The fine art of asking big questions.

As someone whose art practice rarely requires a piece of paper larger than A3, I took the opportunity of a trip to London to visit the Anselm Kiefer retrospective at the Royal Academy of Arts to indulge in the opposite extreme. Kiefer is, in my view, one of the most significant living artists; particularly remarkable because much of his art is based around representational oil-on-canvas works with a deep understanding of perspective. At the same time, his work is deeply symbolic and conceptual, often addressing spiritual issues and trying to make sense of recent German history.

I was drawn to Kiefer when studying for my fine art degree largely because I was interested in the way that his work was simultaneously traditional and conceptual. However, having expressed this interest in Kiefer, my tutors then used his work to challenge me, particularly on how I dealt with scale in my own work. Kiefer’s paintings are large and this, combined with his use of perspective means that you feel that you can walk into the pictures which, in turn, draws you into the symbolism that he is addressing (see: “En route to Milan: more musings about Leonardo”). When you walk into a room of his most recent paintings (the Morgenthau series in this exhibition), you get an additional sensation as 100 square metres of the still-drying paint perfume the air with the fragrance of linseed oil.


Anselm Kiefer’s Northung, (1973) on display at the Royal Academy giving some idea of how scale and use of perspective combine to draw you into the image.

I did experiment with scale in response to my tutor’s goading but working at larger scales creates it’s own problems. Apparently, one external examiner commented that he could spot the work of part-time students because it always had to fit into the back of a car. Not for us the luxury of a three metre high canvas.   Some of my final degree show images were painted onto a series of panels in order to to sidestep this problem but, with this behind me, I decided that I was more comfortable working at a smaller scale. It was not just the practicalities of working from home, my subject matter was already so magnified by three or four orders of magnitude and one more made little difference to the story that I wanted to convey.


A work-in-progress of my own, approximately sixty times smaller than Anselm Kiefer’s Northung (which is, itself, half the size of his largest works).

The intellectual heft of Kiefer’s art remains an inspiration, nonetheless. The quality of his work was put into perspective when I walked around the corner to the Allen Jones retrospective in another part of the Royal Academy.   Jones was part of the Pop art movement of the 1960s and has retained many elements of Pop art in his practice ever since. His brightly-coloured paintings and recycled mass-media imagery looked shallow and vacuous to someone still digesting the visual splendours of Kiefer’s show.


The complex ecology of a submerged stone …

I was back at Smallhope Burn last week (see “Nitzschia and a friend…”), albeit a few kilometres further downstream from the site I discussed back in September.   Despite my visit being in mid-November, many of the stones I picked up here had tufts of young, healthy-looking Cladophora glomerata with, between them, apparently bare rock surface on which I could see the tiny, almost-black shells of Ancylidae snails.   These have rasping mouthparts and move across the stone surface grazing on the microscopic algae (probably mostly diatoms) that inhabit it.   Though the surface of the rock looked bare and felt rough to the touch, there is almost certainly a thin “sward” of diatoms and other algae here. Otherwise, the Ancylidae (the “cows” of my underwater pastures) would not be here.


A boulder from Smallhope Burn covered with tufts of Cladophora glomerata interspersed with Ancylidae snails with (right) a shell of an Ancylidae snail on my fingertip.   The shell is about two millimetres across and the boulder is about 30 centimetres across.

Under the microscope,I can see several different types of diatom, though most look as if they live on or around the Cladophora rather than in the patches between the tufts.   Cocconeis pediculus and Rhoicosphenia abbreviata are both common epiphytes (see “Cladophora and friends”) whilst Diatoma vulgare and Melosira varians form chains that are loosely-attached to the substrate and, if detached, will easily become entangled within the Cladophora tufts.   The Navicula species are both motile forms that can glide in and around the filaments in search of light.   I suspect that my standard method of sampling diatoms (brushing the tops of stones vigorously with a toothbrush) is a little too coarse to get a true indication of how the diatoms differ between the bare patches and the Cladophora tufts.


