A winter’s tale

Inspired by Anne Jungblut’s public lecture at this year’s British Phycological Society meeting, where she talked about the algal life that thrives in Antarctica (available here), I decided that a mere thirty centimetres of snow was not going to deter me from some pond dipping at a local lake.   “I’m going out, I may be some time” I muttered to no-one in particular as I pulled on my boots, filled my pockets with energy bars, and headed into the snow-blasted waste that was County Durham.  

Fortunately, my companion on this expedition has a heritage that embraces the nationalities of both Scott and Amundsen, so I knew that I had a 100% chance of getting there and at least 50% chance of returning home. Undaunted, we made our way across snow-covered fields, through a Narnia-esque woodland and finally emerged at the edge of a Cassop Pond which was, perhaps unsurprisingly, frozen over, foiling my efforts to gain a sample by usual means.   We tracked cautiously around the margin, never quite sure where solid land was replaced by thin ice, until we found the outflow where there was an exposed channel and some dead read stems.   This would have to do as a sampling location so I dug out a sample bottle and plastic bag and pulled on a veterinarian’s disposable glove, designed to be shoved up into the warmth of a cow’s rectum but also a way of keeping your arm dry whilst sampling cold water in the middle of the winter.

A frozen Cassop Pond, January 2021.  

This was the moment, of course, when two acquaintances passed by and, recognising us, wanted to know why I was crouched beside a stream of freezing cold water wearing a bright orange veterinarian’s glove and fumbling around amongst decaying reed stems.   This, I am fairly sure, does not happen to real Polar explorers.   Amidst all the trials and tribulations of life in Antarctica, feeling a bit of a plonker is the least of your worries.

An effective way of collecting the algae off submerged plant leaves and stems is to place them in a plastic bag with a little stream or pond water and give them a vigorous shake.   This is what I did with a couple of handfuls of reed stems and the result was a brownish suspension in the bag which I poured into a sample bottle before allowing our inner Amundsen to guide us home.  Our return route passed a field of Highland cattle all of whom gazed placidly at me in a way that they almost certainly would not have done had they known that I had a veterinarian’s glove in my bag.   

Back home and warmed up, it was time to look at the murky suspension and see what it contained.  I’ve visited Cassop a lot over the years (the very first post on this blog, for example, described a visit, also in January) and had a good idea of what algae I might find.  Whether the unprepossessing substratum of dead reed leaves or the time of year or a combination, there was not quite the rich diversity I was expecting, but there were a lot of cells of Fragilaira (probably F. tenera) and a few other species too.   There were also plenty of tiny Lemna minor plants floating around at this time of year and, as my first ever post showed, these host a number of epiphytic diatoms.  

Algae and protozoa from Cassop Pond, January 2021: a. – e.: Fragilaria cf. tenera; f. Ulnaria ulna; g., h. valve and girdle views of Gomphonema acuminatum; i. possibly Tetrastrum; j. unidentified protozoan.  Scale bar: 20 micrometres (= 1/50th of a millimetre).   

This will be the first of several visits to Cassop pond this year.  Last year was the first time in several years that I did not have a regular focus for my posts (see “Reflections from Castle Eden Burn” for an overview of my 2019 explorations).  I had originally planned a series of visits to a location which, though easily reachable by car, would fall foul of the current lockdown restrictions.  Instead I’m looking at a pond that is walking distance from my house.   Maybe that is not such a problem: not everyone is lucky enough to have a National Nature Reserve on their doorstep and I have, in all honesty, not given this pond the attention it deserves over the years.

The richness of aquatic microscopic life in winter has been a recurring theme in this blog over the years but should that richness surprise us?   We approach the world of algae with mindsets that could be described as “Angiosperm Supremacists”, basing our assumptions on the entire plant kingdom on how we expect higher plants to respond.  Yet, in evolutionary terms, angiosperms are relative newcomers forced to exploit dry land because the best aquatic habitats had already been monopolised by algae.   Away from the protection that water’s high specific heat capacity offers a plant, survival in winter depends on being able to divert energy into a range of protective strategies in order to prevent damage due to freezing (see reference below).   There are algae that live in and on ice but, for most, the environment beneath the ice offers fewer challenges.  Indeed, as most of their grazers are poikilotherms, winter (all other things being equal) is not a bad time to be an alga.   


Knight, M.R. & Knight, P.H. (2012).  Low temperature perception leading to gene expression and cold tolerance in higher plants.  New Phytologist 195: 737-751.

Some other highlights from this week:

Wrote this whilst listening to: John Martyn and, in particular, a 1978 Rock Goes To College set on YouTube that I remember watching when it was first aired. [https://www.youtube.com/watch?v=GYvncpoeV5Q&t=2132s]

Cultural highlights:  A great new film called Sylvie’s Love, set in jazz-era New York.

Currently reading:  The Science Delusion by Rupert Sheldrake

Culinary highlight:  Recipe from The Guardian last weekend: a chocolate and marmalade tart.

