Submerged soap opera …

One of the larger algae in our plankton haul from Windermere was a strange-looking organism whose cell was extended into three horn-like protuberances.   It was a delicate beast that did not enjoy the trip back home and, as a result, the chloroplast was not in good condition.  A relative, found in Kelly Hall Tarn, was photographed much sooner after collection and its yellow-brown chloroplast was still healthy.  I’ve never had the opportunity to write about them before, but I am in the right place now.  A lot of what we know about their ecology in lakes was worked out by scientists working at the Freshwater Biological Association, where we were based.

That yellow-brown colour should give us some hints about how it is related to other algae.   Ceratium is a genus of dinoflagellates, members of the Chromista (see “Unlikely bedfellows …”).   Whilst the Chromista as a group are thought to have evolved from a primitive red alga being engulfed by a protozoan, which then enslaved, rather than digested, its lunch (see “Origin story …”), the dinoflagellates arose when another protozoan engulfed a Chromista cell and decided that it (or, at least, its chloroplast), too, was more useful alive than dead.   These predatory instincts have still not deserted the dinoflagellates, as many still switch between harvesting sunlight and engulfing microscopic particles to fuel their lifestyles (so-called “mixotrophy”). 

A cell of Ceratium hirundinella from Windermere, June 2022.  Scale bar: 50 micrometres (= 1/20th of a millimetre).  The photograph at the top shows the south basin of Windermere looking north from the YMCA jetty.

The photograph of a Ceratium hirundinella cell also shows clearly the two-part pellicle, composed of a number of plates.  Whereas the cell wall in diatoms is composed of silica, the dinoflagellate equivalent is made of cellulose, as is the case for higher plants.   Both the photographs also show a transverse groove within which a flagellum undulates, spinning the cell around.  A second flagellum propels the cell forward.   

In the Lake District, Ceratium hirundinella is a species of the summer months, particularly in nutrient-rich lakes.   It thrives when the surface layers are warmed by the sun sufficiently for a thermocline to develop, above which convection currents circulate the water, preventing cells sinking to the dark, cold waters below.   It uses its flagella to move up and down the water column, moving down at night to a depth of six or seven metres depth then rising again in the morning.   It never moves right to the surface, preferring to stay about three to four metres below, where the sunlight is about ten percent of its strength at the surface.   

In houseplant terms, Ceratium is one that you are not going to leave on a brightly lit windowsill; rather, it is one to move back to where it does not receive too much bright sunlight.  However, its propensity for shade only tells us part of its story.   Peering through our microscopes, it was clear that the most abundant organisms in Windermere last week were nitrogen-fixing cyanobacteria – Anabaena lemmermannii and Aphanizmenon flos-aquae.   If nitrogen is in such short supply that these have a competitive advantage, how does C. hirundinella survive?    The answer is that it is able not just to behave like a plant, but also resorts to its animal tendencies, feeding on smaller phytoplankton cells.  We saw this for a chrysophyte in “Little tarn of horrors …” and a similar phenomenon has been described for dinoflagellates including C. hirundinella.   To push our houseplant analogy a little further, Ceratium is behaving like a Venus flytrap, obtaining nutrition supplements from other organisms rather than relying on what it can obtain from its immediate environment.   

A cell of Ceratium carolinianum from Kelly Hall Tarn, Cumbria, June 2022.  No measurements made at the time, but size range from literature is: 73 – 105 micrometres wide and 125 – 213 micrometres long.

I did not see many cells of Ceratium hirundinella in our net sample from Windermere but this should not be a great surprise, given what I have just written.   Our net haul came from just below the surface, which C. hirundinella actively avoids.   I wrote about some of the limitations of net samples in the previous post and mentioned that it was not an approach that a phytoplankton ecologist would employ routinely.   A better approach is to take a length of polypropylene hose, tie a weight onto one end and lower this into the water.   If you then hold one end at the surface whilst pulling a rope attached to the bottom end, you have a sample that integrates all the vertical changes and gives a better representation of this very dynamic community.   The appropriate length of hose will depend on the depth of the thermocline, with five metres used for phytoplankton studies in the Lake District. 

Peer at a drop of a sample, whether collected by plastic tube or net, through a microscope and you might think you are looking at a random assortment of cells.   In truth, you are looking at a microscopic soap opera, with cells moving on and off stage and different levels of co-operation and conflict.  Ceratium hirundinella plays out its scenes alongside the Vorticella/Anabaena association that we met in the previous post.   And, like all good soap operas, there are many more stories still left to tell …


Callieri, C., Caravati, E., Morabito, G., & Oggioni, A. (2006). The unicellular freshwater cyanobacterium Synechococcus and mixotrophic flagellates: evidence for a functional association in an oligotrophic, subalpine lake. Freshwater Biology 51: 263-273.

Chapman, D. V., Dodge, J. D., & Heaney, S. I. (1985). Seasonal and diet changes in ultrastructure in the dinoflagellate Ceratium hirundinellaJournal of Plankton Research 7: 263-278.

Heaney, S. I., & Furnass, T. I. (1980). Laboratory models of diel vertical migration in the dinoflagellate Ceratium hirundinella. Freshwater Biology 10: 163-170.

Hehenberger, E., Gast, R. J., & Keeling, P. J. (2019). A kleptoplastidic dinoflagellate and the tipping point between transient and fully integrated plastid endosymbiosis. Proceedings of the National Academy of Sciences 116: 17934-17942.

Yoon, H. S., Hackett, J. D., & Bhattacharya, D. (2002). A single origin of the peridinin-and fucoxanthin-containing plastids in dinoflagellates through tertiary endosymbiosis. Proceedings of the National Academy of Sciences 99: 11724-11729.

Some other highlights from this week:

Wrote this whilst listening to: local lad Sam Fender’s Pyramid Stage set at Glastonbury

Currently reading: Just finishing Sally Rooney’s Beautiful World, Where Are You.   Also reading The Power of Ideas, a collection of lectures and essays by the late Jonathan Sachs, former Chief Rabbi.

Cultural highlight:   A talk in York by William Dalrymple on The Anarchists, his recent history of the East Indian Company.

Culinary highlight:  cold celery soup with apple and walnut croutons – a Caesar salad in liquid form.

