Wide Sargassum Sea …

It is, I am afraid, a fact of life that algae usually only attract the media’s attention when they are a problem.   Yesterday’s newspapers contained a good example of this, describing the masses of the brown seaweed Sargassum that have washed up on Caribbean and Latin American coastlines, disrupting the tourist industry.  Sargassum is a natural part of the  for the Sargassum is an interesting organism, living a predominately planktonic (floating) existence rather than living in the coastal zone, like most other seaweeds.  There is a region of the western Atlantic that has been named the “Sargasso Sea” as Sargassum is particularly abundant here.   The Sargasso Sea is a region of relatively still water in the midst of rotating ocean currents (the marine equivalent of the eye of a hurricane) and the Sargassum proliferates here, hosting a unique ecosystem of its own in the middle of the ocean.  It is from here that the larvae of eels start their long journey s across the oceans to our rivers, and to which the adult eels will, in time, return to spawn.

Although we have known about the Sargasso Sea for a long time (it was first named by Christopher Columbus), the arrival of such large quantities of Sargassum weed on beaches is a new phenomenon, and not one that can be explained easily.   Climate change is suspected, influencing the oceanic circulation patterns, but there is no definitive explanation as yet.

That we only read of algae in the popular press when they become a nuisance is, however, a real problem.   It creates the impression that algae are Bad Things that need to be controlled and kept at bay which, in turn, sets the agenda for environmental management.  The reality is that algae are Good Things, without which life on earth (and soft ice cream) would not be possible (see “Every second breath….”, “Healthy streams are slippery streams” and other posts).   However, preventing (or minimising the risk of ) Bad Things, does not necessarily mean that we have created an environment in which Good Things can thrive.  Yet it is hard – very hard – to get that message across.

The invention of microscopy

It is always a challenge to present scientific discoveries to my students from the perspective of the original audiences, many of whom would have been brought up with a world view that explained natural phenomena without the need for the discovery that you want your students to understand.   Worse still, they approach that same discovery with minds already adapted to the new vistas that the discovery revealed.   The discovery of the microscope is a case in point. Who knew, before Anton van Leeuwenhoek in Holland showed us, that there was so much variety of life living in ponds that we cannot see with the naked eye? Who knew how much more about human anatomy could be revealed by examining our tissues at high magnification?  

I have tried to convey some of this early wonder in the form of a conversation between Anton van Leeuwenhoek and his real-life friend, the painter Jan Vermeer but borrowing the style of the American comedian Bob Newhart. Bob Newhart is best known for a series of comic monologues in which he plays the role of ‘straight man’ to an off-screen subject. So, in the conversation that follows, we only hear the voice of Jan Vermeer on an afternoon in the mid-seventeenth century when his friend Anton van Leeuwenhoek has come around to show him his latest discovery…

Come on in, Anton, I’ve got something to show you … my latest painting. It’s a view of Delft and you can see your house and […] okay, I can see you’re not interested in my painting today […] you’ve got something to show me. What is it this time?   Another of those peculiar beasts which are too small to see unless we peer through that weird magnifying contraption that you’ve invented. I must say, it was a bit of a shock to see that huge flea-like thing looming up in front of my face last time you brought it to the tavern … if it is one of those then I’ll have a quick peek but then let’s take it downstairs to show it to my mother-in-law. I’d like to see her face when she … no, you say, it is not something from the canal this time. Well, I’ve got an open mind, and there are all sorts of ponds and ditches that you tell me are also chock-full of amazing creatures so pass it here and let me take a peek. Okay, let me just move to the window and … adjust it until I can … OH MY GOD. AMAZING. You’ve done it again, Anton.   There are hundreds of them … they remind me of tadpoles, but you are going to tell me that they are much much smaller … one fat round end and a long flexible tail, and they are all wriggling around, right in front of my eye. So what are they, and where do they come from? […]

