Unlikely bedfellows …

2022 started with enforced isolation due to a positive Covid test, so my first post of the year has to be desk- rather than field-based, picking up my tour of the major algal groups.   So far, I have covered Cyanobacteria (“Shuffling the pack …”), green algae (“The big pictures …”) and red algae (“Rhapsody in red …”).  This post will deal with the last of the major groups of algae, the Chromista, the kingdom which includes the diatoms, chrysophytes, brown algae and yellow-green algae.  Microscopic silica-encased diatoms and giant kelp may seem like unlikely relations, so read on …

Be prepared for a veritable porridge of terminology, reflecting the gradual evolution of ideas.   From the point of view of someone who wants to understand how different groups of algae are related, all are more-or-less synonyms.  However, each also has a precise usage, representing their place in a hierarchy that also includes non-algae.   The Chromista (also known as SAR (“Stramenopile, Alveolates and Rhizaria”) is a Kingdom (akin to “plants”, “animals” or “fungi”), within which the algae are spread across four Divisions.  Most of the algae that are found in freshwater benthic habitats (the main focus of this blog) are found in the Heterokontophyta (a subkingdom, also known as the Stramenopiles) and, more specifically, in the Ochrophyta (a superphylum).   However, some of the other groups are very abundant in freshwater and marine plankton.   All are thought to share a common ancestor, a red algal-type cell, although many have subsequently lost their chloroplasts.

A guide to the terminology of the Chromista.

ChromistaAlgae with chlorophyll c but not b, evolved from a secondary endoysmbiosis  with a eukaryotic (red) alga, along with protists descended from these which have lost photosynthetic capability and plastids 
HeterokontaOrganisms possessing two flagellae of different lengths for at least part of the life cycle (hetero = different; kontos = punting pole)
StramenopilesOrganisms with a flagellum with short hair-like extensions.   The term is derived from Latin words stramen (= straw) and pilus (= hair).   However, I’ve also seen suggestions that  stramen refers to the yellow-brown colour of the chloroplasts.
OchrophytaRefers to the colour of the cells, from a Greek rather than a Latin root (okhra = yellow). 

One further surprise before we go on is that the non-algal representatives of this group include Cryptosporidium, responsible for gastrointestinal illness, Plasmodium, the parasite that causes malaria, and Phytophthora infestans, which causes potato blight. 

None of the groups in the subkingdom Hacrobia have been covered in this blog, mostly because they are not abundant in the habitats that I spend most of my time studying.   I do see cryptophytes (“Cryptista”) but never in large numbers, and when I do they are invariably moving too fast for me to photograph.  The Haptophyta include the Coccolithophores, which are very abundant in marine plankton, but not in freshwaters.  The only time one has appeared in this blog is in a feature on the Hilda Canter-Lund competition in 2017 (see below).  

Overview of the Chromista, following Ruggeiro et al. (2015).  Groups containing algae are indicated by arrows.  

Harosa, the other subkingdom, is divided into the Rhizaria, comprising non-photosynthetic  amoebae-like organisms and the Halvaria.  The Halvaria contains many important groups of algae.   The first of these is the Alveolata, which includes the dinoflagellates, again mostly found in plankton, both marine and freshwater.  The only mention in this blog (see table below) is not really typical of the group as a whole.   Another major group is the Pseudofungi  (which includes the organism responsible for potato blight) and the final group is the Heterokontophyta, of whose algal interest lies in the superphylum Ochrophyta.

Overview of the Heterokontophyta, following Ruggeiro et al. (2015).  

There are four major groups of algae in the Ochrophyta of which the  diatoms, Bacillariophyceae, are widely-covered in this blog, needing no extra explanation here.  The Chrysophyceae have been encountered a few times but, as for some of the other Chromistan algae, much of their diversity is planktonic rather than benthic.

The best known representatives of the Phaeophyceae are the kelps and other brown seaweeds of marine littoral zones.  I have written about these, but not much.   Michiel Vos’ blog An Bollenssor is a good place to start exploring this group.   There are freshwater representatives, but their only appearance in this blog was to record their likely extinction from the Bodensee.   I was planning to write a post last summer but inadvertently deleted all my photos.   They are probably more common in rivers than most people realise but are easily overlooked and, as a result, rarely recorded.

Finally, the Xanthophyceae, the yellow-green algae, include important freshwater representatives such as Vaucheria and Tribonema. They differ from many of the other algae in the Chromista in that they are typically green in colour, lacking the extra pigments that give many other representatives yellow, orange and brownish hues.   The technical definition of the Chromista is that they contain chlorophyll c as well as chlorophyll a, and Xanthophyceae fulfil this criterion.  However, many of the other Chromista also contain extra pigments (carotenoids and xanthophylls) which are responsible for these other colours.   Xanthophyceae do have carotenoids and xanthophylls, but not the types or quantities that alter appearance.   For a long time, as a result, they were classified with the green algae.   That had a certain superficial logic until people started focussing on aspects of the organisms that were less obvious.  The outcome is a more natural classification but problems when faced with a small greenish cell that doesn’t fit any descriptions in the “green algae” section of an identification guide.   If you’ve managed to reach the end of this post, you’ll have realised by now that taxonomists and phylogeneticists don’t like to make life too easy for the rest of us. 

Further reading

Adl., S., Bass, D., Lane, C.E., Lukeš, J. et al. (2018).  Revisions to the classification, nomenclature, and diversity of eukaryotes.  Journal of Eukaryotic Microbiology 66: 4-119.   