A hitchhiker’s guide to phytoplankton …

Barely had I unpacked my suitcase after running training courses in Ireland than I was repacking and heading off to Windermere to teach on the Freshwater Biological Association’s algae identification course, based at their new headquarters near Lakeside, at the south end of the lake.   This is an auspicious location to teach about freshwater algae, as this lake was the location for much pioneering work on lake ecology by John Lund and others.   Their work started from taking samples from Windermere, peering at them through light microscopes and then pondering on the reasons why different species waxed and waned as the year progressed.  We only had a few days but, nonetheless, this seemed like a good way to structure a course introducing freshwater algae. 

As soon as “housekeeping” and introductions were out of the way, therefore, we all made the short walk from the FBA offices to the jetties where Allan Pentecost talked us through the process of collecting with a phytoplankton net.   This is a funnel-shaped net with a mesh size fine enough to trap most of the algae (typically 30 – 50 micrometres) with a small filter at the narrow end onto which the algae are collected.   The net is attached to a piece of rope, allowing it to be thrown out then hauled slowly back to the jetty (as in the photographs above).   Alternatively, it can be hauled behind a boat for a few minutes.  After the haul, and once the water has drained through, you can unscrew the filter which should have turned a respectable shade of green due to all the trapped algae.  If not, replace the filter and try again.

Many of the smaller phytoplankton species will slip through the mesh (although the effective mesh size will decrease as the haul continues and larger algae get trapped across the meshes).   Another problem is that the net will also trap zooplankton which, if left unattended for too long, will eat the phytoplankton before you have a chance to examine it.   Taken together, these mean that phytoplankton nets are fine for qualitative studies but not great for getting a quantitative understanding of the phytoplankton community dynamics.   

After your hauls, you can wash the algae off the filter and into a sampling jar with distilled water from a wash bottle.  In our case, we had them under our microscopes within a few minutes, alleviating any concerns about zooplankton feasting on our spoils.   Prominent in the samples were chains of the diatom Fragilaria crotonensis, bundles of filaments of the cyanobacterium Aphanomizon flos-aquae and colonies of another cyanobacterium Woronichinia naegeliana.   Of particular interest, were cells of the protozoan Vorticella hitching a ride on a bundle of Anabaena lemmermannii filaments.   Anabaena is a mostly planktonic relative of the Nostoc I encountered in the Burren a fortnight ago (see “Landscape architects …”), sharing its “rosary”-type structure with a few specialised cells called heterocysts (for nitrogen-fixation) strung along chains of vegetative cells.  

Vorticella cells attached to a colony of Anabaena lemmermannii filaments in Windermere, June 2022.   See notes on size below.  The sequence of photographs at the top of the post shows Allan Pentecost sampling the south basin of Windermere with a plankton net.

The Anabaena cells, in this case, are almost black in colour, due to the presence of gas vacuoles, small inclusions inside cells that make cyanobacterium cells more buoyant, helping them to move up in the water column and access more light.   The Vorticella cells are using the Anabaena filaments as life-jackets, making sure that they stay close to the surface to feed on small organic particles including, most likely, very tiny “picoplankton”.  Hilda Canter-Lund and colleagues noted this phenomenon in Windermere and other Cumbrian lakes, suggesting that it took 19 Anabaena cells to keep a single Vorticella afloat.   Presumably the plentiful gas vacuoles are at least partly a response to the extra payload that the Anabaena are carrying.  

This post started out as a description of how to sample phytoplankton with a net so, before I sign off, I need to return to this topic.  Amidst all the excitement of finding Vorticella hitchhikers, I forgot to stress the importance of washing a phytoplankton net after use, to make sure that the next sample you collect is not contaminated by the algae from the last lake you visited.   This is also an important biosecurity step, to make sure that you do not take unwelcome visitors from one lake to another.  There is a naturalist’s mantra that reads: “take nothing but pictures, leave nothing but footprints, kill nothing but time” to which we should probably add: “bring nothing but hope”.


Canter, H. M., Walsby, A. E., Kinsman, R., & Ibelings, B. W. (1992). The effect of attached vorticellids on the buoyancy of the colonial cyanobacterium Anabaena lemmermanniiBritish Phycological Journal 27:  65-74.

Anabaena cf. flos-aquae from Windermere, June 2022.   Note the conspicuous heterocysts (lighter cells) and vegetative cells dense with gas vacuoles.   No size measurements were made but typically vegetative cells are 3 to 5 micrometres in diameter. 


The morning after I posted this, a bloom appeared on the surface of Windermere, encouraged by the warm weather and just on cue for our lectures on “nuisance cyanobacteria”.   Although we already had a good idea of what organism was responsible (from our samples collected earlier in the week), we trooped down to the lake for a demonstration on reactive algae sampling.   As the wind typically blows the bloom towards the shore, there is no need to use a net, and the bloom can be collected simply by dipping a bottle into the water.   As the blooms can release toxins, the sampler should be wearing gloves whilst collecting these samples but, apart from this, the process is very straightforward.   The algae, after all, have already signalled their presence.

A bloom of Anabaena lemmermannii in the margins of Windermere, June 2022.

The bible for anyone concerned about toxic cyanobacteria in fresh water is a WHO publication Toxic Cyanobacteria in Water.  This advises that action needs to be taken if the concentration of potentially-toxic cyanobacteria exceeds 20,000 cells ml-1 although you can pretty much assume that this will be the case for a visible boom floating at the surface, so you don’t need to spend time on counting.   Above this threshold, contact water sports are not recommended, and dogwalkers and farmers are advised to keep their animals away from the water.   An easy “citizen science” option is to upload a photograph to the Bloomin’ Algae app. In most cases, a photograph is enough to confirm whether or not a bloom is composed of cyanobacteria, which provides enough information to assess the risk and make preliminary judgements about what needs to be done.

Sampling the bloom of Anabaena lemmermannii.   Note that the sampler is wearing a disposable glove, as we don’t know at this stage whether or not the bloom is toxic.   The right-hand picture shows the bloom, after been left to stand on a laboratory bench for an hour.  

Some other highlights from this week:

Wrote this whilst listening to: W.A. Mozart – Veni, Sancte Spiritus (Come, Holy Spirit), K.47.    Short choral piece written when he was 12! 

Currently reading: Sally Rooney’s latest novel Beautiful World, Where Are You.   