The Hidden World of Algae

The British Phycological Society meets this week at the University of Nottingham where I’m an honorary professor so, unsurprisingly, I found myself on the organising committee.   “Let’s have an exhibition of Hilda Canter-Lund photographs as part of this” I said, rashly, at an early meeting.   “Good idea” came back the reply, followed, a couple of weeks later by “there isn’t a room at Lakeside Arts that would fit our needs, but they suggested putting the exhibition on boards around Highfield Lake instead”.   That piqued our interest as Highfield Park gets a lot of visitors from the surrounding suburbs so our pictures would get a large audience.   Then came Covid 19 and, overnight, our second-best option became the only show in town.   

If you live in Nottingham, then get along to Highfield Park to look at the exhibition.  We’ve focussed on the Hilda Canter-Lund competition but Hannah Kemp, who is doing a PhD on nuisance green algae, sent some samples of the unsightly green flocs that float in the lake during the summer to Chris Carter and we’ve also been able to show people what these look like when highly magnified.   

If you don’t live in Nottingham, then don’t worry: there is also an online version of the exhibition, created by Hannah using the Artsteps platform.  Use the navigation bar at the bottom of the screen to stroll through the exhibition and enjoy the pictures without the inconvenience of the January weather.   

The display board showing the condition of the lake at Highfield Park during the summer.  The photo at the top of the post was taken by Hannah Kemp.

Under Chris’ microscope the unsightly surface scums on the lake are transformed into objects of great beauty.  Look at the image below of Spirogyra, with its characteristic helical chloroplast.   These filaments are each only about a fortieth of a millimetre across, so the casual observer has no idea of how beautiful these can be unless they have access to a microscope.   Other flocs consisted of Cladophora glomerata, a broader (though still less than a tenth of a millimetre across) branched filament.  Cladophora, unlike Spirogyra, is rough to the touch and the absence of superficial slime means that other algae, such as yellow-brown diatom cells are able to piggy-back on its filaments to absorb some sunlight.  

The green alga Spirogyra, from surface scums growing in the lake at Highfield Park, Nottingham.  Photograph: Chris Carter. 
Filaments of the green alga Cladophora glomerata from flocs in the lake at Highfield’s Park, Nottingham.  Photograph: Chris Carter.
The diatom Rhoicosphenia abbreviata growing on a filament of Cladophora glomerata, from a floc growing in the lake at Highfields Park, Nottingham.  Photograph: Chris Carter.

These unsightly flocs are becoming increasingly common around the UK and Hannah is attempting to understand why this is the case during her PhD.  The literature on this topic is surprisingly thin: many words have been devoted to understanding how shallow lakes can swing from having diverse assemblages of macrophytes to being dominated by “pea soups” of suspended phytoplankton but, somehow, the reasons why flocs of filamentous algae can develop instead of phytoplankton has not been addressed.   Like many PhD students, Hannah’s plans have been thrown off course by the pandemic but sampling is, at least, underway now, so maybe we will have some hypotheses ready over the coming months.

Some other highlights from this week:

Wrote this whilst listening to: cellist-songwriter Lucinda Chua and, for nostalgia, Sade’s Diamond Life from 1984.

Cultural highlights:  Soul, the new Pixar film and the 2017 film Phantom Thread.  You may have heard of “Chekhov’s Gun”: this film features Chekhov’s Mushroom.  That might be a spoiler.  Sorry.

Currently reading:  G.K. Chesterton’s Napoleon of Notting Hill.  For a book group.  Otherwise I would probably have given up and reached for something a little less dated.

Culinary highlight:  a Sinhalese cook-at-home meal provided by Hoppers restaurant in London (“Cash and Kari”).  A Christmas present from our daughter.

The end of the road?

My final post for the year has traditionally been a round-up of the previous 12 months and a look ahead to the year to come.  This year, however, with the publication of the UK-EU trade agreement on Christmas Eve, there are serious matters that need to be considered.   The UK leaves the EU at 11pm on 31 December 2020 with, if the press releases are to be believed, reassurance that high environmental standards will be maintained, thanks to key clauses in the agreement (“Title X: Good Regulatory Practice and Regulatory Co-operation”).  Let’s put this to the test, using the “thoughtful reform” set out by Environment Agency Chief Executive James Bevan earlier this year (see “But …”).

Bevan’s call for “thoughtful reform” seemed to dilute the “one out, all out(1OAO) rule” that is at the heart of the Water Framework Directive, so let’s see how this might be handled under the terms of the trade deal.   This is not about the pros and cons of the 1OAO rule, only about whether a system that deviated from the 1OAO rule could be construed as violating the terms of the trade deal.

The first clause of the General Principles under this Title is: “Each Party shall be free to determine its approach to good regulatory practices under this Agreement in a manner consistent with its own legal framework, practice, procedures and fundamental principles49 underlying its regulatory system.”.   So long as the UK has appropriate primary and secondary legislation in place, in other words, the 1OAO rule is fair game.   Let’s read on.

Chapter 7 of this Title deals with Environment and Climate and Article 7.2 deals specifically with non-regresssion (“A Party shall not weaken or reduce, in a manner affecting trade or investment between the Parties, its environmental levels of protection or its climate level of protection below the levels that are in place at the end of the transition period, including by failing to effectively enforce its environmental law or climate level of protection”).   Most ecology professionals would regard weakening the 1OAO rule as “regression” but does it affect trade or investment?   