Diatoms from Smallhope Burn, Low Meadows, November 2014. a. Cocconeis pediculus; b.,c. d. Rhoicosphenia abbreviata; e., f. Diatoma vulgare; g. Ulnaria ulna; h. Melosira varians; i. Navicula tripunctata; j. Navicula gregaria.   Scale bar: 10 micrometres (1/100th of a millimetre).

Our thinking on the ecology of Cladophora has changed over the past few years. If you consult literature from the 1970s, you’ll see a general agreement that Cladophora prefers waters that are rich in nutrients. This is, indeed, my own observation but, at the same time, you can find a lot of Cladophora in rivers with quite low levels of nutrients and, sometimes, no or little Cladophora in rivers that are nutrient-rich. A recent paper from Ireland helps put these observations into perspective, by demonstrating that the quantity of Cladophora is strongly influenced by the density of grazers as well as the quantity of nutrients.   My suspicion is that grazing invertebrates can keep Cladopora under control until a “tipping point” is reached when either the density of grazers drops or production of Cladophora acceleratesers to an extent that the grazers can’t keep up with the rapid growth of the alga, at which point the bed becomes smothered.   It may even be an example of the “alternative stable states” theory developed by Brian Moss and colleagues for the Norfolk Broads, though that would take some more work to confirm.


Moss, B. (2010). Ecology of Freshwaters. A View for the Twenty-First Century. 4th Edition. Wiley-Blackwell, Oxford.

Sturt, M.M., Jansen, M.A.K. & Harrison, S.S.C. (2011). Invertebrate grazing and riparian shade as controllers of nuisance algae in a eutrophic river.   Freshwater Biology 56: 2580-2593.

Whitton, B.A. (1970). The biology of Cladophora in freshwaters. Water Research 4: 457-476.


“They don’t do much, do they?”

I spent the early part of yesterday evening listening to Richard Fortey talk on “Survivors: the animals and plants that time has left behind” at Van Mildert College in Durham.   Fortey is a palaeontologist, best known for his work on trilobites, but who has also presented popular television series on natural history topics.   In this lecture, he talked about the small number of organisms that were well represented in the fossil record (some pre-dating dinosaurs) yet which had survived the various mass extinctions and which could still be found today. Did these organisms have anything in common, he wondered.

One group of organisms that he talked about were the blue-green algae (Cyanobacteria) responsible for forming “stromatolites” which are found both in Precambrian rocks over a billion years old and in a few locations today.   I’ve talked about blue-green algae in many of my posts (e.g. “More reflections from the dawn of time …”) but what amused me this evening was Richard Fortey’s anecdote about a discussion with a BBC producer as they devised a television series based on his book:

Fortey: “These are the most important organisms in the history of the earth” (commenting on their role in creating the oxygen-rich atmosphere that every organism since has relied upon)

BBC producer: “they don’t do much, do they?”

It is a subject that I have addressed several times in this blog (see “The sum of things …”, “Every second breath …”): how do we address the imbalance in natural history broadcasting between the charismatic “few” and the unfashionable “many”, bearing in mind, of course, that these are, in many cases, the hard-working, unglamorous “back office staff” who keep our planet running.   Television natural history programmers are in the entertainment business first and I’m not going to pretend that a stromatolite made of blue-green algae is, on its own, a recipe for compelling television.   But I also feel that there are possibilities that could be explored, and that we may be held back by a lack of imagination on the part of broadcasting creatives and commissioning editors.   They, too, are children of the television age, brought up on a style of broadcasting from Zoo Quest through Life On Earth and onwards that is interested only in the televisual aspects of natural history. Whoa .. hold it there … I’m coming dangerously close to criticising David Attenborough … Saint David … that’s close to heresy.


Fortey, R. (2011). Survivors: the animals and plants that time has left behind.   Harper Collins, London.

