Hilda Canter-Lund competition 2021

The British Phycological Society’s 2021 Hilda Canter-Lund competition is now underway, with one important change from previous years.  In the past, entries had to be emailed to us and only the shortlist was available for general viewing.  This year, however, there is a facility on the BPS website that allows entries to be uploaded directly by competitors [https://brphycsoc.org/canter-lund-2021-entries/], and for these entries to be displayed for all to see in our gallery.  A screenshot of the gallery at the time of writing is at the top of the post.  Click on any of the images in the gallery and you get some more details about the image and you can even add your own comments.

In previous years, the shortlist was chosen by a panel of art-inclined phycologists.   This year shortlist selection will be by a vote of the BPS membership, again via the BPS webpages.   In the past, the judges have strived for a balance of themes and techniques amongst the shortlisted images.   This year, the most highly-rated images may reflect the inclinations of the BPS membership so the rules allow the popular vote to be overridden to ensure balance.   The winning entry will be chosen, as in previous years, by a vote amongst the BPS Council.   The practice of awarding a second prize to an image in a contrasting style (i.e. of a microalga if an image of a macroalga wins, and vice versa) will continue, and this is one reason that there needs to be scope for a discretionary override of the popular vote.  It may not be needed, but it is there if necessary.

Whilst you do not need to be a BPS member to submit an entry to the competition, you will need to be a member if you want to vote for the shortlist.   If you want to join the society, go to the membership pages of the BPS website. it only costs £10.50 to join as an ordinary member without the journal, so it is not a large investment.  

You do, of course, need a good image to upload.  Head to https://brphycsoc.org/hilda-canter-lund-prize/ to look at previous shortlists, and check out some of the posts I’ve written over the past few years for ideas on what makes a great image.   The most recent of these is How not to win the Hilda Canter-Lund competition and there is a list of older posts that address algal photography at the end of this.

The closing date is 25 July 2021 so you’ve got about six weeks to get a great image to submit.   

“Awesome Brown”: Erasmo Macaya’s image from the 2020 shortlist showing Macrocystis pyriifera, the giant kelp, the largest seaweed on earth.

Wrote this whilst listening to:   Path of Wellness, new album by Sleator-Kinney.  Guitarist Carrie Brownstein also stars in Portlandia, a very good comedy sketch show that used to be available on Netflix.

Cultural highlights:  The Sound of Metal: thought provoking film about deafness that, fortunately, contains less heavy metal music than the title might suggest.

Currently reading:  Maggie O’Farrell’s Hamnet.

Culinary highlight: Just finished lunch in the garden in friends, where the highlights were rhubarb crumble ice cream, from an old Delia Smith book, and a fresh watermelon.

Promising young algae …

Spring has arrived in Cassop Vale.  Leaves are appearing on many of the trees and the ground vegetation has the green flush of a new beginning.   More importantly, the herd of emo-fringed highland cows have been moved away, to give the plants more chance of flowering, and there is some warmth in the sun in the middle of the day.

From my point of view, the biggest change since I was last here is the appearance of an extensive floc of green algae covering much of the pond’s surface.   I had a hunch, from their appearance, that these would be predominately Spirogyra, but was not expecting the sight that greeted me when I put a small piece of a floc under the microscope. 

Flocs, predominately Spirogyra, in the margins of Cassop Pond, April 2021.

I find Spriogyra and its relatives quite regularly on my travels, but usually in the vegetative state.  It is relatively unusual to find them as they undergo sexual reproduction (see “Fifty shades of green …”).  But there was plenty of evidence of this process (termed “conjugation” in Cassop Pond’s green flocs.  There were plenty of vegetative filaments, each about 20 micrometres wide and with a single helical chloroplast.  But there were also many ellipsoidal zygotes apparent.   When I looked more closely, these were inside filaments which were linked to an adjacent filament by a narrow tube.   What started out as an early morning natural history trip has turned out to be the algal equivalent of Saturday night on Newcastle Quayside.   

For those of you unused to dating, Spirogyra style, here is a quick guide.   First, put on your best helical chloroplast (two or more, if you are daring), then head out to find a partner amongst the many other filaments in your particular floc.   Little is known about Spirogyra’s preferences, but we can assume that many species are not heterosexual, so don’t be shy: sidle up to any filament you fancy.   He/she/it might well play hard to get at first, so maybe you need to drop a hint.  Make sure your potential date gets a whiff of your aftershave (that’s what I assume “hormonal interactions between the paired filaments” means).  If he/she/it gets the hint, then you can indulge in a little mutual meiosis to get yourselves into the mood.    

Spirogyra from flocs in Cassop Pond, April 2021.   a. vegetative filament; b. two filaments undergoing sexual reproduction with zygotes in the lower filament.   Narrow filaments of Aphanizomenon gracile are also present.   Scale bar: 20 micrometres (= 1/50th of a millimetre).  

