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