The next clause read: “The Parties recognise that each Party retains the right to exercise reasonable discretion and to make bona fide decisions regarding the allocation of environmental enforcement resources with respect to other environmental law and climate policies determined to have higher priorities, provided that the exercise of that discretion, and those decisions, are not inconsistent with its obligations under this Chapter”.  So maybe the UK government could argue that, regrettable though it may be to ditch the 1OAO rule, they are only doing this to strengthen other aspects of environmental protection.   

So let’s hypothesis that the 1OAO rule is scheduled to be ditched as part of a post-Brexit overhaul of environmental protection policy for the reasons outlined above but that the EU cries “foul”.  What next?   We skip several paragraphs until we reach Article 7.7 Dispute Settlement.  The text goes on to say: “The Parties shall make all efforts through dialogue, consultation, exchange of information and cooperation to address any disagreement on the application of this Chapter”.   If that doesn’t sort it out, then there are three remedies available: Articles 9.1 [Consultations], 9.2 [Panel of experts] and 9.3 [Panel of experts for non-regression areas].  Article 9.1 seems to be a continuation of the reference to “all efforts” in 7.7 whilst the other two Articles refer to a Panel of Experts.  These will consist of three people with “specialised knowledge or expertise in …  environmental law”, which seems to point to lawyers rather than ecologists in our case study, and they should be independent of both UK, EU and Member State governments.   They can receive written submissions from persons with relevant specialised knowledge and they produce a report which will determine whether or not the UK proposal to weaken 1OAO are contrary to the terms of the deal.  

Let’s say the panel of experts decides that the UK’s actions contravene the non-regression clause but the UK government disagrees.   At this point, an arbitration procedure starts up with, at the end, a tribunal (legal experts wholly independent of UK and EU courts) delivering a verdict.  If that finds against the UK, then there is the option of “suspension of obligations” (meaning, I presume, that the EU introduces some quid pro quo sanctions against the UK).   However, there seem to be plenty of ways for a competent government lawyer to game the system well before it reaches these latter stages so the 1OAO rule is, I suspect, doomed.  

This is all, I hasten to add, hypothetical: the 1OAO rule is a convenient pawn with which to test the new system largely because the Environment Agency have already signalled their intent.  The 1OAO rule is, let’s be honest, far from perfect.   The more general lesson would seem to be that whilst ecology and biodiversity standards that we inherit from the EU appear to be protected by the trade deal, in fact there are enough loopholes to make them extremely vulnerable.   Maybe we are naïve to expect more: this is a trade deal after all and the focus is on aspects of environmental protection that will affect competitiveness.   For every other aspect of safeguarding our environment and biodiversity, we are on our own …

Some other highlights from this week:

Wrote this whilst listening to:  Adrianne Lenker (of Big Thief)’s songs and instrumentals and Sing Me Home by Yo-Yo Ma and the Silk Road Ensemble

Cultural highlights:  Revisiting old films on the BBC iPlayer, including The Godfather and Tamara Drew.

Currently reading:   Rodham, by Curtis Sittenfeld: a novel describing an alternative future in which Hilary never married Bill Clinton.   Ennerdale Water makes a brief entrance.

Culinary highlight: Christmas Dinner, of course: roast turkey, potatoes roasted in goose fat, brussels, parsnips, gravy, cranberry sauce, bread sauce, Christmas pudding, brandy butter …

As old as the hills ..

I need to start with a confession: fieldwork in Cumbrian streams in December has a few drawbacks, not least of which is the water temperature.  Picking up boulders from a stream involves plunging your arm into cold water.  I’ve tried different sorts of gloves, but these inevitably result in a loss of dexterity and, unless the air temperature is really low, it is better to grit your teeth, roll up your sleeve and make sure that there is a warm fleece waiting bankside when you finish. 

This invariably means that my encounters with the submerged plants in this streams are brief and it is easy to miss features of interest. Nonetheless, on my most recent visit to the River Irt  a couple of weeks ago, I noticed some dark spots on some boulders that, despite the temperature, required a closer look.   Given the constraints of fieldwork under these conditions, I was not even sure at first whether I was looking at algae or moss.   It was only when I was back in my warm study, viewing the pictures on a big screen and with my samples teased out in a Petri dish that I was able to work out what I was seeing.   It was actually an acrocarpous moss (name, at present, not known) but accompanied by (and only just visible with the naked eye) tufts of Cyanobacterial filaments at a few points along the stem.   

A submerged boulder in the River Irt, December 2020.  Dark patches are mosses with associated cyanobacteria (and some young filaments of Lemanea fluviatilis) and green patches are mostly Mougeotia, Spirogyra and Zygnema.  The picture at the top of the post shows Cinderdale Bridge on the River Irt.  

