Both sides now …


I diverted from my usual haunts in the upper River Ehen in Cumbria recently in order to explore Ennerdale Water in greater detail.   I am used to see it from the western end as we do our fieldwork, but the length of the journey to and from the River Ehen means that we rarely have time to linger.  Finally, however, we found a July day when we could circumnavigate the lake.  “July day”,”Lake District” and “fieldwork” sounds like an intoxicating combination.  However, the photograph above shows it was not quite as idyllic as it might have been (or, even, as it was on the day before).  Hence the title of this post, borrowed from a beautiful Joni Mitchell song which includes the line “But clouds got in my way”.

In the far past, the lakes of the Lake District were thought to have “evolved” at different speeds following their formation at the end of the last Ice Age.  Ennerdale Water and Wastwater, surrounded by hard volcanic rocks which erode very slowly, were regarded as the two most “primitive” lakes, whilst Windermere and Esthwaite Water were thought to be the two most “evolved”.   That is now known not to be the case: the geology is very important in determining the type of lake, not just because erosion is the source of the inorganic salts that give the water a particular chemical character, but also because this influences how man uses the lake.   In the case of Ennerdale Water, only about five per cent of the catchment is cultivatable, and this, in turn, influences the amount of inorganic fertiliser that is added to the meagre supply of salts provided by the underlying rocks.   Ennerdale is, as a result, one of the least chemically-disturbed of all English lakes.

At the far south east end of the lake, close to where the River Liza enters the lake, I was intrigued to see some very dark spots on the rocks.  They looked like they might be cyanobacterial colonies, so I picked a few off with my forceps and put them into a bottle for later investigation.  When I was able to look at them, the following day, I saw clumps with brown filaments radiating out, and each gradually narrowing towards the tip.   Closer examination showed that the cells that made up each filament had a blue-green colour, but were each enclosed in a brown pigmented sheath.   The filaments showed a characteristic form of “false” branching, in which the daughter filament breaks off from the mother, but is contained within the same sheath.   At the base of many of the filaments, I could see a modified cell (slightly lighter and less granular than the others) called a “heterocyst”, which was responsible for nitrogen-fixation.   These are all characteristics of the genus Rivularia, which is a good indicator of very high status water.


A cobble (about 15 cm long) from the littoral zone of Ennerdale Water, SW end.  The dark cyanobacterial colonies are about 3-4 mm across.


Rivularia biasolettiana from the littoral zone at the south east end of Ennerdale Water, Cumbria, UK.  a. low power (x100) image showing radiating filaments gradually narrowing in width; b. filaments showing false branching (a heterocyst is present, but hard to see); c. false branching in a filament of Rivularia with heterocyst arrowed.   Scale bar (b. and c.): 10 micrometres (= 1/100th of a millimetre).

The presence of Rivularia here was interesting to me for several reasons.   First, it continues a series of observations that suggest that this genus is not confined to hard water habitats in Britain and Ireland, as once thought (see “more about Rivularia” and links) although earlier posts have also referred to its presence in soft water habitats in Norway.   I’m also fairly sure that the organism that I collected from this trip to Ennerdale is different to the one that I find in the River Ehen and, indeed, at other locations around the Ennerdale perimeter, but that is a subject for another day.

The second comment to make is that the presence of cyanobacteria (blue-green algae) is usually a sign of an unhealthy, enriched habitat, not the very high quality habitat that Ennerdale, in fact, represents.  Blue-green algae in the phytoplankton is, very often, a bad sign, suggesting enrichment by inorganic nutrients.  Several species combine the ability to fix nitrogen with positive buoyancy, which means that they have two distinct advantages over other algae as they compete to exploit limited light and nutrients.  Some of these blue-green algae are also toxic, which has implications for how the lake and its water is used.

Those blue-green algae that live attached to surfaces in streams and in the littoral zone of lakes play by a different set of rules, however.  As they cannot use positive buoyancy to compete for light, they are more likely to be overgrown by faster-growing algae in the scrabble to capture available light.   This means that investment in expensive nitrogen fixation machinery is only an advantage when other algae, too, are very short of nutrients.  And a shortage of nutrients is the natural state for most freshwater ecosystems.