Now we’ve got that all-important emotional (okay … hormonal) connection, it is time to get physical.   An embarrassing bulge appears on the side of your filament but, fortunately, a similar one should appear on the side of your date’s filament at about the same time.   Eventually, these fuse to form a tube that links you both together.  The correct term for this is the “copulation canal” which is as frank as it is alliterative (it could also be called a “tupping tube”, I guess?). The protoplast of both cells now contracts and one (the “boy”, for want of a better analogy) crawls, amoeba-like, through the tube and fuses with the “girl” protoplast to form a zygote.  That’s as far as our frisky filaments in Cassop Pond have got.  If our phycological peep-show continued for longer, we would see the green zygotes gradually become brown in colour as thick, resistant walls grew around them, and the cell contents were processed into starch and lipid-rich food reserves.   They would then sink to the bottom of the pond and rest, dormant, until conditions were ripe for its germination.

Features of Spirogyra conjugation: a. a vegetative cell in one of the two aligned filaments; b. conjugation canals developing between the aligned filaments; c. a zygote.  Scale bar: 20 micrometres (= 1/50th of a millimetre).  

Why here, why now?   Nitrogen limitation has been quoted as one of the triggers for conjugation and the presence of a nitrogen-fixing cyanobacterium (Aphanizomenon gracile) plus nitrogen-fixing diatoms (Epithemia– see “Working their passage”) in the pond at the same time lends support to this hypothesis.  Also, the yellow-green appearance of the flocs is also a hint that they may be nitrogen-limited.   However, there are also reports of conjugation happening on a predictable annual pattern in some locations.  The two possibilities are not mutually exclusive, we should remember.  

Meanwhile, on dry land, there are plenty of other plants getting down to the complicated business of reproduction too.   We saw goat willow (Salix caprea) and hazel (Corylus aveana) as well as lesser celandine (Ficaria verna) in flower, and leaves of primroses yet to bloom.   You can read more about those here.   Just remember, when enjoying the sight of spring flowers, that the botanical bacchanalia takes place in less obvious ways in the water too.

Some other highlights from this week:

Wrote this whilst listening to:  Horses and Easter by the Patti Smith Group (see below).   And a 1977 BBC “Sight and Sound in Concert” recording of Jethro Tull, which I remembered seeing when it was first broadcast.

Cultural highlights:   The film Black Bear – a rather dark and challenging, but ultimately rewarding, film.

Currently reading:  Just Kids, by Patti Smith.  Best read with Horses and Easter as a soundtrack.  The geographer in me also reads it with a map of New York to hand, as it is a book with a very strong sense of place.

Culinary highlight:.our local Indian restaurant makes a rather good lamb shank, cooked in aromatic spices which, with basmati rice and a side order of bhindi, is just about unbeatable.

Structural engineering with diatoms …

I’ve been looking at shallow, calcareous lakes in two very different locations over recent weeks: on the Shetland Islands north of Scotland and in Greece.   Climatically, they are different worlds but there are surprising similarities in the diatoms that I find in the two habitats: many species are common to both but, even when the species are not identical, genera that are not widespread in other habitats are well represented in these lakes in both the Shetlands and Greece.   There must be something about these lakes that makes them attractive to a few genera over almost all other possible habitats despite the differences in climate.   

One of the genera that falls into this category is Epithemia, which I also find in my local calcareous pond (see “Working their passage …”); another is Rhopalodia, a relative of Epithemia and a third is Mastogloia, the subject of this post.   Mastogloia has a very unusual structure.   If you focus carefully on the top of the valve, you see striae and a raphe; if you then adjust the focus very slightly a series of chambers (“partecta”) will come into view, arranged in a row along each side of the valve.  They look a little like a row of cabins along the two sides of a boat.

Mastogloia (probably M. lacustris) from Limni Trichonida in Greece, December 2020.   Seven focal planes of the same frustule, seen in girdle view showing how the organisation of the partecta on girdle bands on either side of the cell.   The image at the top of the post shows Mastogloia species from the Shetland Islands: a., b., c., d., g.: M. baltica; e., f.: M. dansei; h., i. M. elliptica; j. M. dansei.  g. – k. from Carter & Bailey Watts (1980).  Scale bars: 10 micrometres (= 100th of a millimetre).

When seen from the side, rather than from above, we see that Mastogloia cells are, typically, rather deep so, pushing our nautical metaphor just a little further, they are rather ungainly.   Although they have raphes and are, in theory, capable of movement, these are not going to be found darting around like species of Nitzschiaand Navicula, constantly adjusting their position in relation to light and other resources.  Instead, Mastogloia have a very different set of priorities, with the partecta playing a key role in enabling these.