I’ve encountered cyanobacteria associated with mosses in this area in the past (see “River Ehen … again”) and initially assumed that this was the same genus, Tolypothrix.  However, a closer look showed this not to be the case.  The lower image shows the broad arrangement of cyanobacterial filaments, with a row of cells (the “trichome”) lives within a thick sheath and then, in the upper image, two filaments appear to collide and veer off out of the sheath.  That’s called a “false branch” in cyanobacterial jargon: “false” because the trichome itself doesn’t branch even though the whole filament looks like it has branched.  False branches are a characteristic of a relative of Tolypothrix, Scytonema.   I’ve reported on Scytonema from this catchment before (see “Close to the edge in Wastwater“) but this species is different in both habitat and appearance.  The one I wrote about before was attached directly to the rock and had sheaths that were heavily pigmented whereas this species (probably Scytonema crispum) grew on mosses in the river that flows out of Wastwater and had little or no pigmentation in the sheath. 

Scytonema crispum from the River Irt at Cinderdale Bridge, December 2020.  Scale bar: 20 micrometres (= 1/50th of a millimetre)

These alga were growing in a river that flowed through some spectacular landscapes: the Wastwater screes rise up dramatically from the south-eastern shore and, at the northern end of the lake, the peak of Scafell Pike, England’s highest mountain is often visible.   These are composed of rocks of the Borrowdale Volcanics group, dating from the Ordovician era, approximately 450 million years ago.   That means that they are about twice as ancient as the dinosaurs.  By contrast, fossil remains of the cyanobacteria have been found from rocks that are 3.5 billion years old.  That means that, relatively speaking, the mountains surrounding Wastwater are mere babies compared with these algae.   Of course, cyanobacteria will have evolved over this time; however,  the Borrowdale Volcanics have been weathered, faulted and folded over the millenia too.   So, so long as you remember that change is the only constant in both geology and biology, these simple, largely inconspicuous filaments are, quite literally older than the hills.

Some other highlights from this week:

Wrote this whilst listening to:  RM Hubbert and Aidan Moffat’s Ghost Stories for Christmas.   Deliciously dark Christmas album from 2018.   But not as dark as Lou Reed’s Christmas in February.

Cultural highlights:  The film Ma Rainey’s Black Bottom, with Viola Wilson and Chadwick Boseman

Currently reading:   just finished The First Christmas by Marcus Borg and John Dominic Crossan and just starting Merlin Sheldrake’s Enchanted Life, about the fascinating world of fungi.

Culinary highlight: made my annual batch of Christmas ice cream, with mincemeat and plenty of cinnamon, cloves and nutmeg.  Served this with pears poached in ginger wine and port and some 

Curried diatoms?


Last week’s musing on mayfly anatomy has crystallised this week into a finished image of a nymph of Baetis rhodaniifeeding on stream algae.   One mandible is visible on the left cutting through a mixture of green algae and diatoms whilst a glossa – the nymph’s equivalent to a tongue – probes the biofilm at the centre right of the image.   At the back, you can see the nymph’s right foreleg extending up above the stone surface.   The algae in the picture are common in Lakeland streams: Gomphonena acuminatum and Tabellaria flocculosa along with the green alga Ulothrixon the left foreground, as an example of the thicker biofilms giving way to, on the right, an assemblage typical of heavily-grazed biofilms, with Cocconeis lineata prominent.    

Cocconeis lineata is often prominent at a location in Croasdale Beck, a small tributary of the Ehen that we visit regularly.  This is also a location where we often see large numbers of mayfly grazers as well as other invertebrates that can feed on algae (see “Blind to the obvious …”). It is often cited as a diatom that is resistant to grazing due to its low profile.  However, the story is not quite so straightforward as that as there is an unusually large number of broken valves, suggesting that the nymphs, even if they do not eat as many of the Cocconeis as they do other algae, do manage to damage them in the process.  Not only were there significantly more broken than intact valves but also the upper valves were more likely to be damaged than the lower ones, which would be in line with expectations, given what we know of how mayfly nymphs feed.   

Cocconeis lineata from Croasdale Beck, Cumbria, September 2020.  Top two rows: rapheless (upper) valves; bottom row: raphe (bottom) valves.  Scale bar: 10 micrometres (= 1/100th of a millimetre).  

The literature often refers to “selective grazing” and these illustrations may offer us a way of thinking through what this means.   Firstly, from the point of view of a mayfly nymph or a snail, the scale difference, even between the mouthparts and the algae, means that this only going to operate at a fairly coarse scale.  If grazing is selective then, to use a human analogy, it means choosing a restaurant serving French rather than Indian food rather than preferring broccoli to carrots.    Most of the species within biofilms are too mixed up together for us to contemplate an organism the size of an Ecdyonurus or Baetis nymph selecting one species over another (the situation may be different for smaller grazers such as the Chironomidae).   It is easier to conceive of the nymphs sensing the gross composition of a biofilm – whether there are lots of succulent young filaments of green algae or less nutritious cyanobacteria, for example. 

Broken valves of Cocconeis lineata from Croasdale Beck, September 2020.   Top row: rapheless (upper) valves; bottom row: raphe (bottom) valves.  Scale bar: 10 micrometres  (= 1/100th of a millimetre).  