Derelle, R., López-García, P, Timpano, H. & Moreira, D. (2016).  A phylogenetic framework to study the diversity and evolution of the Stramenopoiles (= Heterokonts).  Molecular Biology and Evolution 33: 2890-2898.  https://doi.org/10.1093/molbev/msw168

Martin, W.F., Garg, S. & Verena, Z. (2015).  Endosymbiotic theories for eukaryotic origin.   Philosophical Transactions of the Royal Society of London Series B  3702014033020140330 http://doi.org/10.1098/rstb.2014.0330

Ruggiero, M.A., Gordon, D.P., Orrell, T.M., Bailly, N., Bourgoin, T., Brusca, R.T., Cavalier-Smith, T., Guiry, M.G., Kirk, P.M. (2015).  A higher level classification of all living organisms.  PLOSone DOI:10.1371/journal.pone.0119248


Links to posts describing the major groups of Chromista found in freshwaters (and, in one case, marine habitats).  Only the most recent posts are included, but these should contain links to older posts (you can also use the WordPress search engine to find older posts).

CryptistaThe underwater world of Ennerdale Water …
HaptophytaHow to win the Hilda Canter-Lund Prize (4)
AlveolataInvisible worlds at Malham Tarn
    BacillariophyceaeToo numerous to mention.  Most recently:
Every cloud has a silver lining …
Eyes wide open in Cassop’s muddy fringe …
    ChrysophyceaeThe little tarn of horrors …
Fade to grey …
A brief excursion to Norway
    PhaeophyceaeDepths of imagination …
Swimming in a sea of ignorance … 
    XanthophyceaeWhen a green alga is not necessarily a green alga …
The littoral ecology of Lough Down …

Elegy for Cassop …

I made the last of my monthly visits to Cassop Pond a couple of days ago, in conditions very different to those during my first visit this year.  Then, the snow lay deep and crisp and even.   Now we are trapped under a cycle of weather fronts that guarantees dank conditions unlikely to ever inspire a Christmas carol.  It was not actually raining as we made our way along the paths towards Cassop but the mist came down as we approached the pond, and we could barely see the far side from where we stood.    

Over the past year I’ve looked at the algae growing in different habitats around the edge of the pond.  I’ve focussed on the aquatic liverwort, Riccia fluitans, as this is one of the rarer plants in the pond and, therefore, the algae associated with it are less well known.  However, I’ve also taken time to look at the algae growing on reed stems, submerged rocks, fine sediments and on duckweed.   Unfortunately, I have not yet had time to complete my analyses of the most diverse group of algae, the diatoms: 2021 proved to be a busy year for routine diatom analyses for me, with over 400 samples logged, and many of these proving quite demanding.   The prospect of finding time to analyse yet more species-rich samples in my evenings and weekends was too much, and I’m well behind with analysing these.  I gave an overview of the situation early in the year in “The diatoms of Cassop Pond” back in June but an assessment of the remainder will have to wait a little longer. 

The other news from Cassop Vale is that it is no longer a National Nature Reserve (NNR).   Heather learned this after questioning the condition of the reserve with our local Natural England staff (see her post here).  NNR status refers to how a reserve is managed, and sits alongside the designation of a Site of Special Scientific Interest, which defines the conservation value itself.   The Natural England website regards 93% of the reserve to be in either favourable condition or recovering towards favourable condition; however, only one of the units has been assessed since 2014.  Losing its designation as a NNR does not affect the SSSI designation but parts of the SSSI now look to be in quite poor condtion.

That tells another story.  I’ve commented before on my fears over the impact of Brexit on the UK environment but there is another, more insidious, demon lurking in the wings.   The EU set a broad ambition for Member States, always after an extensive period of consultation and negotiation (the Brexiteers conveniently forgot that part). It then left individual Member States to put policies and practices in place to meet that ambition.   The real problem in the UK is not lack of ambition, but the lack of public funds.   From the global financial crisis of 2008 through George Osborne’s shameless use of “austerity” to justify cuts to public services to a series of elections where low taxes have been the dominant campaign message, the state apparatus necessary to administer environmental legislation has been consistently starved of funds.   Off the record, Environment Agency and Natural England staff will tell you bleak stories of how much they are expected to do with budgets a fraction of what they were in real terms a decade earlier. 

I don’t know the full story behind the loss of Cassop Vale’s NNR status but can’t help thinking that “issues around land ownership” is the type of challenge that a local Natural England team might have had time to tackle a decade ago, but which require more time to unravel that they currently have.   More to the point, landowners have a legal duty to maintain SSSIs, and Natural England have a statutory duty to help landowners in this task.  So, again, deregistration of the NNR does seem to suggest an avoidable breakdow.   But, as I have already said, our environmental and countryside stewards are struggling for reasons beyond the control of the Poor Bloody Infantry who have to work on the ground with landowners.   

Sorry for ending my posts for 2021 on such a gloomy note.   Cassop Vale has brought both of us a lot of pleasure this year: hopefully, you will have picked up this message from our blogs.   There has been a real joy in having a SSSI (if not an NNR) within walking distance of our home during lockdown, and I hope that we have provided a small but necessary counterweight to television natural history that tends to focus on the distant and exotic.   

Some other highlights from this week:

Wrote this whilst listening to:    Mike Oldfield’s Ommadawn   

Cultural highlights:   Jane Campion’s latest film The Power of the Dog, with Benedict Cumberbatch and Kirstan Dunst.   And the original film version of West Side Story.

Currently reading:  The Violins of Saint-Jacques by Patrick Leigh Fermor.

Culinary highlight:  Christmas dinner (on Boxing Day): roast goose, stuffing, roast potatoes, parsnips etc.

Every cloud has a silver lining …

We’ve had a very wet autumn this year.   This has manifested itself in epic spates (see: “The algae that got away …”) but also in the problems we’ve had getting out into the field.   Days when we planned to go out had to be scratched because river levels were too high, and rescheduled dates had to be squeezed in amongst other commitments.  Some of these rescheduled dates, too, turned out to be unsuitable, so the process repeated itself.  Eventually, we did get out into the field, but the clouds were low and there were no spectacular vistas of the Lake District to greet us as we arrived.  A river never looks its best in December, and I did not even bother to photograph the River Ehen during our trip last week.  The picture at the top of the post is from a year earlier, and then taken mainly to record a fallen tree that had led to a build-up of silt (see: “On the pleasures of untidiness …”).  