I chose the title of this piece, originally, because I felt that I had looked at Ennerdale Water from both sides now.  However, the same lyric could just as well apply to blue-green algae.   The water manager sees them as a problem; in some situations, however, they can be a positive sign.   So we can, in fact, look at blue-green algae from both sides too … from give and take and still somehow … I really don’t know life (microscopic life especially) at all ….

How to win the Hilda Canter-Lund competition (2)

My previous post on this subject (see “How to win the Hilda Canter-Lund competition”) considered the dichotomy between the “decisive moment” – the spontaneous recognition of the potential of a view to become a great image – and the painstaking preparation – and post-production work – that is often necessary to produce a really stunning image of the microscopic world.   In this post, I am going to take a step backwards, then approach the topic of photographing algae from a different angle.

Let’s take as a starting point a desire to simply provide a good representation of an alga in order to convey some essential information that allows someone else to recognise or name that organism.   You might try to simplify the background to throw the subject into sharper definition, and you will aim to get as much of the organism in sharp focus.   You will also try to offer the viewer an indication of scale, particularly important when dealing with the microscopic world.  A good example of such an image which made the shortlist in 2010 is Chris Rieken’s image of the desmid Micrasterias radiata.   You would be very pleased to open a guide to desmids and find an image as clear as this to help you identify your own specimens.


Left: Chris Rieken: Micrasterias radiata Prox (2010 shortlisted image); right: Petr Znafor: Freshwater phytoplankton dominated by desmids (2016, co-winner).

Compare Chris’ image with Petr Znachor’s image which won a prize in 2016.   Both are of desmids, but they are very different.  Chris has focussed on representation of the organism and has produced a beautifully crisp image whilst Petr has used the fact that some of the desmids in his image are not in sharp focus to create an aesthetically-pleasing pattern.   It is still, recognisably, of desmids, and you may be able to name the genera, yet it is harder to say exactly what species are present.   The two images, in other words, illustrate a tension between representation and abstraction that runs through many of the winning and short-listed entries of the microscopic world (Lira Gaysina’s image of Trichormus variabilis, shown in my earlier post, also demonstrates this tension.


Günter Forsterra: Octopus’ Garden (2015 winner)

Günter Forsterra’s winning image from 2015 illustrates another direction that images of algae can take.  He photographed marine macroalgae – several orders of magnitude larger than the microalgae discussed in the previous paragraph –but, like Petr Znachor and Lira Gaysina, he was not aiming to create a technically-perfect image that would allow a viewer to name the organisms present.  Instead, he takes us into another world, one that is hidden to all but a small number of initiates.   The temptation is to refer to the underwater landscape portrayed by Günter as “surreal”, but this term has a precise meaning in cultural studies (relating to the interface between dreams and reality) should not really be applied haphazardly.  I prefer to the term “other worlds”, recognising that his image conveys an impression of a different, altogether stranger, world than most of us have ever experienced.


Conceptual diagram of the tensions inherent in algal photography.  Scientific illustrations, designed primarily to inform, sit at the top of the pyramid; moving away from straight representation towards either of the other corners creates images with greater aesthetic value but, perhaps, at the cost of information.

There are, in other words, at least two tensions that can work on an image of an alga to create an aesthetically-pleasing image; I’ve summarised these in the diagram above.   Chris Rieken’s image would lie close to the apex of the triangle, with “representation” predominant; Petr Znachor’s image would lie closer to the “abstraction” corner, whilst Günter Forsterra’s is in the opposite corner, “other worlds”.   All of the images that are submitted can fit onto this triangle somewhere; the question is how these tensions are balanced to raise a straightforward representation of an alga into an image that combines informative, technical and aesthetic properties and creates a work of art.