Cultural highlight:   Danny Boyle’s series Pistols, a dramatization of the history of the Sex Pistols.  I remember watching their notorious appearance on the ITV Today programme with Bill Grundy back in December 1976. 

Culinary highlight:  A general shout-out to the Rusland Pool Hotel, just off the A590 near Ulverston where I’m staying whilst teaching on the FBA algae identification course.  They not only serve breakfast at a sensible hour (rare in the Lake District!) but also have an extensive vegetarian / vegan menu.

Intimate strangers …

The limestone from which the Burren is built is a famously permeable rock, so any rain quickly seeps through the surface layers and standing or flowing water at the surface is relatively rare in limestone country, except where the water table is relatively close to the surface.  Even so, the water table rises and falls throughout the year, meaning that lakes in these regions tend to be fluctuate in size and, in many cases, dry up altogether.  In the Burren, these transient lakes are referred to as “turloughs” and are one of the characteristic landscape features of the area.

You get a better sense of the nature of Lough Gealáin, one of these turloughs, standing near the summit of Mullaghmore.   The light blue zone is shallow water overlying marl with a darker blue zone indicating deeper water.  Surrounding the shallow water there is an area that grades into the true terrestrial vegetation, characterised by crisp white mats of dried-out filamentous algae that crunched underfoot as we walked around.   These represent a zone that would have been submerged during the winter, but which is now exposed as the water table falls back.  All turloughs are fed by groundwater springs and, in this case, the deep zone is thought to overly a collapsed cavern which itself may be a channel through which groundwater flows, ebbing up to the surface when the flow is too great for the channel to accommodate.   

Lough Gealáin, May 2022, seen from near the summit of Mullaghmore.  The photograph at the top of the post shows Mullaghmore, with Lough Gealáin in the foreground.

Approaching the shore of Lough Gealáin, I noticed several spherical or hemispherical white jelly-like blobs sitting on the exposed marl.   These are colonies of a protozoan, Ophyridium versatile, an organism which contains many tiny algal cells (called “zoochlorellae”).   It was of particular interest to me because I had been explaining to my students in Galway how the earliest algal cells were the result of a protozoa-type organism engulfing a primitive alga and then, rather than digesting it and using its energy straight away, preferring to enslave it, reaping its energy over a longer time period.   “Enslave” might be a harsh term as these relationships are often viewed as “win-win”, with the alga gaining protection in exchange for the renewable energy it provides to the protozoan.

Colonies of Ophyridium versatiie on the shore of Lough Gealáin, May 2022.  

By coincidence, we also saw Ophyridium versatile at a very different habitat during our fieldtrips to Connemara (to the west, rather than the south, of Galway).  The water here is much softer (conductivity: 108 µS cm-1rather than 330 µS cm-1) and the colonies much greener in appearance but the organisms inside looked remarkably similar.   Unfortunately, in both cases the cells did not enjoy their journey from the west of Ireland to my microscope and were well past their best by the time that I photographed them.  Apologies: I basically broke several of the rules I set out in “What’s in a sample (2)”.  You can, nonetheless, make out the zoochlorellae inside the protozoan mothership.   There are better images of Ophyridium versatile in “On fieldwork”.

Colonies of Ophyridium versatile on the upper surface of a cobble from the outflow of Lough Adrehid to the Owenriff River at Quiet Man Bridge, May 2022.

Also visible in the gel matrix (but difficult to photograph) were many small diatoms.   Others have noted the presence not just of diatoms, but of other algae, bacteria and protozoa also hitching a ride in the Ophyridium colonies.   Whilst the zoochlorellae are within the cells within the gel, these are outside the cells but within the gel.  For the diatoms, the relationship is not obligatory but still likely to be a “win-win” symbiosis.  They gain protection whilst the oxygen they produce contributes to the overall buoyancy of the colonies.   The most abundant diatom seemed to be a species of Encyonopsis but this is a difficult genus to identify in the live state, so I’ll need to get it digested and mounted before I can write more.   There does seem to be some evidence that the Ophyridium colonies develop a characteristic assemblage of diatoms, different to that in the surrounding habitat, so it will be interesting to see just what is in my sample.

Unless you know what you are looking for, Ophyridium colonies are easily overlooked or dismissed.  But they pose some interesting questions about how organisms interact.   It should not be a surprise that one of the papers I found in my scan of the literature was co-authored by Lynn Margulis, who first recognised the importance of symbiosis to evolution (see “Origin story …”).   Although the Ophyridium cells are still nominally functional heterotrophic protozoans, studies have shown that all their carbon is supplied by their resident algal cells and the main contribution from their “feeding” is other nutrients such as nitrogen and phosphorus.   There is sufficient interdependence that the next steps of Margulis’ endosymbiosis theory – loss of unneeded genetic material from the zoochlorellae– seems entirely plausible.  But, then, alongside this very tight partnership, the Ophyridium colonies also have these looser associations with diatoms and other microorganisms.   Maybe these are more like our own gut microbiomes, playing a role in the overall “health” of the colony in ways we are yet to discover?   Understanding the role of the human gut microbiome is now a big research question.   It is quite intriguing to think that the same type of questions occur right across the living world, even for apparently primitive protozoans.    

Three cells of Ophyridium versatile from colonies in the Owenriff River, Conemara, May 2022.  Scale bar: 50 micrometres (= 1/20th of a millimetre).


Dute, R. R., Sullivan, M. J., & Shunnarah, L. E. (2000). The diatom assemblages of Ophrydium colonies from South Alabama. Diatom Research 15: 31-42.

Duval, B. & Margulis, L. (1995). The microbial community of Ophyridium versatile colonies: endosymbionts, residents, and tenants.  Symbiosis 18: 181-210.

Eaton, J.W. & Carr, N.G. (1980).  Observations on the biology and mass occurrence of Ophyridium versatile(Müller) (Ciliphora: Peritrichida) and associated algae in Lough Ree, Ireland.  Irish Naturalists Journal 20: 55-60.

Mark, A., McKim, S., Lowe, R., & Kociolek, J. P. (2019). Diatom community composition within Ophrydiumcolonies in Northern Michigan and the description of a new species of Encyonopsis Krammer. The Great Lakes Botanist 58: 221-232.

Sand‐Jensen, K., Pedersen, O., & Geertz‐Hansen, O. (1997). Regulation and role of photosynthesis in the colonial symbiotic ciliate Ophrydium versatileLimnology and Oceanography 42: 866-873.