There is, however, some evidence of diatoms producing compounds that deter grazers, and also that this trait varies between species.   Most of the studies, to date, come from the marine environment rather than streams so we need to extrapolate with care.  One paper does include some freshwater diatoms in a survey of aldehyde production although none tested positive.   That does not mean that freshwater diatoms do not produce aldehydes: one of the problems is that the algae that are easy to culture are often the fast-growing unfussy species and these tend to be the ones on which studies are focussed.   My suspicion is that aldehyde production is more likely to be found in the less abundant species which divert some of their energy to this rather than to simply growing and dividing.   A diverse community that includes a few aldehyde producers might be less attractive to grazers than a community where one non-aldehyde producer dominates.   Therefore, the greater the success of a diatom, relative to other algae, the more vulnerable it will be to grazers.  Crop back this prolific grower and the aldehydes will be more noticeable to the sensila on the nymph’s glossa.   It is another variant of the cat-and-mouse games I described in The stream easts itself … with a similar end-result of justifying diverse assemblages.

To extend my analogy of humans preferring a French restaurant to an Indian restaurant, one plant-based constituent of Indian meals (Capsicum spp.) produces a secondary metabolite which itself probably evolved to deter mammalian grazers (capsaicin) that is detectable even at relatively low concentrations relative to other ingredients.   Basmati rice is, as it were, protected from grazing by anyone who dislikes spicy food, even though it is not naturally spicy itself.  Several other common ingredients of Indian cuisine (potato, tomato, aubergine) are from the same family as Capscicum spp but are not spicy so, once again, we can extend this to diatom-dominated biofilms and speculate that a few species could provide enough aldehyde to protect the many, and that aldehyde production does not need to be a general response of all diatoms.   

There might, of course, be diatom equivalents of groups of lads who role up at their local Tandoori restaurant at the end of a drinking session on a Saturday night determined to eat the hottest curry on the menu, but there I go again: stretching a metaphor to breaking point and then giving it a gentle push into the realm of the absurd.  Regular readers should be used to this by now …


Wichard, T., Poulet, S.A., Halsband-Lenk, C., Albaina, A., Harris, R., Liu, D. & Pohnert, G. (2005).  Survey of the chemical defence potential of diatoms: screening of fifty one species for alpha, beta, gamma, delta-unsaturated aldehydes.  Journal of Chemical Ecology 31: 949-958.

Willoughby, L.G. (1988).   The ecology of Baetis muticus and Baetis rhodani (Insecta, Ephemeroptera) with special reference on acid water backgrounds.   Hydrobiology 73: 259-273.

Also: a poster and an abstract from Gary Caldwell’s research group at the University of Newcastle:https://core.ac.uk/download/pdf/326529331.pdf  and https://search.proquest.com/openview/98edae085a20d7367d7a8b5bcff2f31e/1?pq-origsite=gscholar&cbl=37953

Some other highlights from this week:

Wrote this whilst listening to:  Tom Waits and, in acknowledgement that Christmas is just two weeks away, Christmas in Puebla, 17th century Mexican Christmas music from Siglo de Ora.  Come to think of it, my Tom Waits session started on a Christmas theme, with “Christmas Card From A Hooker in Minneapolis”.  That’s about as festive as my Christmas playlist gets, I’m afraid …

Cultural highlights:  The well-received film Saint Frances, written by and starring Kelly O’Sullivan.   We’ve been waiting to see this for some time and it has finally arrived on streaming services in the UK.  

Currently reading:   The Book of Lost Things by John Connolly, a rare excursion, for me, into fantasy fiction.  

Culinary highlight:    Homemade Spirulina pasta filled with smoked salmon, cream cheese and dill served in a lobster bisque (the latter, I have to confess, from a tin).  

Flatpack flies …

Emboldened by last week’s foray into the world of invertebrate ecology, I thought I would push ahead with a picture of a different mayfly nymph grazing on algae as a “compare and contrast” exercise.   Mayflies form a distinct order and just as we would not expect a human to behave similarly to a gibbon or baboon, so we should not assume that members of different families within the Ephemeroptera feed in the same way.  Trying to convey this pictorially at the scale of the algae on which mayflies graze, however, requires quite detailed knowledge of the mouthparts of different species.  

My explorations of how Baetis rhodanii, another important grazer, feeds led me to a 1950 paper by T.T. (“Kitten”) Macan, an entomologist at the Freshwater Biological Association.  In this paper he lays out the mouthparts of various species of Baetis almost as if they were the parts in an Ikea instruction manual (come to think of it, “Dagslända”, the Swedish word for “mayfly”, would make a very plausible name for an Ikea product).

Structures of Baetis pumilus from Macan (1950).   Mx: maxillae; H: hypopharynx; L: Labium; Md: mandibles; 1-7: gills, numbered from the front; f,m,h: fore, mid and hind legs.

We do not get much of a sense from these drawings, however, of how they fit together and, more importantly, how they interact to manipulate food into the nymph’s mouth.   The same is true for many photographs of Baetis rhodaniilargely, it must be said, because the mouthparts are on the underside of the head and, therefore, difficult to photograph when the organism is alive.   I’ve included two labelled photographs taken from Kenny Gifford’s excellent website The Microscopic Life of Shetland Lochs which, along with Macan’s scale drawings, give me some raw material from which to plan a painting of a Baetis nymph feeding on algae.