Neither “abstraction” nor “other worlds” are unambiguous concepts; both require an interaction with the viewer.   To someone familiar with freshwater algae, Petr Znachor’s image is clearly of desmids, and many will be able to identify the two genera that are present (Cosmarium and Staurastrum).   However, someone who knows little of algae will just see a collection of colours and shapes.  The boundary between representation and abstraction, in other words, is fluid; the viewer is never neutral and, for this reason, the legend becomes very important, providing a bridge between the image and the viewer.  In a similar way, Günter Forsterra’s image could appear, to the uninformed, to be something from a science fiction movie.  Again, the legend acts to locate the image firmly on Planet Earth and, hopefully, to raise awareness of the importance of algae to healthy marine ecosystems.


Eileen Bresnan: Chaetoceros chaos (2010 shortlist).  An example of a very abstract depiction of an alga.

Depiction of “other worlds” is harder for those of us who study the microscopic world, due to the problems associated with shallow depths of field (see “How to win the Hilda Canter-Lund competition”); microscopic images, as a result, tend towards “abstraction”.  However, it is not just the shallow depth of field that is an issue here: we also have to consider the disruption caused to a microscopic ecosystem caused by the sampling process, and then as it is teased apart, squashed onto a microscope slide and viewed at unnaturally high light intensities.   That is why I prefer to use paints to recreate the microscopic world in situ.  The results are, I know, partially the result of my imagination but, then again, everything that we view down a microscope is, to some extent, manipulated and artificial.

This post, and the previous one, have focussed less on how to take a great photograph than on what makes a great image.   I hope that it inspires you to go out and have a go.   We’ll come back to some of the technical issues in microphotography in a future post.

More about the Hilda Canter-Lund competition can be found here

Escape to Southwold


We took advantage of the quiet mornings at Latitude to drive off the site and explore the countryside around Southwold.  I had memories of a family holiday here in 1968 and little seems to have changed: it is traditional seaside town, seemingly frozen in time, with a pier, beach huts (as in the image above), a lighthouse and a row of cannons facing out into the North Sea.

As we followed footpaths along the dykes beside the creeks, I noticed a red mat of vegetation covering the surface in one of the stagnant areas close to the A1095.   Closer inspection revealed this to be the floating fern Azolla filiculoides, an introduced plant that is quite common in the south of England but which is an unusual sight to an adopted northerner such as myself (see also “No longer a dispassionate observer of nature…”).   Inevitably, I was soon down on hands and knees to pull out a small sample for closer inspection.


Azolla filiculoides in Buss Creek near Southwold, July 2016.  

When seen in close up, each individual plant is about a centimetre across, but is composed of tiny fronds, each no more than a couple of millimetres in size.   Long hair-like roots hang underneath the plant.   The red colour is due to pigments called anthocyanins, which belong to a class of compounds called flavonoids and which offer the plant some protection against very high light intensities (an alternative strategy to that seen in Cladophora in the previous post).   Interestingly, anthocyanin production also takes place in response to low temperatures, possibly because the generally low metabolism of the plant under such conditions leads to the same build-up of excess energy when there is abundant light, because the cell machinery is grinding along at too slow a pace to keep up with photosynthesis.


Left: collecting Azolla filiculoides from Buss Creek near Southwold, July 2016; right: fronds of Azolla filliculoides in the palm of my hand.

One of the intriguing features of Azolla is that it, along with the pea family and a few other groups of organism an ability to fix nitrogen.  This allows it to grow in habitats where nitrogen, a naturally scarce plant nutrient, is in short supply.  Like the pea family, Azolla does not, itself, capture and transform nitrogen into the compounds it needs to grow, but carries a complement of passengers who do this work for the plant.   The symbiotic organism in the case of Azolla is the cyanobacterium (blue-green alga) Anabaena and I was keen to have a closer look at my Azolla to see if I could tease these out.  However, as I mentioned in my previous post, festival conditions are far from ideal for preserving fragile plant specimens, and my material was not in a very healthy state by the time I got it under my microscope.