Seamen? I can’t quite hear you properly, Anton. There was a cart going past just outside the window, but I thought you mentioned something about seamen.   So, you went down to the quay and a seaman gave you something and you thought you would look at it under your magnifying thing, is that what happened? […]   No? Don’t tell me a seaman came back from the Indies with some weird pustule and you had a poke at that? Please don’t tell me that’s what you did, because the last thing this family needs now is an untreatable skin disease. […]   No? Well that is a relief but I think you are skirting around the subject, Anton. Not “seamen”. I must have misheard you, then. […] Not “seamen”? Sounds like “seamen”? Are you playing a game with me, Anton? Something that sounds like “seamen” but is nothing to do with ships or sailing? Nothing like a brain teaser, mid-afternoon, eh? Here I am, an impoverished north European painter trying to make the most of the limited daylight and along comes my friend Anton with his toy which, by coincidence, also needs my precious daylight to be used and now he’s asking me for a word that sounds like “seamen” but is not actually … no … I’m going to close my eyes and take a deep breath and then you are going to tell me that this is not what I think it is. […] It .. is . what .. I .. think .. it .. is.


A glazed earthenware tile from Delft from the 1640s, around the time that Jan Vermeer and Anton van Leeuwenhoek were active.

Okay. Okay. That really is quite a lot for me to take in.   […] No, Anton, I agree with you that it is absolutely fascinating to think that human semen is so jammed full of these tiny little tadpole-like things all wriggling around, and that this does open up myriad possibilities for the study of human biology. But it does also raise some other, equally pertinent, questions. Tell me, Anton, if this is not too personal a question – this is, I presume, your semen […] it is. […]   So was it obtained, single-handed, shall we say, or with technical assistance from Mrs van Leeuwenhoek? […] The latter?   Okay.   Again, Anton, excuse the personal nature of the question but if you show these to other people then they are sure to wonder, so it is better for you if you have an answer prepared.   So you made sweet love to your wife and then, just as she was lying back in post-coital bliss, you leaped out of bed and reached for your magnifying contraption.   And you are sure that, during all of this, Mrs van Leeuwenhoek was not feeling just a little bit … shall we say … “used”?   […] She stormed off, you say?   She had a point. Mrs Vermeer would have done just the same. Did you manage to show her these tadpole-like things when she calmed down? […] You did? […] And what did she say? […] She slapped you? Hard? And accused you of picking up strange infections from Greet, the well-endowed barmaid down at the tavern?

Well, it does beg a question, doesn’t it, Anton. […] Yes, I’m sure you’ve been asking it yourself. What exactly are these tadpole-shaped things in your semen?   Hypothesis number one, the one that will ensure that the name of Anton van Leeuwenhoek is never forgotten, is that these minuscule wriggly things in your semen are the key to a full understanding of human existence.   But, and let’s be absolutely honest now, Anton, hypothesis number two is that these are, as Mrs van Leeuwenhoek suggests, something that you picked up from Greet in an upstairs room at the tavern. Now I, as you often point out, am no more than a humble artist, unversed in the subtleties of science, but I would suggest – as a friend, I hasten to add – that maybe you need to unravel that particular mystery as quickly as possible. […] You’ve already thought of that, you say?   […] And all you need, you say, is specimens of semen from a variety of subjects but especially from good family men who would never dream of cavorting with Greet in the upstairs room at the tavern. And … how do you intend to get those specimens .. let’s be honest, you need to know someone pretty well before you make such a personal request. […]

ABSOLUTELY NOT. Two reasons: first, Mrs Vermeer would make her own views very clear if I was to suggest it; and, second, the intimacy required for us to produce your specimen would be just that little bit harder to achieve if we knew that you were sitting outside the bedroom door clutching a swab and your magnifying contraption, poised to dash in as soon as we had finished. […] I’m glad you understand. So how, then, can a poor impoverished artist help in this endeavour?   […] You are thinking more along the lines of the single-handed option for semen production, are you? And recruitment would be so much easier if your volunteers could keep themselves focussed on the job in hand. So to speak.   I agree. Absolutely.   […]   A big picture of Greet naked? No, no, no, that’s not my style. […] No, I accept that Greet reading a letter or pouring milk into a jug is not particularly erotically charged but that is how I paint. Sorry.   You could go to Antwerp and ask Peter Paul Rubens, perhaps?   […]   That’s too far to travel is it? What about Greet looking coyly out of the picture wearing a pair of pearl earrings? With a smouldering intensity that encapsulates a suppressed eroticism that few will ever surpass? […] No, no. You are probably right about that one. It would never work as a painting.

