Diatoms from the Troodos mountains

Troodos_snowscape_Apr19

Back in April, I wrote two posts about the algae from a stream draining a chromite mine in the Troodos mountains in Cyprus (see “Survival of the fittest (1)” and “Survival of the fittest (2)”).  I also planned to write a post about the diatoms growing in the stream but the slide I prepared has been sitting on my desk over the summer whilst I was distracted by other things.  However, I have just started looking at some samples from metal-enriched streams in the northern Pennines and, curious to see whether a Cypriot chromite mine had similar effects, I blew the dust off the slide and slipped it under my microscope.

The principal effect of toxic pollution is to reduce the number of species found and, in this respect, my sample from the outflow of the Hadjipavlou mine outflow was true to form, containing just eight species.  The most abundant of these was Meridion circulare, accounting for one in four of all the cells.  What is more, many of the cells were visibly distorted (see images a., c. and d., in particular, in the plate below).  This is quite a common phenomenon in metal-polluted streams (see “A twist in the tale”) though I have not seen it quite so obviously in Meridion circulare before. My own pet theory is that one of the enzymes involved in laying down the silica cell wall has a metal co-factor that is displaced by heavy metals.

Meridion_circulare_Hadjipavlou_Apr19

Meridion circulare from thepebbles from the stream draining Hadjipavlou chromite mine in the Troodos mountains, Cyprus, March 2019.  Scale bar: 10 micrometres ( = 1/100th of a millimetre).   The photograph at the top of the post shows snow on the Troodos mountains near the mine.

The only other diatom that was at all common in the sample was Hantzschia amphioxys, which also occurred alongside a smaller population of Hantzschia abundans.  I’ve not come across Hantzschia in metal-enriched streams before: it is a species that is most often associated with habitats that are not permanently submerged.  That may be the case at Hadjipavlou but the water that flows from mines comes from groundwater rather than rainfall so would not be subject to the strong seasonal variations that we associate with Mediterranean streams.  It is hard to draw a firm conclusion from a single visit.   Unlike Meridion circulare, however, neither population of Hantzschia showed any obvious distortion, perhaps due to the Hantzschia cells being more heavily silicified than those of Meridion circulare.

The extent to which cellular distortions are obvious does vary between species, as can be seen in “A twist in the tale …”  which compared three different representatives of the same genus in a metal-polluted stream.  I chose the word “obvious” with care as I do think that these phenomena are more easily seen in long thin cells than in shorter ones.  In the same Pennine streams where distorted Fragilaria are common, for example, I can also see distorted cells of smaller diatoms such as Achnanthidium minutissimum.  But you need a keen eye to spot these reliably.   Some other people have used fluorescent stains to look at other cellular irregularities, such as the position of the nucleus and damage to the nuclear membrane, but these require specialist approaches whereas distortions to cell outlines can be spotted from a standard analysis.

Hantzschia_spp_Hajipavlou_Apr19

Hantzschia abundans (k., l.) and Hantzschia amphioxys (m. – p.) in the from the stream draining Hadjipavlou chromite mine in the Troodos mountains, Cyprus, March 2019.  Scale bar: 10 micrometres ( = 1/100th of a millimetre). 

A few years ago I was involved in a study of diatoms from streams in Cyprus and I dug out some of these data in order to put the Hadjipavlou sample into context.  One immediate surprise was that many of the “reference” (i.e. pristine or near-pristine) samples in that survey also had relatively low diversity.   The 45 samples in this subset had, on average, nine species, and a mean Shannon diversity index of 1.7, compared to eight species and a Shannon diversity index of 1.42 for the Hadjipavlou sample.   I’ve never been a fan of diversity indices as measures of ecological quality (see “Baffled by the benthos (2) and links therein”) although I suspect that average diversity at Hadjipavlou measured over a period of time will always be low whereas average diversity at unimpacted sites is more likely to fluctuate. Equally, low diversity coupled with a second strand of evidence, such as distorted valves, is a useful sign to an ecologist that something untoward is happening.

diversity_indices

Number of taxa (left) and Shannon diversity (right) recorded in 45 samples from “reference” sites (i.e. minimal evidence of anthropogenic alteration) in Cyprus.  The arrows indicate the location of the Hadjipavlou stream within this dataset. 

The irony of writing about a heavily-polluted stream in the Troodos mountains is that the geological conditions which created the metal-rich veins hereabouts also create conditions for many plants endemic to Cyprus.   The serpentine and other ultramafic rocks create metal-rich soils within which few plants can survive (more about these here. I suspect that few of the plant enthusiasts drawn to Cyprus will ever cast more than a cursory glance at the green flocs adorning the abandoned mines of the Troodos mountains.

