A load of balls …


This post is still mostly about the ecology of Lough Down, though it draws heavily upon photographs taken at Lough Cullin, in County Mayo, Ireland.   Lough Down shares some characteristics with Lough Cullin, but more with Lake Wobegon.   I suspect that the summers in Lough Down are not quite as long or as hot as those experienced around Lake Wobegon but, also, that a walker passing around the edge of Lake Wobegon would not see the round balls of algae that are a common sight along the shoreline of Lough Down.   Maybe I’m wrong: if anyone in Minnesota knows differently, please do let me know.

From a distance, these look like an unsightly mass of algae cast up on the foreshore; it is only when you get close that you see that this mass is, in fact, composed of a large number of discrete spherical growths.   You can see, in the photograph below, where Bryan Kennedy, my erstwhile Lough Down correspondent, has built a few of these into an Andy Goldsworthy-esque sculpture.   These are “Cladophora balls”, a phenomenon encountered in lakes around the northern hemisphere.  In Japan, they’ve even made their way onto postage stamps.


Aegagropila linnaei washed up on the shore of Lough Cullin, Co. Mayo, Ireland.  The photograph at the top of the post also shows Lough Cullin (photographs: Bryan Kennedy).

Until relatively recently, as their name suggests, the alga from which these balls are formed, belonged to the genus Cladophora, a frequent subject on this blog (see “The pros and cons of cell walls” for a recent example).   Like Cladophora, these are branched filaments composed of relatively large, multinucleate cells with a reticulate chloroplast.  This was, however, recognised as a different species to Cladophora glomerata, the common species of enriched lowland rivers: Cladophora aegagropila.  However, recent molecular studies have shown that it is not so closely related to Cladophora glomerata as its outward appearance suggests, leading to the resurrection of a very old name, Aegagropila linnaei.

In rivers, Aegagropila linnaei forms carpet-like growths of short filaments, not growing into the long wefts that we associate with Cladophora glomerata.  However, C. glomerata can sometimes be profusely branched as well, so telling these two species apart both in the field and under the microscope can be tricky.   One of the most useful characteristics is that the branches of Aegagropila are sub-terminal, meaning that they arise just below the end of the parent cell, rather than at the end, as is the case in Cladophora (see diagram below).   It is strange that two such similar species in appearance are, in fact, not particularly closely-related.  This is, however, an important distinction asA. linnaei prefers, as far as we can tell, less enriched conditions than C. glomerata.


Left: a section through a ‘Cladophora’ ball from Lough Cullin and, right, profusely-branched filaments of Aegagropila linnaei.  Photographs: Bryan Kennedy.

Why does it form these distinctive spherical growths in lakes?   I have not managed to find a paper that gives an authoritative explanation so here are a few possibilities, none mutually exclusive.  First, filamentous algae that display apical growth and copious branching tend to form hemispherical growths if attached and spherical ones if not.  We’ve seen that for Cyanobacteria such as Rivularia (see “More about Rivularia”) and Gloeotrichia (see “Rewriting history at Talkin Tarn”).  Second, the constant ebb and flow in the lake littoral zone will create a physical stress on attached carpets of Aegagropila leading, eventually, to parts becoming detached.  Third, the profuse branching that is characteristic of Aegagropila will mean that adjacent filaments will become entangled around another, creating a Velcro-type effect.   Finally, the apices of the filaments will continue to grow towards the light, meaning that the free-floating balls gradually expand in size.

Aegagropila’s dislike of nutrient-rich conditions mean that the number of places where it is found has been decreasing over recent decades.   It was, for example, recorded from several locations in the Netherlands in the past but not since 1967.  There are records from in the UK, but mostly from the more remote regions.   There are also a number of records from loughs in Ireland, as is the case here  The river form is, in my opinion, hard to differentiate unequivocally from Cladophora glomerata without very careful examination and this raises the spectre of “identification by association”, particularly when it is recorded by macrophyte surveyors who often do not have time to check material under the microscope.   Christian Boedeker, who has done much of the recent work on Aegagropila, thinks that a limited dispersal capability will mean that it will be slow to re-colonise habitats once it has been lost.

So that’s another day over here at Lough Down, a quiet lake that no-one has visited but everyone has got to know very well.   It’s one of those places, I like to think, where naturalists notice all of nature, not just the pretty, cuddly and exciting things.  Everyone leaves a little wiser, even if only because they have noticed that something everyone else overlooks is, actually, a thing of great intrinsic beauty.  As Garrison Keillor himself once said: “Thank you, God, for this good life and forgive us if we do not love it enough”.