Last time I was here, the algae were scarce, following a period of very high flows.  This time, the algae were reasserting themselves.   We saw this in our measurements, but also with the naked eye: bare rocks – the larger ones especially – now bore a distinct brown coat of diatoms.   Looking closely, this brown coat resolved into myriad small brown tufts, typically a couple of millimetres across.   Under the microscope, these were revealed as tufts of Gomphonema cells, around which chains of Tabellaria flocculosa are entangled.    The Gomphonema cells are those that have perplexed me on previous occasions (see: “Diatoms and the space-time continuum …”) but they are widespread in this part of the River Ehen.   There were also filaments of the green alga Klebsormidium flaccidum, but this was present in smaller quantities than the diatoms.

A boulder in the River Ehen with an extensive growth of diatoms, December 2021.  The photograph at the top of the post shows the River Ehen at the point where the Coast-to-Coast footpath crosses.

Inevitably, we generalise about the condition of a river, as if we always deal with a homogeneous channel and uniform vegetation.  I hinted in the previous paragraph, for example, that the biomass here was high. However, the photograph of the diatom-rich boulder shows us that this is not the whole story.   All stones on a riverbed are equal but some are more equal than others.  The large boulder wears its cloak of brown proudly whilst the smaller cobbles, pebbles and gravel around it appear bare.  I say “appear” because there are algae present, but they are not obvious to the naked eye.  That seems to support the comment I made last month about stones rolling around: the smaller ones are more easily moved than the larger ones, hence have had less time to allow algae to grow back.   I suspect that even this boulder would have been moved by the very high flows in November, so we are looking at about six weeks of regrowth on this stone.

A colony of Gomphonema along with a single trapped cell of Tabellaria flocculosa from the boulder in the River Ehen pictured above. Scale bar: 20 micrometres (=1/50th of a millimetre).   
A chain of Tabellaria flocculosa from the same boulder in the River Ehen.  Scale bar: 20 micrometres (= 1/50th of a millimetre).

There is evidence, in fact, that some algae not just survive the scouring that accompanies spates, but actually thrive.   Several reasons have been suggested, but I suspect that, in this river, there is less grazing in winter, allowing algae numbers to bounce back more rapidly than in the summer.  I do see invertebrates – chironomid larvae in particular – throughout the winter but tiny as these are, they are still two or three magnitudes larger than the diatoms on which they feed, meaning that they will be more exposed to the scour that accompanied the spate than the diatoms.   My suspicion is that invertebrates are also hammered by the spates, but that their populations take longer to recover than those of the algae.

Like Noah and his family, to stretch a metaphor (a flood was involved), the algae which do manage to survive the deluge emerge to a world  in which they can multiply and be fruitful and increase in number.   The big difference in the Lake District, is that the bit with the promise that there will never again be a flood (Genesis 9:11).  I confidently predict at least a couple more before the winter is out.  


Peterson, C.G., Weibel, A.C., Grimm, N.B. & Fisher, S.G. (1994). Mechanisms of benthic algal recovery following spates: comparison of simulated and natural events.  Oecologia 98: 280-290.

Stevenson, R.J. (1990).  Benthic algal community dynamics in a stream during and after a spate.  Journal of the North American Benthological Society 9: 277-288.

Wrote this whilst listening to:    boygenius, supergroup composed of Phoebe Bridgers, Julienne Baker and Lucy Dacus.  Their eponymous EP’s cover is a clever pastiche of Crosby, Stills and Nash’s debut album, which is a fine way of grabbing my attention.   

Cultural highlights:   Dave’s We’re All Alone In This Together

Currently reading:  Just finished Does Santa Exist? By Eric Kaplan.  The answer seems to be “no”, if you use logical reasoning, but “yes” if you draw on the Kabbala.  

Culinary highlight:  Family meal (daughter’s 30th birthday) at VorV, excellent vegetarian restaurant in Sheffield.  .

How to make a mountain …

Back in September, I wrote a post called “Building landscapes …” in which I explained how cyanobacteria acted as “ecosystem engineers”, helping to build impressive structures in the hills around Malham Tarn.   This post picks up that idea and takes it even further, suggesting that without cyanobacteria mountains themselves may not exist.  

That’s a bold claim so let’s take it slowly. Mountains exist because the rocks from which they are made move around, sometimes contorting, sometimes piling up against one another.   John Purnell and Conor Brolly of the University Aberdeen suggest that the friction generated when rocks came into contact would have been so great that any movement would have been impossible.   For the type of movement that would have produced the mountains that we see around us now there would need to have been a lubricant of some type involved.   

Their theory is that, about two billion years ago, the quantity of cyanobacteria in the oceans increased dramatically.  One consequence of this was the creation of the oxygen-rich atmosphere that we now take for granted but another was that dead cyanobacteria accumulated on the ocean beds and formed, over time, sediments that were much more carbon-rich than before.    When subjected to heat and pressure, this carbon was transformed into graphite, a form of carbon that is widely-used in the modern age as a dry lubricant.  

Rocks, in other words, were more likely to slide over one another and pile up as a result of layers of sedimentary rocks with a high algal content which could act as a lubricant, leading to the formation of mountains.   Purnell and Brolly offer several examples, including the Himalayas (whose foothills near Shimla are shown in the photograph at the top of the post) and the mountains of northern China where graphite-rich sediments facilitated the movement of rocks that led to their formation.   As Purnell and Brolly point out, the world would be a much flatter place were it not for cyanobacteria.

The Great Wall of China snaking across mountains north of Beijing.  The photo at the top of the post shows the foothills of the Himalayas near Shimla.


Parnell, J. & Brolly, C. (2021).  Increased biomass and carbon burial 2 billion years ago triggered mountain building.  Nature Communications: Earth and Environment 2:238

Wrote this whilst listening to:    Neil Young and Crazy Horse’s new album Barn.