References

Licursi, M., & Gómez, N. (2013). Short-term toxicity of hexavalent-chromium to epipsammic diatoms of a microtidal estuary (Río de la Plata): Responses from the individual cell to the community structure. Aquatic Toxicology 134-135: 82-91.  https://doi.org/10.1016/j.aquatox.2013.03.007

Hard cheese …

A day or so after my return from my trip to Orleans, The Guardian published an article on deadly algae on Brittany’s beaches.   The alga in question is Ulva, which I have written about a few times in the past.  It is a genus that is often associated with elevated concentrations of nutrients (see “Venice’s green fringe” and “News from Qingdao …”).  In Qingdao, the accumulations of algae caused problems during the 2008 Olympic sailing events but, in Brittany, there have actually been deaths associated with these growths.   Although green algae do not produce toxins themselves, the mats are so thick that the algae at the bottom cannot get the light and oxygen they need and so die and rot.   However, the thickness of the mats also means that the bacteria involved in breaking down dead plant matter are also starved of oxygen and, under such conditions, they can use sulphate as an energy source.  This, however, produces the toxic gas hydrogen sulphide which accumulates until released by, in this case, people stepping on the mats.

The problem in Brittany is concentrated on the north coast, close to where the Seine empties into the English Channel, rather than the south coast, where the Loire joins the Bay of Biscay.  Seine or Loire, the problem is similar: France has a large and vociferous farming lobby and inorganic nutrients, much deriving from agriculture, spill out of the rivers into the sea where they encourage the growth of algae.  It is not just green algae: there are also toxin-producing dinoflagellate blooms which can render shellfish dangerous for human consumption.  The combination of seashores piled high with rotting algae and restaurants unable to source local produce for their “fruits de la mer” is a major worry in a region where tourism makes a significant contribution to the economy.   It is also the classic environmental challenge, as economically-rational activities have malign consequences 100 km or more away, creating major headaches for policy-makers.

There is, however, good evidence from modelling studies that a reduction in the nitrogen in rivers that empty into the coast around Brittany will have positive effects.  One of these went so far as to envisage the adoption of organic farming in all agricultural areas of the Seine basin, leading to a halving of nitrogen load and a likely very significant reduction in the frequency of dinoflagellate blooms.   Another study indicated a likelihood of much less Ulva if river nitrate concentrations were much reduced.

That’s the theory. Putting such reductions into practice is a different matter because it means taking on the farming lobby.  There is a simple logic, in a farmer’s eyes, to raising output by adding more of the nutrient that limits growth.  The flaw in the argument is that nitrate is highly soluble and a proportion of the nutrient that a farmer spreads on his fields will be washed into nearby water courses when it rains.   No farmer wants to pay for fertilizer that is not nourishing his plants so there ought to be a solution that is agreeable to both them and the environment.   In reality, implementing policies that protect one sector (seafood harvesting, in this case), whilst not undermining another (agriculture), all within a framework in which market forces drive much of the decision-making is a fiendish challenge.

I think that this is one of the reasons why right-leaning politicians are rarely enthusiastic about the environment: simply leaving market forces to decide outcomes means that “externalities” – consequences of a commercial activity that are not reflected in the price – will be ignored.   Environmental regulation implies a need for interventions to control activities in order to protect wider interests, but that is an anathema to free market purists.  Regulation should, in theory, limit the “externalities” and create an environment in which sectors such as agriculture, seafood harvesting and tourism can co-exist.  Again that’s the theory but regulating the environment invariably results in labyrinthine bureaucracies that soak up money from taxes which free market purists would prefer not to have levied in the first place.

That’s why I really would encourage you to read Kate Raworth’s Doughnut Economics (see “The limits of science …”).  Every environmental scientist needs to reflect on how the changes they want to see need structural alterations that permeate throughout society, and not just technological fixes.  And, yes, those changes might affect our own lifestyle too. If French farmers use less fertiliser then they will produce less milk per hectare.  That, in turn, will result in less of the wonderful French cheeses that we all love and, probably, higher prices.  So, in the final analysis, it is not just the use of nitrate fertiliser that will have to change, it is our own aspiration.  Before we can make a difference we will have to live differently ourselves.  That’s the tough challenge we all have to face.