We see the partecta as empty chambers because we usually look at diatoms after they have been treated with oxidising agents that remove all organic matter.  When viewed live, however, Mastogloia are often seen surrounded by extracellular strands, capsules and tubes and it is assumed that these are secreted from pores which are, in effect, the “portholes” associated with the partecta.   The empty “cabins” we see under the microscope are, in fact, busy little slime factories.  A lot of different extracellular structures have been described, particularly from the many marine representatives of this genus, and most seem to be designed to keep the cell in one place, rather than to help it adjust position. 

For the freshwater species, calcareous habitats offer some particular challenges to organisms: the porous nature of the rock means that there is often a high risk of drying out, high calcium carbonate concentrations lead to the precipitation of calcite.  In the process, phosphorus is also removed from the water, trapped in the calcite crystals.  Evelyn Glaiser and colleagues suggested that this combination of characteristics favoured organisms that produced a lot of extracellular polysaccharides.  Firstly, the strands act to bind inorganic particles and the microbial life into dense aggregations and slows rates of desiccation.  Second, this dense moist matrix will provide not just organic matter but also microbes that can break it down to recycle nutrients for the diatoms and other organisms to use.   Third – not mentioned by Evelyn Glaiser and colleagues but touched upon in “A journey to the headwaters of the River Coquet” and other posts – the algae themselves may contribute to this recycling via enzymes present in their extracellular polysaccharides. 

A schematic view of a Mastogloia cell with polysaccharide strands emerging from pores and tangled around mineral particles. 

Mastogloia, in other words, is not just part of the structure of biofilms in in shallow calcareous lakes and ponds, it actively creates these.   In the Florida Everglades it is a keystone species, around which thick microbial mats form and within which, in turn, other species, some unique to these ecosystems, are found.   It does this through diverting energy and resources to produce extracellular polysaccharides and because the scant nutrients mean that more competitive algae are kept out.   However, if this delicate balance is disrupted and nutrients become more widely available, then Mastogloia is out-competed, the mats lose the structural integrity that Mastogloiaimparts, and the biodiversity associated with them disappears.   A classic ecological cascade: for want of a nail, the shoe is lost and so on …


Carter, J.R. & Bailey-Watts, A. (1981).  A taxonomic study of diatoms from standing waters in Shetland.  Nova Hedwigia 33: 513-629.

Glaiser, E., La Hée, J.M., Tobias, F.A.C. & Wachnicka, A.H. (2016).  Mastogloia smithii var. lacustris Grun.: a structural engineer of calcareous mats in karstic subtropical wetlands.  Proceedings of the Academy of Natural Sciences of Philadelphia 160: 99-112.

Hain, M.K., Winsborough, B.M., Davis, J.S. & Golubic, S. (1993).   Extracellular structures produced by marine species of Mastogloia.  Diatom Research 8: 73-88. 

Some other highlights from this week:

Wrote this whilst listening to: The Go-Betweens, an Australian indie band from the early 1980s.  There has been press coverage of a new book about one of their members and this reminded me of the one occasion I saw them whilst a student in London in 1982 or 1983.   I remember that the venue was full of goths hoping to see another band on the bill, The Dancing Did, who did not show up for some reason.  I found their sole album, And Did Those Feet, on Spotify too: 

Cultural highlights:   Watched the new film Ammonite about Mary Anning.   It plays fast and loose with history (see “It all started here …”) but is well-acted.  Charlotte Murchison, the character played by Saoirse Ronan, lived for a while in Barnard Castle, about 30 kilometres from Durham.

Currently reading:  Persepolis by Marjane Satrapi, autobiographical graphic novel about growing up in Iran during and after the 1979 revolution.

Culinary highlight:  Normandy-style galettes followed by a chocolate and ginger cheesecake.

Baffling Brachysira …

I should have been in the Lake District last week on a sampling trip.  It was not lockdown that stopped me but the weather.   There was rain at the weekend and the river levels went up.  I then watched the hydrographs slowly sink back but not quite to a safe level for wading before Storm Christoph blew through and the river levels went up steeply.   After two days of almost constant rain, the temperature dropped, then the rain turned to snow which is great news for me because snow on the fells means that the river levels start dropping, even if it is fiendishly cold.  As I write (Sunday) the levels are just about back to conditions that permit safe wading, albeit with air temperatures below freezing.  We should get out early next week.  Meanwhile, I am left thinking about the lakes and streams rather than actually experiencing their chilly reality.

My ruminations took me back to Ennerdale Water and along themes that I explored in a post from 2017 (“Lost in detail?”).  Once again, we are looking at the genus Brachysira in this lake but this time, rather than pick up on the identity of a single species, I want to reflect on just how many different species of Brachysira seem to inhabit the littoral habitat of one lake.  This also links with two other recent posts: The stream eats itself … and Curried diatoms?.