Cultural highlights:   Rewatched the 1986 film Clockwise, starring John Cleese.  Very dated but still enjoyable. The central premise depends entirely on the principal characters not having mobile phones.

Currently reading:   Does Santa Exist? By Eric Kaplan.   Please don’t spoil the ending for me.

Culinary highlight:  Lebanese meal at The Bake in Newcastle

Cassop Pond in November

My latest trip to Cassop Vale was, by some margin, also the shortest.   The very worst of Storm Arwen had blown through overnight but the winds were still considerable, and I had to steer the car around trees that had fallen across the roads.   I parked in Cassop village, then darted down the hill to the pond amidst the sleet.   All I did when I got to the edge of the pond was dip my hand in to grab some of the flocs of Riccia fluitans, and stuff this into a bottle, before dashing back up the hill to the warmth of the car.   Don’t judge me: the thermometer was hovering around zero and the considerable wind chill made it feel much colder.   You would have done the same.

Flocs of Riccia fluitans overlain by Lemna minor at the margins of Cassop Pond, November 2021.

These flocs of Riccia fluitans have been present around the edge of the pond all year, typically floating just under the surface.  I’ve written about them on several occasions already (most recently in “Microscopic mysteries in Cassop Pond …”).  The main difference apparent with the naked eye today was that there was more duckweed on top of them than on previous visits. This, however, could be due to nothing more than wind action on the surface of the pond.   Duckweeds float at the water surface rather than just underneath, as Riccia fluitans doe, so are more susceptible to be moved around by the wind.   

Under the microscope, the main difference was that the fronds seem to have lost some of their vitality.  There are more dead or dying cells, it seems, and these impart a brownish, rather than green, hue to many of the fronds.  In addition, the Nostoc that had smothered the Riccia fronds during the summer had disappeared, leaving just a few cells of Epithemia as epiphytes.  They are quite hard to see against the brown backdrop of the Riccia fronds, so I have arrowed them in the photograph below.   One way or another, nitrogen-fixing organisms have been an ever-present in Cassop Pond over the course of the year, which must be telling us something about the pond’s supply of nutrients. 

Microscopic view of a frond of Riccia fluitans from Cassop Pond, November 2021.  The position of Epithemia cells are indicated by arrows.  Scale bar: 20 micrometres (= 1/50th of a millimetre).

We recently bought a copy of Gordon Graham’s Flora and Vegetation of County Durham, first published in 1988 when we were too impoverished to afford a copy.   I remember Gordon Graham expressing great scepticism of my first report of Riccia fluitans from Cassop, but I must have convinced him to look because he records it in his book as “in abundance” here, along with just two other records from the county.   This is about as far north in the country as you will find this species.  Quite why it flourishes here but in so few other places, I do not know.  Just ahead of Riccia fluitans in the flora is Ricciocarpos natans, the only other aquatic liverwort in the UK.   Again, there are just a few records in the county, one from Cassop Pond and the others from ponds nearby.   I remember Ricciocarpos natans being quite abundant in the pond in the past but I have not seen it this year.   The Atlas of British and Irish Bryophytes mentions that there has been a decline in in R. natans which began in the 1950s and has continued to the present day, with a brief resurgence in the 1980s (when I first found it here).  That gives me confidence that its absence from Cassop is not simply due to my overlooking it, but it does not really offer any cogent explanation.  A species at the northern limit of its range and said to favour eutrophic water would seem to be encouraged, rather than threatened, by recent changes across the country.

Noticing an absence is harder than recording a presence.  It needs a long-term perspective, and we will only ever have the personal memory that is required for a few locations.   In other cases, we may have the benefit of other people’s records (see Heather’s parallel account of the poor condition of the terrestrial flora at Cassop, but having that personal link over time adds a personal, poignant element to the experience.   There does not seem to be an obvious human-induced cause of its decline nationwide, so I am not led to reflections of the follies of mankind.  But it does reinforce in me an awareness of change: that things that were are no longer.  Not knowing why only adds further layers of reflection.   

Enough for now. I am getting maudlin when there is no real need.   Eleven months into my investigations into Cassop Pond have reignited memories that have pulled me 35 years back into the past.  One month left and my year of visits will be complete.   Then I will need to step back and see if I can put all the pieces of the jigsaw together again. 

Wrote this whilst listening to:    Christmas in Puebla, 17th century Christmas music from Siglo de Ora.

Cultural highlights:   Petit Maman, latest film from Céline Sciamma, best known for Portrait of a Lady on Fire.   Wonderful film, well worth seeking out.

Currently reading:  The Thursday Murder Club by Richard Osman.

Culinary highlight:  A chocolate and almond cake from Claudia Roden’s The Food of Spain.

The algae that got away …

Unusually, for a blog that is mostly about algae, this post is about the absence of algae.  Not the complete absence of algae; that would be extremely unlikely but certainly the absence of visible algae from locations where, at this time of year, they are usually either conspicuous from the bankside or apparent as soon as you get close to the stones on which they usually thrive.  

We are now well into the season of unpredictable weather.  Most of the rainfall, and subsequent increases in flow are an inconvenience when trying to plan fieldwork (see “On fieldwork”), but have only limited effects on the river itself.   This is particularly the case for the River Ehen where the lake just upstream from our sampling sites acts as a huge buffer that damps down the impact of any changes.  A couple of weeks ago, however, there was heavy rain, leading to very high river levels and some local flooding.    I had watched this via the weather forecast and on the hydrographs, but this was my first opportunity to see what this had actually done to the river.

River levels in the River Ehen in October and November 2021 (from www.riverlevels.co.uk).  The horizontal red line shows the maximum river levels that are typically encountered and the two arrows indicate the dates of our two most recent visits.  The photo at the top of the post shows Croasdale Beck.  