Diagrams of branching patterns in Aegagropila linnaei (a.) and Cladophora glomerata (b.).   Note how the branches of A. linnaei arise just below the end of the cell (“sub-terminal”, indicated by arrows) whereas the branches of C. glomerata arise at the ends.


Boedeker, C., & Immers, A. (2009). No more lake balls (Aegagropila linnaei Kützing, Cladophorophyceae, Chlorophyta) in The Netherlands? Aquatic Ecology. https://doi.org/10.1007/s10452-009-9231-1

Boedeker, C., Eggert, A., Immers, A., & Wakana, I. (2010). Biogeography of Aegagropila linnaei (Cladophorophyceae, Chlorophyta): A widespread freshwater alga with low effective dispersal potential shows a glacial imprint in its distribution. Journal of Biogeography. https://doi.org/10.1111/j.1365-2699.2010.02309.x

Boedeker, C., Kelly, C. J., Star, W., & Leliaert, F. (2012). Molecular phylogeny and taxonomy of the Aegagropila clade (Cladophorales, Ulvophyceae), including the description of Aegagropilopsis gen. nov. and Pseudocladophora gen. nov. Journal of Phycology. https://doi.org/10.1111/j.1529-8817.2012.01145.x


Some other highlights from this week:

Wrote this whilst listening to: This post has been a long time in gestation, so ’ve listened to a lot.  These included Bob Dylan’s Shot of Love, Infidels and Real Live, as well as Courtney Barnett’s A Sea of Split Peas and Arvo Pärt’s Tabula Rasa.

Cultural highlights:  The National Theatre At Home’s Streetcar Named Desire, starring Gillian Anderson.

Currently reading:   JK Rowling’s Harry Potter and the Philosopher’s Stone.  Comfort reading.

Culinary highlight:   I have to admit that fish, chips and mushy peas from Bells in Gilesgate was hard to beat.

Twisted tales …


As opportunities for field work are still limited, I have returned to the banks of Lough Down for this post.   Lough Down, as some of you will have worked out for yourselves, is not somewhere that can be defined in terms of exact geographic co-ordinates, rather it is a state of mind.  However, that means that, in ecological terms, it is as diverse as I want it to be and, as such, it offers plenty of opportunities for writing about algae that I would not otherwise come across.   Thankfully, Chris Carter is another habitué of Lough Down and its environs, so I can use his pictures to illustrate these posts.

I used a Pasteur pipette to suck up a likely-looking patch of algae growing over some fine sediments in the littoral zone of Lough Down and brought this back to examine under my microscope.  When magnified, I was presented with the view of blue-green coloured helices twisting and turning across my field of view which means that this is almost instantly identifiable as the Cyanobacterium genus Spirulina.   It is, in effect, a helical cousin of genera such as Phormidium and Oscillatoria which we have encountered many times in this blog.   If you look closely, you’ll see that there are no heterocysts – the specialised cells responsible for nitrogen-fixation – whilst this particular population also has no gas vacuoles.  These are structures inside the cell which make the cells buoyant.  Many of the Spirulinaspecies found in warmer parts of the world have these, enabling them to live suspended in the water, whereas the temperate species tend to live at the bottom of lakes and ponds.  Whilst a few species definitely prefer freshwaters, most are associated with brackish and marine habitats, including saline lakes in Africa such as Lake Chad.

Spirulina is not a particularly common alga in UK and Irish freshwaters, but there is one habitat where it can be conspicuous: the shelves of health food stores.   All sorts of claims have been made for its health-giving properties – some supported by evidence, others not – earning it the epithet “superfood”.   There is, for example, evidence that women from communities around Lake Chad who regularly ate Spirulina (“Dihé”) had higher levels of Vitamin A than those who did not.   However, vitamin A deficiency is common in the region and the effects would not be pronounced in regions where there was a greater range of sources of vitamin A in the everyday diet.   On the other hand, Spirulina comes from the same sub-class as a number of Cyanobacteria known to produce neurotoxins, and there is some evidence (admittedly much less than for other genera) for it also producing toxins.   The aggressive marketing of Spirulina is enough to make me wary: there is no such thing as a “superfood”, except as one small part of a balanced diet.   Buy it and use it, by all means, but do not expect miracles.