As was the case for the 2017 post, the slide was used in the UK/Ireland diatom ring test, which means that it was scrutinised by more analysts than just myself.  All of us, however, agreed that several species of Brachysira were present with, in one case, eight different species being recorded by a single analyst.   I’ve included illustrations of all of them and the first comment that anyone who is not familiar with diatom taxonomy will make is, almost certainly, that they don’t look particularly different from one another.   There are differences but these mostly lie just at the edge of the resolution of the light microscope.  More pertinently, those analysts who do not have light microscopes with the very highest specification will be unlikely to discern these differences.   Whereas 25 years ago, you could probably do a perfectly adequate analysis of a sample such as this with a microscope equipped with a 100x achromatic objective with a numerical objective of 1.4, now you need a plan achromatic objective with a numerical objective of 1.25 and a differential interference contrast condenser and you will still struggle to differentiate some of these species.   

Brachysira intermedia, Ennerdale Water, June 2020. Similar to B. brebissonii (pictured at the top of the post) but slightly drawn-out ends and with undulating longitudinal lines dividing the striae into two, rather than three, areolae.  Scale bar: 10 micrometres (= 1/100th of a millimetre).  Photos: Bryan Kennedy.

Several questions arise.  One is that if there is so much diversity discernible (albeit only just) with a light microscope (i.e. “semi-cryptic variation”), how much more are we missing because it is not discernible with a light microscope (“cryptic variation”)?   For some freshwater diatom genera we have been able to walk away from taxonomy’s traditional reliance on morphology and approach the problem from a different perspective.  Mostly, in this age, this different perspective comes from molecular genetics and in some cases (e.g. Fragilaria, Nitzschia, Sellaphora) it suggests that there really is variation beyond that readily discernible with light microscopes.  In others (e.g. Gomphonema) the evidence is less clear cut and it is even possible that taxonomist’s enthusiasm may have run ahead of the actuality.  Unfortunately, we don’t have any detailed molecular studies of Brachysira with which to test the ideas of species limits developed with morphological approaches.  

A second question is whether we need all this information in order to draw the ecological insights that catchment managers need in order to decide what measures, if any, are needed to keep the water body in a healthy state.   The autecological information that we have suggests that Brachysira species are mostly associated with healthy, low nutrient, circumneutral water bodies.  Where there are differences, it is primarily due to the hardness of the water rather than to the levels of human-derived pressures.   The very fact that we see several species in one lake is evidence that their preferences for these conditions, in any case, overlap.   So there is little evidence that different species of Brachysira “indicate” starkly different environments.

Brachysira microcephala (formerly B. neoexilis and, further back still, Anomoensis exilis), Ennerdale Water, June 2020. Scale bar: 10 micrometres (= 1/100th of a millimetre).  Photos: Bryan Kennedy.

As I suggested in Curried diatoms?, however, there may be some value in knowing that there are several species present but for reasons that are not associated with rather naïve associations between species and chemical measurements.  As the present generation of methods for assessing lake or river health are tied to these tired notions of indicator values there is probably not a lot of extra “signal” to be squeezed from splitting Brachysira further.  

Brachysira procera, Ennerdale Water, June 2020. Generally longer and broader than B. microcephala.  Scale bar: 10 micrometres (= 1/100th of a millimetre).  Photos: Bryan Kennedy.

Having said that water hardness plays a greater role in determining the distribution of Brachysira species than water quality, one of the oddities of this sample was that there were small numbers of two species associated with hard water (B. neglectissima and B. vitrea).  There is absolutely no limestone or any other rocks that might create hard water conditions within the Ennerdale catchment, so why are these species here?   I have found B. vitrea, especially, in small numbers in other soft water areas so these are not isolated occurrences.   Do they represent genuine viable populations hanging on at the extreme edge of their range (and, one assumes, competing for resources with physiologically “fitter” Brachysira species) or are they “noise”, carried into the catchment by wind or on the feet of mammalian vectors such as, er…, myself?   The latter has implications: firstly, it lends support to the controversial “everything is everywhere, environment selects” hypothesis (that I’ve mentioned in the past but never fully explained … I’ll do so in a post in the near future) and it also casts doubt on some of the claims of metabarcoding enthusiasts that they can extract more ecological information because the sequencing depth that is now possible exceeds that of traditional ecological analyses.  If what we hope is “signal” is, in fact, “noise”, then that depth is as likely to confuse or even mislead as it is to inform better decision making. 

Brachysira garrensis, Ennerdale Water, June 2020. Similar to B. microcephala but with denser striae (very difficult to see without very good optics).  Scale bar: 10 micrometres (= 1/100th of a millimetre).  Photos: Bryan Kennedy.