November is usually the month when the algae in the river are at their most prolific, which may come as a surprise as this is also the time of year when the trees have lost most of their foliage.  The reasons are still not entirely clear, but it is likely that the invertebrates that would normally graze the algae have finished their lifecycles and hunkered down for the winter whilst the algae are benefiting from the lake-warmed water.   On this visit, however, the stones on the river bed had only a slight covering of algae, certainly not apparent with the naked eye. 

Memories can be deceptive, however.   When I scanned back through photographs of the river bed, the river bed rarely looked particularly algae-rich. That’s partly because a lot of the algae that are present are diatoms, whose yellow-brown colouration blends in with their rock substrata.   Three of the six years whose photos I checked had visible green growths, but 2021 had unusually low concentrations of all algae, not just greens.   However, that needed a measurement rather than an observation to confirm.   2019 was clearly an aberration in terms of the extreme quantities that we found, for as yet unknown reasons, but the photos show that algae are not always obvious here, possibly because this particular site has a lot of small, easily-rolled pebbles rather than cobbles and boulders, and the algae are easily scoured away.

Photos of the bed of the River Ehen just downstream from the outflow of Ennerdale Water, photographed in October or November over six years.

Compare the images in this plate with those I presented in “The Wrong Kind of Green?”   My point in that post was to show how the quantities of visible algae varied over the course of a year in a stream.  The photographs of the River Ehen’s riverbed in this post show how much variation there is in the same month between years.  Now try to rank these photos in terms of the quantity of algae and compare your findings with the graph below, which shows the quantities of algae that we measured.  Whilst 2019 clearly has the most algae by both reckonings, 2018 comes second with the measurements but not the photos, whereas 2016 probably comes second from photos.   So there is rough, but far from perfect, agreement between the two approaches.   We’ve also noticed, over the years, that green algae tend to be patchier than the other groups.  You can see this with the photos, but it also means that our measurements of green algae are more variable than those of other groups.   

Algal biomass (as chlorophyll concentration) at the same location in the River Ehen in October or November since 2016. 

Something else that we noticed was that some of the stones that presented a very “clean” surface had conspicuously darker and slimier undersurfaces.   These must have been stones that were rolled by the storm and we wonder if this creates miniature “compost heaps” under the stones as the light-deprived algae slowly wither and are decomposed by the microorganisms in the stream.   That, in turn, would suck some of the oxygen out of the surface sediments, perhaps imperilling the young mussels that need a steady supply of oxygen-rich water flowing through the sediments in order to survive. 

Two views of the same cobble from the River Ehen in November 2021: the upper surface on the left, almost devoid of algae, and the lower surface on the right which had more algae and which was, we presume, facing upwards until the stone was rolled during the recent high flows.  

A few kilometres away, Croasdale Beck, the River Ehen’s unruly sibling, also shows the effects of the rain.  Just above the site where we sample the stream has cut a wide meander into the bank, through which the channel flows through unconsolidated sediments.   At about this time of year in 2017 I wrote about how a storm just before I visited had changed the path of the water through this channel (see “What a difference a storm makes”) and today we noticed that the channel had shifted back to where it had been before the 2017 flood (photo at the top of the post).  

That was due to Storm Ophelia and, as I write, Storm Arwen is battering the countryside.   I will not know what effect this has on the River Ehen until I get there for my next round of field work but – here’s the rub – it might also mean that fieldwork plans have to be postponed.  Far more than any other aquatic ecosystems, streams and rivers have an intimate and immediate connection with atmospheric processes.  Watching streams and rivers closely makes you aware of how rainfall can be converted into raw physical power.  I can feel it pushing against my waders as I collect samples, even in a small stream such as Croasdale Beck.   So I should not be surprised that it also has the capacity to affect the plants and animals that live in and around the channel.   The problem is that the famous unpredictability of the British weather means that there is also inherent unpredictability in the ecology of our streams.  Just as the British love talking about the weather, so a few of us will always finding something unexpected to talk about when we visit a stream …

Wrote this whilst listening to:    Too Busy Thinking About My Baby and other Motown classics by Marvin Gaye.  And the extremely atmospheric soundtrack to Spencer by Jonny Greenwood.

Cultural highlights:  Spencer, the new film about Princess Diana.   Closer in mood to The Shining than The Crown, which is just fine by me.

Currently reading:  Dancing with Bees by Brigit Strawbridge Howard.

Culinary highlight:  My mainly-vegetarian daughter allows herself one steak per year and I joined her to cook and devour a medium-rare fillet steak from a local organic farm, accompanied by a homemade peppercorn sauce.

The bathroom botanist …

Many of my posts focus on the diversity and beauty of algae that inhabit our most remote and pristine habitats.  This one is not one of them.   It is about a relatively ubiquitous and rather prosaic alga; so prosaic, in fact, that I’ve been looking at it for months without really noticing it, or thinking that it might be the subject of a post.  The habitat for this particular alga is my bathroom or, to be more particular, a mist sprayer that we use to moisten the leaves of some orchids growing on the window ledge.   Over time, the base of the clear plastic bottle of this sprayer has grown a distinctly green tinge and the time arrived, this weekend, to have a look at this under a microscope.    

Part of the reason that I had ignored it for so long is because this type of green growth is a common feature in any plastic bottles left full of water in warm, well-lit rooms.  I used to see it develop in wash bottles when I worked in laboratories: a clear sign that the pure water we thought we were using may not be as pure as we thought.   And we had a name for the alga responsible too: Stichococcus bacillaris.   Under the microscope it could form short filaments but, more commonly, we saw isolated rod-shaped cells each with a single chloroplast wrapped around the inside of the cell wall

This has been described as “one of the most common and widely distributed algae in the British Isles” due to its ubiquity.   It is probably more accurate to say that it is one of the most common and widely used names, as there is considerable genetic diversity within the small pill-shaped algae.   A couple of years ago I wrote about “little round green things” – the phycological equivalent of the ornithologist’s “little brown jobs” and similar problems apply here too: there are simply too few morphological characters visible with the light microscope to allow the human eye to sort these reliably into coherent groupings.  