26 hours in Oslo

My meeting at the Norwegian Environment Agency finished at lunchtime whilst my flight did not leave Gardermoen until 19:20, so I had a few hours on a beautiful autumn afternoon in which to enjoy Oslo. These interludes in my travels are perk of the job although experience has shown me that I need to be disciplined if I am to get the most out of a short time in a city. Set one goal, something really worth seeing, and do not be distracted. In my case, having read Thor Heyerdahl’s accounts of his voyages when younger, a visit to the Kon-Tiki museum was a must. It was actually a ‘must’ on a previous fleeting visit to Norway but on that occasion (some years ago now), the museum was closed for a private function hosted by Thor Heyerdahl himself. Second time lucky …

It is a great little museum containing both Kon-Tiki, on which Heyerdahl made his epic crossing of the Pacific in 1947, and Ra II, on which he crossed the Atlantic. They are tiny, flimsy-looking vessels, far too fragile, one would imagine, to contemplate crossing a lake, let alone a great ocean. Yet he did, and went on to make further voyages and, in the process, establish an experimental tradition in archaeology and anthropology which, though not offering conclusive proof, does at least suggest possibilities. Heyerdahl’s initial hypothesis that Polynesian islands were colonised from South America rather than from islands to the west was dismissed as fanciful at the time, yet he was able to prove that it was possible, and subsequent DNA analyses of Polynesian islanders have confirmed that some settlers had South American ancestry.


Kon-Tiki (left) and Ra II (right) at the Kon-Tiki Museum in Oslo, October 2015.

I had been contemplating using my remaining time to visit the National Gallery and pay homage to Edvard Munch’s The Scream. However, as the bus wound it’s way back through Oslo’s suburbs, I realised from my map that I was close to one other site that I had enjoyed on my previous visit and that the crisp autumn afternoon was too good to waste indoors. So I hopped off the bus and walked up a side road in search of Frogner Park, home to a collection of sculptures by Gustav Vigeland (1869-1943), a Norwegian artist far too little known outside his homeland.

Frogner Park contains over 200 sculptures in granite and bronze, mostly based on his studies of the human form.   There are babies and old people, single figures and groups, couples in love, and groups fighting.   They capture moods ranging from exuberance and anger through to contemplation and exhaustion.   The park is built on a hillside and visitors gradually ascend towards the centre point of the installation, a circle of granite stairs topped by a 17 metre high column which consists of 121 tightly-packed human figures struggling to reach the stop or, in a few cases, trying to save themselves from falling.   The backdrop to all these sculptures was an ultramarine sky and the trees of Frogner Park in all their autumnal glory.

And that was about all I had time to do.   I walked from Frogner Park until I reached a metro station, then travelled to Central Station and then, via the Airport Express, to Gardermoen. A couple of hours later, I was boarding my KLM flight to start the journey home.


Gustav Vigoland’s monolith and granite sculptures on the surrounding plinth in Frogner Park, October 2015.


The fountain in Frogner Park, Oslo, October 2015.

Picture this?


A curious moment of serendipity saw me stuffing a new scientific paper into my bag to read on the train as I travelled to a workshop on reduction linocut printing. A second instance of serendipity occurred when I walked close to the site of Thomas Bewick’s studio in Newcastle as I contemplated the contents of this paper whilst walking from Newcastle Station to Northern Print‘s workshop in the Ouseburn Valley. I was, clearly, destined to write a post on natural history illustration, and the problems of reproducing images.

The paper I was reading related the efforts of Carlos Wetzel and colleagues to understand the taxonomy and nomenclature of a group of very small diatoms, historically placed in the genus Navicula but more recently spread between Sellaphora and Eolimna. The problem they address is essentially one of calibration: do the names we use for modern diatoms correspond to the organism to which the name was first applied, or has our understanding of that species gradually ‘drifted’ over time so that we now use it either for a different species altogether, or for a number of species that match the original description?

The plate below puts the problem into perspective. It shows a number of specimens corresponding to the description of what we thought was Eolimna minima at the time, though should now probably be called Sellaphora nigri. These cells are mostly less than a hundredth of a millimetre in length, have a linear-elliptical outline and few surface features that can be resolved easily with the light microscope.    Small variations in the valve outline and the density of striae had encouraged diatomists to establish new species and varieties until there were a large number of names in circulation and it was not always easy to separate the wheat from the chaff.   Wetzel and his colleagues had tracked down the original descriptions and the “type material” (the specimens that formed the basis of these original descriptions) in an effort to sort out the mess.