Studies of the microscopic world are only ever as good as the technology available.  But, equally important, studies of microbial diversity are also complicated by the observer’s expectations.  How different do two cells have to be before you treat them as separate species?   Not only did Hustedt not have such good microscopes as are now available when he wrote his Flora in 1930, but he also assumed that diatom species concepts were much broader than we now know to be the case.  And the final twist is that the ability of anyone to match what s/he sees with the images in the literature.  Hustedt used a single drawing to illustrate “Anomoensis exilis” (what we would now call Brachysira microcephala) in his Flora whereas Bryan Kennedy used 96 photographs, taken with differential interference contrast lighting, along with 31 scanning electron micrographs in his 2017 paper highlighting, in the process, four different morphotypes. Whether these represent different species is yet to be determined.  My point is that “seeing” depends partly on how light stimulates the optical nerve (which depends on the quality of equipment we have), but more on how that raw signal is processed by our brains.  

Brachysira neglectissima, Ennerdale Water, June 2020. Like B. garrensis, this has denser striae than B. microcephala.  Note, too, the undulating pattern of areolae.  Scale bar: 10 micrometres (= 1/100th of a millimetre).  Photos: Bryan Kennedy.

Postscript: we finally got out into the field on Monday, catching a gap in the weather when the rivers were low but the snow did not impede travel.  We had some spectacular views of snow-covered Pennines, High Street, Blencathra and Skiddaw on the way over, but the western Lakes were virtually snow free.   We even found time for a short walk around Loweswater on the way back, making the most of a rare opportunity to travel during Lockdown 3.0. 

Brachysira vitrea, Ennerdale Water, June 2020. Generally broader (>5.5 micrometres) than B. microcephala.  Scale bar: 10 micrometres (= 1/100th of a millimetre).  Photos: Bryan Kennedy.


Hustedt, F. (1930).  Susswasserflora von Mitteleuropa 10: Bacillariophyceae.  Gustav Fischer, Jena.

Kennedy, B. & Allott, N. (2017).  A review of the genus Brachysira in Ireland with the description of Brachysira prageriand Brachysira conamarae, new raphid diatoms (Bacillariophyceae) from high status waterbodies.  Phytotaxa 326: 1-27.

Some other highlights from this week:

Wrote this whilst listening to: Brandon Marsalis’ soundtrack album for the film Ma Rainey’s Black Bottom and Arvo Pärt’s Spiegel im Spiegel.

Cultural highlights:  White Tiger, new film set in India.   

Currently reading:  Still reading The Science Delusion by Rupert Sheldrake

Culinary highlight:  Homemade piccalilli pickle.   Too soon to give a definitive opinion on flavour (it needs three weeks to mature) but I’m fantasising about piling it into a thick ham sandwich already.

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.

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.


Whatever doesn’t kill you …


The previous post focussed mostly on the higher plants that I found in the short stream that connects White’s Level with Middlehope Burn.  I mentioned the mass growths of algae that I found growing immediately below the entrance to the adit, but I did not talk about them in any detail, instead spinning off on a tangent while I mused on why the water cress had a purplish tinge.

When I did find time to examine the algal floc, I found it to consist of a mix of three different algae, the most abundant of which was Tribonema viride, but there were also populations of a thin Microspora (not illustrated) and Klebsormidium subtile.   I talked about Tribonema in the drainage from the Hadjipavlou chromite mine in Cyprus last year (see “Survival of the fittest (1)”) and both Microspora and Klebsormidium are also genera that are known to frequent these habitats.  Indeed, there is evidence that the populations that grow in these extreme habitats have physiological adaptations that help them to cope with the conditions.  Brian Whitton, my PhD mentor, led several studies on these adaptations in the streams of the northern Pennines in the 1970s, and Patricia Foster did similar studies in Cornwall at about the same time.   There is probably a mixture of physiological strategies involved, including the production of low-molecular weight proteins, which bind the toxic metals, and the production of extracellular mucilage.  Most of the populations I find in such habitats have a distinctly slimy feel due to the production of extracellular polysaccharides, and it is possible that these play a role in trapping the metal ions before they can get into the cell and cause damage.


Filamentous algae from the drainage channel below White’s Level, upper Weardale, April 2020.  a., b. & c.: Tribonema cf. viride, showing the characteristic H-shaped cell ends.   d.  Klebsormidium cf. subtile.  Scale bar: 10 micrometres (= 100th of a millimetre).   The picture at the top of the post shows an artist’s impression of Chamaesiphon cf. confervicolus on the upper surface of a Potamogeton polygonifolius leaf. 

