watercolour painting has a special place in my heart.   It is called Duria Antiquior and it is in the collection of the National Museum of Wales, though not on display.  You have to make a special request to see it, and will be given white cotton gloves to ensure that you cause no damage.  The artist was Henry de la Beche, a geologist by training, and it is significant because, when he painted it in 1830, no-one previously had attempted to portray dinosaurs as living organisms, interacting with each other.   My interest in the science/art interface led to me picking on this picture as the subject for my final year dissertation during my Fine Art degree, during the course of which I was able to reflect on the possibility of extending this type of imaginative reinterpretation to the microscopic world.   

De la Beche was a geologist and dilettante familiar with the Jurassic coast of Dorset and an acquaintance of the fossil collector Mary Anning.  When an economic depression affected Mary Anning’s income, de la Beche painted a watercolour interpretation of the fossils that Anning found and sold to other collectors.  This was then converted to a lithograph and sold to Anning’s more wealthy customers for £2 10s with all proceedings going to her.   The alternative title of the picture was “A More Ancient Dorset” and, though hard to imagine now, it presented a shocking and subversive view not just in the portrayal of a very alien Dorset, but also in the challenge that this posed for mid-nineteenth century society whose view on the distant past was shaped more by the Church of England than by science. 

The picture offers a split viewpoint – very likely the first time that this had been used – with a calm, almost neo-Classical seascape (albeit with rather more reptiles than Poussin or Claude would have included) at the top and a heaving, violent sub-aquatic world below.  The upper part of the image draws on his time managing family plantations in Jamaica (more obvious in the engraving, which has several prominent palm trees) whilst the lower part is crammed with depictions of the organisms whose skeletons Anning was extracting from the soft cliffs around Lyme Regis.  De la Beche clothed the ichythosaurs and pleisosaurs in what he assumed would be plausible arrangements of muscle and skin and then took one step further: predicting relationships between the different organisms.  He assumed, for example, that the larger ichythosaur would have preyed upon smaller pleisosaurs so made their struggle into the central feature of his composition and also, if you look closely, has added a stream of faeces emerging from the panicking plesiosaur (“coprolites” – fossil faeces – were common finds along the Jurassic coast).   This is 1830, remember, and I can think of no other 19th or early to mid 20th century artist who dared to include faeces in their work.   

The importance of Duria Antiquior is twofold. First, he pushed palaeontologists into thinking holistically rather than considering fossil skeletons in isolation.  That brings metaphor and analogy into play as he considered the relationships amongst the various fossil organisms found on the Jurassic coast.   That type of thinking is second nature today so it is hard for us to conceive of a time when that did not happen.  Alongside this, however, he also took a controversial scientific debate into a much wider arena, and suggesting the existence of a world that cannot be readily explained by the Genesis narratives.  To us, conditioned by many subsequent and improved depictions of the prehistoric world, Duria Antiquior is a quaint and dated image.  To the first audiences, it screamed: “The bible is wrong and, by the way, here are some faeces”.

De la Beche shares a common starting point with my own work, both faced with biological material wrenched drastically out of context, and having to draw heavily on the imagination if we are to put this back into context.  But imagination, at the same time, has to be constrained by the evidence.  The ichythosaur has fins, not legs, so has to inhabit the water rather than the land.  It has sharp teeth so it is reasonable to assume it is a predator. Arrangement of other bones suggests analogies with fast-moving hunters.  And so it goes.  A picture emerges that is (or at least, should be) imagined without being imaginary.   Like a fugue, a sonnet or a life study there are constraints and it is through those constraints that great art often emerges.  Maybe great science too, because the evidence, albeit scanty, only offers a certain number of end-points.  The process of building up the available evidence into visual images that are more than the sum of the parts allows “thought experiments” as ideas are tested and turned over in the mind.   

One of my concerns is that ecology, whilst developing rapidly as a discipline, has taken a path towards greater and greater abstraction.  Sophisticated computational techniques reveal more yet, at the same time, we are at risk of losing touch with reality, particularly when dealing with the microscopic world.  The combination of genomic technologies and “big data” could mean that we are drawing insights about organisms that we have never seen.   By contrast, stepping back and thinking in visual terms about how organisms interact, starting from (but certainly not limited to) the evidence of our own eyes, seems to offer an important corrective.  And it all started in 1830 with Henry de la Beche. 

Wrote this whilst listening to: Shirley Collins and Davy Graham’s beautiful 1965 album Folk Routes, New Routesand 1970s jazz/prog rock group Focus.   

Cultural highlights:  The Trial of the Chicago Seven.   Film about Vietnam-era civil rights protesters in the USA.   

Currently reading:  Wilding, by Isabella Tree.  Well worth reading.   f Mercy, by Rose Tremain.