The blue-green filaments of Anabaena were, nonetheless, conspicuous, once I had squashed a few fronds gently under a coverslip.  Anabaena is a close relative of Nostoc (see “Nosing around for blue-green algae …”) and also forms long chains of bead-like cells that resemble rosaries.   Look at the photograph below and note how there is a larger cell spaced at intervals along each filament.   These are the “heterocysts”, the specialised cells that contain the enzymes responsible for nitrogen fixation.   The ease with which Azolla grows in damp habitats, particularly in warm climates, and the ability of “Team Anabaena-Azolla” to catch large quantities of nitrogen means that Azolla is grown as a “Green Manure” in some parts of the world, as it bypasses the need to buy expensive artificial fertiliser.



Anabaena filaments from a squashed frond of Azolla filiculoides from Buss Creek near Southwold, July 2016.   Scale bar: 10 micrometres (= 1/100th of a millimetre).

Sample safely collected, we followed the dyke across the marshes (all slightly below sea level here) until Buss Creek joined the River Blyth and we then turned towards the sea.   As we reached Southwold Harbour, we found a small café offering fresh crab sandwiches, which sounded too good to resist, even though it was barely 11:00.   And, from there, it was just a short walk back to Southwold.   A few kilometres away, the Latitude Festival was getting under way again, and our brief sojourn in Southwold had to be curtailed in favour of other attractions, culminating in a rather impressive headline set by The National.  For one weekend in the year, at least, Suffolk is not quite the boring county that most of us think.


Janes, R. (1998).  Growth and survival of Azolla filiculoides in Britain. 1. Vegetative reproduction.  New Phytologist 98: 367-375.


The National’s headline set from Latitude 2016


Good vibrations under the Suffolk sun …


After writing 371 blog posts, mostly about algae, you will forgive me if I tell you that the first thing I noticed about this picture was the algal flocs on the pond behind the sheep – the pink, fluorescent sheep – quietly nibbling the grass in the Suffolk countryside …   This is the Latitude Festival 2016 and I had to pass these flocs (and that flock) every time I walked from my tent to the arena or back.  By Sunday morning, the temptation to lean over the bridge and fish out a handful using a handy reed stem was too great.

Unfortunately, the specimen had to live in a small plastic bag stuffed into my shirt pocket whilst I stood around in a hot field at a music festival for several hours (Prince Charles talks to his plants; I take mine to listen to Laura Mvula and The Lumineers …).   By the time I got it under a microscope, I could confirm that the rough wiry filaments were a sparsely-branched variant of Cladophora glomerata, mixed in amongst some other algae including (probably) Spirogyra and Mougeotia but, having just written a post on how to take great pictures of algae, I do not feel that I should share these particular images with you all.


A view of the Cladophora glomerata flocs in the lake at Henham Park, location for the Latitude Festival (left) and a close-up of a handful of Cladophora filaments (and some Lemna fronds).

The glorious weather had one unfortunate consequence for me, as my feet and legs turned red after I had sat in the morning sun for too long before applying sunscreen.   That, in turn, led me to wonder how these particular algae survive floating on the surface of a pond in the full glare of the sun all day.   I have written in the past about how some algae produce extra pigments to protect them against high light (see “An encounter with a green alga that is red” and “Fake tans in the Yorkshire Dales”); however this Cladophora was also exposed to high light but has no on-board sunscreen. What is happening?

Think of sunlight as a stream, the cell as a mill using the stream’s energy, and the waterwheel as the photosynthetic apparatus.   Too much sunlight sets the wheel spinning so fast that there is far too much energy for the mill to use.  Something has to be done with all that excess energy, otherwise the mill’s machinery will be damaged.   Cladophora, and other green algae (which are the ancestors of all land plants) have compounds called xanthophylls which act like sponges inside the cell, soaking up the excess energy and then dissipating it as heat (the process is called “quenching”).  D1, one of the proteins associated with the photosynthetic machinery, can be damaged if strong light is not sufficiently quenched but cells also have a clever mechanism whereby the psbA gene that replaces this damaged D1 is switched on by light.   This ensures a steady supply of replacement D1 to keep the photosynthetic machinery running as smoothly as possible.