Some other highlights from this week:

Wrote this whilst listening to: The Corrs Unplugged.   Sharon Corr was the support act for Jeff Beck (see below), leading me back to their music.

Currently reading: Very readable translation of Delphine de Vigan’s short but moving novel Gratitude, then Cyprian Ekwensi’s 1962 novel Burning Grass, about the nomadic Fulani of northern Nigeria.

Cultural highlight:   I bought tickets to see sixties guitar legend Jeff Beck before the first lockdown.   The concert was cancelled twice before finally going ahead last week.   The concert would have attracted little attention beyond men of a certain age with a penchant for jazz-inflected rock were it not for the announcement earlier in the week that Johnny Depp was making guest appearances on the tour.  Depp won his high-profile libel case on the day we saw them, which pushed the concert onto the front pages of all the newspapers the following day.

Culinary highlight:  recreated a recipe we had encountered at the Seafood Bar in Galway: “rhubarb and custard”, with the custard replaced by a sabayon made with white port.

Landscape architects …

As my teaching in Galway straddled a weekend, we took advantage of the location and snuck off to the Burren for a couple of days where, fortuitously, the sun shone and our waterproofs stayed packed in the bottoms of our rucksacks.  The Burren is an area of limestone geology mostly in County Clare in the west of Ireland, noted for its botanical diversity.  Some of these plants (such as spring gentian – Gentiana verna) we already knew from Upper Teesdale but the Burren is much larger and the mild Atlantic climate allows some unique plant assemblages to thrive. 

Of particular interest are the extensive areas of limestone pavement, whose grikes are crowded with the wild flowers for which the area is famous.  This is a classic feature of Karst landscapes influenced by glaciers.   In Britain, the best-known site is Malham Tarn in north Yorkshire, though the pavements themselves did not make it into my most recent series of posts from that region (see “Building landscapes …”). But I’m in Ireland now, looking out at limestone pavement on a scale that dwarfs anything Yorkshire has to offer and I’ve also found a way of weaving this landscape feature into a blog primarily concerned with algae… 

The surface of the limestone pavement is pitted with solution hollows – depressions typically 30 cm or more in diameter that probably formed at points where rainwater collected, starting a slow process of chemical and physical erosion.   The mild acidity of rainwater gradually dissolves the limestone, but achingly slowly – probably no more than five millimetres of limestone is removed every 100 years – so the hollows that I photographed for this post were several thousand years in the making.    

A solution hollow (“kamenitza”) on limestone pavement near Mullaghmore, June 2022.   The photograph at the top of the post shows limestone pavement on the hillside above the Caher valley in the Burren, with the hills of Connemara in the far distance.   

There were unprepossessing dark-brown lumps at the bottom of several of these which could easily have passed for some type of animal droppings.   Close-inspection, however, showed these to have a gelatinous quality rather than the fibrous nature we might expect if these were droppings.   These are colonies of the cyanobacterium Nostoc commune, a frequent subject on this blog.   The last time I wrote about these in detail I explained how neglected patches of Nostoc on the gravel roadway of a Cumbrian farm were the pioneer stage of plant succession (see “How to make an ecosystem (2)”) and we are seeing exactly the same process happening here on the Burren.   First, the tough, resilient colonies of Nostoc arrive, capable of surviving both the high radiation experienced on the light-coloured limestone and the long periods of desiccation.   Nostoc, moreover, has the ability to fix atmospheric nitrogen, effectively acting as a natural “fertilizer”.  Slowly, over time, the Nostoc traps windblown soil and creates a “soil” within which mosses and higher plants can take root.   The early arrivals are likely to be grasses and sedges, but we saw a wide range of plants, including orchids, growing in solution hollows.

Close-ups of the solution hollow from the previous photograph, showing Nostoc commune growing in the bottom.

We mostly live in places where the local rock has already been weathered into soils, or where other natural processes have dumped weathered rock from elsewhere.  So we rarely stop to consider where soil comes from.   It is only in a few places such as a limestone pavement that we can see the primordial stages of soil – and, therefore, habitat – creation taking place under our noses.   Even here, the process is very slow but, nonetheless, we can stand on the Burren and reflect that at one point in the past, everywhere was bare rock, and if it were not for unphotogenic brown blobs that might pass for animal droppings, it would never have been converted into soil at all.

Nostoc commune from solution hollows on limestone pavement in the Burren, May 2022, at two different magnifications.  Scale bar: 10 micrometres (= 1/100th of a millimetre).  


Cabot, D. & Goodwilie, R. (2018).  The Burren.  New Naturalist, HarperCollins, London. 

Doddy, P. & Roden, C.M. (2014).  The nature of the black deposit occurring in solution hollows on the limestone pavement of the Burren, Co. Clare.   Biology and Environment: Proceedings of the Royal Irish Academy 114B: 71-77.

Doddy, P. & Roden, C.M. (2018).  The fertile rock: productivity and erosion in limestone solution hollows of the Burren, Co. Clare.  Biology and Environment: Proceedings of the Royal Irish Academy 118B: 1-12.

Some other highlights from this week:

Wrote this whilst listening to: musical methadone to ease the cold turkey arising from a week and a half in Ireland.  In particular, Glen Hansard’s band The Frames and The Corrs.  What’s their connection? (answer at the bottom)

Currently reading: David Cabot and Roger Goodwillie’s New Naturalist volume on The Burren.

Cultural highlight: while I was in Ireland, I started watching the adaptation of Sally Rooney’s Conversations with Friends on the RTE Player.

Culinary highlight:  Dinner at The Cliffs of Moher hotel at Liscannor featuring a baked fillet of John Dory and a rather good fondant potato followed by a splendid sunset.

Answer: Glen Hansard and The Corrs all had roles in the 1991 film The Commitments.

What’s in a sample? (2)

The previous post was about the theory of sampling, without giving any practical details.  This one takes the next step: having removed an algal growth in order to identify it, we now need to get it from its natural habitat to the laboratory without it suffering any damage that might make it harder to identify the organisms present.

One potential answer is, rather than transport the alga to a microscope, to take the microscope to the alga.  I’ve written about this before (see “The highs and lows of microscopy in the field”).  In brief, the theory is fine but the weather in the northern temperate climes is not always a willing partner, and manipulating drops of sample on flimsy coverslips when there is any wind is not easy.   The field microscope definitely has its uses, but it is not always practicable.