I also had a look at the algae growing on the submerged leaves of Potamogeton pergonifolius in the channel between the adit and Middlehope Burn.   One easy way of examining them is to add a small amount of stream water then shake the leaves vigorously in a plastic bag.  The result is a brownish suspension of algae that can be sucked up with a Pasteur pipette and placed on a microscope slide.  When I did this, I found a community that was dominated by a short cyanobacterium, closest in form to Chamaesiphon cf. confervicolus.  The other abundant alga in the sample was Achnanthidium minutissimum, which is often common in minewaters, along with smaller numbers of a few other species.  The total number of species in the sample was just 12, which is low by the standards of streams without metal pollution, but such suppression of all but the hardiest species is another characteristic effect of heavy metal pollution.

I’ve added a “cf” (from the Latin conferre, meaning “compare to”) to my identification of Chamaesiphon confervicolus because this is the closest name, based on a comparison with images in the Freshwater Algal Flora of Britain and Ireland.  However, it is not an exact match.  Whether this is because the metals have strange effects on Chamaesiphon (as we saw for diatoms in “A twist in the tale …”) or whether our knowledge of the species within this genus is imperfect is not clear.  But discretion is the better part of valour in this instance.  Chamaesiphon species fall into two groups: those that live on stone surfaces (see “Survival of the fittest (2)”) and those that live on algae and plants, such as the one we see today (another is illustrated in “More from the River Ehen”).   They consist of a single, elongate but gently tapering cell, attached at one end to the plant and enclosed in a sheath.   The upper end of the filament forms small spherical buds (technically “exospores”).  One reason that I am wary of calling this population C. confervicolus is that most illustrations of this species show a stack of exospores in the sheath, whereas the White’s Level population all had just a single exospore.


Chamaesiphon confervicolus, growing on Potamogeton polygonifolius in White’s Level outflow, April 2020.   Note the exospores at the end of the cell.  f. and g. show the sheath very clearly.  Scale bar: 10 micrometres (= 100th of a millimetre). 

The picture at the top of this post shows an artist’s impression of the Chamaesiphon cf confervicolus on the upper surface of the Potamogeton leaf.   I wanted to get some idea of the size, shape and arrangement of the epidermal and stomatal cells on the Potamogeton leaves and resorted to the tried and tested technique of painting a layer of clear nail varnish onto the leaf surface, then peeling this off when it had dried.  This had the added (and unexpected) benefit of also pulling of the epiphytes, giving some idea of their arrangement on the leaf surface at the same time.   One extra observation that this yielded was that upper surface was dominated by Chamaesiphon, growing in clusters, whilst the lower surface had greater representation of diatoms.   I’ve also tried to portray the chloroplasts in the stomata guard cells.  Plant epidermal cells generally do not contain chloroplasts, as their purpose is to protect the mesophyll cells that are the main centres of photosynthesis.  Guard cells of stomata, however, need energy to open and close the stomata so these are the exception to this rule.  I had not even been sure that I would see stomata on the upper surface of the cell, as these are mostly found on the underside of leaves; however, Potamogeton appears to have stomata on both surfaces.  As ever, there is a certain amount of evidence along with a dose of extrapolation.   Imagined, but not imaginary …

You can find a description of the terrestrial plant life of Slitt Mine and its environs in this post on Heather’s blog.


Foster, P.L. (1982).  Metal resistances of Chlorophyta from rivers polluted by heavy metals. Freshwater Biology 12: 41-61.

Harding, J.P.C. & Whitton, B.A. (1976).  Resistance to zinc of Stigeoclonium tenue in the field and the laboratory. British Phycological Journal 11: 417-426.

Robinson, N.J. (1989).  Algal metallothioneins: secondary metabolites and proteins.  Journal of Applied Phycology 1: 5-18.

Say, P.J., Diaz, B.M. & Whiton, B.A. (1977).  Influence of zinc on lotic plants. I. tolerance of Hormidium species to zinc.  Freshwater Biology 7: 357-376.

Sorentino, C. (1985).  Copper resistance in Hormidium fluitans (Gay) Heering (Ulotrichaceae, Chlorophyceae).  Phycologia 24: 366-368.

(Note that Hormidium is the old name for the genus Klebsormidium.  There is an orchid genus called Hormdium and, as this was described first, it takes priority.)


Some other highlights from this week:

Wrote this whilst listening to: Bob Dylan’s New Morning and Pat Garrett and Billy the Kid.   Also, Samuel Barber’s Prayers of Kirkegaard.

Cultural highlights:  The Netflix series Unorthodox, about a young woman fleeing a Hassidic community in New York.

Currently reading:  Agatha Christie’s A.B.C. Murders.

Culinary highlight:   Arroz con leche (Spanish rice pudding) served with peaches poached in madeira.

A reasonable excuse for exercise ..