Actually, when you take characteristics that are only apparent when you study cultures over many generations, and when the molecular genetics of these strains is also considered,  eight distinct genera have been recognised in place of the catchall Stichococcus.   A very rough analogy is to think of the herbs we use when cooking, many of which belong to the family Lamiaceae (basil, sage, oregano, majoram, mint etc).   When I was a student we used to buy a packet of “Italian seasoning”, which was mostly composed of these.  Calling all small rod-shaped green algae Stichococcus is roughly the same as chucking a handful of Italian seasoning into some mince and calling the product Bolognese sauce.   The modern view of this alga is not of a single packet of “Italian seasoning”  but of a row of neatly-labelled jars on a shelf, each with a distinctive identity.   We’re not quite there with “Stichococcus” yet: quite how the ecologies of these eight genera of rod-shaped algae differ is still not clear, nor do we know how anyone without access to a metabarcoding facility will make use of this new knowledge.  In this respect, we are still no more sophisticated than the student cook who liberally sprinkles any herbs he can find into a bastardised spag bol.  But at least we’ve made a start.

“Stichococcus bacillaris” from a plastic bottle in my bathroom, November 2021.   Scale bar: 20 micrometres (= 1/50th of a millimetre).  


Pröschold, T. & Darienko, T. (2020).  The green puzzle Stichococcus (Trebouxiaceae, Chlorophyta): new generic and species concept among this widely-distributed genus.  Phytotaxa 441: 113-142.

Some other highlights from this week:

Wrote this whilst listening to:    Wakafrica by the late Cameroonian musician Manu Dijango

Cultural highlights:  Spent part of last week suffering from a virus that drained my energy.  The highlight of several films watched in my comatose state was 24 Hour Party People, about the 1980s Manchester music scene starring Steve Coogan.   Also watched Edgar Wright’s new film Last Night in Soho.   

Currently reading:  The Lie of the Land by Amanda Craig.

Culinary highlight:  Ginger parkin and a Sicilian pasta sauce made from sardines.

Eyes wide open in Cassop’s muddy fringes …

The previous post mused on the distinction between “what I see” and “what I look for”.  They seem like two ways of saying the same thing, but actually hint at an awkward truth: ecology fieldwork is not always the objective process we like to pretend that it is.  My most recent trips to Cassop Pond have pushed this idea: for eight months I looked for algae amongst the Riccia fluitans flocs, on the rush stems and on duckweed.  There are other habitats that I could explore, but I chose not to.  What I looked for shaped what I saw.   In September and October I have redressed this by looking at a habitat relatively unfamiliar to me: the surface of the mud in the shallows at the edge of the pond.

If I used a pipette to hoover up some of the brown oozy mud and squirted that onto a microscope slide, I would probably see lots of fine sediment particles, plenty of dead and decaying organic matter but very few algae.   We know that they are there, and that they are often abundant, but they are hidden amongst all this other crud.   Instead, microscopists have devised two ways of separating the algae from the mud and I tried both of these on some of the Cassop mud which I scooped up with a plastic spoon and popped into a plastic bottle

The first of these involved letting the mud settle in the bottle, then pouring off as much of the overlying water as possible.  I then poured some of the mud that remained into a Petri dish and carefully lowered a coverslip onto the mud surface.   I left this overnight hoping that those algae capable of movement would glide up to the surface of the mud until they encountered the coverslip.   In the morning, with Andrew Marr grilling Rishi Sunak about the impending budget in the background, I carefully lifted the coverslip from the mud with a pair of forceps and dropped it onto a drop of water on a microscope slide.  

At the same time as I removed the cover slip, I placed a piece of lens tissue gently onto the mud surface and left it there for the rest of the day.  In the evening, I lifted it up and cut out a 5 x 5 mm square from the centre and placed this in a drop of water on a slide.  I then teased the fibres apart with a pair of dissecting needles before lowering a cover slip on top.   The idea behind both the coverslip and lens tissue methods is that muddy surfaces favour motile algae and that these will move up from the mud and onto the coverslip or tissue. 

Methods for sampling algae from fine sediments: a. coverslip placed on mud surface; b. lens tissue freshly placed on mud surface; c. lens tissue after lying on mud surface overnight; d. fragment of lens tissue (approx. 5 x 5 mm) placed in a drop of water on a slide then teased out with dissecting needles.

Both approaches yielded similar species, with a motile Navicula (possibly N. trivialis) most abundant, along with a small Trachelomonas (see “Microscopic mysteries in Cassop Pond).  Second most abundant by number of cells was Cymatopleura solea although the larger size of the cells, relative to those of N. cf. trivialis, might well mean that these contributed more to the total algal biomass.  Cells of Cymatopleura solea are shaped a little like the body of a violin when seen from above, and have a raphe around the margins that enables them to glide around.   Occasionally, whilst watching them move, one would slip onto its side revealing undulations on the surface that are not easily seen when looking from above.  I tried to describe the shape of C. solea to a class some years ago and, as I was grasping for appropriate adjectives, one student suggested “voluptuous”.  I have found C. solea in other samples from Cassop this year, but not in such numbers as from the mud surface.

Algae from the mud surface in Cassop Pond, October 2021.   a, b, valve and girdle views of a cell of Navicula cf. trivialis; c., d. valve and girdle views of a smaller Navicula; e. girdle view of Pinnularia sp.; f. valve view of Neidium cf. ampliatum; g., h. Synura petersenii.   Scale bar: 10 micrometres (= 1/100thof a millimetre).  