Sellaphora nigri / Eolimna minima from Menahyl River, St Mawgan Bridge, Cornwall, September 2009. The scale bar is approximately 10 micrometres (= 1/100th of a millimetre) long.   Specimens are arranged into two “morphotypes”: “narrow” and “blunt”.   Photographs: David Mann.

Our understanding of diatoms is driven in large part by the technology available to scientists at any point in history. Not surprisingly, the first diatoms to be described tended to be the larger species, relatively speaking, and it is no surprise that the earliest descriptions of the very small forms that are the subject of this post are rather basic.   These date back to Kützing in 1849, Rabenhorst in the 1850s and Grunow in the 1860s, all of whom would have had relatively basic microscopes by modern standards, and who worked without electric light with which to illuminate their specimens. They also did not have access to high resolution mountants, which only became available in the middle of the twentieth century. Nor were they able to photograph their specimens and, indeed, any drawings that they made would have had to be passed to a specialist engraver, who would have transferred the image either to a woodblock (using the ends of hard woods such as box and cherry rather than cutting into the grain) or a metal plate.   So there would have been at least two steps between the observer’s initial view of the diatom and the published illustration which, in the case of diatoms such as these, was working right at the edge of the resolution of the light microscopes of the day. It is no surprise, then, that the organism that Kützing described as “Synedra minutissima” and which later workers considered to be a small Navicula has subsequently bounced through several genera (and families), before Wetzel and colleagues decided on the basis of light and electron microscopical observations of Kützing’s original material that it probably belonged to Halamphora.

Image reproduction is, I suspect, almost as significant as optical technology in determining the rate of advances in understanding of diatoms. You only have to look back at papers in Diatom Research published only 20 years ago, and compare both the quality and quantity of images to understand this. Photo-editing packages such as Photoshop and CoralDraw are the unsung heroes of modern diatom taxonomy, enabling images to be edited and rearranged in multiple combinations.   We can now do in a couple of hours what would have taken weeks of time for an engraver in the 19th century, capturing images of a quality that would have been beyond Kützing’s wildest dreams.   Having done this, we can then discuss the results via email and Skype with people in other countries, or even different continents.

Yet there is one final twist to this tale: the plate of Sellaphora nigri / Eolimna minima is one of a series of plates that David Mann put together last year whilst he and I were pondering some RbcL sequences from field populations.   The genetic information seemed to be telling us that there were several distinct genotypes within complexes that we were identifying, with the light microscope, as Eolimna minima.   The scale of difference was such as to suggest that these genotypes may well be distinct species, albeit barely discernible even with the very best light microscopes available. We put that work aside, distracted by other, more pressing tasks, but I dug out the plates when thinking around the issues I’ve discussed in this post.   So it is quite possible that we have still not solved all the mysteries of this group of tiny, but very common, diatoms.


Wetzel, C.E., Ector, L., van de Vijver, B., Compère, P. & Mann, D.G. (2015). Morphology, typification and critical analysis of some ecologically important small naviculoid species (Bacillariophyta).   Fottea, Olomouc 15: 203-234.

More about the life and work of Thomas Bewick in:

Uglow, J. (2006). Nature’s Engraver: A Life of Thomas Bewick.   Faber and Faber, London.

The picture at the top of the post is the result of my labours at Northern Print. It is a reduction linocut (also known as a “kamikaze linocut”, as the plate is destroyed during the production of the image) showing desmids from Upper Teesdale (see “Abstraction and Reality in Upper Teesdale”)

‘Signal’ or ‘noise’?

Ehen_15107_musselsI’ve been visiting the River Ehen now for three years and this is my 32nd post on this small Cumbrian river.   You might think that, after about 40 visits to each of four locations, I should be beginning to understand the biology of the Ehen. I sometimes find myself being lulled into this false sense of complacency myself: I have a fairly good idea of where in each reach particular algae can be found, and when, in each year, they will be most abundant.   It was no great surprise, last week, for example, when Maria finished measuring the biomass with her BenthoTorch and announced that it was higher than the measurements she made last month. We’ve seen this trend of a sharp increase in the quantities of algae at this time in previous years.   Similarly, we were expecting (and therefore looked for) the pink blushes of the red alga Audouinella appearing on the rocks at the lowermost site. Again, these had been a common sight in the river during the cooler months throughout the period of our visits.