High_Mill_falls_Apr2020A redefinition of the travel restrictions hereabouts means that “driving to the countryside and walking (where far more time is spent walking than driving)” it is now “likely to be reasonable” within the terms of Regulation 6 of the The Health Protection (Coronavirus, Restrictions) (England) Regulations 2020. That means that, rather than plan another post about the fascinating ecology of Lough Down, I can look a little further afield.   As both Heather and I are writing chapters for a forthcoming book on the Natural History of Weardale, we turned our eyes to the hills, largely for exercise and a change of scenery, but also as part of our background research for these chapters.

We parked the car at Westgate and followed a path alongside Middlehope Burn, a tributary of the Wear with a long history of lead mining and, as such, a case study in how man has shaped the ecology of Weardale, both terrestrial (Heather’s domain) and aquatic.  The first part of the walk is through Slitt Wood, where the stream cascades over a series of low step-like waterfalls, alternately sandstone and limestone, illustrating the bedrock geology of the area.   The air is full of birdsong and there are patches of primroses feasting greedily on the light that is still plentiful on the forest floor at this time of year.   However, this idyll is short-lived as, passing through a gate we emerge into a grassed area surrounded by derelict mine buildings.  Early on a Saturday morning in the midst of the pandemic, we have the place to ourselves and it is a struggle to imagine this place as a busy industrial site.   Similar sites are scattered throughout Weardale and the surrounding dales; all are now closed but once they would have employed large numbers of people.  There would have been the miners, working underground, of course, but also gangs of people (including women and children) breaking down and sorting the ore as it was brought to the surface, plus ancillary workers involved in construction, both above and below ground.

A couple of hundred metres beyond the site of the main shaft at Slitt Mine, I spot an adit (a shaft driven horizontally into a hillside) and make my way towards it.  These are intriguing habitats for ecologists interested in the interactions between man and nature and I was intrigued to see what was growing in this one, White’s Level.  The mine’s levels and shafts act as natural drainage channels, collecting water that has percolated through the rocks but, because the miners have driven the levels along the mineral veins, the water comes into contact with lead, zinc and cadmium during the course of its underground journeys, emerging with concentrations far in excess of those deemed safe by toxicologists.  However, the channel immediately downstream of the entrance of White’s Level was lush with vegetation.   I could see thick wefts of filamentous algae giving way to beds of water-cress (Rorippa nasturtium-aquaticum) and bog pondweed (Potamogeton polygonifolius).  The latter two were surprising as, in my experience, most of the streams draining north Pennine adits are dominated by algae rather than by higher plants.


The stream flowing from White’s Level to Middlehope Burn, April 2020.  The left-hand image shows the beds of water-cress very clearly whilst the right hand image shows the filamentous algae growths immediately below the entrance.   The picture at the top of the post shows Middlehope Burn at High Mill Falls, just upstream from Westgate.

The water cress had a distinctive purplish tinge which is probably a response to stress.  We’ve encountered this type of colour-change in response to stress elsewhere (see “Escape to Southwold”).   In this post, and in “Good vibrations under the Suffolk sun …” I talked about how plants have to regulate the amount of energy from sunlight in order that their internal photosynthetic machinery is not overwhelmed.  Those posts were both written after a hot weekend in July, but this was a chilly and overcast April morning in the Pennines where the prospect of plant cells being overcome by heat seems faintly ludicrous.   Here, instead, is my alternative hypothesis.

Although White’s Level and the other mines in the northern Pennines were driven by the demand for lead, lead is a relatively insoluble element and zinc, which is found alongside the lead in the metal-rich veins of the northern Pennines, is more soluble and, therefore, has a greater toxic influence on the plants and animals in these streams.  Zinc affects the metabolism of plants in several ways, one of the most important of which is to reduce the effectiveness of the chlorophyll molecules which are responsible for photosynthesis.  It does this by nudging the magnesium atom, which lies at the heart of every chlorophyll molecule, out of place.


Macrophytes in the stream flowing from White’s Level to Middlehope Burn, April 2020.   Left: Potamogeton polygonifolius; right: Rorippa nasturtium-aquaticum.

What this does, then, is alter the balance of the equation that tries to balance energy inputs and photosynthesis.   If your chlorophyll molecules are hobbling along, then the point at which they are overwhelmed by even the meagre Pennine sunlight shifts so that  the need for the plants to manufacture their on-board sunscreen kicks in sooner.   Just a hypothesis, as I said: if you have a better explanation, please let me know.