Culinary highlight: Baked cheese cake    

The Hidden World of Diatoms

A character in Rose Tremain’s latest novel, set in Victorian Britain, finds solace in his microscope:  “… it soothed Ross to think that he could find ‘wonder’ in the detritus swept from his hearth or from a sliver of matter tugged out from his eyelid”.   “The microscope,” he announced …. “reminds us that we’re born blind to the intimate secrets of everything in the world”.   

That could be the leitmotif for this blog: there are more wonders on our doorstep than most of us realise.  The question is how do bring these to the attention of a wider audience?

This week’s post is a little different.  Rather than me writing, I am going to direct you all to a short video I made last week, in which I talk to Emanuela Samaritani.   She has written a book for children, The Hidden World of Diatoms, in which she tries to capture this wonder in an accessible form.   Watch the video, then visit her website and maybe buy this book or its companion, The Hidden World of Testate Amoebae

Some other highlights from this week:

Wrote this whilst listening to:  Julian Baker’s new single, Hardline followed by Mumford and Son, the latter being the result of unexpected connections with the next item on the list: Sutton Hoo is in Suffolk, the location for the Latitude festival.  Carey Mulligan, who stars in The Dig, is married to Marcus Mumford, who we saw performing in Suffolk with Mumford and Sons at the Latitude Festival in 2017.

Cultural highlights:  The Dig, new film about the discovery of the Sutton Hoo, an Anglo-Saxon burial site in Suffolk.  Available on Netflix.

Currently reading:  Islands of Mercy, by Rose Tremain.

Culinary highlight:  Goan Fish Curry.   

Baffling Brachysira …

I should have been in the Lake District last week on a sampling trip.  It was not lockdown that stopped me but the weather.   There was rain at the weekend and the river levels went up.  I then watched the hydrographs slowly sink back but not quite to a safe level for wading before Storm Christoph blew through and the river levels went up steeply.   After two days of almost constant rain, the temperature dropped, then the rain turned to snow which is great news for me because snow on the fells means that the river levels start dropping, even if it is fiendishly cold.  As I write (Sunday) the levels are just about back to conditions that permit safe wading, albeit with air temperatures below freezing.  We should get out early next week.  Meanwhile, I am left thinking about the lakes and streams rather than actually experiencing their chilly reality.

My ruminations took me back to Ennerdale Water and along themes that I explored in a post from 2017 (“Lost in detail?”).  Once again, we are looking at the genus Brachysira in this lake but this time, rather than pick up on the identity of a single species, I want to reflect on just how many different species of Brachysira seem to inhabit the littoral habitat of one lake.  This also links with two other recent posts: The stream eats itself … and Curried diatoms?.

As was the case for the 2017 post, the slide was used in the UK/Ireland diatom ring test, which means that it was scrutinised by more analysts than just myself.  All of us, however, agreed that several species of Brachysira were present with, in one case, eight different species being recorded by a single analyst.   I’ve included illustrations of all of them and the first comment that anyone who is not familiar with diatom taxonomy will make is, almost certainly, that they don’t look particularly different from one another.   There are differences but these mostly lie just at the edge of the resolution of the light microscope.  More pertinently, those analysts who do not have light microscopes with the very highest specification will be unlikely to discern these differences.   Whereas 25 years ago, you could probably do a perfectly adequate analysis of a sample such as this with a microscope equipped with a 100x achromatic objective with a numerical objective of 1.4, now you need a plan achromatic objective with a numerical objective of 1.25 and a differential interference contrast condenser and you will still struggle to differentiate some of these species.   

Brachysira intermedia, Ennerdale Water, June 2020. Similar to B. brebissonii (pictured at the top of the post) but slightly drawn-out ends and with undulating longitudinal lines dividing the striae into two, rather than three, areolae.  Scale bar: 10 micrometres (= 1/100th of a millimetre).  Photos: Bryan Kennedy.

Several questions arise.  One is that if there is so much diversity discernible (albeit only just) with a light microscope (i.e. “semi-cryptic variation”), how much more are we missing because it is not discernible with a light microscope (“cryptic variation”)?   For some freshwater diatom genera we have been able to walk away from taxonomy’s traditional reliance on morphology and approach the problem from a different perspective.  Mostly, in this age, this different perspective comes from molecular genetics and in some cases (e.g. Fragilaria, Nitzschia, Sellaphora) it suggests that there really is variation beyond that readily discernible with light microscopes.  In others (e.g. Gomphonema) the evidence is less clear cut and it is even possible that taxonomist’s enthusiasm may have run ahead of the actuality.  Unfortunately, we don’t have any detailed molecular studies of Brachysira with which to test the ideas of species limits developed with morphological approaches.  

A second question is whether we need all this information in order to draw the ecological insights that catchment managers need in order to decide what measures, if any, are needed to keep the water body in a healthy state.   The autecological information that we have suggests that Brachysira species are mostly associated with healthy, low nutrient, circumneutral water bodies.  Where there are differences, it is primarily due to the hardness of the water rather than to the levels of human-derived pressures.   The very fact that we see several species in one lake is evidence that their preferences for these conditions, in any case, overlap.   So there is little evidence that different species of Brachysira “indicate” starkly different environments.