The algae, in other words, can sit in the cool water of Henham Pond secure in the knowledge that evolution has provided them with the tools they need to keep their photosynthetic machinery in top-notch condition throughout a hot July weekend.  The only question left is what did they think of the music?   The algae stuffed into my shirt pocket were not amused, but that might be because that particular microenvironment is far from ideal for algal growth.  I have found one paper that subjected rose plants to different types of music.  This particular study showed Indian classical music and Vedic chanting to have positive effects on growth whilst rock music had negative effects, possibly due to its vibrations.   It is, I have to say, not the most rigorous study I have ever seen (I can’t even find an impact factor for this particular journal) but it gives food for thought.  Fortunately, the rock music used in the study (death metal) did not feature on the Latitude bill.  35,000 people would argue that this rather narrow study needs to be broadened out to encompass the huge diversity of modern music.   At Latitude, we encountered only good vibrations …


Latitude 2016.   The Lumineers (left) and Laura Mvula (right) entertaining the crowds on Sunday afternoon.


Chivukula, V. & Ramaswamy, S. (2014). Effects of different kinds of music on Rosa chinensis plants.  International Journal of Environmental Science and Development 5: 431-434.

Fujita, Y., Ohki, K. & Murakami, A. (2001).  Acclimation of photosynthesis light energy conversion to the light environments.   Pp. 135-171.  In: Algal Adaptation to Environmental Stresses (edited by L.C. Rai & J.P. Gaur).  Springer-Verlag, Berlin.

Häder, D.-P. (2001).  Adaptation of UV Stress in algae.  Pp. 173-202.  In: Algal Adaptation to Environmental Stresses (edited by L.C. Rai & J.P. Gaur).  Springer-Verlag, Berlin.

Vershinin, A.O. & Kamnev, A.N. (1996).  Xanthophyll cycle in marine macroalgae.  Botanica Marina 39: 421-426.

How to win the Hilda Canter-Lund competition

If you asked me the secret for winning the Hilda Canter-Lund competition, I would answer: “be a male marine biologist, living or working in the southern hemisphere and with a professional interest in seaweeds”.   I would then offer the data on which I based this conclusion to anyone teaching a basic statistics course who wants a good example of the danger of over-interpretation of a small dataset.  There have been exceptions to every one of the criteria I list (Lira Gaysina, 2011 winner, ticks none of these boxes, for example) but it is still a useful starting point for wondering what it takes to create a great image of algae.


Lira Gaysina: Blue-green necklace – Trichormus variabilis (2011 winner).

Gender (five of seven winners are male) is almost certainly chance association rather than a causal factor as is, probably, the southern hemisphere link (again, five of the seven) but the tendency towards marine macroalgae may not be.   I do the initial sift of entries with two colleagues in order to produce the shortlist and it is clear from this that there are fewer really good entries that feature microalgae.  This, in turn, may reflect a bias within the phycological community towards the study of seaweed (I haven’t done any analyses to support or disprove this) or it may simply indicate that photographing microalgae is intrinsically more challenging.

There is a category of prize-winning images that fulfil Henri Cartier-Bresson’s maxim of the “decisive moment”.  Tiffany Stephen’s image this year falls into this (see “Hilda Canter-Lund prize winner 2016”) as does Mariano Sironi’s from 2009.   In both cases, the photographer grabbed an opportunity as it was presented to them.   The skill lay in framing the image and there was a minimal need for subsequent manipulation beyond, perhaps, cropping to enhance the composition.  Both could, potentially, have been taken on a camera phone as the end-product was dependent upon the “eye” of the photographer as much as on his or her equipment.


Left: Mariano Sironi: Southern Right Whale and calf swimming through a green tide (2009 winner); Right: Tiffany Stephens: Swell Life (2016 winner).

At the other end of the scale we find images such as those of Chris Carter (2013) and John Huisman (2014), both of which are the result of very careful preparation and planning.  The subject matter, in both cases, is at the border between the micro- and “macro” worlds, and both photographers have had to overcome the very shallow depth of field that is available to a microscopist.   This can be achieved using image stacking software but there is an inevitable loss of spontaneity.   Such images require care, patience and deep understanding of the tools available.   Many of us take usable images of the microscopic world; I suspect that few of us really devote the time that is necessary to produce a truly stunning image.