References

Passy, P., Le Gendre, R., Garnier, J., Cugier, P., Callens, J., Paris, F., … Romero, E. (2016). Eutrophication modelling chain for improved management strategies to prevent algal blooms in the Bay of Seine. Marine Ecology Progress Series 543: 107-125.  https://doi.org/10.3354/meps11533

Perrot, T., Rossi, N., Ménesguen, A., & Dumas, F. (2014). Modelling green macroalgal blooms on the coasts of Brittany, France to enhance water quality management. Journal of Marine Systems 132: 38-53. https://doi.org/10.1016/j.jmarsys.2013.12.010

 

A river runs through it …

Loire_at_Orleans_Sept19

I made an journey via Paris to Orleans last weekend to wave off my wife and daughter as they walk part of the Camino de Santiago.   The part of this austere Medieval pilgrimage route that they chose to follow happens to be one that meanders along the Loire Valley, passing chateaux and wineries en route.   Apparently, blisters are providing an element of self-mortification to keep the spirit of pious ascetism alive.

Orleans has a beautiful Medieval old town, dominated by a cathedral, along with plenty of reminders that it was here that Joan of Arc whupped the English.   More importantly, for a freshwater ecologist, a river runs through it.   The mighty Loire – the longest river in France – rises in the Masif Central and then flows north until it reaches Orleans, then it swings round to flow west to join the Atlantic Ocean at Nantes, a total length of just over 1000 km.  The river at Orleans is broad and shallow, divided into two channels by a wooded island; the left-hand chnnel is braided, with many small gravel islands, some with grass and herbaceous vegetation, and the water is generally shallow.  However, the bed of the river itself was a dark green in colour.  The Loire Valley is known as the “Garden of France” and this gives a clue to the scale of nutrient enrichment that we might expect in the river.  In the backwaters, this green backdrop was enlivened by patches of red due to the aquatic fern Azolla (see “Escape to Southwold”).

Azolla_Loire_Sept19

Patches of Azolla floating over algae-smothered substrata in a backwater of the River Loire at Orleans.  The picture at the top of the post shows a view looking downstream from the left side of the Pont George V. 

I brought a sample of the algae from some stones that were just within reach of the shore home on the Eurostar in a Perrier Water bottle for a closer inspection and was surprised by the diversity. In particular, I noticed several clumps of a narrow cyanobacterium that proved hard to photograph (possibly Homoeothrix janthina: see “Algae from the Alto Duoro”) along with many green algae.  I also saw Cladophoraglomerata, which is one of the classic indicators of nutrient rich conditions, along with Stigeoclonium, two forms of Spirogyra, two forms of Oedogonium and myriad green unicells and coenobia.  Stigeocloniumis another good indicator of nutrient enrichment,as  the filaments narrow to long colourless “hairs” when key nutrients are scarce – these cells are physiological adaptions to scavenge phosphorus and their absence at Orleans shows that this nutrient is not in short supply (see “A day out in Weardale”).

Stigeoclonium_Loire_Orleans_Sept19

Stigeoclonium cf. tenue (based on properties of erect filaments) from the River Loire at Orleans, September 2019.  Scale bar: 10 micrometres (1/100thof a millimetre). 

As well as green algae and cyanobacteria, there were also a lot of diatoms.  A few of these are illustrated below, and I’ll describe the diatoms in more detail in a future post.   As well as those I have photographed, I also saw long chains of a species of Fragilaria and another small araphid (possibly Staurosira) as well as Ulnaria ulna and some cells of Gomphonema and Navicula.   Note, in particular, the tube of Encyonema (possibly E. prostratum).   I’ve talked about tube-forming diatoms before (see “An excuse for a crab sandwich, really …”) but still can’t really explain what advantage this structure confers on a diatom.   What we can, perhaps, say, is that tube-dwelling is one of a several habits represented in the diatoms from Orleans – chains, erect, free-living motile, epiphytes  and more – and the mass of other algae create a rich diversity of microhabitats that the diatoms can exploit.

diatoms_Loire_Orleans

Some diatoms from the River Loire at Orleans: a. – d. Diatoma vulgare; e. Cocconeis pediculus; f. Encyonemasp.   Scale bar: 10 micrometres (= 1/100thof a millimetre).  The identity of the tube-dwelling form will have to wait until a cleaned sample is available. 

This abundance and diversity of green algae reminded me of some of the lush growths I had seen in UK rivers during the 2018 heatwave (see “Talking about the weather …”).  In a healthy river in the UK, I would expect to find less conspicuous growths than this, as invertebrate grazers would keep the algal biofilm shorn to a short stubble.   If, for any reason, the invertebrates cannot keep up with the algal growth, then a feedback loop is set up: the algae suck the valuable oxygen the invertebrates need from the water, the grazing reduces in intensity yet further, leading to a situation such as that I saw in the River Loire is the result.

