Last words …

2018_wordcloud

Looking back at the pessimistic post that I wrote at the end of 2017 (see: “So that was 2018 …”), I am struck by how little has changed in the course of a year.   This time last year I was bemoaning the uncertainty around Brexit and the implications of this for the environment.   A year on, there is no more clarity, with a “told-you-so” attitude amongst the remainers clashing with a head-in-the-sand response from the hard Brexiteers.  The result is a political stalemate that seems impossible to resolve in the time remaining.  The only certainty on the morning of March 30this that the country will be more divided than at any point during any point in most people’s lifetimes.   That is a pathetic legacy for our present generation of political leaders, left or right.

I passed some personal milestones during the course of the year: my trip to Cyprus means that I have now visited all 28 Member States of the European Union.  Alongside this, I have also managed to complete a literary journey around Europe, reading either a novel by a writer from each country or by someone writing about that country.  With the exception of a couple of novels by George Simeon, all have been in English, but there is a host of good fiction available in translation.  Indrek Hargla’s medieval crime novel Apothecary Melchior and the Mystery of St Olaf’s Church, for example, enlivened my visit to Tallinn in May.   Crime fiction often has, I have learned, a strong sense of time and place that can help a visitor understand a city.

Another personal milestone was the end of an almost 10-year relationship with Newcastle University, as the course I taught there came to a natural end, and the start of a new relationship with the Geography Department at Nottingham University where I am an Honorary Professor for the next three years.   I’ve also seen my 100thscientific paper appear.

I will finish with two pictures from September’s visit to Lisbon: the first shows the ornate carvings on the arches surrounding the cloisters of the Jerónimos Monastery at Belém, on the outskirts of Lisbon.  Belém is the point from which the Portugese explorers set off on their voyages in the late medieval period, and Vasco de Gama is buried in the monastery church.    A short distance away, overlooking the Tagus estuary, there is the Monument to the Discoveries, which celebrates the exploits of Portugese explorers, from Henry the Navigator onwards.   Roger Crowley’s book Conquerors (Faber & Faber, 2015) describes the explorations of Vasco de Gama and his contemporaries in the late fifteenth century, and it is sobering to realise that, by the end of the medieval period, people knew more about life on the other side of the planet than they did about life in the ponds at the end of their gardens.  How much has changed over the subsequent centuries?   The microscopic world is still a closed book to many people, which is largely why I started to write this blog in the first place.

The motivations for the Portugese explorers were, however, very worldly.  They wanted to bypass established trading routes, they made unrealistic assessments of the situation in order to persuade their king to support their hair-brained schemes and they had great disdain for the cultures they encountered on their way to the fabled lands.   The Monument to the Discoveries encapsulates a sanitised version of a national ideal (it was built during the reign of the right-wing dictator Salazar) but it also speaks to our own time and place.

Belem_Sept18

Belém, near Lisbon.  Left: cloisters of the Jerónimos Monastery; right: Monument to the Discoveries.

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Mystery, wonder and joy

My Advent reading this year was Michael McCarthy’s The Moth Snowstorm: Nature and Joy (John Murray, 2015), a meditation on the reasons why humans love the natural world, and how engagement with nature can, in turn, be beneficial for our wellbeing.   His personal fascinations with butterflies, moths and birds provide most of the examples but, as I was reading this book at the same time as I was writing the previous post on “little round green things”.  As a result, I found myself reflecting on my own fascinations with the microscopic world.

A characteristic of ecologists, I have realised, is that there is almost always a tension between their scientific training and a primeval emotional response to nature.   This is not unique to ecology: geologists and astronomers certainly share it, but it is not a universal trait of scientists.  In those disciplines where it occurs, however, interactions with the natural world occasionally transcend strictly dispassionate objective observation and spill over into the language of joy and wonder.   “Joy” being, in McCarthy’s words, “concentrated happiness” whilst “wonder” is “a sort of astonished cherishing or veneration … often involving an element of mystery”.   We are straying away from the language of science and towards a religious and spiritual dimension that many ecologists would, I suspect, be reluctant to acknowledge.

“Mystery” is the word that ties together the disparate worlds of science and religion.   It implies “missing knowledge”, but much more than just an absence of necessary facts.   Every time I peer at samples from the River Ehen through my microscope I get the full gamut of joy-wonder-mystery-related emotions even though I have seen similar views many times before.   Part of this can be attributed to “missing knowledge” but not all.  I am acutely aware of my own shortcomings as I struggle to identify the organisms that I see, as well as the limitations of the taxonomic literature on which I depend.  I am, in addition, perpetually astonished that so much diversity can live on such a small scale and, even when I have done my best to name the algae present, I still struggle to explain why the communities differ over the space of a few metres and between our monthly visits.