Who needs a “red list” anyway?

The previous two posts suggested that it might be possible to construct a provisional red list of freshwater diatoms, albeit with several caveats.   The question that still needs to be answered is whether there is any real benefit to such an exercise.

I think we can say with some confidence that a red list of freshwater diatoms will not precipitate a crisis of conscience amongst the national conservation bodies or wildlife trusts, there will be no rush to draw up plans to add rare diatoms to Biodiversity Action Plans and no Sites of Special Scientific Interest will be designated because of the unique diatoms found there.   So why bother?

One problem that I identified in the first post in this series (see “A red list of endangered British diatoms?”) is that those of us who have been studying algae have never been part of the widespread tradition of wildlife recording that takes place around Britain and which is the basis for the red lists of many other groups of plants.   We make our own lists, for sure, but there is no centralised system for either recording or validating records.   This activity has, for many groups, been the preserve of enthusiastic amateurs and, whilst there are amateur phycologists, numbers are well below that required to develop meaningful distribution maps. At present, for many freshwater algae, the distribution maps are more likely to show you where the small number of collectors are most active, rather than offer any profound insights into biogeography.   The freshwater diatoms are an exception here, as I hope I have shown, albeit with several caveats.

The benefits of better recording are twofold.   The first is simply to raise the profile of algae amongst the conservation movements.   I have already shown that algae represent a large part of UK’s total biodiversity (see “The sum of things …”).   In so doing, I added myself to the long list of phycological whingers and windbags who vent their spleens at the way that algae are invariably overlooked by conservationists.   If we want to be taken seriously, we need to start producing evidence of a quality equivalent to that for other groups of organisms.   Distribution maps are a step in that direction.   They are possible not just for some freshwater diatoms but also for some other types of freshwater algae (see ““Looking” is not the same as “seeing”” for an example).   My hope is that production of a preliminary list might, itself, flush out further records and generate a dialogue amongst phycologists and beyond.

The second point is that systematic recording of distributions will, itself, throw up some testable hypotheses. I suggested, in the previous post, that Gomphonema tergestinum might have a restricted distribution that cannot be explained solely by chemical conditions. I’ll return to that in a future post but I suspect that there may be others that also show unexpected patterns. In other words, better recording might well lead to better insights into the ecology of these organisms. We may, indeed, have missed the boat on this topic: the distribution patterns of many species have already been shown to change in response to climate warming (see below for a reference to one example).   Last year I wrote about Hydrurus foetidus, a chrysophyte that I found growing in high altitude streams in Norway (see “A brief excursion to Norway”).   I know that it has been recorded in this country but I have never seen it here. It would be interesting to look at locations where it has been found in the past and see if there is any evidence for it growing now and, indeed, whether there have been any shifts in its distribution patterns.

And my final point is even more basic.   There is already a provisional atlas of the slime moulds of Britain and Ireland. If they can do it for slime moulds, surely we can do it for freshwater algae too. Our professional pride is at stake …


Fox, R., Oliver, T.H., Harrower, C., Parsons, M.S., Thomas, C.D. & Roy, D.B. (2014.) Long-term changes in the distribution of British moths consistent with opposing and synergistic effects of climate and land use change. Journal of Applied Ecology, 51, 949-957.


The Really Rare Diatom Show

Having set out the limitations of my exercise to define nationally-scarce or rare diatoms, I have drastically reduced my list of candidates from 377 species down to eight.   I suspect that gathering some more data (see point 1 in my previous post) will mean that I can reinstate a few more species to the list, but that will have to wait for another day.

Six of the ten species on my list belong the genus Gomphonema or near relatives.   One of these is Didymosphenia geminata (see “A journey to the headwaters of the River Coquet”); of the others, the most intriguing is Gomphonema tergestinum, a species that occurred in 81 hectads but which seems to be particularly common in north-west England and south-west Scotland, for reasons that I do not fully understand. This needs further investigation but it could be another species that has a distinct biogeography that is not explained solely in terms of a particular chemical environment.   All six of these species qualify as “nationally scarce” rather than “rare” and do remember that my analyses are, at this stage, very preliminary.