Warm weather exacerbates the situation because water holds less oxygen at high temperatures.  In my posts about the River Wear last summer I commented that the plants in the river suggested that the river was more enriched with nutrients than was actually the case and I suspect that this was the result of these interactions.   The more southerly, more continental climate of the Loire Valley will experience these effects more often and it is possible that what I am looking at in Orleans may become the norm for UK rivers, as global warming intensifies.  Over the past decade I’ve worked on how to estimate the threshold concentrations of nutrients that a healthy river can endure.  However, nutrients rarely exert a direct effect on the plants and animals in a river but, instead, work through their effect on other factors such as oxygen. That will mean that global warming may wipe out any benefits of expensive nutrient reduction programs based on current estimates of the relationship between nutrients and river ecosystem health.  That’s a rather depressing prospect.

So I’ll end on a more cheerful note: the reason Heather and Rosie chose to start their Camino in Orleans was that they wanted to avoid a flight if possible.  At least that is how they sold it to me.   That they also chose to start their pilgrimage in a town close to the Sancerre vineyards may be pure coincidence.   Or maybe not ….

References

Surt, M.M., Jansen, M.A.K., Harrison, S.S.C. (2011).  Invertebrate grazing and riparian shade as controllers of nuisance algae in a eutrophic river. Freshwater Biology 56: :2580-2593

Wilco, C.E., Verbrak, P., Durance, I., Vaughn, I.P. & Ormerod, S.J. (2016).  Field and laboratory studies reveal interacting effects of stream oxygenation and warming on aquatic ectotherms.  Global Change Biology 22: 1769-1778.

Orleans_cathedral_Aug19

Orleans cathedral, August 2019.

Tales from prehistory

Stonehenge_Aug19

Microscopes and Monsters has been quiet for a couple of weeks, as I have been on holiday, part of which was spent “off grid” at the Green Man Festival in Wales.  From there, we headed to London for a Proms concert (two music festivals in a week!) via the Cotswolds and the ancient landscapes of Salisbury Plain.

My first visit to Stonehenge was 50 years ago, at which time you could pull off the A303 and wander amongst the columns unconstrained by fences and barriers.   Now the visitors are guided to a visitor centre two kilometres from the site, and offered a shuttle bus after being relieved of £20.  Or, if you prefer, you can walk across Salisbury Plain to the monument.  On a sunny afternoon in August this becomes part of the experience as there are ancient burial mounds (some pre-dating Stonehenge) both alongside the path and dotted around the horizon.   Stonehenge itself gradually rose up ahead of us, and we experienced a little of what the ancients must have felt as they approached Stonehenge along the processional way.

The last time that I was here was a stop off between field work on the nearby River Wylye and a meeting in Reading.   At the time I was engaged with two separate projects concerned with the health of chalk streams, which are characteristic of this part of southern England.   The approach we used elsewhere in the country was to compare what we found in samples we collected with what we expected to find if that site was in a pristine condition.

There was, at the time, a vigorous debate about how this “reference condition” should be defined.   This debate had a theoretical component (epitomised by Brian Moss’ paper in the reference list) but also a more pragmatic element (encapsulated by the other paper).  This was necessary because an ultra-strict, but theoretically sound, approach might not yield enough data from which a robust prediction of the “expected” ecology could be derived.   In essence, we searched out remote regions of the UK where population density was low and agriculture was not intensive and used these to derive our understanding of what to expect in the more densely-populated regions of the country.

Avebury_Aug19

Part of Avebury stone circle, Wiltshire, August 2019.  The photograph at the top of the post shows Stonehenge.

This worked quite well (although Brian Moss, predictably, had his own pithy thoughts on the approach).  However,  we simply could not find any sites that fulfilled our criteria of low population density and a low intensity of farming in those parts of lowland Britain where the underlying geology was Jurassic limestone, Cretaceous chalk or another formation that resulted in very hard water.  Our estimates of ecological health in such regions depend, as a result, on extrapolation and judgement rather than evidence.   That is all well and good for an academic journal but, in the case of the River Wylye, Wessex Water were being asked to spend hundreds of thousands of pounds to upgrade sewage works and, rightly, felt that they needed something more in order to explain the consequent price rises to their customers.

The OS maps of the region around my sampling points on the Wylye were dotted with symbols marking ancient monuments (long and round barrows, in particular) and the huge, mysterious religious sites of Stonehenge and Avebury lie just to the east.  Together, they point to continuous occupation of the area for over four thousand years, which means that it is hardly a surprise that we found no sites that met our criteria for a “pristine” stream.   The chalk streams of southern England are famous and rightly regarded as a threatened habitat, but they are not natural.  It is better to think of them as aquatic equivalents to hay meadows or hedgerows: ecologically-rich habitats that have been created by human activity, rather than as a result of “natural” ecological processes.