I should mention, in closing that “Spirulina”, as commonly understood, is actually two genera: Spirulina and Arthrospira.  Much of the material sold as health food actually belonging to the genus Arthospira, which is broader than Spirulina and has more distinct cross-walls.   Looking at the Freshwater Algal Flora of the British Isles, I see a record for Arthrospira jenneri from a pond just a short cycle ride from my house from 1938.  Maybe I should make a trip one day soon to see if it is still there …


McCarron, P., Logan, A. C., Giddings, S. D., & Quilliam, M. A. (2014). Analysis of β-N-methylamino-L-alanine (BMAA) in Spirulina-containing supplements by liquid chromatography-tandem mass spectrometry. Aquatic Biosystems. https://doi.org/10.1186/2046-9063-10-5

Roy-Lachapelle, A., Solliec, M., Bouchard, M. F., & Sauvé, S. (2017). Detection of cyanotoxins in algae dietary supplements. Toxins. https://doi.org/10.3390/toxins9030076

Soudy, I. D., Minet-Quinard, R., Mahamat, A. D., Ngoua, H., Izzedine, A. A., Tidjani, A., … Sapin, V. (2018). Vitamin A status in healthy women eating traditionally prepared Spirulina (Dihé) in the Chad Lake area. PLoS ONE. https://doi.org/10.1371/journal.pone.0191887

Wrote this whilst listening to: Bob Dylan’s Live at Budokan, Slow Train Coming and Saved.  Also, Big Thief’s new single Love in Mine.  Still not sure how I missed their set at Green Man 2019.

Cultural highlights:  Enjoyed the film Peanut Butter Falcon, an indie hit last year which we missed first time around.   Also discovered a podcast on Spotify called Winds of Change by American journalist Patrick Radden Keefe.  It might be about American soft power and psy-ops at the end of the Cold War or it might just be a loopy conspiracy theory.  Not sure I know myself yet.

Currently reading:   Just about to start Sarah Walter’s The Paying Guest.

Culinary highlight:   Either a Yotam Ottolenghi recipe for tamarind and tomato braised chickpeas from the Guardian [https://www.theguardian.com/food/2020/may/09/tamarind-tomato-braised-chickpeas-savoury-porridge-browned-butter-lime-rice-pudding-yotam-ottolenghi-thrifty-recipes] or an improvised East-meets-West better-than-it-sounds risotto topped with steamed sea bass with ginger and spring onions.

How not to win the Hilda Canter-Lund competition


The 2020 Hilda Canter-Lund competition for the best photograph of an alga is underway again, with a closing date of Friday 5 June.  Over the years I’ve written a few posts to encourage entries, by focussing on what makes a good entry for the competition (listed at the end of this post).  This time, however, I’m coming at the problem from a different angle because, each year, as we make our first review of entries in order to prepare a shortlist, the judges always reluctantly leave one or two images out due to fairly basic flaws that could have been corrected prior to submission.   At least two of our winners have used smartphones for their photos and even these now have basic editing capabilities, so there really is no excuse for a little cropping or tonal adjustment prior to submission, if that is what it takes.

A photograph is a record of a unique event.   It is objective, up to a point, but it reflects a decision, made by the photographer, about when to release the shutter.   The microscopist scans a slide, and picks out particularly well-presented organisms or cells, not overlain by other cells or detritus in the sample, and also for pleasing juxtapositions of cells or filaments.   The same applies to those who photograph larger algae.  Tiff Stephens, the 2016 winner, could have waited a few moments longer, taken a step along the deck to her left or right, or held the camera at a slightly different angle.   Each would have given her a slightly different image of essentially the same phenomenon.  Whether photographing landscapes or using a microscope, there is nothing sacrosanct about the image beyond it being a record of the photographer’s decision to press a button.  Indeed, I suspect that most of our shortlisted entries are not unique records of the phenomena they record, but one of a number of images, and that a second stage of decision-making is needed to select the image that will be used.


Tiffany Stephen’s Swell Life: winner of the 2016 Hilda Canter-Lund prize.   The images at the top of the post show the 2009 and 2010 winners of the Hilda Canter-Lund competition, by Mariano Sirioni and Ernesto Macayo respectively. 

Having challenged the idea that the image, itself, is sacrosanct, there is no particular reason why you should not apply a third stage of decision-making and edit the image to enhance the story that you want to tell.   The field of view that is recorded when you press the shutter release is somewhat arbitrary.  You may be able to modify this, in a generic sense, in your camera’s settings but we usually adjust these only rarely and it is easier to adjust the pictorial space post hoc, using crop and rotate commands in a photo editing package.  The microscopist is further limited because most microscope stages do not rotate so the orientation of an organism can only be adjusted after the image itself has been collected.  Similarly, those of us who are photographing larger algae have only the small screens on our cameras with which to check images in the field, possibly in the face of inclement weather.  There is no disgrace in some judicious imaging editing once we can examine the image on a large screen, and the rules allow for this, along with focus stacking and stitching, essential tools in the microscopist’s armoury.