We are, then, obliged to take most samples back to the laboratory.  During the time which elapses, however, we need to make sure that the algae do not change.   The best approach to minimise these changes will depend upon individual circumstances, but my approach is to make sure that everything is examined within about 48 hours of collection and to leave plenty of airspace in the sample bottles.   There is a temptation to remove a hefty chunk of an algal growth but, as we are dealing with microscopic features, a portion just a few square millimetres in size will provide ample material.  I try to collect four or five patches of this size from a location (to ensure representativeness), all of which I pop into a single plastic sample bottle along with a little water from the lake or stream.   In total, no more than a fifth of the tube needs to be filled, and there will be enough oxygen in the air that fills the remainder to allow them to respire (oxygen is not very soluble in water so we cannot rely on dissolved oxygen for this).   I keep each different type of algae that I find at a site in a separate tube, making a note, at the same time, of roughly how abundant each was.  Finally, I drop the labelled sample bottles into a cool box while I finish off my fieldwork and for the journey home.     

Good sampling practice: a small amount of algae, a small amount of water, and plenty of headroom for air.  The photo at the top of the post shows Lough Adrihid from the outflow to the Owenriff River, Connemara, May 2022.

Much has been written about the use of fixatives and preservatives to store algae but, for short periods, these are not necessary.   These terms are often used as synonyms of each other, but they do, in fact, refer to different processes.  A fixative stabilizes the cross-linkages in proteins, ensuring that there is little change in their appearance whilst a preservative stops microbial action that might lead to decay of the specimen.   Both act on fundamental biochemical processes and, bearing in mind that we share about half our DNA with bananas and cabbages, anything that we add to a sample to interrupt these processes also has the potential to interfere with our own physiology.   All fixatives and preservatives are, by their very nature, toxins, so better to avoid using them, if at all possible.  

When I collect samples for diatom analyses, I often add preservative because they are likely to be stored for some time and, because I am primarily interested in the silica cell walls for identification, any damage to the soft tissues wrought by a preservative will be irrelevant.   I use either ethanol or Lugol’s iodine, depending on what is to hand.   “Ethanol” is a reliable fall-back because, if all else fails, you can buy a bottle of local hooch and use that.    Neither Lugol’s iodine or ethanol is a perfect preservative if you are interested in soft tissues, but they are relatively safe, in contrast to formaldehyde and formalin, both of which are carcinogenic.  Gluteraldehyde maybe the best option for other freshwater algae, but I do not use it personally, so cannot give more details.    

The answers to the question in the title of the post, then, should be “not much” and “don’t wait too long to find out”.   “Not much” at the scale we encounter the world can translate into “great diversity” when we consider the size of the organisms we are dealing with.   But it is also important that we don’t think solely in material terms: a sample also tells us a story about the location it came from, and that will be the subject of the next post in this series.    

Some other highlights from this week:

Wrote this whilst listening to:  Skinty Fia, new album by Irish indie/punk band Fontaines D.C. .  What I am definitely not listening to is Ed Sheeran’s Galway Girl.

Currently reading:   Silverview, John le Carré’s final novel.

Cultural highlight: Popped into Charlie Byrne’s bookshop in Galway to buy maps and a guide to the Burren and stumbled on the launch party for Galway’s Early Music Festival, Musica & Scientia.  As a result, we went to a late evening concert in a Medieval church entitled “Discovering Light” which set Baroque flute/harpsicord music against a changing backdrop of pictures of the night sky.  The irony, given the title, was that the harpsichordist had to stop at one point because she couldn’t see her music.

Culinary highlight:  Meal at The Seafood Bar in Kirwan’s Lane, Galway, just a few minutes walk from our hotel. 

What’s in a sample?

The photograph above shows me looking for algae in the littoral zone of Wastwater on a cold January morning.   I have a list in my notebook of eleven algae that I found that morning, and there will be 20-25 diatoms to add to that list once I get around to looking at them too.   Those names came from collecting portions of visible algal growths, taking them home and examining them under a microscope.   Ecology is, in essence, based on endless variations of this same pattern: go somewhere and record what you see, along with an unspoken subclause that you should take away small portions of what you can’t name in the field to check later.   For larger organisms, a photograph may well be an adequate alternative to a physical specimen.

The English word “sample” is derived from the Old French word “essample”, meaning “example” which, itself, comes from a Latin word “exemplum”.  This, in turn, originates from “eximere”, which combines “ex” (out) and “emere” (take).  So far, so good: when we sample, in other words, we take something away that will serve as a representative example for that particular organism at that location on that day.   That may be the end of the process – if your purpose is to study a particular organism, perhaps – or you may go one stage further and infer some property from your representative example.   In the case of my visit to Wastwater, for example, I may conclude that this is a nutrient poor, soft water lake*.   

Technically, I can only draw a firm conclusion about the location that I visited at the time I visited, but we’ve done enough work over the years to conclude that, for UK lakes (which are relatively small on a global scale), there is variation in algal life around the perimeter, but inferences about the general condition will not change that much.    The same applies to rivers with the caveat that rivers change naturally along their length, so any conclusion is only valid for, at most, a few kilometres upstream and downstream.   The extent to which we can generalise from a small “example”, in other words, depends on prior knowledge of the system being studied.

One further complication comes when we want to compare two locations, or the same location on two different dates.   We need to be sure that any differences we observe are not just because we have sampled the two locations in slightly different ways.   We need to be consistent, with every aspect of the process performed in the same way each time you collect a sample.  If we do this, we can say that the sample is representative of the time and place where it was collected.  The method you use does not have to be fully comprehensive (budget and time constraints invariably intrude) but, having applied this to every single sample you collect, you can interpret results in terms of ecological conditions with confidence.   

That’s not the only way to sample, however.  Someone who is more interested in particular groups of organisms rather than environmental processes might prefer a targeted sampling approach, homing in on particular habitats where those organisms are likely to be particularly abundant or diverse.   You can read about a good example of this approach in “Desmid masterclass…”.   For this, we “stalked” our prey, pacing the perimeter of a tarn to find likely habitats for desmids, before moving in to collect material.   We were hunters rather than samplers, but we got what we needed.  If we wanted to make a rigorous comparison of the desmids of different Lake District tarns, we would have had to adapt our approach so that our samples were representative, though this might still involve specifying a particular type of habitat and necessitating a preliminary reconnaissance on arrival at the site.  Even representative sampling involves targeting to some extent.   