That means that it we need to diverge from a strict definition of “reference conditions” in order to set a baseline for ecological expectations in such circumstances.  For macrophytes – the larger aquatic plants – there is an expectation that the flora in this baseline state will be rich; however,  this assumption does not work for the microscopic algae in chalk streams.  We also found that river stretches where the macrophytes are thriving and, apparently, healthy, often have diatoms that suggest nutrient enrichment.  That is a puzzle for which we think we may have a solution, and which I will write about in a future post.

Silbury_Hill_Aug19

Silbury Hill, part of the Avebury World Heritage Site.  It is a Neolithic site whose original purpose is unknown though, to a visitor from north-east England, it looks remarkably like a slag heap.

We use low population density and absence of intensive agriculture as a proxy for “natural” in the uplands but need to treat this assumption with care too.  There might be fewer grand Neolithic monuments in the north of England or Scotland but signs of ancient habitation are there if you care to look (see “More reflections from the dawn of time”).   The moorland where these streams rise is, itself, an artificial habitat, created when early agriculturalists removed the natural tree cover.  Modern streams in these areas are, therefore, exposed to more light than in their primeval states and that will have important consequences for the plant life that lives within them.  They may be the best we have, but are hardly “natural”.

Two factors, both highly pragmatic, brought this debate to a close.   The first was realisation that, whatever the rights and wrongs of purist versus practical standpoints, most of our rivers are very degraded and alterations in the approach used to define the “expected” condition would be unlikely to change this broad scale picture.   About sixty-five per cent of our rivers fail to achieve good ecological status despite the flaws in the reference concept.  The second factor was simply that, since the financial crisis in the 2008-2010, the UK environment agencies have had too few resources to improve the reference concept.   As any such “improvement” will almost certainly make the true state of UK rivers look even worse than it does at the moment, a more cynical argument is that few of the bureaucrats involved in the process have any great enthusiasm for the task anyway.

References

Moss, B. (2008).  The Water Framework Directive: total environment or political compromise.  Science of the Total Environment400: 32-41.

Pardo, I., Gómez-Rodríguez, C., Wasson, J.G., Owen, R., van de Bund, W., Kelly, M., Bennett, C., Birk, S., Buffagni, A., Erba, S., Mengin, N., Murray-Bligh, J. & Ofenböeck, G. (2012).  The European reference condition concept: A scientific and technical approach to identify minimally-impacted river ecosystems.  Science of the Total Environment420: 33-42.

 

When is an icon not an icon?

Florence_from_Fiasole_May19

Yet another change in location, this time to Florence for a wedding, but with some time set aside to gorge myself on early Renaissance painting.   That means traipsing around a lot of churches (because much of the best Italian art remains in situ) and a long queue to get into the Ufizzi gallery (because some of it doesn’t), emerging at the end footsore and with more questions than answers.

Having immersed myself in Eastern Orthodox imagery earlier this year (see “Secular icons?”) my first response on looking at the earliest works by Giotto and Cimabue was “those are icons”.  Stylistically and in subject matter, there is nothing to distinguish them from contemporary Eastern Orthodox icons: the flat, gilded backgrounds, the poses of the Madonna and child, and the saints, are all identical.  That made me wonder if the Medieval believers had approached these images in the same way that an Orthodox Christian would have done, in which case we need to think of the Renaissance not just in the conventional art-historical terms (epitomised by Kenneth Clark’s Civilisation) but also in terms of a change in belief.    This is important because, in most cases the artists would have been working to strict instructions from their clerical paymasters and would not have had much latitude to experiment with new designs.

A case in point is Giotto’s Madonna and Child with four saints, which looks very much like a row of icons on an Orthodox iconostasis. Except that this was originally altarpiece and that, itself, tells a story.   The Orthodox iconostasis stands between the priest who conducts the eucharist and the congregation whereas a Catholic altarpiece sits behind the altar, so that the congregation (that part beyond the rood screen at least) can see the ceremony and, in particular, the part when the priest elevates the host.   Theological developments in the 13thcentury, therefore, drove changes in the arrangement of church furniture and, in turn, led to some of the changes that we see in art during this period.

Giotto_Madonna_&_Child_Ufizzi

Giotto: Madonna and Child with St Nicholas, St John the Evangelist, St Peter and St Benedict the Redeemer.  Tempera on wood, 1337.   Ufizzi Gallery, Florence.