Yet, in some other ways, the River Ehen has changed over the course of our visits. Most noticeably, the uppermost site, just below the outfall from Ennerdale Water, had some lush growths of the alga Nitella flexilis when we visited last week.   I’ve recorded this from the Ehen before (see “Finding the missing link in plant evolution”) but not from this particular location, and not in such quantities.   Growths of the submerged angiosperm Myriophyllum alterniflorum were also more conspicuous at this site than on previous occasions.

A few kilometres below the outfall, at the lowermost site that we visit routinely, I also noted that the mats of Phormidium autumnale, a cyanobacterium (blue-green alga) that is an ever-present at this site also seemed to be more conspicuous than on any of our previous visits.   The mats of this alga were generally most obvious at the stream margins, where they were periodically exposed to air (see “In which the spirit of Jeremy Clarkson is evoked …”). However, last week, they were also prolific at some permanently submerged locations.


Nitella flexilis growing in the River Ehen, about 400 metres downstream from the outfall from Ennerdale Water, October 2015. The clump is approximately 25 cm in length.

Are these changes in the distribution of alga in the Ehen telling us something about how the river itself is changing or are they within the range of “natural variation”?   My suspicion is that, even after three years close observation we have not seen every nuance of the river’s behaviour. Yet three years is a long time by the standards of many ecological studies.   We also know that the river has changed over the period that we have been visiting.   In particular, Ben Gill, a tributary stream that had been redirected to flow into Ennerdale Water in the 19th century, has recently been reconnected to the River Ehen. This should mean that the flow regime in the river is now more natural but we’ve noticed a lot more fine sediment in the river on occasions since this happened.   The lake acts as a huge sediment trap so maybe this sediment itself is a ‘natural’ feature of the stream?   There is a temptation to define ‘natural’ in terms of our own experience, which can make it hard to evaluate the significance of events that happened more than a lifetime ago.


A mat of Phormidium autumnale on the bed of the River Ehen, about five kilometres from the outfall from Ennerdale Water.   The scale bar indicates approximately one centimetre.

Indeed, I would not even be writing about the Ehen today had I not been called in to look at the river due to the excessive growth of algae.   This brings in another facet to the story: my colleague in this study, Ian Killeen, is an expert on the ecology and conservation of pearl mussels. He had seen enough rivers with healthy pearl mussel populations to know that the quantities of algae that he could see in the Ehen were unusual, and he then got in touch with me.   We have to be aware, as applied ecologists, that we often do not start collecting data until someone perceives a problem.   That, too, creates difficulties when trying to understand the ‘natural’ or ‘baseline’ condition of a river.

These are not new themes for this blog. I’ve talked about the need for broadly-skilled, observant field-based biologists as the foundation for any effective environmental management process (see “Slow science and streamcraft”) and pointed out the limitations of pursuing highly-specialised tech-based approaches (see “Replaced by a robot?”).   On the other hand, I am also realistic enough to recognise that the luxury of having a biologist look at the same stream on a monthly basis is way beyond the means of most regulators.   So we need to find a compromise and, in the process, we need to agree on the non-negotiable elements of any compromise.   Suffice it to say, ensuring that experienced biologists have enough time to visit the sites that they are expected to assess would have to be part of any package.   However, don’t take that for granted: the line has, I am afraid, already been crossed by some environmental regulators.

When is a diatom like a London bus?

This post takes us back to Semer Water (see “Lake Lakelake Lake”) for a closer look at some of the diatoms that live in the littoral zone.   I studied this lake back in 2012 as part of a project funded by Natural England, and recently used one of the samples collected as part of that study for a “ring-test” amongst diatomists involved in routine ecological assessment in the UK and Ireland. This provides an opportunity for a number of experienced analysts to take a detailed look at the diatoms present in a sample and compare notes.