Left: Chris Carter: Chara virgata (2013 winner); Right: John Huisman: Herposiphonia (2014 winner).

The shallow depth of field introduces a second problem that besets microscopists: presenting their organisms in a context to which the viewer can relate.   An image of an organism against a plain background may be fine for an identification guide, as the viewer’s attention can be focussed entirely on particular characteristics of the organism that are necessary in order to name it.  But it does not tell us a story about where it lives, or how it interacts with the organism with which it shares a habitat.  Look at the great works by the 19th century Impressionists: their pictures are always rich in extraneous detail, yet this detail is crucially dependent upon the depth of field that was available to this generation of painters, due to an understanding of perspective acquired during their formal training.  As Impressionism gave way to post-Impressionism depth of field was sacrificed in pursuit of a more schematic articulation of form before, in the early 20th century, form itself was dumped in favour of abstraction.

Abstraction, however, presents a conundrum within the context of the Hilda Canter-Lund competition, as the brief is for an image on a phycological theme that combines informative, technical and aesthetic qualities.  Travel too far down the road to abstraction, and the image ceases to be a representation of a living organism (as Hilda Canter-Lund’s own images always were) and, instead, becomes a collection of shapes and colours.   A useful question to ask of a picture before submitting it to the competition is whether you can step back from the image and tell a story about why the alga that is depicted grows where it does.  It may be a great image.  It may channel the spirit of Paul Klee, Jackson Pollock or Mark Rothko.   But if you can’t put it into context in the real world, then it is probably not appropriate for this particular competition.

More on this topic in a future post.

News from Qingdao …


I wrote about my travels through China earlier in the year, even managing to work algae into one of my posts (see “Older … but not necessarily wiser?”).  My son, Ed, however, has managed to beat me at my own game, sending some pictures he took during his travels at the end of his year teaching in Chongqing.

He had flown to Qingdao, in north-east China en route back to Beijing and, from there to the UK.  Qingdao is on the Yellow Sea and was, in the past, a German concession, similar in status to Hong Kong or Shanghai.   Now, it is a major port and manufacturing centre, with the German heritage still evident in the huge Tsingtao brewery.   Like many other parts of China, however, the rapid economic growth has been accompanied by environmental problems. In the case of Qingdao, one of the most conspicuous manifestations of this is the enormous masses of green algae which appear annually on the coasts, and which have to be removed manually from the beaches in order to protect the tourist industry.

The alga that is responsible for these enormous growths is Ulva (formerly Enteromorpha) prolifera.  We have met this genus of algae before in both freshwater  (see “The River Wear in summer”) and marine (see “Venice’s green fringe”) environments.   Members of the genus often thrive in the shallow littoral zones of coasts where there is enrichment with nutrients such as nitrogen and phosphorus that plants need in order to thrive.  The rapid expansion of China’s industrial cities, coupled with limited environmental regulation has, in this particular situation, created a classic imbalance: one species thrives, whilst others are smothered or have no oxygen due to the prolific growth of the alga.


Collecting Ulva prolifera on a beach in Qingdao, Shandong Province, China, July 2016. Lower picture: a heap of Ulva prolifera.  The upper picture shows Qingdao’s shoreline.

We see similar imbalances in the coastline around Britain; however, the scale is inevitably much greater in China.   Writing about China demands superlatives, but western liberals need to reserve at least one of these superlatives for their own righteous indignation that accompanies almost any article about China’s environment (see “Reflections from the banks of the Yangtze”).   The growth of the Chinese economy is, in large part, fuelled by China’s own citizen’s desire for the same consumer goods that we in the West take for granted.


Hilda Canter-Lund competition 2016 second prize winner


A short while ago I wrote about Tiffany Stephens winning entry for the 2016 Hilda Canter-Lund prize.   Following that, the Council of the British Phycological Society agreed that a second prize, of equal value, would also be awarded, starting this year, which means that I am very pleased to announce that Petr Znachor’s image of summer phytoplankton from the Řìmov Rservoir in the Czech Republic will also be honoured by the society.