The head of a nymph of Baetis rhodanii from Fitch Burn, Shetland Mainland, collected and photographed by Kenny Gifford (www.shetlandlochs.com) with labelled mouthparts. The head is about a millimetre across.

Some of the mouthparts are relatively straightforward to interpret, as they have direct mammalian analogues, and because Baetis feed by chomping (for want of a better term) on the algae on a rock surface. So we can see a basic apparatus of upper and lower jaws (maxillae and mandibles respectively) plus upper and lower lips (labrum and labium respectively).  Where mayfly nymphs differ from humans is in the various “palps” that accompany the mouthparts.   In the previous post I mentioned how the labial palp of Ecdyonurus was adapted into a brush-like appendage that swept the algae towards the mouth.  In the case of Baetis, the key feeding action is the downward thrust of the mandibles rather than the brushing of the labial palps, so these are not so distinctive.

One other important characteristic visible in the illustrations are the glossae and paraglossae, extensions of the labium roughly analogous to our tongues.   These, like our tongues, are equipped with sensory organs that, presumably, have some control over the nymph’s feeding behaviour.   Baetis nymphs, unlike humans, make little or no use of vision when feeding, so these other senses are particularly important.   The head of the Baetis nymph is about a millimetre across, or between 50 and 100 times larger than the organisms on which it feeds, to give you some idea of scale. 

A different view of the head of a Baetis rhodanii nymph with some different features labelled.  Again, the head is about a millimetre across.  Photographed by Kenny Gifford.

All of this is, as I said at the start of the post, preparation for a painting of Baetis grazing on stream algae.  This preoccupation with anatomy as a precursor to art puts me in noble company (see “I am only teaching you how to see …”) even if my intentions are rather more modest than Leonardo’s.   The point where we meet is also, however, a launchpad for the imagination: at some point we need to couple the anatomical evidence with a dash of imagination in order to bring viewers a little closer to experiencing life on a different scale. 


Gattolliat, J.-L. & Sartorini, M. (2008).  What is Baetis rhodani (Pictet, 1843) (Insecta, Ephemeroptera, Baetidae)? Designation of a neotype and redescription of the species from its original area. Zootaxa 1957: 69-80.

Macan, T.T. (1950).  Descriptions of some nymphs of the British species of the genus Baetis (Ephem.).  Transactions of the Society for British Entomology 10: 143-166.

Some other highlights from this week:

Wrote this whilst listening to:  When Strangers Meet by Yo-Yo Ma and the Silk Road Ensemble which includes a divine interpretation of Filippo Azzaiole’s Chi passa per’sta strada (“those who pass along this street”) played on oriental instruments.   And Odin’s Raven Magic by Sigur Rós.

Cultural highlights:  The National Theatre production of The Three Sisters, adapted from Chekov’s original by Inua Ellams.

Currently reading:   still Wanderlust: A History of Walking, by Rebecca Solnit. 

Culinary highlight:    Mushroom risotto made with spelt rather than rice and served with creamed spinach and homemade crispbread.

Mayfly mayhem …

If my previous post, on the role viruses may play in ecological cycles was just a little too close to home, maybe this post will be an antidote.  It continues the theme of organisms interacting to create the ecosystems we see in streams, but this time dealing with the effect that invertebrates, rather than microorganisms and viruses, may have on the algae that live in our lakes and streams.  

The painting at the top of this post is the end result of picking a mayfly nymph off a stone submerged in the River Ehen and realising that I only had the sketchiest of ideas about how it went about feeding on algae.   I brought it home with me, managed to identify the genus, if not the species to which it belonged (Ecdyonurus) and took a photograph.    You can see the characteristic flattened head that identifies it as a member of the Heptageniidae, along with the two large, upward-facing eyes, a row of plate-like gills along the abdomen and three tails protruding from the final segment.  

A nymph of the mayfly genus Ecdyonurus (Heptageniidae) from the River Ehen, Cumbria.  The organism, including the tail, is about 1.5 cm long.  

What we cannot see in this image are the mouthparts, hidden below that bulbous head.  I had to search around the internet to find detailed images of the mouthparts of Ecdyonurus, eventually locating some useful scanning electron micrographs in a paper by Todd Wellnitz and J.V. Ward.  These images are quite difficult for a non-entomologist to decipher, because insects have extremely different mouthparts to vertebrates.  In brief, they have, like us, upper and lower jaws (the maxillae and labium respectively) but both of these can have jointed extensions (“palps”) that are, in effect, “arms” with built-in cutlery, each adapted to that insect’s particular diet.  Imagine if a human had wanted to do all the things that we do with our arms but didn’t want to stop walking on four legs.  Now imagine that humans evolved a short pair of arms on either side of the face.   If that doesn’t sound bizarre enough, some arthropods have these palps on both the upper and lower jaws, so there could be four separate items of cutlery descending upon an unsuspecting prey organism.   