Alongside these were smaller numbers of Pinnularia, Nitzschia and a large Neidium (possibly N. ampliatum).   Bustling around, too, were some colonies of Synura petersenii, a flagellated chrysophyte that we have not met before in this blog.   There were, in addition, a few filaments of Spirogyra which has no means of moving so which must have moved onto the lens tissue by another means, perhaps through capillary action.    That brings me back to my initial musing about the difference between “what I see” and “what I look for”.   Using coverslips and lens tissue means that I see a different assemblage of algae to those that I find using my regular collection methods.  But, at the same time, I’m seeing the edges of Cassop Pond through a different filter.   These techniques are used because the assumption is that the algae that live on fine muds need to be able to move in order to survive but we test that assumption using a method biased to those algae that can move.  Staurosirella lapponica is a diatom associated with soft sediments that is incapable of movement, so any records from a coverslip or lens tissue approach would be “by-catch” and not give a true indication of its contribution to primary productivity.   There’s no perfect way of looking at worlds that we cannot ordinarily see.  But knowing that there is no perfect way of seeing does, at least, encourage us to keep on looking.

Cymatopleura solea from surface mud in Cassop Pond, October 2021.   a., b. valve views; c.,d. girdle views; b. and c. are two views of the same cell which obligingly rolled over whilst I was watching.  Scale bar: 10 micrometres (= 1/100th of a millimetre).  


Eaton, J.W. & Moss, B. (1966).  The estimation of numbers and pigment content in epipelic algal populations.  Limnology and Oceanography 11: 584-595. 

Moss, B. & Round, F.E. (1967).  Observations on standing crops of epipelic and episamnic algal communities in Shear Water, Wilts.   British Phycological Bulletin 3: 241-248.  

Yang, H., Flower, R.J. & Battarbee, R.W. (2010).  An improved coverslip method for investigating epipelic diatoms.  European Journal of Phycology 45: 191-199. 

Some other highlights from this week:

Wrote this whilst listening to:    New albums from War on Drugs (“I Don’t Live Here Anymore”) and local boy Sam Fender (“Seventeen Going Under”)

Cultural highlights:  Pedro Almodóvar’s recent short film The Human Voice, starring Tilda Swinton.

Currently reading:  American Dirt by Jeanine Cummins.

Culinary highlight:  Homemade ribollita.  

On fieldwork …

I could – maybe should – define fieldwork as the process by which a researcher engages with natural systems in a completely objective, dispassionate manner, collecting the data from which inferences will be derived.   But it isn’t quite that easy.  Fieldwork is also the point at which nature interacts with the researcher: sunshine and blue skies one day, howling winds and horizontal rain another.  Take a look at my field notebook, largely written with wet hands whilst standing in the middle of a river: it isn’t always that easy for me to interpret my scrawlings when I transcribe them a day later – let alone for anyone else to understand what I was observing.   So, rather than writing about fieldwork in terms of my subject matter, I thought I should also write about how it affects me.   

Pages from my field notebook; the transcribed version, along with additional notes following microscopic examination of samples, behind.   The picture at the top of the post shows leaves accumulating at the edge of the River Irt, October 2021.

Sue Stuart-Smith, a psychiatrist and psychotherapist who is also a keen gardener, wrote: “what we think is challenged by what we see.  But what we see is also shaped by what we think”.   And the garden (in her case) and the streams and lakes I visit on fieldwork (in mine) are the points where our inner and outer worlds collide – where “me” and “not me” overlap.   The need to collect data in as consistent a manner as possible is paramount but taking a task-focussed approach, and repeating it over and over again is never a purely mechanical process.  When in the field, I immerse ourselves into my work and a contemplative, meditative state can arise in which I can be open to new ideas about how ecosystems work.   Because I am working at a fine scale, I should be in a position to notice smaller differences than would be the case if I was simply passing through a landscape.   Last month, for example, I noticed small green gelatinous blobs on stone surfaces in the River Ehen that turned out to be colonies of Ophyridium versitale, a protist which has endosymbiotic algal cells.  They were not there – or, at least, I had not noticed them – when I was here a month ago, or when I returned a month later.   I can make that later statement with some confidence because I went back with eyes conditioned in a way that they had not been in September.   I’m not so sure that I had not simply missed them on earlier visits, but I have been to the River Ehen so often that I am sure I would have found them if they were always present.

Ophyridium versatile from the River Ehen, September 2021.  Scale bar: 50 micrometres (= 1/20th of a millimetre)

That type of philosophical speculation is all very well, but last week’s questions of how fieldwork affects the fieldworker were more pragmatic: would I even be able to get into to the streams I visit safely?   For many ecologists, rain is unfortunate but not a reason to cancel a fieldtrip.  For those of us who work in rivers, rainfall before we go out can make our work dangerous or impossible.   Even slightly elevated flow can mean that more of my attention is focussed on keeping my footing on the river bed rather than on collecting the observations that I need.   

A fortnight or so before a field trip I start to watch the long-range weather forecast which predicted rain in west Cumbria.  A week or so before I went out, I started to watch the flow gauge and weather forecast with concern.   We were due out on the 12 October, and I had made a hotel reservation for the night before.  But a week before our trip, there was a spate, followed by three days of light rain and drizzle.  Then it was dry, and the flow gauge started falling.  But would it have fallen far enough by Tuesday?   I know from experience that a flow of less than 200 MLD (megalitres per day) in the River Ehen is ideal and, extrapolating from Monday’s measurements suggested that this would just about be achieved by the time we arrived on Tuesday.   So I packed the car on Monday afternoon and headed off.

Readings from the flow gauge at Bleach Green on the River Ehen during early October 2021.  The arrow indicates the point when our fieldwork was planned.

Autumn is late this year, and most of the trees are still green, with just a few starting to turn yellow and brown.   From the top of the Pennines, my first views of the Lake District are of low cloud obscuring the peaks, so my pessimism about our prospects return.   But the rivers are low enough for us to work in, and the clouds lift as the day progresses.  By late afternoon we can even feel the warmth of the sun on our skin.   Though the trees still seem to be holding their leaves, there are plenty drifting down with the current, and flocs of green, orange and brown leaves are caught amongst branches and rocks at the margins.  They are a reminder that, despite our extreme close-up view of the algae in these ecosystems, much of the energy that sustains the rivers comes not from organisms that live in the river but from terrestrial vegetation around the river channel.    The danger of specialising on one group of tiny organisms is that it is easy to lose the big picture.   We all need to lift our heads up once in a while to put our observations into context.  