Nationally scarce Gomphonema species? a. Gomphonema clavatum; b. Gomphonema insigne; c. Gomphonema ventricosum; d. Gomphosphenia (Gomphonema) grovei; e. Gomphonema turgestinum. Scale bars: 10 micrometres (1/100th of a millimetre). All images from or

One species that may qualify as genuinely rare is Tetracyclus emarginatus, for which we have just two records.   The genus itself is rare, and known mostly from the fossil record but is also sufficiently distinctive that it would not be misidentified or overlooked by analysts.   Another representative of the genus, T. rupestris, has been recorded from Britain but does not feature at all in our database.   When it has been recorded, it is from rock surfaces and damp mosses rather than submerged in streams, so it could have been overlooked in my preliminary analysis. A third representative of the genus, T. lacustris is, as the name suggests, likely to be under-represented in a database composed of samples from rivers, so I will reserve judgement on the rarity of this species though I suspect that it is another candidate for the red list.


Tetracyclus emarginatus. Scale bar: 10 micrometres (1/100th of a millimetre). Image from (photographer: Bernie ní Chatháin).

Another candidate is Cymbellonitzschia diluviana. Though I have tried not to comment on the distribution of species found in lakes, I will make an exception for this species because the habitat is quite well understood, thanks to the work of David Jewson and colleagues at the University of Ulster.   They found it to be most abundant on sand grains exposed to wave action in the littoral zone of Lough Neagh and a few other loughs and lochs with hard water and high pH.   As this combination of characteristics is relatively rare in the UK, it is reasonable to assume that C. diluviana will also be very limited in its distribution.


Cymbellonitzschia diluviana (left: valve view; right: girdle view of two recently-divided cells. Scale bar: 10 micrometres (1/100th of a millimetre). Image from (photographer: David Mann).

Finally, Chris Carter has suggested Entomoneis ornata as a candidate for the diatom “red list”, pointing out that it has not only rare in this country, but is also already on the Red List of Plants of Germany and is also considered to be rare in The Netherlands. Cells of Entomoneis are characteristically twisted around the apical axis, which tests even Chris’ photographic skills, and the genus is more common in brackish and marine waters than in freshwaters. However, it is certainly a species that should be on our preliminary list, and deserves further investigation.

In the next post I’ll consider the pros and cons of a “red list” of British diatoms.


Entomoneis ornata from the Oxford Canal, England, photographed by Chris Carter. Scale bars: 10 micrometres (1/100th of a millimetre)


Carter, C.F. & Belcher, H. (2010). A UK record of Entomoneis ornata (J.W. Bailey) Reimer in Patrick & Reimer 1975. Diatom Research 25: 217-222.

Jewson, D.H. & Lowry, S. (1993). Cymbellonitzschia diluviana Hustedt (Bacillariophyeae): habitat and auxosporulation.   Hydrobiologia 269/270: 87-96.

Ludwig G., Schnittler M. (1996) Rote Liste Gefahrdeter Pflanzen Deutschlands. (12 volumes but available as the list only from

A “red list” of endangered British diatoms?

I have had two conversations about rare algae over the past two weeks. The first was an invitation to contribute to an exercise to develop a list of diatoms that might form the basis of a “red list” of endangered algae. The second was a retort from a colleague that such an act would be meaningless as algae don’t have the same biogeographical restrictions on their distributions as higher organisms, and that all algae will grow anywhere so long as the environment is suitable.   The argument that algae don’t have biogeographical restrictions is an old one (summarised as “everything is everywhere, the environment selects”) but several recent papers have shown this to be wrong. Some species do appear to be cosmopolitan, as my previous post shows, but others do seem to be restricted to particular regions. Even if the local environment does play a large role in determining the algae that are found at a location, that does not seem to obviate the need for a list of endangered algae. On the contrary, it might even help focus attention on locations where efforts to restore a site might make a real difference.