Ehen_Mill_181212

Regular visits for five years have not diminished my wonder at the microscopic world of the River Ehen: this submerged boulder has obvious patches of brown diatoms and green algae, but also gaps where the algae are much less abundant. We can make coarse predictions about which species are likely to be found in particular locations, but the factors that determine their distribution on much finer scales are still shrouded in mystery.

The word “mystery” in short, carries an emotional heft that simply “not knowing” does not.  It rises above ignorance, partly because mystery, by definition, implies an awareness of this lack of knowledge.   The word “mystery”, in a modern, scientific context, also links to the concept of complexity, recognising that interactions between variables is often such that it is very difficult to predict outcomes.   That “astonished cherishing” that forms part of McCarthy’s definition of wonder needs to include an element of wariness.  We approach – or, at least, we should approach – ecosystems in the same cautious manner that Moses approached the burning bush.   Whether or not you believe in a higher power, recognition of both the complexity of nature and our limited understanding of this is humbling.   Humility, in turn, generates reverence, and we have completed the journey from the hard, dispassionate language of science to the fringes of spirituality and religion.

None of this precludes trying to improve our understanding of the natural world, nor of using this knowledge to inform decision-making.   What I have written above is no more than the Precautionary Principle, albeit expressed in quasi-mystical language.   Whilst the Precautionary Principle is an instrument of policy, my interpretation is more personal.   Each of us, individually, should be finding time to revel in the wonder of nature which, in turn, will fuel the sense of mystery and, in turn, temper any inclination to rush to intemperate conclusions.

Ehen_181212_diatoms

Some of the diatoms that are abundant in the River Ehen.  Top left: colonies of Gomphonema(see “Diatoms and dinosaurs” for more about this species); top right: colonies of Fragilaria tenera, which shares the habitat with at least two other similar representatives of the same genus; bottom left: Tabellaria flocculosa.  Genetic studies suggest that this, too, is probably a complex of morphologically-similar species.   Scale bar: 20 micrometres (= 1/50thof a millimetre).

We should, however, never assume that joy, wonder and a sense of mystery are ever-presents in the make-up of ecologists.   McCarthy makes the point that a love of nature is not a universal human attribute, although a propensity to love nature may be.   Just as that propensity can be nurtured through adolescence into an adult appreciation of the natural world, so a failure to exercise that appreciation as an adult can lead to it withering again.   I am acutely conscious that ecologists of middling seniority and above often spend more time staring at spreadsheets and in teleconferences than they do engaging directly with nature.  Within government agencies the reduction of time available for field ecology since the onset of austerity in the UK means that I often now deal with people who are unable to conjure visual images from the words and numbers that populate their datasets.  And, in my own work, I have to consciously make time to observe the natural world beyond the tight constraints of my professional life.

Above all, never forget that this love of nature exists in the first person, present tense or not at all. Natural history documentaries on the television and (dare I say) blogs such as mine are the herbs and spices that enliven your diet, but the naturalist’s basic sustenance needs a commitment that goes beyond staring at a spreadsheet or sitting on a couch.

 

Little round green things …

Apatococcus_on_Fence

Nature does not get much more prosaic than this: my garden fence covered with a fine, powdery green coating. For most of the year this is hidden behind the foliage of our apple and willow trees but as autumn gives way to winter, so the bare green slats became visible again.  Last week, staring out of the window whilst completing my previous post, it occurred to me that, in the six years that I have been writing this blog, I have never made the short journey across the grass to look at one of the most common algae in the country.

I scraped a single-sided razor blade across the surface of one of the slats to harvest a small quantity of the damp, powdery film, and put a few specks under my microscope in order to take a closer look.   What this revealed was lots of clumps of small near-spherical green cells.   That, along with an ability to live in terrestrial habitats are about all the natural historian has to go on when trying to name this organism.  My old copy of West and Fritsch suggests Pleurococcus naegelii, adding that “there is probably no other alga about which there has been so much confusion” whilst the latest guide to British algae would call it either Apatococcus lobatus or Desmococcus olivaceum– their descriptions are very similar.   Desmococcus olivaceum has been described as “the commonest green alga in the world”, which is a bold claim.  Certainly, green powdery coatings such as these are found in shaded locations in a great many places but is the singular “alga” really appropriate?  Cells such as these offer so few visual clues that the microscopist is apt to latch onto a phrase such as “one of the commonest terrestrial algae” alongside a description that roughly matches the material, and considers it to be job done.  These groups have also been referred to as “LRGT” (“little round green things”) – the phycological equivalent of the ornithologist’s “little brown jobs”.   Recent molecular studies suggest that there is a lot of diversity within these powdery films, and this is almost certainly going to be very difficult to resolve with traditional methods.  It looks as if we going to struggle with these “LRGT” for the foreseeable future.