In the case of Ecdyonurus, the labial palps are brush-like appendages that it uses to sweep the algae that live on the stones towards its mouth.  That’s what the structure on the right of the image is supposed to represent, and part of my intention is to show this in relation to the size of the algae that are typically found in the habitats where Ecdyonurusfeeds.  The individual bristles that make up this brush are about five or ten micrometres (= 1/200th to 1/100th of a millimetre) apart, whereas the smallest diatoms are about ten micrometres long.   So Ecdyonurus should be pretty effective at scraping up most of the algae that it encounters.  

By way of analogy, a 1.5 cm Ecdyonurus nymph grazing on stream diatoms of this size is roughly equivalent to a human eating peas.  And all this is done, remember, without the mayfly actually seeing what it is doing – its eyes, if you remember, are on the top of the head.   Some mayfly nymphs have been shown to have sensory receptors in their labial palps, so it is reasonable to assume that Ecdyonurus has something similar.  This doesn’t necessarily mean that it feeds with any great discrimination, rather it chomps through all the algae, just leaving behind those that are too firmly attached to be removed easily.   Whether it can separate out two algae of similar sizes mid-meal (selecting peas but leaving sweetcorn, as it were) seems unlikely.  But then, if you know anything about insect lifecycles, you’ll know that mayfly nymphs don’t have parents they can easily annoy, which takes away most of the fun of separating peas from sweetcorn.  Or, by analogy, one species of Achnanthidium from another. 


Wellnitz, T.A. & Ward, J.V. (1998).  Does light intensity modify the effect that mayfly grazers have on periphyton. Freshwater Biology 39: 135-149.

Gaino, E. & Reborna, M. (2004).  The sensilla on the labial and maxillary palps of Baetis rhodani (Ephemeroptera, Baetidae).   Research update on Ephemeroptera and Plecoptera (E. Gaino, editor), University of Perugia, Perugia.

Some other highlights from this week:

Wrote this whilst listening to:  Gryphon, early seventies band who blended medieval and folk music with progressive rock.  

Cultural highlights:  Rewatched the film Amélie, probably my favourite film about Paris. 

Currently reading:   continuing with Wanderlust: A History of Walking, by Rebecca Solnit.  

Culinary highlight:    Continued the French theme with hake steaks on a cassoulet made with roast fennel, followed by crêpes suzette, made with garden apples rather than oranges.

The stream eats itself …

Do you mind if I write a post about viruses?   If you’ve had enough of viruses in 2020, feel free to skip this and wait until next week when normal service will be resumed.  For those of you that are still with me, this is, I hope, a first step in rehabilitating the reputation of viruses amongst natural historians.  

I’ve been meditating on the contents of a short review on the role that fungi and viruses play in microbial mats, and wondering if there are clues in this paper to some of the questions I’ve raised in this blog over the years about the extraordinary diversity of microscopic algae (see “Baffled by the benthos (1)” and “Baffled by the benthos (2)”).   To set the scene, I’ve included a plate showing at least four different species from the same genus present in a single sample from a loch on Shetland (the same one I discussed in “Quantifying our ignorance”).   Classical theory about niches helps us understand why we may get this level of variety in a single genus in different samples but is less effective at explaining how these species can apparently co-exist in such close proximity.   It was this that stimulated G. Evelyn Hutchinson to pose the Paradox of the Plankton which, in turn, was the starting point for my own admission to being Baffled by the Benthos. 

Five species of Cavinula from a single sample collected from Petta Water, Shetland Mainland, May 2019.  a. – g.: C. jaernefeltii; h. – k.: C. pseudoscutiformis; l. – m.: C. intractata; n. C. cocconeiformis; o. – s.: Cavinulasp.   Scale bar: 10 micrometres (= 1/100th of a millimetre).  Photos: Lydia King.   The photograph at the top of the post shows mixed algal growths (mostly Spirogyra spp.) growing in the River Irt, Cumbria.   Could it be that these clumps are sustained by viruses?

There is already some evidence that tiny chytrid fungi can affect algal abundance (see “Little bugs have littler bugs upon their backs to bite ‘em …”) and also that diatom species differ in their tolerance to such infections.   Chytrids can be seen by a keen observer using a light microscope and it is reasonable to expect viruses, which we cannot see with a light microscope, to have similar effects.   How might these explain the presence of so many members of one diatom genus in a single sample?

If we assumed that all four species of Cavinula were competing for the same limiting resources (light, nutrients etc) then we might expect the one that was most efficient at acquiring the resources it needed to thrive at the expense of the others.   However, by virtue of being successful, this same species will become the most obvious target for any pathogenic organisms that are present.   Just as the very success of humans at exploiting niches right across the planet has created ideal circumstances for Covid-19 to spread, so the most successful Cavinula species in a Shetland loch is going to be most likely to succumb to viral infections.  Theoretical studies have shown that this “kill the winner” strategy can explain the coexistence of closely-related species in circumstances that can be readily transposed to habitats where we find benthic diatoms.   That means that viruses are, ironic as it may seem from our present standpoint, partly responsible for the extraordinary diversity of life on earth.