Between us, we found over 90 different species that we could name in a single sample, amongst which there were a number that caused us no disagreement and a few where we struggled to achieve a consensus.   And there was one group where we achieved a consensus of sorts insofar as the entities that we found matched the pictures in the latest reference works, but shared a sense of misgiving about whether the names we used told the whole story.   The diatoms that caused these problems were representatives of a group of small diatoms that, for a long time, were grouped in the genus Fragilaria but which, following a paper by David Williams and Frank Round in 1987, were split between several different genera including Pseudostaurosira, Staurosira and Staurosirella.   This generated some controversy although, as the dust settled, most people agreed that these taxa definitely did not belong in Fragilaria, even if the exact allocation of species between the genera continued to excite debate. The plate below shows three “species” that we found in Semer Water although the suspicion is that the seven forms I’ve called “Staurosirella pinnata” may represent several different species.


Small Fragilaroid diatoms from the littoral zone of Semer Water August 2012.   A. Pseudostaurosira brevistriata; b. Staurosirella leptostauron; c. – i. different morphotypes within the “Staurosirella pinnata” complex. Scale bar: 10 micrometres (= 1/100th of a millimetre).

However, my purpose today is not to get bogged down in the minutiae of these nomenclatural squabbles but to take a step back and look at their ecology.   Members of this complex are widely distributed across a wide range of water type but they are particularly abundant in hard waters, both standing and running.   What interests me is that they often seem to occur together.   Hence the title of the post: like London buses, you wait ages for one small Fragilaroid species to appear in a sample, and then three come along at once…

In order to test this association, I searched my database and found 705 records where at least one of the more common species in the complex were found (out of a total of 3838 records).   309 (44%) of these contained more than one species, but this figure leapt to 82% when I only considered samples where the sum of these species exceeded two per cent, and a mighty 98% when I just included the 90 samples where the sum exceeded ten per cent.   You can see this trend clearly in the graph below where I have plotted the percentage of one species against the sum of the percentages of the other four that I have considered.   The issue gets more complicated when we consider that some of the so-called species could, themselves, be complexes of several species that can co-exist (as in the case of Staurosirella pinnata in the plate above).


Co-variation in relative abundance of common Fragilarioid species. Each plot shows the percentage of one species (or species complex) on the x axis, and the combined percentage of the other four species on the y axis. Log scales are used for the sake of clarity.   a. Pseudostaurosira brevistriata; b. Staurosira construens (and varieties); c. Staurosirella leptostauron; d. Staurosira elliptica ( = Pseudostaurosira trainorii); e. Staurosirella pinnata complex.

What is going on here?   If they all live in the same habitat then, in theory, the “competitive exclusion” principle should work to eliminate all but the fittest.   That two or more appear to co-exist on a regular basis suggests that they are occupying distinct niches that we are not recognising with our usual methods of studying the microscopic world of lakes and rivers (see “Baffled by the benthos (1)” and “Baffled by the benthos (2)”).   It might be a physical niche, but the niche could also be defined by chemical or biological factors.   Could it be, for example, that these different but (fairly) closely-related forms differ in their levels of resistance or tolerance to fungal or viral infections?   Or do they have subtle variations in the amount of light that each needs, but which are obliterated by our unsubtle sampling methods?

The result is the diatom equivalent of a “perfect storm”: neither the taxonomy nor the ecology are described with any great clarity.   It is possible that a better understanding of the taxonomy will lead to a more nuanced appreciation of their ecology. Taxonomists often dangle this bait, but the sad truth is that there are few cases where ecologists emerge blinking into the light after the taxonomists have finished their fiddling. But ecologists must take their share of the blame, being very conservative in the methods that they use to deduce ecological differences between species.   I could, in fact, use my 1930 edition of the Süsswasserflora vön Mitteleuropa to identify this group of species and, apart from the name changes, reach exactly the same  conclusions as I might have done 85 years ago.

Thanks to Ingrid Jüttner (National Museum of Wales) for the diatom photographs, and Eduardo Morales (Bolivian Catholic University, Cochabamba, Bolivia) for taxonomic assistance.


Williams, D.M. & Round, F.E. (1987).   Revision of the genus Fragilaria. Diatom Research 2: 267-288.

A flavour of the subsequent debate is given in:

Morales, E.A. & Trainor, F.R. (2008). A new paradigm for freshwater fragilarioid diatom classification? A critique of Lange-Bertalot’s new system. Journal of Phycology 37 (supplement): 36-37.