It is not just the position of the image that changed in Catholic churches during Medieval times: subject matter also changes from schematic images painted to prescribed formulae to styles that demanded more mental engagement by the viewer.  Look at Gentile da Fabriano’s altarpiece depicting the Adoration of the Magi, painted about a century after Giotto’s Madonna and Child.   The Madonna and child are still present but are now set in a context that would allow the viewers to imagine that they were participants at the original event.   Note, too, how the subjects in the picture are dressed in contemporary attire and original audiences might also have recognised the patron and members of his family painted into the front of the crowd.   At one level, these altarpieces function as a “poor man’s bible”, bringing elements of the Gospel to the largely illiterate congregations but, at the same time, they are also drawing the viewers into the story, ensuring that they are not just passive observers and, in turn, demanding a response.

Adoraton_of_Magi_Fabriani_Ufizzi

Gentile da Fabriano’s Adoration of the Magi.  Tempera on wood, 1420. Ufizzi Gallery, Florence.

As the fifteenth century progresses, we see the influence of the Renaissance in the images growing. In particular, a better understanding of linear perspective allowed artists to place the characters in their paintings in more plausible settings, drawing the viewer into the pictorial space.   Fra. Angelico’s Annunciation is painted onto a wall at the top of a staircase leading to monk’s cells in the Convent of San Marco, so the engagement with the viewer would be brief: no more than a short pause and a prayer before moving on.   The quiet scene depicted here is, perhaps, better suited to a monastery’s cloisters than the busy-ness that we saw in the Adoration of the Magi but, by focussing on just two people, pictures of the Annunciation create spaces that need to be filled if the illusion of pictorial depth is to be maintained.   And so we see, in the background of both Fra. Angelico’s and Leonardo’s Annunciations, the first tentative steps at depicting landscapes.

Annunciation_Fra_Angelico

Fra. Angelico’s Annunciation at the Convent of San Marco, Florence.  Fresco, 1437-1446.

Annunciation_Leonardo

Leonardo da Vinci’s Annunciation. Oil and tempera on wood, 1472-1474.  Ufizzi Gallery, Florence.

The painting style may have developed through the early Renaissance but one feature that all these pictures still share with their Gothic predecessors, and with Byzantine icons, is that they are still “applied art”: each was painted with a particular purpose in mind, whether for a church or a monastery, and 21stcentury notions of aesthetics have to bear this in mind.   On our trip to Florence this aspect was exemplified by Ghirlandaio’s The Last Supper, also at the Convent of San Marco.  This is in rather better condition than Leonardo’s depiction of the same scene in Milan (which is about a decade younger) but is similar in other ways (some think that Leonardo may have been inspired by Ghirlandaio’s treatment of the subject) and, significantly, was also painted life-size onto the wall of a refectory.   Once again, we can see clever use of linear perspective to create an illusion of depth and, in the background, trees that suggest that, instead of looking at a flat wall we are, in fact, looking into an extension of the room that we are in which, in turn, has windows that look out onto a garden.   That gives us an important clue to unlocking the meaning of the image.

The Refectory where we find The Last Supper is now the gift shop for the San Marco museum, but there are wooden benches along two of the walls where you can sit down and try and put yourself into the place of the monks and their visitors who would have eaten their meals here.   The painting creates the illusion that they were eating in a room that seemed bigger than it really is, and where there were a dozen or so extra guests whose presence was a constant reminder of one of the most important events in the Gospels.  This is the acme of Renaissance thinking: scientific and mathematical principles being utilised to create a work of art that, in turn, synergised man’s relationship with God.   C.P. Snow described what he saw as a profound gulf between arts and sciences in the Two Cultures, written in 1959.  Even then he could conceivably have extended this observation to three cultures by including religion too.  That would have been an anathema in the fifteenth century, when the boundaries between art, science and spirituality were much more fluid.  We’ve learned a lot in the intervening five hundred years but, at the same time, there is much that we have forgotten to remember.

Last_Supper_Angelico

Domenico Ghirlandaio’s The Last Supper in the Small Refectory at the Convent of San Marco, Florence.  Fresco, 1486.

Santa_Croce_from_Palazzo_Vecchio_May19

The church of Santa Croce rising above the rooftops of central Florence in May 2019.    The photograph at the top of the post shows a view of Florence from Fiesole.

Hyperepiphytes in the Shetland Islands

Gossa_Water_May19

I was lucky enough to spend a couple of days in the Shetland Islands during last week’s spell of warm weather and spent one of my mornings there hiking in shirtsleeves across moorland to a remote loch.   Good infrastructure is a legacy of the Shetland Islands’ association with the oil industry, and this includes a strong mobile network, meaning that I managed to find this particular loch using the Ordnance Survey maps on my smartphone. I would not normally rely upon a mobile signal to navigate across such remote terrain but in Shetland it is often possible.  I would, nonetheless, recommend keeping a paper map and a GPS in your kit just in case, as I did lose the signal on a few occasions during my stay.