This is the first of a series of posts on techniques that I’m planning to write over the next few months.  I’m giving two courses to students and this blog is their pre-course reading list.  However, these posts will be interspersed with more usual fare for regular readers.  I’m hoping, too, that explaining the “how” behind the “wow!” will persuade those who read the blog to have a go themselves.  As Confucius said: “I hear and I forget, I see and I remember, I do and I understand”.

* type “Wastwater” into the search box on the right to learn more about the algae from this lake.


Kelly M.G., A. Cazaubon, E. Coring, A. Dell’Uomo, L. Ector, B. Goldsmith, H. Guasch, J. Hürlimann, A. Jarlman, B. Kawecka, J. Kwandrans, R. Laugaste, E.-A. Lindstrøm, M. Leitao, P. Marvan, J. Padisák, E. Pipp, J. Prygiel, E. Rott, S. Sabater, H. van Dam, J. Vizinet (1998) Recommendations for the routine sampling of diatoms for water quality assessments in Europe.   Journal of Applied Phycology 10: 215-224.

King, L., Clarke, G., Bennion, H., Kelly, M.G. & Yallop, M.L. (2006).  Recommendations for sampling littoral diatoms in lakes for ecological status assessments.  Journal of Applied Phycology 18: 15-25

Kelly, M.G., Snell, M.A. & Surridge, B.W.J. (2018). Use of littoral algae to detect zones of nutrient enrichment in the littoral of an oligotrophic lake.  Fundamental and Applied Limnology 191: 213-232.

Some other highlights from this week:

Wrote this whilst listening to:  Mavis Staple and Levon Helm’s Carry Me Home, and the debut album by Radiohead side project Smile.

Currently reading:   Sayaka Murata’s Convenience Store Woman and still reading PJ Harvey’s Orlam.

Cultural highlight: House of Gucci: 2021 film about people who make overpriced handbags being nasty to one another.   

Culinary highlight:  Burnt basque cheesecake with cherries and almonds and a dash of Advocaat.

Winning ways: Gerd Günther

You now have just over a week to upload an image for this year’s Hilda Canter-Lund photography competition.   You are running out of time if you still need to take a photograph but, if you have a photograph which you are already considering submitting, take a few moments to consider whether any editing is required in order to show your image at its very best.  Each year, I find myself wondering why on earth a photographer did not spend just two or three minutes cropping an image that would have been worthy of the shortlist were it not for a wonky composition.  This is allowed within the rules (so long as the basic integrity of your image is not compromised) and so very easy to do, even on a smartphone.

Following Sophie Steinhagen’s tips from a couple of weeks back, I thought I would ask her co-winner from 2021, Gerd Günther, what advice he would like to pass on to this year’s winners.  Sophie’s photographs featured marine macroalgae whereas Gerd focusses on microalgae so, together, there should be something for everyone in this pair of posts.   As well as his hints, Gerd has also kindly provided some of his other images to demonstrate his techniques.  

Rhodobacteria and filamentous cyanobacteia together with a Spirogyra filament in a sample from the botanic garden in Düsseldorf, Germany.  The picture at the top of the post is Gerd’s winning entry from the 2021 competition: Pyrocistis fusiformis

1. “Decisive moment” or carefully-crafted composition?

It depends on which samples I am examining.  I usually fall between these two approaches. When I process cultured material, I almost always try to create a considered composition of several, representative cells. When documenting raw samples, I am often guided by chance. The longer and more intensive the observation of a sample, the more “random” compositions can be found. However, the most important goal always remains the serious and realistic documentation of what I see.

2. what photo editing software do you use?

I use Adobe Lightroom in combination with Photoshop. In Lightroom I do all keywording and image organizing together with the basic RAW development. For most of the images, there is no need to process them in Photoshop too. When I photograph plant stem sections, I stitch them together with Photoshop. 

Biddulphia alternans, a marine diatom found in the North Sea at the German Bight

3. What routine editing steps do you apply to your image (e.g. cropping, adjusting levels/curves/brightness etc, stitching, stacking)?

Routinely I use especially the white balance and a careful correction of the highlights, shadows and overall brightness. Cropping the image remains the exception. When documenting microalgae, I do not use stacking or stitching. Routine steps for me also include the removal of dust particles that create unwanted bull’s eyes on the image file. However, the best way to avoid this is to clean the camera sensor regularly.

4. Do you ever “retouch” images to remove blemishes and improve their appearance?

Occasionally I retouch the background, removing unwanted detritus particles or bacteria, for example.

Lepocinclis (formerly Euglenaacus, together with some Phacus species found in Gerd’s garden puddle.

5. Are there any photographers who particularly inspire you? 

A source of regular inspiration for me is and remains the book by Hilda Canter Lund. I really appreciate her compositions and her feeling for colours and shapes. In addition, images by Wim van Egmond inspire me again and again.  

A colony of the diatom Meridion circulare from in the Eifel, a mountainous region of western Germany. All photographs in this post by Gerd Günther.

Reflections from remote lochs …

Naturalists make a big thing out of rarity – that an organism is considered scarce is one of the most basic reasons for wanting to protect and encourage those populations that remain.  But rarity is an elusive concept to pin down for all sorts of reasons, one of which is that the people who are likely to notice rare species are, themselves, scarce.   So it is that relative rarity of different orchid species is quite well understood, but rareness is harder to assess for freshwater algae because there are fewer people who study these organisms in sufficient detail.  A limited number of interested naturalists multiplied by a limited number of habitats where the organism is found inevitably results in a poor understanding of its distribution.   

Look at the paperclip-shaped object in the bottom right image of the figure below.   I found a lot of these in a sample from the littoral zone of a small loch in Shetland and it took me some time to associate them with the small elliptical diatom valves that cropped up in the same sample (the plate shows lots of the valves but only one of the paperclip-shaped girdle bands whereas, in reality, there were far more of these than there were valves).    The penny dropped, eventually, and I realised that I was looking at a very rare diatom, Oxyneis binalis var. ovalis.   These are relatives of Tabellaria (see “The bluffer’s guide to Tabellaria ”) and, like this genus, have several girdle bands, each with a silica plate (“septum”) between the two valves.   Indeed, until relatively recently, Oxyneis species were considered to be part of Tabellaria.