A few hundred metres further on, there is another lush growth of water cress in the stream flowing out of another adit, Governor and Company Level, this time even extending beyond the metal grille designed to keep the curious from harm.  I most associate watercress farms with the headwaters of chalk stream, which are characteristically spring-fed and, therefore, have very stable conditions.   The adits of the northern Pennines are, this respect, very similar to springs insofar as their flow, temperature and chemical conditions vary little over the course of a year.   In that respect, it is perhaps less of a surprise that we find water cress growing so prolifically here.   The zinc, admittedly, is a complication we don’t find in most springs but, that apart, the adits could be thought of as man-made springs, creating a series of almost unique, but largely overlooked habitats.

In the next post, I’ll talk about the algae that I found in the White’s Level channel.


A prolific growth of water cress in the drainage channel below Governor and Company Level, April 2020. 

Some other highlights from this week:

Wrote this whilst listening to: Still working through Dylan’s back catalogue: John Wesley Harding, , Nashville Skyline and Self-Portrait, the latter a blip in an otherwise superb run of albums.   Next up is New Morning but I want to re-read the chapter in Dylan’s Chronicles Volume One where he describes the genesis of this album before listening.

Cultural highlights:  My book group looked at Pride and Prejudice but, being deep into The Mirror and The Light, I did not had time to read this.   We watched the 2005 film version starring Kiera Knightly instead.   Turned out that three of the six participants in the book group had also watched the film the night before our Zoom meeting, rather than (re-)reading the book itself.

Currently reading:  Finally finished The Mirror and The Light which was, definitely, worth the effort.  Started Kate Atkinson’s Big Sky.

Culinary highlight:   Home-made tortellini filled with mushroom paté, served with a consommé made from turkey stock from the freezer.  Culinary ambition hereabouts always goes sky high in the week of the MasterChef finals.

The littoral ecology of Lough Down


My recent overviews of the major groups of algae have been useful as a way of highlighting which families and orders I’ve neglected.  That’s mostly because my posts are largely reactions to the circumstances I find myself in, rather than as a comprehensive overview of the world of freshwater algae.  My travels, this week, have brought me to Lough Down, a little-known Irish lake to which many of us have journeyed over the past few weeks.   Today, I thought I would peer at the littoral zone in the hope that I might find an alga from an order I have not previously written about.

I seem to be in luck: there has not been much rain recently and there is recently-exposed mud.  When I look closely, I see tiny green spheres, each the size of a pin head, dotted across the mud surface.   These are vesicles of the alga Botrydium and, despite their bright green colour, they actually belong to the Xanthophyceae (see “When a green alga is not necessarily a Green Alga …”).   Below this pear-shaped vesicle there is a system of branched rhizoids which anchor the plant to the surface (see lowermost photograph).  Surprisingly, the whole plant is a single cell, a similar situation to the one we encountered in Vaucheria, another representative of the Xanthophyceae (see “The pros and cons of cell walls”).

The vesicle itself is green, and a close look reveals the presence of many chloroplasts and also (less easy to see without special stains) nuclei.   You can also see, on the image below, crystals of calcium carbonate which are deposited on the vesicle.   However, if the marginal mud where Botrydium thrives is flooded again, the cell contents divide into a large number of spores, each with a single nucleus and two flagellae, which are liberated.  On the other hand, if the pond continues to dry, then a different type of spore is produced, as the cell contents retracts into the rhizoids where it forms thick-walled spores, which can survive long periods of desiccation.   Once the mud is dampened again, these spores germinate into motile spores.


A vesicle of Botrydium granulatum spotted with crystals of calcium carbonate.  The photograph at the top of the post shows vesicles on the bed of a pond (both photos: Chris Carter).

Botrydium is a small genus, with just eleven species listed on AlgaeBase, of which just one, B. granulatum, is recorded from the UK and Ireland.  It fills in one glaring gap in my coverage of the Xanthophyceae, leaving just two Orders still to feature.  These are the ones containing the awkward little single cells and colonies that are difficult to identify and easy to confuse with similar-shaped forms in the Chlorophyta.   I’ll get around to writing about these one day.   Maybe I’ll find representatives from them on a future visit to Lough Down.  Who knows how much time I will have to become acquainted with this fascinating lake?


A complete Botrydium granulatum plant, showing the vesicle on the left with a series of rhizoids extending out below.  The lowermost rhizoids are obscured by soil particles (photo: Chris Carter).  All images in this post are from material collected from Pitsford Water, Northamptonshire.

 Some other highlights from this week:

Wrote this whilst listening to: J.S. Bach’s St Matthew’s Passion and Laura Marling’s new album, Song for Our Daughter.  My systematic review of Dylan’s back catalogue has reached the incomparable Blonde on Blonde.

Cultural highlights:  Portrait of a Lady on Fire.   French arthouse film.  I know, I know …

Currently reading:  Drawing to the close of The Mirror and The Light .

Culinary highlight:   Buying a bag of strong white flour after many abortive attempts.   And a Simnel Cake, in celebration of Easter.