Most of the lochs in the northern part of mainland Shetland are shallow, peaty water bodies, with soft water and relatively sparse assemblages of aquatic plants.   Parts of the littoral zone of this particular loch, however, had extensive growths of submerged mosses.  It is a long time since I was proficient at identifying aquatic mosses but these clumps look likeWarnstofia fluitans to me, though I am willing to be proved wrong.  I did try to remove some leaves and have a proper look but that task was complicated by tufts of attached filamentous algae.   In their submerged state, these formed distinct clusters at intervals along the straggly stems of the moss but, once removed, the filaments collapsed to smother the leaves and confound my attempts to run a scalpel blade along the stem.

Warnstofia_Gossa_Water_May19

Submerged colonies ofWarnstorfia fluitans(?) smothered byOedogoniumfilaments in Gossa Water, north Mainland, Shetland (HU 4354 6047). Gossa Water (one of five that share this name in the Shetland Islands!) is illustrated in the photograph at the top of this post.

The filamentous alga proved easier to unmask: the unbranched filaments, reticulate (net-like) chloroplasts and distinctive ‘cap cells’ all identifying it as the green alga Oedogonium.  As is often the case, however, the populations lacked any sexual organs so it was impossible to know which species (see “The perplexing case of the celibate alga“ and, for a rare case of a sexually-mature filament, “Love and sex in a tufa-forming stream”).   Abundant epiphytes can be another feature of Oedogonium: unlike several other filamentous green algae it produces little mucilage which makes it easier for diatoms, in particular, to colonise.  As well as colonies of needle-shaped cells of Fragilaria gracilis there were also several Achnanthidium cells and, entangled around the filaments and the moss, chains of Tabellaria flocculosa.   Given that the Oedogonium was, itself, an epiphyte, these diatoms are ‘hyperepiphytes’, a term that attracts remarkably few Google hits, almost all associated with lower plants.

The ‘cap cells’ are one of the most distinctive features of Oedogonium and results from a distinctive mode of cell division that leaves rings of scar tissue at the point where the two cells split.   That we see four or more of these scars on a few cells whilst the great majority have none suggests that we are looking at a primitive form of specialisation, with a few cells in a filament being responsible for all the cell division.  What is more, these cap cells are also often the ones that form oogonia (see “Love and sex in a tufa-forming stream” for an illustration of this) and asexual zoospores, so there must be something slightly different in the biochemistry within these cells that drives these processes.   However, at this point the formal scientific literature goes strangely silent apart from a single paper published in 1962.  Curiously, the evolution of multicellularity is one of those big questions that attract a lot of top academics (see the reference to a recent paper in Nature Scientific Reports below)  whilst a genus of algae that seem to show some faltering first steps towards specialisation of some cells are largely ignored.  Another case of the “trailing edge” of science?

Gossa_Oedogonium

Oedogonium filaments growing on Warnstofia fluitans in the littoral zone of Gossa Water, north Mainland, Shetland, May 2019.   The arrow on the top image shows the “cap cells”.   Note also the cluster of Fragilaria gracilis(plus a few cells of Achnanthidium) on the lowermost filament and, in the middle image, two of the many cells of Tabellaria flocculosa that were entangled with the Oedogonium filaments and moss stems.  Scale bar: 20 micrometres (= 1/50thof a millimetre). 

Oedogonium_zoospores

A zoospore being released from a filament of Oedogonium.  This series of photographs was taken by me in about 1993 and I have no details of the location from which it came.  The filament is about 40 micrometres (= 1/25thof a millimetre) in diameter.

Reference

Herron, M.D., Borin, J.M., Boswell, J.C., Walker, J., Chen, I-C. K., Knows, C.A., Boyd, M., Rosenzweig, F. & Ratcliff, W.C. (2019).  De novo origins of multicellularity in response to predation.  Nature Scientific Reports 9, Article number: 2328

Rawitscher-Kunkel, E. & Machlis, L. (1962).  The hormonal integration of sexual reproduction in Oedogonium.   American Journal of Botany 49: 177-183.

St_Ninians_tombola_Shetland_May19

Sightseeing in Shetland: the tombolo (sandy isthmus) linking St Ninian’s Isle with Mainland in the Shetland Islands, May 2019.