Low Wood, Wasdale, showing its autumn colours as we walked to our field site on the River Irt.


Stuart-Smith, S. (2021).  The Well-gardened Mind.  Rediscovering Nature in the Modern World.  Harper Collins, London.

Some other highlights from this week:

Wrote this whilst listening to:    The Chieftains, following the death of Paddy Maloney.  Brought back memories of seeing them at the Empire Theatre, Sunderland, many years ago.   And Fully Qualified Survivorby Michael Chapman, also recently deceased, bringing back memories of Green Man in 2014.

Cultural highlights:  first episode of a new season of Shetland on BBC1, which I spent location-spotting, particularly for the scenes shot in Lerwick.

Currently reading:  How To Kill Your Family by Bella Mackie.   A novel, not a handbook.

Culinary highlight:  pizza at Rudy’s in Manchester.  

Evolution’s “granny flats” …

I’ve written quite a lot about the cyanobacterium Stigonema in Lake District lakes and streams over the past couple of years (see: “Ever changing worlds …” and “Tales from the splash zone …”).   These posts do not, however, tell the whole story about this genus.  George West and Felix Fritsch, for example, wrote in 1927 that species of this genus “occur principally on damp or wet rocks” whilst Allan Pentecost’s habitat notes were “forming a thin turf … over soils, rocks and trees”.   Although “Tales from the splash zone …” did fit West and Fritsch’s “damp or wet rocks” criterion, much of my focus has been on Stigonema that was fully-submerged in the River Liza.  So I am pleased to redress the balance in this post, writing about a Stigonema growing on the trunk of an oak tree in a Welsh forest.  

The discovery was made by Chris Carter during a British Bryological Society field excursion to Coed Ganillwyrd National Nature Reserve just north of Dolgellau in west Wales.  This is considered to be one of the riches sites in western Europe for mosses and liverworts.   However, there were also jelly-like growths smothering some of the smaller liverworts present on tree trunks which intrigued Chris.   These, it turned out, were mostly due to a small unicellular green alga called Coccomyxa confluens, which produces copious mucilage around its cells.  Within this mucilage, however, there were filaments of Stigonema minutum, similar in appearance to the S. mamillosum I’ve written about before, but, as the name suggests, smaller.   

Curiously, the account for Stigonema minutum in the Freshwater Algal Flora of Britain and Ireland records “bark of oak trees near waterfall, North Wales (A. Pentecost, personal communication)” which made Chris and I wonder if Allan had been hunting in the same locations at some point in the not-so-distant past.  

Stigonema minutum growing within mucilage produced by Coccomyxa confluens at Coed Ganllwyd NNR in Gwynedd, Wales (photo: Chris Carter).   The photo at the top of the post shows a waterfall in Coed Ganllwyd.  The tree with these algal growths overhung this gorge (photo: Calum McLennan).

The tree trunk fits the habitat description given by West, Fritsch and Allan Pentecost: the proximity of the waterfall and the shaded forest will have ensured a constantly humid atmosphere, and little risk of the bark drying out completely.   The mucilage produced by the Coccomyxa would also have provided an additional layer of protection from desiccation.  This protection, however, will come at a cost, as both the forest canopy and the Coccomyxa will absorb much of the sunlight.   Nonetheless, as we’ve seen before, many cyanobacteria are adept at playing a long game, and are content to grow slowly in the nooks and crannies where other organisms dare not tread.  

Stigonema is about as sophisticated as a cyanobacterium can be: it has filaments that are several cells thick with true branches as well as a thick sheath well-supplied with natural sunscreen compounds, and is capable of nitrogen fixation.   Together, these decrease its reliance on water to the extent that we can find it growing in damp terrestrial habitats such as a woodland in west Wales.   Yet, somehow, in the far, far distant past, it was outpaced in the race to conquer land by other groups of primitive plants.   There are good reasons for this: cyanobacteria such as Stigonema are prokaryotes, without distinct organelles within their cells.   That places constraints on the cell, because processes such as photosynthesis (which builds up simple sugars) and respiration (which breaks the same sugars down to release energy) can be compartmentalised and made more efficient.  Even simple plants, such as Coed Ganllwyd’s mosses and liverworts, have an advantage over Stigonema in this respect.  Over time, then, fortunes have been reversed and cyanobacteria, the pioneering photosynthetic organisms, now live in the shadow (literally) of their evolutionary descendants.   Which means, I guess, that damp bark of an oak tree in west Wales is the evolutionary equivalent of a granny flat. 

A close up of filaments and branches of Stigonema minutum and Coccomyxa confluens from Coed Ganllwyd NNR in Gwynedd, Wales (photo: Chris Carter).


Pentecost, A. (1984).  Introduction to Freshwater Algae.  Richmond Publishing Company, Richmond.

Velai, T. & Vida, T. (1999).  The origin of eukaryotes: the difference between prokaryotic and eukaryotic cells. Proceedings of the Royal Society of London Series B 266: 1571-1577.

West, G.S. & Fritsch, F.E. (1927).  A Treatise on British Freshwater Algae.   Cambridge University Press, Cambridge.

Some other highlights from this week:

Wrote this whilst listening to:    Nigerian highlife (Igede by Celestine Ukwu and His Philosophers International) and juju music (various old King Sunny Ade tracks) and, from Gabon, Hilarion Nguema.   And African-inflected jazz from Vula Viel.

Cultural highlights:   Options limited by a bad cold.  Watched Austin Powers: International Man of Mystery but not claiming it to be in any sense a cultural highlight.

Currently reading:  English Pastoral by James Rebank, for a second time.

Culinary highlight:  sole meurnière with fresh samphire.