What about adjustment of colour and tone?   Bear in mind that colour, in the macro world with which we are most familar is reflected and objects can only reflect those wavelengths that reach them.  That means that colour and tone, in underwater photography especially, is not really a fundamental property of the organism you are photographing.   Move the same alga from a deep location to a shallow one, and it will look different for no other reason than the amount and quality of light transmitted through the water will change.   The microscopist is less likely to deal with reflected light, as the camera will be recording light that has passed through a specimen but, here too, the light is far from natural.  It will depend on the type of bulb, the intensity of light that you are using and the set-up of the microscope itself.  Once again, the colour and tones recorded are not fundamental properties of the specimen.   Under such circumstances, there seems to be no particular reason not to use the “levels” and “curves” options in editing packages to produce an image that is visually pleasing.  The judges are looking for basic authenticity and honesty in the image, so as not to deceive or misrepresent the natural world to the viewer, but there is a wide tolerance around this criterion because, frankly, natural light is, itself, so changeable.

The pair of photographs below illustrate this point well.  I was walking through local woodlands as I was thinking about this post.  May in the UK is the time when woodland floors turn a spectacular violet-blue due to the flowers of the bluebell (Hyacinthoides non-scripta).   I took the upper photograph on my iPhone then walked a few steps into the woodland to remove the dead tree that runs diagonally across the foreground.  I went back to my original position and took another photograph.   No more than 30 seconds elapsed between the two pictures, but the colour balance is completely different.   It may be a product of the metering in the camera itself (I’ve cropped both to show the same scene but the upper image had more bluebells and less woodland than the lower one) and this introduces another source of variation: the oh-so-clever electronics inside even fairly basic cameras that are making decisions on your behalf.


Two images taken within 30 seconds of each other from the same spot in woodland near Shincliffe, Co. Durham, May 2020.  The images at the top of the post show the 2009 and 2010 winners of the Hilda Canter-Lund competition, by Mariano Sirioni and Ernesto Macayo respectively. 

Most scientists assume that photography offers a “truthful” account of the objects that they are recording.   That’s at odds with the approach of critical theorists in the arts and humanities who recognise how many interventions lie between any object and the final image that is presented to third party viewers.   Susan Sontag, for example, challenges the “presumption of veracity” – less of an issue, perhaps, for fine artists but almost everything we think of as “documentary photography” or “photojournalism” is loaded with presumptions by both photographer and viewer, and it is a small step from those disciplines to scientist’s efforts to use photographs as objective evidence in their research.

The Hilda Canter-Lund competition is, however, not about photography as a scientific tool, but as a means of communication.  Appreciating the artificial nature of photography should be a liberation not a constraint: you, as photographer, probably have as accurate a memory of the image you have captured as the jpeg or tiff file that represents the digital record of the moment you released the shutter.   So feel free to open up the file in an editing package and use your discretion to adjust all the factors that were either in-built constraints or impulsive spur-of-the-moment decisions.   And send the final image to us for consideration for the 2020 Hilda Canter-Lund prize.

You can find the rules of the competition at https://brphycsoc.org/hilda-canter-lund-prize/ along with examples of recent shortlists to inspire you.


Sontag, Susan (1977).  On Photography.  Penguin Books, Hamondsworth.

Other posts on photographing algae

How to win the Hilda Canter-Lund prize

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

How to win the Hilda Canter-Lund prize (3)(guest post by Chris Carter, twice winner of the competition)

How to win the Hilda Canter-Lund prize (4)


Some other highlights from this week:

Wrote this whilst listening to: still working through my resolution to listen to all Bob Dyla’s albums in sequence.   This week I listened to The Basement Tapes, Desire, Hard Rain (much underrated in my opinion) and Street Legal.  Also enjoyed Jagged Little Pill by Alanis Morissette.

Cultural highlights:  The Assistant is an excellent but gruelling film that references the predatory behaviour of Harvey Weinstein but manages to do this almost entirely by inference and implication.

Currently reading:  Tamed by Alice Roberts, about the domestication of plants and animals, is interesting but rather turgid so I’m alternating chapters with Slaves of New York, a 1986 short story collection by Tama Janowitz which I borrowed from my son’s bookshelf.