Beyond the Tower of Babel …

Danube_at_Vienna_May19

A week after I return from China, I was off on my travels again; this time to Vienna for a workshop between molecular ecology specialists and ECOSTAT, the committee of Member State representatives who oversee ecological aspects of Water Framework Directive implementation.   As ever, I found some time to visit some art galleries around the meeting and, as Vienna has one of the most impressive collections of paintings by Pieter Brueghel, I could not resist spending some time in front of his “Tower of Babel”.  A few years ago I cheerfully included this picture in a talk on EU ecological assessment methods, as we tried to make sense of the myriad national approaches.   Three years after the Brexit vote, however, it seems to better reflect UK domestic politics where, ironically, language is one of the few things that all protagonists do have in common.

The River Danube seems to encapsulate the reasons why Europe needs collaborative thinking on the state of the environment.  It is the second longest river in Europe, after the Volga, and flows through ten countries, with tributaries extending into nine more.   Eight of the nine countries through which the river flows are members of the EU (the ninth, Serbia, is in the process of joining) so the river represents a case study, of sorts, on whether EU environmental policies actually work.   This is not just an academic question: ecologists are generally in favour of integrated management of entire catchments whilst the EU operates on a principle of “subsidiarity”, which means that decision-making is devolved to the lowest competent authority (individual Member States in the case of the environment).   Finding the right balance between these principles takes a lot of patient discussion and is one reason why EU decision-making can appear to be agonisingly slow.

Breughel_Tower_of_Babel

Pieter Bruegel’s “Tower of Babel” in the Kunsthistorisches Museum in Vienna.

And there are more problems: the Water Framework Directive evaluates the sustainability of water bodies by their naturalness yet very large rivers such as the Danube have been very heavily modified by human use for centuries.   The river has been broadened, deepened and impounded, and its banks have been straightened and strengthened in order to make it navigable, and there is a huge human population, with associated industry, living on its banks.  The stretch of the Danube along which I walked on my last morning in Vienna was also lined with embankments to protect the surrounding land from flooding but these, at the same time, cut the river off from the ecological benefits of the floodplain.

What hope for a large river such as the Danube in the face of all these challenges?   First of all, when dealing with rivers such as these we need to adjust our expectations, recognising that they are so central to the economic life of the regions through which they flow that there are limits to their capacity to ever resemble truly natural rivers.   Once we have done this, we can start to unpick the challenges that can be addressed by individual Member States.  In the case of water quality, in particular, the story for the Danube is encouraging and European environmental legislation has played its role in this process.  By the time the Danube reaches the borders with Romania, for example, nutrient concentrations are low enough for many of the benthic algal-communities to meet criteria for “good ecological status”.

You can see this in the graph below, from a paper that we’ve published recently.   The Romanian sites are largely clustered at the top left hand side of the graph, relative to data from other countries – indicating low phosphorus concentrations and good ecology (expressed as “ecological quality ratios”, EQRs).   Thanks to an extensive exercise that took place a few years before I started grappling with the Romanian data, we already had a consensus view of the EQR boundaries for high and good status, and most of the Romanian data fits into the band representing “good status”.  That’s encouraging and whilst these communities are just one element of a much more complex ecosystem, but it is a clear step in the right direction.

RO_VLR_intercalibration

The relationship between dissolved phosphorus and ecological status of the phytobenthos (expressed as the Ecological Quality Ratio, EQR, based on the intercalibration common metric (which gives a harmonised view of status between Member States).   Horizontal lines show the average position of “high” (blue) and “good” (green) status boundaries.   RO = Romanian data; XGIG = data from other Member States.   See Kelly et al. (2018) for more details.  

Romania is, of course, a long way downstream from where I was standing in Vienna.  Before the Danube gets there it has to cross Slovakia, Hungary and Serbia.  The river also forms the boundary between Romania and Bulgaria for about 300 kilometres, so it is important that there is joined-up thinking between those responsible for water quality on the two opposite banks.  That’s why the EU is so important for the environment on a pan-European scale.  It is easy for those of us crammed onto our insignificant archipelago in the north-west corner of the continent to overlook this, but the Danube is really a great success stories for European environmental collaboration and, indeed, a reason for staying with this ambitious project into the future.   Too late, I know, but it needs to be said.

Reference

Kelly, M.G., Chiriac, G., Soare-Minea, A., Hamchevici, C. & Birk, S. (2018).  Defining ecological status of phytobenthos in very large rivers: a case study of practical implementation of the Water Framework Directive in Romania.  Hydrobiologia 828: 353-367.

Vienna_sights_May19

Sightseeing in Vienna: Stefansdom, the historic cathedral in the city centre and the Ferris wheel at the Prater amusement park, which played a starring role in Graham Greene’s The Third Man.