The rationale for the decision is that Hilda Canter-Lund was primarily a photographer of the microscopic world, yet five of the seven winners of the competition to date have either been of images of macroalgae or (in the case of the 2009 winner) a seascape in which an algal bloom is prominent.  I suspect that there are a number of reasons for this, but the greater technical challenges facing anyone who wishes to photograph the microscopic world plays a key role.  The first prize is awarded based on a vote by members of the BPS Council; the second prize, by contrast, will be awarded at the judge’s discretion, but for an image in a contrasting style.   This year, as Tiffany Stephens won with an image of the macroalga Durvillaea antarctica, the award goes to Petr Znachor but there is no reason why, in future years, a microalgal image may get the most votes, in which case a macroalgal image will get the other prize.

Petr’s image shows summer phytoplankton in the eutrophic Řìmov Rservoir dominated by the desmids Cosmarium and Staurastrum. It was taken during examination of a sample that was collected as part of a long-term monitoring program and concentrated with 20 µm plankton net.  He used an Olympus BX51 microscope with Nomarski contrast lighting and an Olympus DP70 camera.


Petr Znachor received his Ph.D. from the University of South Bohemia (Czech Republic) in 2003. He is currently a research associate at the Institute of Hydrobiology where his research focuses on phytoplankton ecology and, in particular, the ecology of reservoirs and analyses of long-term time series of data. Ever since he first looked through a microscope he was astonished by the myriad beautiful shapes and colours of phytoplankton existing in a single drop of water. He hopes that his pictures raise awareness of the importance of these tiny organisms.

As do we.

Pleasures in my own backyard


One of the delights of my part of County Durham is the range of natural history that is available without the need to travel great distances.  That, indeed, has been the theme of this blog right from the start (see “Cassop”) and today’s post continues the theme of nature on my doorstep, with a visit to a local nature reserve within walking distance of my house.  Like Cassop Pond, it is at the foot of the Magnesian Limestone escarpment and, at this time of year, the grassland is rich with Northern marsh and Common spotted orchids.   It is, of course, the ponds that draw my attention: they are rich in aquatic plants including, once I start to look closely, beds of the alga Chara, which I’ve written about before (most recently in “Everything is connected …”).  And then, once my eyes are adjusted to looking at natural history at this more intimate scale, I can see that the stones on the bottom of the pond are covered with tiny snails (probably Hydrobiidae) with shells coiled in the shape of an ice-cream cornet.  Freshwater snails crawl across submerged surfaces rasping off attached algae with their tough radula so I started to wonder what snails in this particular pond might be feeding upon.


Submerged stone from the pond at Crowtrees Nature Reserve, County Durham, covered in Hydrobiidae snails (left: the stone is about 10 cm across) and (right) a stone removed from the bottom of the pond showing the marl-covered part that was exposed and the marl-free part that was buried in the sediment. 

Viewed from just above the water, the surface of the stone looked as if it could be an algal film but, when I picked it up, the stone did not have the yielding texture that I associate with such films, but was a hard, mineral-rich marl.  More intriguingly, it was only present on the exposed surfaces, possibly, I suspect, due to the subtle interactions between chemistry and biology that I wrote about in “Everything is connected …”.

The calcite crystals make it hard to get a good view of the material under the microscope, but I managed to see a number of diatoms, mostly Gomphonema pumilum, or a relative, but also a good number of tiny, slightly asymmetric cells of a species of Encyonopsis, a genus that was, until recently, included in Cymbella, and which is usually a good indication that the water is about as untainted by human influences as it is possible to get.   It is, however, hard to get a really clear view of these under the microscope as they were scooting around.   With valves that are barely more than a hundredth of a millimetre long, I really needed to use an oil immersion objective to see them clearly, but the calcite crystals on the slide made it almost impossible to get a clear view of the live cells.  Not surprisingly, most of what we know comes from studies of carefully-cleaned preparations of the empty frustules.   Encyonopsis shares with Tyrannosaurus Rex the distinction of being an organism better known dead than alive.   It is rather ironic, given that healthy populations are living so close to my house, but that’s very often the case with diatoms.