The Class Trebouxiphyceae seems to have a particularly large number of LRGT.   Some (such as the one I am describing in this post) are free-living and capable surviving desiccation, but this group also includes many of the algae that unite with fungi to form lichens, whilst others prefer to live in truly aquatic situations.   But it is the fence-dwelling forms that are of interest to me today, and even if I cannot put the exact name onto my powdery film, I can perhaps offer some thoughts on why it thrives where it does.

Apatococcus_lobatum_181218

Cells of Apatococcus lobatum(?) from a garden fence in County Durham.  Scale bar: 10 micrometres (= 1/100thof a millimetre).   The photograph at the top of the post shows the fence in my back garden from which it was collected.

Some of the other terrestrial (or semi-terrestrial) green algae that I’ve described in this blog are endowed with brightly coloured pigments that protect them from the damaging ultra violet rays in sunlight (see “Fake tans in the Yorkshire Dales” and “An encounter with a green alga that is red”).  Apatococcusand Desmococcus, by contrast, do not come with preloaded sunscreens.  They thrive, by contrast, in relatively shaded locations where the gradual accumulation of cells on the fence surface means that the outer cells take the primary ultra violet hit and, in the process, protect those cells underneath.   There is also evidence of Apatococcus producing lots of stress compounds.  These belong to a class of compounds call “polyols” – complicated alcohols.  A lifestyle that involves single cells sitting on a damp fence indefinitely might seem like an evolutionary dead end.   However,  they have the last laugh as, unlike us, they are genetically adapted to produce their own booze when the going gets tough.

A further adaptation that has been observed is that the cells can switch between producing their own simple sugars via photosynthesis, and absorbing sugars and other organic compounds directly, a strategy known as “mixotrophy”.   Walls and fences are challenging habitats for any organism so having the ability to mop up any spare fuel (leaking down from one of those outermost cells that took one for the team, perhaps?) might give the organism a slight competitive advantage over time.

Back when I was doing my Fine Art degree, I was using algae to explore the boundaries between abstraction and representational art.  My thesis was that an image of an alga could be either representational or abstract depending on how much prior knowledge the viewer brought to the image.   I used the Apatococcus (or is it Desmococcus) from my garden fence as subject matter for this exploration, creating a sextych (honestly, that’s the word for a painting on six panels) that juxtaposed the minimal outline of fence panels with microscopic views of the alga.  The three fence panels offer the unprepossessing view that most people will walk past for their entire life without a thought, whilst the microscopic views give an insight into the hidden world even though the arrangement of shapes and colours will not match any of the schemata lodged in the memories and experiences of most of the viewers (see “Abstracting from reality …”).

Apatococcus

Apatococcus. 2008 50 x 130 cm.  Acrylic and photomicrograph on canvas.

References

Gustavs, L., Schumann, R., Karstens, U. & Lorenz, M. (2016).  Mixotrophy in the terrestrial green alga Apatococcus lobatus(Trebouxiphyceae, Chlorophyta).  Journal of Phycology52: 311-314.

Laundon, J.R. (1985). Desmococcus olivaceus– the name of the common subaerial green alga.   Taxon 34: 671-672.

Lemieux, C., Otis, C. & Turmel, M. (2014).  Chloroplast phylogenomic analysis resolves deep-level relationships within the green algal class Trebouxiphyceae.  BMC Evolutionary Biology14: 211.

 

The big pictures …

If you read this blog regularly you will, I hope, have some sense of just how varied are the algae that live in our freshwaters.   It occurred to me, however, that, in cataloguing this diversity, I don’t often step back and give you some idea of how these many forms relate to one another. I drop terms such as “diatom” and “green algae” into my posts but have not, perhaps, discussed the meaning of these terms in very much detail for some time.

One of the problems is that the meaning of these terms can vary, as knowledge unfolds.  For the early part of my career, for example, I could define “green algae” quite easily, and point to several authoritative textbooks to support my case.   Depending on who wrote the book (and when), green algae were either a separate division (“Chlorophyta”) or a class (“Chlorophyceae”).  There was some dispute about whether Chara and relatives belonged in this group or formed a separate group (“Charophyta”) but that was pretty much the end of the story and taxonomists then got down to arguing about how the many genera and species of green algae should be arranged within this broad heading.