Oxyneis binalis var. elliptica from Lamba Water, Shetland Isles, October 2021.  Top row: valve views; bottom row left: partially intact frustule in girdle view (note the large number of girdles); bottom right: single girdle band in valve view.  Scale bar: 10 µm (= 100th of a millimetre).  

I’ve looked at several samples from this loch over recent years and have not noticed this species before.  I use the word “noticed” deliberately, as I’m now worried that I’ve overlooked it in the past.  However, I’ve also looked at samples collected after the one where I first found it and did not find it there, despite being aware of the likelihood that it might be there.  That means that we need to add an extra coefficient to my equation: a patchy distribution over the course of a year further reduces the chance that it will be noticed by one of a limited number of naturalists who just happens to visit one of the limited number of locations. 

Two intact frustules of Oxyneis binalis var. elliptica in a cleaned sample from Lamba Water, Shetland Isles, October 2021.   Scale bar: 10 µm (= 100th of a millimetre).

By coincidence, at about the same time as I was finding Oxyneis binalis var. elliptica in the Shetland Isles, Chris Carter send some photographs from a population of Oxyneis binalis var. binalis collected by Chris Johnson from Lochan an Fheòir on the Isle of Harris, in the Outer Hebrides.  This species has a distinct “dumbbell” shape and, once again, many more girdle bands than valves.  The literature hints that Oxyneis binalis var. binalis tends to form straight chains whilst O. binalis var. elliptica forms zig-zag chains.   However, our photos offer only limited support for this and, in any case, many of the chains will disintegrate on preparation.  That both these specimens come from remote peripheries of our archipelago only seems to emphasise their rarity.

Oxyneis binalis from Lochan an Fheòir on the Isle of Harris, colllected by Chris Johnson and photographed by Chris Carter.  a., b.: two focal planes showing girdle and valve face; c., d.: two focal planes of a girdle band; e., f.: two focal planes of a girdle view of a partially-intact frustule beside a valve view.  Scale bar: 10 µm (= 100th of a millimetre).
Live cells of Oxyneis binalis from Lochan an Fheòir on the Isle of Harris.

Should we even be concerned about rarity?   All I’ve said so far equates rarity with quantities – numbers of organisms and numbers of habitats, complicated by the numbers of biologists actually interested enough to do the counting combined with an element of chance.  Anna Kondratyeva and colleagues from the Sorbonne in Paris think that this is a naïve way of thinking about ecological diversity and ask questions about what unique characteristics these “rare” organisms bring to ecosystems.   If they are just variants on themes already well represented by other organisms in a habitat, then does rarity matter?  On the other hand, if they exhibit “functional originality” (i.e. they bring distinctive characters to an ecosystem, influencing the way that energy flows through trophic levels) then they are more than just a tick on a naturalist’s recording sheet; they are active contributors to the uniqueness of a particular habitat.   The problem we have is that we don’t know enough about the inner workings of individual diatom species to have much of an idea about what Oxyneis binalis brings to a habitat that species of Tabellaria do not.   It encapsulates the diatomist’s dilemma: we know the shape of everything and the meaning of nothing …


Three of these papers give background information on what makes Oxyneis different from Tabellaria, one includes some earlier records from the Shetland Isles and the final reference explains the theory behind “rarity” and “originality” 

Carter, J. & Bailey-Watts, A.E. (1981).  A taxonomic study of diatoms from standing waters in Shetland.  Nova Hedwigia 33: 513-630.

Flower, R.J. 1989. A new variety of Tabellaria binalis (Ehrenb.) Grun. from several acid lakes in the U.K. Diatom Research. 4: 21-23.

Kingston, J.C. (2000).  New combinations in the freshwater Fragilariaceae and Achnanthidiaceae.  Diatom Research15: 409-411.

Kondratyeva, A., Grandcolas, P. & Pavoine, S. (2019).  Reconciling the concepts and measures of diversity, rarity and originality in ecology and evolution.  Biological Reviews 94: 1317-1337.

Round, F.E., Crawford, R.M. & Mann, D.G. (1990).  The Diatoms.  Biology and Morphology of the Genera.  Cambridge University Press, Cambridge.

Some other highlights from this week:

Wrote this whilst listening to:  Radiate Like This, latest album by Warpaint

Currently reading:   PJ Harvey’s Orlam: poetry in Dorset dialect.

Cultural highlight: a visit to Yorkshire Sculpture Park on a sunny Sunday afternoon, enjoying, in particular, the tranquility within James Turrell’s Deer Shelter Skyspace.   .   

Culinary highlight: Vegan peanut butter and banana brownies

Winning ways: Sophie Steinhagen

The 2022 Hilda Canter-Lund competition is now underway, and you can upload your entries at the BPS website.   You may well have an image saved up for the competition this year, but it is not too late to take a photograph to submit this year.  

Last year, the winning entry came from Sophie Steinhagen, a researcher at the University of Gothernburg’s Department of Marine Sciences.   Her image Forestal was taken with a half-submerged camera to show both the terrestrial pine forests and the Fucus-dominated vegetation that is found just below the water surface along the Swedish coastline.   Both ecosystems not only play important roles in contributing oxygen to the atmosphere, but they also provide invaluable habitats for vertebrates, invertebrates and billions of microorganisms.  This is, to the best of my knowledge, the first shortlisted image to be taken on a GoPro, and thus reinforces the message drawn fro Zoe Loffler’s winning image from 2019 (taken on a smartphone): you do not need piles of expensive, technically-sophisticated equipment to take a great photograph.  You just need to have a good eye.

Last year I asked a number of previous winners for some tips on taking good photographs of algae (see Erasmo Macaya’s answers here) and I’ve asked the same questions of Sophie this year.  She’s also kindly lent me some more photographs to illustrate her answers. 

1. “Decisive moment” or carefully-crafted composition?

To me, nature photography should display the true beauty of nature, therefore I am always on the hunt for decisive moments. However, I put a lot of effort in the setup and arrangement of the composition in microscopical pictures.

Nudibranch on Fucus.  Photoraphed by Sophie Steinhagen.   The image at the top of the post is Forestal, Sophie’s winning image from the 2021 competition

2. what photo editing software do you use?