Brachysira microcephala (formerly B. neoexilis and, further back still, Anomoensis exilis), Ennerdale Water, June 2020. Scale bar: 10 micrometres (= 1/100th of a millimetre).  Photos: Bryan Kennedy.

As I suggested in Curried diatoms?, however, there may be some value in knowing that there are several species present but for reasons that are not associated with rather naïve associations between species and chemical measurements.  As the present generation of methods for assessing lake or river health are tied to these tired notions of indicator values there is probably not a lot of extra “signal” to be squeezed from splitting Brachysira further.  

Brachysira procera, Ennerdale Water, June 2020. Generally longer and broader than B. microcephala.  Scale bar: 10 micrometres (= 1/100th of a millimetre).  Photos: Bryan Kennedy.

Having said that water hardness plays a greater role in determining the distribution of Brachysira species than water quality, one of the oddities of this sample was that there were small numbers of two species associated with hard water (B. neglectissima and B. vitrea).  There is absolutely no limestone or any other rocks that might create hard water conditions within the Ennerdale catchment, so why are these species here?   I have found B. vitrea, especially, in small numbers in other soft water areas so these are not isolated occurrences.   Do they represent genuine viable populations hanging on at the extreme edge of their range (and, one assumes, competing for resources with physiologically “fitter” Brachysira species) or are they “noise”, carried into the catchment by wind or on the feet of mammalian vectors such as, er…, myself?   The latter has implications: firstly, it lends support to the controversial “everything is everywhere, environment selects” hypothesis (that I’ve mentioned in the past but never fully explained … I’ll do so in a post in the near future) and it also casts doubt on some of the claims of metabarcoding enthusiasts that they can extract more ecological information because the sequencing depth that is now possible exceeds that of traditional ecological analyses.  If what we hope is “signal” is, in fact, “noise”, then that depth is as likely to confuse or even mislead as it is to inform better decision making. 

Brachysira garrensis, Ennerdale Water, June 2020. Similar to B. microcephala but with denser striae (very difficult to see without very good optics).  Scale bar: 10 micrometres (= 1/100th of a millimetre).  Photos: Bryan Kennedy.

Studies of the microscopic world are only ever as good as the technology available.  But, equally important, studies of microbial diversity are also complicated by the observer’s expectations.  How different do two cells have to be before you treat them as separate species?   Not only did Hustedt not have such good microscopes as are now available when he wrote his Flora in 1930, but he also assumed that diatom species concepts were much broader than we now know to be the case.  And the final twist is that the ability of anyone to match what s/he sees with the images in the literature.  Hustedt used a single drawing to illustrate “Anomoensis exilis” (what we would now call Brachysira microcephala) in his Flora whereas Bryan Kennedy used 96 photographs, taken with differential interference contrast lighting, along with 31 scanning electron micrographs in his 2017 paper highlighting, in the process, four different morphotypes. Whether these represent different species is yet to be determined.  My point is that “seeing” depends partly on how light stimulates the optical nerve (which depends on the quality of equipment we have), but more on how that raw signal is processed by our brains.  

Brachysira neglectissima, Ennerdale Water, June 2020. Like B. garrensis, this has denser striae than B. microcephala.  Note, too, the undulating pattern of areolae.  Scale bar: 10 micrometres (= 1/100th of a millimetre).  Photos: Bryan Kennedy.

Postscript: we finally got out into the field on Monday, catching a gap in the weather when the rivers were low but the snow did not impede travel.  We had some spectacular views of snow-covered Pennines, High Street, Blencathra and Skiddaw on the way over, but the western Lakes were virtually snow free.   We even found time for a short walk around Loweswater on the way back, making the most of a rare opportunity to travel during Lockdown 3.0. 

Brachysira vitrea, Ennerdale Water, June 2020. Generally broader (>5.5 micrometres) than B. microcephala.  Scale bar: 10 micrometres (= 1/100th of a millimetre).  Photos: Bryan Kennedy.

References 

Hustedt, F. (1930).  Susswasserflora von Mitteleuropa 10: Bacillariophyceae.  Gustav Fischer, Jena.

Kennedy, B. & Allott, N. (2017).  A review of the genus Brachysira in Ireland with the description of Brachysira prageriand Brachysira conamarae, new raphid diatoms (Bacillariophyceae) from high status waterbodies.  Phytotaxa 326: 1-27.

Some other highlights from this week:

Wrote this whilst listening to: Brandon Marsalis’ soundtrack album for the film Ma Rainey’s Black Bottom and Arvo Pärt’s Spiegel im Spiegel.

Cultural highlights:  White Tiger, new film set in India.   

Currently reading:  Still reading The Science Delusion by Rupert Sheldrake

Culinary highlight:  Homemade piccalilli pickle.   Too soon to give a definitive opinion on flavour (it needs three weeks to mature) but I’m fantasising about piling it into a thick ham sandwich already.