There was one other abundant alga living amidst the rock (and, indeed, probably the major food source of the snails), but I am having some problems giving it a name, so a full account of that one will have to wait until another day.


Diatoms at Crowtrees Nature Reserve, July 2016: a.-d.: Gomphonema (possibly G. pumilum) in girdle and valve views; e.-g.: Encyonopsis sp.   Scale bar: 10 micrometres (= 1/100th of a millimetre).

You must be taking the piss?


You can find algae growing in the most unlikely places.   Look at the photograph above.   To the left you can just see The Swan and Three Cygnets, a popular pub beside Elvet Bridge in Durham.  The arches of Elvet Bridge extend onto the bank of the rivers, and one sits just beside the pub (hidden, in this photograph, by a large tree).  Under this arch, growing on the wall in a patch from approximately 30 centimetres above the ground, there is a lush patch of green algae.

Think about it: pub; arch nearby that is sheltered from the elements and from the gaze of passers-by; patch of algae from slightly below waist height downwards.  The technical term amongst ecologists for algae that like such habitats is “nitrophilous”: an alga that thrives in environments where the nitrogen concentrations is elevated.   Do I need to spell it out?  Pub, beer, sheltered archway, waist height …

I do not usually lurk around such unsavoury environments, but I was looking for a particular genus of green algae called Prasiola, which is known to favour habitats such as these.  Indeed, I have in front of me a paper from a learned journal that states “… consistent dampness and nitrogenous availability from animal wastes is likely to be the primary determining factor” for those trying to understand the distribution of this genus.


Left: the arch of Elvet Bridge with the Swan and Three Cygnets pub to the left; right: a patch of Rhizoclonium cf riparium on the north side of the arch.  Top image shows the Elvet Bridge with Durham Cathedral and Castle in the background.

To the naked eye, these patches of green algal growths on the damp, shaded arches, confirmed my pre-conceptions, so I was a little surprised when I put a small piece pulled from one of these under my microscope and saw unbranched filaments of cells, instead of the flat sheets that are characteristic of Prasiola.  The combination of unbranched filaments with a single net-like chloroplast indicates that this belongs to the genus Rhizoclonium, and Chris Carter, when he examined the material, suggests it is R. riparium, a common species of brackish and marine environments, including habitats such as salt-marshes where it will be periodically exposed to the atmosphere.  These patches of Rhizoclonium are like mini-vertical saltmarshes, subject to occasional immersion in squirts of high conductivity liquid, which will then be retained within the tangle of filaments.  Gradual evaporation from these patches (limited, due to the shaded microhabitat within the arch) will make the residual liquid yet more concentrated, and offering a selective advantage to an organism adapted to coping with salinity fluctuations in estuarine environments.


Rhizoclonium cf riparium from a damp arch of Elvet Bridge, Durham, April 2016 (photograph: Chris Carter)

Fabio Rindi and Mike Guiry made a particular study of algae associated with subaerial environments a few years ago but, curiously, their papers include no records of Rhizoclonium.   By contrast, I have so little experience of these habitats that I cannot say whether this was just a lucky (or unlucky – I was looking for Prasiola, remember) coincidence.  However, it does serve as an intriguing reminder that algae grow in some very unlikely places.  The problem is not that algae can’t grow on urine-soaked walls; it is that not many of us are interested in examining the natural history of such unsavoury habitats.


Rindi, F. & Guiry, M.D. (2003).  Composition and distribution of subaerial algal assemblages in Galway City, western Ireland.   Cryptogamie, Algologie 24: 245-267.

Rindi, F. & Guiry, M.D. (2004).  Composition and spatial variability of terrestrial algal assemblages occurring at the bases of urban walls in Europe.   Phycologia 43: 225-235.

Rindi, F., Guiry, M.D., Barbiero, R.P. & Cinelli, F. (1999).  The marine and terrestrial Prasiolales (Chlorophyta) of Galway City, Ireland: a morphological and ecological study.   Journal of Phycology 35: 469-482.