I do not use any particular editing software and mainly just work with the camera settings. At the computer I mainly adjust the brightness, which is often hard to do when photographing underwater, as the light often changes within seconds. However, different brands come with their own editing software, and it is always worth checking the brand´s webpages for free editing software (e.g. for Olympus or GoPro).

Fields of Fucus and Chorda in a shallow bay.   Photograph by Sophie Steinhagen.

3. What routine editing steps do you apply to your image (e.g. cropping, adjusting levels/curves/brightness etc, stitching, stacking)?

Cropping and brightness adjustments are the main editing steps I apply. 

4. Do you ever “retouch” images to remove blemishes and improve their appearance?

Only in microscopic pictures, where the structure of interest is sometimes located next to the cover glass margins or other unwanted structures.

Fucus meadows.  Photograph by Sophie Steinhagen.

5. Are there any photographers who particularly inspire you?

I am inspired by any photograph that captures a unique situation and induces a feeling in the observer. I think that Sebastião Ribeiro Salgado has a unique way to capture scenery and transmitting images of nature, people, and social situations in a way that allows the observer to “feel” the photographs.

Rocky shore seaweed community.  Photograph by Sophie Steinhagen.

Springtime surprises …

My last few trips to the Lake District have been plagued by indifferent, if not inclement, weather.  High flows are the ultimate curse of anyone working on rivers, and recent trips have all been uncertain until almost the last moment as I watched the fluctuations of weather forecasts and hydrographs.  Even once we had arrived, clouds were low and we never seemed to be out on one of those crisp winter days that offers views of distant, snow-capped peaks.   Finally, last week, the sun was able to break through the clouds, at least occasionally, daffodils, primroses and cowslips were in flower and the woodlands were heady with the scent of wild garlic.   

Life under water, however, follows a different trajectory to life on land.   At this time of year, stream beds in West Cumbria tend to look less, not more, verdant.   The algae that are so prolific during the winter were still there, but nowhere near as prolific now.   That was the case at several of the sites we examined but one – the River Cocker just below Crummock Water – bucked this trend in quite a dramatic way.  Peering through my bathyscope, I saw bright pink-red growths, particularly on fronds of the moss Fontinalis antipyretica.   These turned out to be filaments of the red alga Audouinella hermainii, which also smothered many of the stones.

Audouinella hermainii epiphytic on the moss Fontinalis antipyretica in the River Cocker, just downstream from Crummock Water, April 2014.  The photo at the top of the post shows the site where this photograph was taken.

The growths on the stones looked different to those on the mosses, with longer filaments and a brownish, rather than red, colour.  The colour difference may simply be due to the balance between reflected and transmitted light in the two locations; however, the difference in growth form between the two habitats is harder to explain.  In the River Ehen the same alga (so far as I can tell) has the habit shown in the top photo, but here growing on rocks rather than on mosses (see “Not so bleak midwinter?”)

The other complication is that, in the River Ehen, Audouinella hermainii is extremely abundant in the winter and early spring but is not visible between about May and August, after which it starts to become obvious again.   The growths I saw last week were not the first records from this site, but they are both the most abundant records and the only time it has been so prolific this late in spring.   I also found one record from the River Crake, just below Coniston Water, where A. hermainii was prolific in June.  What’s more, neither the Freshwater Algal Flora of the British Isles nor West and Fritsch’s Treatise on the British Freshwater Algaemakes reference to this species having a particular predilection for winter and spring.   The former says it is “… most common as an epiphyte on … bryophytes” whilst the latter says “… usually attached to rocks and stones in rapid rivers”.   Both agree, however, that it is more likely to be encountered in streams and rivers than in lakes.  It is the Ehen that seems to be the outlier, but it is also the river where I find it most often, hence my inference about its seasonality.   

Audouinella hermainii on stones in the same stretch of the River Cocker as the epiphytic growths in the previous photograph.   

Another reason for treading cautiously is that the red algae present us with some particular challenges when it comes to identification (see “Something else we forgot to remember” and “Reflections from the trailing edge of science”).   Although the view through a microscope shows similarities amongst these populations, these differences in habit and seasonality make me question whether I am looking at the same organism across all these locations. 

I’m conscious that my understanding of this species is drawn from records from a limited geographical area.  On the other hand, the “big picture” for other people may encompass different sites to mine but, I suspect, will include fewer records from the depths of winter.   Then again, mid-winter and early spring in rivers flowing out of lakes will have quite different thermal and hydrological characteristics to the same seasons in unregulated streams flowing off the Alps, for example.   Is anyone’s “big picture” ever big enough to make generalisations?

Vegetative filaments of the red alga Audouinella hermainii from the River Cocker, just downstream from Crummock Water.   Scale bar: 20 micrometres (= 1/50th of a millimetre).  

There are certain other algae that I also associate with late winter and early spring (Ulothrix zonata, Draparnaldia glomerata, for example).  However, most of these turned out to show similar patterns to Audouinella hermainii when I collated my data, with just enough outliers to confound my expectations.  The likelihood is that these plants do not have circannual rhythms hard-wired into their physiology, but are opportunistic, reacting to circumstances.  Their optimal conditions may be more likely to occur at particular times of the year, but there are also exceptions, giving rise to my observations last week.   

That unpredictability is what keeps me wanting to head out into the field, even when the weather is not ideal.  It is also a reason to want to keep going back to the same sites, so that I can watch patterns unfold, and also a reason to want to visit different sites, so that I can fit my observations drawn from a limited area into a broader perspective.  Beware the ecologist who speaks with too much confidence.  The chances are that they are not spending enough time getting cold and wet in the field.   

Records of Audouinella hermainii from West Cumbrian rivers and streams, 2020 – 2022.  The y axis shows the cover of the alga using the 9-point scale adopted for macrophyte assessments in the UK.   Vertical lines indicate the twelve months of the year.  

Some other highlights from this week:

Wrote this whilst listening to:  Easter music: Stanier’s Crucifiction and Bach’s St Matthew’s Passion.

Currently reading:   Still Colm Tóibín’s The Magician.

Cultural highlight: The Raphael exhibition at the National Gallery.   

Culinary highlight: Grilled mackerel on Asian salad, prepped and made at the Cordon Bleu cookery school in London during a short course on knife skills.