Opinion has, however, shifted over the last couple of decades, with the green algae now split between two separate phyla within the kingdom Plantae.   One of these phyla is the Chlorophyta and the other is the Charophyta, which includes not just Chara and relatives but also some quite important Classes of green algae.    We have met representatives from many of the Classes from both of these phyla in this blog over the years, with the exception of the Prasinophytes, which is an important group of marine plankton with only a few freshwater representatives, and the Trebouxiphyceae.

Viridiplantae_organisation

The organisation of the “green algae” subkingdom (“Viridiplantae”) showing division into two Phyla, and the major Classes found in freshwaters within each Phylum.   The organisation follows Algaebase and the Tree of Life website (see also Lewis & McCourt, 2004). 

Back in the summer I described a number of green algae that I found in the River Wear.   In “Summertime blues …” I wrote about algae that belong to the Chlorophyceae whilst, later in the summer, I explained how these had been joined by a number of desmids, which belong to the Conjugatophyceae (see “Talking about the weather …”).  The plate in that post includes a cell of Pediastrum boryanumbeside some of the desmids; if I was to put together a plate of animals sharing a similar level of kinship, I might include a human and a slug – representatives of two separate phyla within the same kingdom, Animalia (see “Who do you think you are?”).  That is a remarkable amount of diversity to pack into a group of microscopic cells.

The next figure shows the organisation within the Conjugatophyceae, one of the Classes of Charophyta.  The biggest group, in terms of number of species, is the Desmidales, which have featured in quite a few posts (see “Desmid diversity …”), but this class also includes Mougeotia and Zygnema, which we met in the previous post.  Again, just to give you some idea of the scale of the differences, Mougeotia and Zygnema are as closely related as we are to chimpanzees (different genera, same family), whilst their kinship to a desmid is on a par with ours to a warthog (different families, same order).

If you think that you are rather more different to a warthog than one microscopic green alga is to another, there are two things you need to remember: the first is that humans are, relatively speaking, rather good at knowing what features set different types of mammal apart, and that the absence of two short tusks protruding from the sides of the mouth, coupled with a bipedal gate, are highly relevant factors when struggling to decide whether or not the organism in front of you is a man or a warthog.  When trying to understand microscopic organisms such as algae, there are fewer obvious characters, and some of the most useful (such as the presence of flagellae during the reproductive stages) may be present only for a short period of the life cycle.   Straightforward observation, quite simply, is not so useful when trying to determine relationships between microscopic organisms.

Conjugatophyceae_orders

Organisation within the Conjugatophyceae, showing division into two Orders and Families.  After Algaebase and the Tree of Life website.

The other point to bear in mind is that algae having had far longer to evolve than mammals.   The two green algae lineages may have separated before the end of the Precambrian era, whilst the primates, the Order to which humans belong, split from other mammals only 65 million years ago.   That means that the green algae have had eight times as long to evolve subtle differences as humans have had to ensure no confusion with warthogs.   Just because these differences are not manifest in obvious features such as tusks does not mean that they are not there.

This brief overview of the green algae has had a side-benefit for me, as it has highlighted a couple of groups I have not previously written about.  One of these groups (the Prasinophytes) is uncommon in freshwaters but the other (Trebouxiphyceae) is quite common and I can even see a green patch formed by a member of this Class from my window as I write this post.   At least I know now what I should write about next …

References

Lewis, M.A. & McCourt, M.M. (2004). Green algae and the origin of land plants.  American Journal of Botany91: 1535-1556.

Leliaert F, Smith DR, Moreau H, Herron MD, Verbruggen H, Delwiche CF & De Clerck O (2012) Phylogeny and molecular evolution of the green algae. Critical Reviews in Plant Sciences 31: 1-46.

Appendix

Links to posts describing representatives of the major groups of green algae.  Only the most recent posts are included but these should have links to older posts.

Group Link
Chlorophyta  
Chlorophyceae Keeping the cogs turning …

Summertime blues …

Ulvophyceae Includes many important filamentous and thalloid genera from freshwaters:

Chaetophorales: Life in the colonies …

Cladophorales: Cladophora and friends

Oedogoniales: More about Oedogonium

Trentepoliales: Fake tans in the Yorkshire Dales

Ulothrichales: Spring in Ennerdale

Ulvales: Loving the low flows

Trebouxiphyceae Watch this space …
Prasinophyta Watch this space …
Charophyta  
Charophyceaee Life in the deep zone …
Conjugatophyceae Desmidiales: Desmid diversity

Zygnemetales: Fifty shades of green

Klebsormidiaceae The River Ehen in November

 

A day out in Wasdale

Irt_LundBridge_Nov18

A few days after my trip to Weardale I found myself beside the River Irt, a few hundred metres below the point where it flows out of Wastwater, in the western part of the Lake District.   Whereas the River Wear drains a catchment underlain by Carboniferous rocks, including a high proportion of limestone (see “Co. Durham’s secret Karst landscape”), the Irt’s catchment is largely underlain by ancient volcanic rocks, resulting in much softer water.   I was curious to see how different the algae were here compared to those in the Wear.