Culinary highlight:   Baked cod topped with a pesto made from garlic mustard (Alliaria petiolata) foraged from the garden and allotment.

The dark side of the leaf …


Having mentioned in my previous post that the epiphytes on the top and bottom surfaces of a Potamogeton polygonifolius leaf were different, I have produced a companion piece to the painting I showed in that post.   The new painting is of the lower surface, and shows a greater number of diatoms than are present on the upper surface.  In order to explain why this is the case, it is helpful to look at the structure of the Potamogeton leaves.  The first image, therefore, shows a section through a leaf. It is quite a thick section but we can see the upper epidermis, the palisade mesophyll cells below this, which have plenty of chloroplasts in order to capture the sunlight that the plant needs for photosynthesis.  Below this, we can see parenchymous tissue arranged to create some large internal air spaces which contribute to the leaves buoyancy. Finally, at the bottom, there is a single layer of epidermal cells.   All this is crammed into a thickness of about half a millimetre.


Part of a section of a leaf of Potamogeton polygonifolius.  The leaf vein is on the left, thinning to the leaf blade on the right.  The leaf blade is about half a millimetre thick.   The picture at the top of the post shows an artist’s impression of diatoms and Chamaesiphon cf. confervicolus on the lower surface of a Potamogeton polygonifolius leaf. 

 Viewed from the underside, these parenchymous tissues create polyhedronal chambers, ranging from about 100 to 200 micrometres (a tenth to a fifth of a millimetre) along the longest axis.  There are also a few stomata scattered across the leaf surfaces (see the right hand image below).

With this in mind, take a look at my impression of the epiphytes growing on the lower surface of a Potamotgen polygonifolius leaf.   There are a number of cells of Chamaesiphon cf confervicolius, as seen on the upper surface, but there are several cells of the diatom Achnanthidium minutissimum, growing on short stalks, plus a few long, thin cells of Ulnaria ulna, growing in small clusters on the leaf surface (there were a few other species present, but such low numbers that I have not included them here).    It might seem strange to think of two surfaces of a leaf having such different communities of epiphytes but that’s because we’re thinking like large land-dwelling organisms, not like algae.   The longest alga visible in the image of the leaf underside is Ulnaria ulna, at about a 10th of a millimetre in length.  Therefore, to get a realistic impression of the two images, we really need to put a distance of five of these between them, and then pack the gap with chloroplast-rich mesophyll cells inside the Potamogeton leaf.   Allowing for foreshortening, this distance is about five times the height of the image.


The structure of a Potamogeton polygonifolius leaf viewed from the underside.  The left hand image (100x magnification) shows a leaf vein running diagonally across the lower right hand side along with the polyhedron-shaped chambers; the right hand image (400x magnification) shows the outline of one of these chambers superimposed behind the epidermal cells with a stomata with two guard cells visible just above the centre.   Scale bar: 20 micrometres (= 1/50th of a millimetre). 

The epiphytes on the upper surface of the leaf get first dibs at the meagre Pennine sunlight, which then has to pass through the upper layers of the Potamogeton leaf, where the mesophyll cells will continue to feast on the tastiest wavelengths, leaving relatively meagre pickings for the epiphytes that hang around on the underside of the leaf.

Chlorophyll, the molecule that makes plants green, absorbs light over a relatively narrow range of wavelengths – predominately red and blue – and this means that there are plenty of other wavelengths awaiting an organism with different pigments.   Diatoms have chlorophyll, but they also have some carotenoids (principally fucoxanthin) that grabs energy from the green part of the visible light spectrum (which is reflected, rather than absorbed by chlorophyll) and passes it to the cell’s photosynthetic engine.  Having this capability means that they can survive in relatively low light, which is why we see more diatoms on the underside of the Potamogeton leaf than on the top.

And that, best beloved, is the story of how Potamogeton got its epiphytes …


Some other highlights from this week:

Wrote this whilst listening to: more Bob Dylan.   I’ve got to the mid-70s, which means the live version of Like a Rolling Stone on Before the Flood plus the great Blood on the Tracks.  Also, as I was reading Ian Rankin, I listened to John Martyn’s Solid Air.

Cultural highlights:  we’re watching the BBC adaptation of Sally Rooney’s Normal People

Currently reading:  Ian Rankin’s Rather be the Devil.

Culinary highlight:   A rather fine vegetarian chilli, from Felicity Cloake’s column in The Guardian last week.   Served with corn bread, using a recipe we got from a hand-me-down American housekeeping magazine during our time in Nigeria.