The problem, in my opinion, is more basic: phycologists working in freshwaters do not have a strong tradition of systematic recording of the distribution of organisms. You only need to look at the Freshwater Algal Flora of the British Isles, and to see how many species are described as “probably cosmopolitan”, to realise the scale of the problem.

Because of their widespread use in ecological assessment, the diatoms are one group of freshwater algae where there may be enough data to start making some sensible judgements about the rarity, or otherwise, of individual species. I had a look at a dataset compiled for a project that I was involved with a few years ago in order to see what might be possible. This dataset comprises 6500 samples from 3305 sites spread across Great Britain and Ireland, most of which also have location information. The basis for conservation assessments is the distribution in 10 km squares, termed “hectads”, of which 1111 were represented in my dataset, out of a total of about 3000 in Britain.   The two criteria I am using are “nationally rare” for species that occur in 15 hectads or fewer, and “nationally scarce”, for those which are only found in 16 to 100 hectads. Using these criteria, I produced a “long list” of 150 diatom taxa that are “nationally scarce” and a further 226 which may be “nationally rare”. This, however, is where the real work starts.

Scanning down this list, I see several problems that need to be addressed before we can make serious judgements about the rarity, or otherwise, of particular taxa. However, I do also see a number of taxa on this list that I do believe to be genuinely rare or scarce and which are, at least, worthy of more study.   The problems are many and will spill into the next post but let’s make a start:

  1. The dataset I’m using is for rivers, and I will need to merge it with some additional datasets to get good coverage of lakes and also of soft water and acid habitats.   I would not trust this provisional analysis to give an accurate overview of the distribution of acid-loving Eunotia species, for example, nor of planktonic diatoms such as Asterionella formosa;
  2. I also noticed some species typical of brackish taxa which have been recorded occasionally in freshwaters (e.g. Bacillaria paxillifer). More comprehensive coverage of coastal and estuarine environments would probably show many of these to be quite common.   The same reasoning applies to those diatom species associated with terrestrial habitats (e.g. Hantzschia amphioxys).
  3. Most of the samples in our database come from rock or plant surfaces and it is likely that diatoms that prefer other substrata have been under-recorded, which will complicate interpretation of their distribution. Absence of evidence is not evidence of absence.
  4. Many of the taxa that are rarely recorded belong to taxa that have been subject to taxonomic uncertainty over the past few decades, leading to variations in how they have been recorded. Some of the rare diatoms are “varieties” of common species but as these often are (or were) poorly described in the literature, many analysts have not tried to distinguish them.
  5. Finally, we have to be sure that the records actually represent living populations. Because diatomists usually work from the empty silica frustules, we cannot tell whether a cell was alive at the time it was collected.   If you find a number of frustules of the same species, then it is reasonable to assume that some of these were alive, but if a species is represented by a single frustule, we have to consider the possibility that this was washed into the site from elsewhere, and never actually grew there.

The positives from this process are that I think we can start to make some judgements about the rarity (or otherwise) of diatoms that are reasonably well circumscribed in the literature (i.e. a low chance of misidentification) and where the underlying taxonomy has been relatively stable. A further criterion at this stage is that the candidate taxa must be common in streams and rivers and, ideally, associated with hard surfaces rather than soft sediments.   That’s quite a lot of caveats, but in the next post I’ll start to sort through the list and see if we have some genuine candidates for “scarce” or “rare” diatoms.


The dataset referred to was developed for:

Kelly, M.G., Juggins, S., Guthrie, R., Pritchard, S., Jamieson, J., Rippey, B, Hirst, H. and Yallop, M (2008). Assessment of ecological status in U.K. rivers using diatoms. Freshwater Biology 53: 403-422.