The river bed at this point is dominated by boulders of granite, which host a patchwork of mosses, filamentous algae and discrete growths of diatoms (visible on the right-hand side of the figure below).  Between these there were areas of pebbles and gravels, suggesting good habitat for freshwater mussels.   The patches of filamentous algae (mostly no more than a couple of centimetres in length) were a mixture of Mougeotiaand Zygnema, similar to the forms that I find in the River Ehen, a 30 minute drive to the north.   These two species differ in the form of their chloroplasts (Mougeotiahas a flat plate whilst Zygnemahas two star-shaped chloroplasts, attached by thin cytoplasmic strands to resemble an animal skin stretched on a frame) but are closely-related, both belonging to the family Zygnemtaceae.

Irt_substratum_Nov18

An underwater photograph of the substratum of the River Irt in November 2018 showing patches of filamentous green algae, mosses and (on the right-hand side) diatoms growing on granite boulders.

Irt_greens_Nov18

Filamentous green algae from the River Irt, November 2018.   The upper photograph shows cells from a filament of Mougeotiawhilst the lower image shows two filaments of Zygnema. Scale bar: 20 micrometres (= 1/50thof a millimetre).

In between the tufts of filamentous algae were apparently bare patches of rock (they almost certainly had a very thin biofilm that would be hard to sample in isolation from the lusher algal growths that shared their habitat) and some conspicuous orange-brown growths of colonial diatoms.  These turned out to be almost pure growths ofGomphonema hebridense, or a close relative (I can’t give a definitive answer until I have examined cleaned material), growing on long mucilaginous, sometimes branched, stalks to create a veritable “bush” of diatoms.  There were a few other species of diatom growing within this bush, most notably some cells of Achnanthidium (cf.) caledonicumthat seemed to be growing on short stalks attached to the Gomphonemastalks, but also a few cells of Gomphonema capitatum(which also grows on long stalks) and some chains of Tabellaria flocculosa.

Gomphonema hebridenseis a diatom that I have written about several times before, as it is also common in the River Ehen, and also presents a number of interesting challenges to taxonomists (see “Diatoms and dinosaurs”). Whatever future studies reveal, however, the presence of colonies of this (or these) species that are visible with the naked eye is something I associate with only the cleanest rivers in the country during the cooler times of year.  It should not have been a great surprise to me to find it flowing out of one of the most pristine lakes in England (see “The Power of Rock …”).

Gomphonema_Irt_x1000_Nov18

A close up of cells within a colony of Gomphonemacf hebridense.  Several mucilaginous stalks are also visible as well as (top left) a cell of Achnanthidiumcf caledonicum.   Scale bar: 10 micrometres (= 100th of a millimetre).

The predominance of boulders over smaller, more easily moved stones, suggests a river that has more energy than the River Ehen, one of my regular Lake District haunts.   Both flow out of lakes whose catchments include some of the wildest and most mountainous terrain in the country.   Lakes tend to act as shock absorbers in catchments, slowing down the water that pours off the fells after heavy rain.   Streams in this part of the world that have no such impediments to flow tend to have rocky, mobile beds and relatively sparse algal communities.   By contrast, the Irt and Ehen just below their respective lakes have relatively lush growths of algae.   The substrates of the two rivers, however, are very different: the Ehen having very few boulders in comparison to the Irt, due to the presence of a weir at the outfall. This allows Ennerdale Water to be used as a water supply for the towns of north west Cumbria but, at the same time, turns the lake into an even more effective hydrological shock absorber.  Yet more of the energy that should be washing smaller stones down the river is no longer available except after the most exceptional storms.

That’s my working hypothesis, then: the Irt is a river that is subject to just enough high energy events to move the rocky substrates around yet no so many that rich algal communities cannot develop between these.  The Ehen, by contrast, has fewer events, leading to fewer opportunities for the algae to be scoured away, whilst unregulated streams such as Croasdale Beck (see “What a difference a storm makes …”) have such regular scouring spates that the algal communities are usually sparse.   I might be wrong, of course and I might be back in a years time with a better hypothesis.  Until then …