There’s a second potential benefit that viruses bring to stream ecosystems: the end result of killing the winner is the breakdown of the cell membranes, making its constituents available to other organisms.  I’ve written before about how the algae in a healthy streams are usually hungry for nutrients (see “Blessed are you that hunger …”) so any nutrients that seep into the water in the aftermath of a viral infection will be rapidly hoovered up.    I’ll go one step further and suggest that this type of pathway (a variant on the so-called “microbial loop”) may explain why we often see algae in healthy rivers growing in clumps: proximity to other organisms means proximity, too, to any leaked nutrients as well as some protection from stream currents which might whip any nutrients away before they can be reabsorbed by other nutrients.   The title of this post is an adaptation of a sentence from the start of Barbara Kingsolver’s Poisonwood Bible: “The forest eats itself and lives forever”. That’s a fine encapsulation of a general ecological principle that works as well in a cold stream or Scottish loch as it does in a forest in the Congo.  

Flicking through some of the books on my shelf, I note just a single reference to viruses in T.T. Macan and E.B. Worthington’s New Naturalist volume Life in Lakes and Rivers (1951) and one in Brian Whitton’s River Ecology(1975).  Both of these refer to the potential presence of human pathogens in polluted water. By 2015, Brian Moss’s revision of the New Naturalist book, Lakes, Loughs and Lochs, contains eight references, only one of which alludes to human pathogens (and then only to mention Macan and Worthington’s single reference).  What can we conclude?  That there is yet another variant of the New Normal, this time with viruses recognised as key players in ecological processes.


Carreira, C., Lønborg, C., Kühl, M., Lillebø, A.I., Sandaa, R.-A., Villanueva, L. & Cruz, S. (2020).  Fungi and viruses as important players in microbial mats.  FEMS Microbiology Ecology 96 fiaa187. https://doi.org/10.1093/femsec/fiaa187

Short, S.M. (2012).  The ecology of viruses that infect eukaryotic algae.   Environmental Microbiology 14: 2253-2271.

Thingstad, T.F. (2000).  Elements of a theory for the mechanisms controlling abundance, diversity and biogeochemical role of lytic bacterial viruses in aquatic systems.  Limnology and Oceanography 45: 1320-1328.

Some other highlights from this week:

Wrote this whilst listening to:  Jazz 625: BBC4 programme about the British jazz scene, featuring Sons of Kemit and Ezra Collective, bands we enjoyed at Green Man in 2019.   Also, humming Janet Kay’s Silly Games, after its use in Small Axe

Cultural highlights:  Small Axe: Steve McQueen’s dramas on BBC1: the first, Mangrove, was a tough watch, focussing on racism in west London in the 1960s, but the second in the season, Lover’s Rock, has a more uplifting vibe.

Currently reading:   Wanderlust: A History of Walking, by Rebecca Solnit. 

Culinary highlight:   A Persian meal, supplied by Taste of Persia, formerly a Durham takeaway, now a London-based mail order company.  

On the pleasures of untidiness …

Go, sit upon the lofty hill,
and turn your eyes around
where waving woods and waters wild,
do hymn an autumn sound.”
 Elizabeth Barrett Browning, The Autumn 1833

Naturalists are explorers, of a sort. They are not necessarily of a type that ranges far and wide in search of exotic phenomena.  That’s one sort of exploration, for sure.  Another type is to travel to the same place over and over again and watch how it changes.   That type of journey is through time rather than space, but it is no less of an adventure, so long as your senses are attuned to what is happening around you.   Indeed, watching how much one location can change both through seasons and between years offers a cautionary tale to anyone who thinks that isolated, concentrated bursts of activity at a distant location (what our archetypal “explorers” are doing) are likely to yield definitive insights.

With that thought in mind, I was back at the River Ehen last week.   I’ve been coming here for eight years now, so I think I know it quite well but one of the things I have learned is that there is always more to discover.   Sometimes, this is because the river really has changed, sometimes (quite often, I suspect) it is because I have noticed something that has been there for a while but which I have hitherto overlooked.  Sometimes, it is a mixture of the two.

That fallen tree on the right hand side of the image at the top of the post is a case in point.   When I first started coming here, eight years ago, there was a patch of Nitella flexilis tucked under the footbridge close to the right bank.  A couple of years ago it disappeared for no apparent reason. I presume that it had been dislodged in a spate and washed downstream.   Then, over the past few months, I’ve gradually seen patches of Nitella appear again, though not in the same place.  Some of the most prolific stands are in the lee of the tree, where fine sediments have gradually accumulated.   It grows there along with Myriophyllum alterniflorum (alternate water milfoil) and Callitriche brutia ssp. hamulata (intermediate water starwort), creating a hotspot of macrophyte diversity, at least until that tree is dislodged and this area is exposed to the full force of the Ehen’s current again.  

Nitella flexilis (left) and Callitriche brutia var. hamulata (right) in sediments downstream of a fallen tree in the River Ehen, November 2020.  The fallen tree can be seen just to the right of the footbridge in the photo at the top of the post.

Aquatic ecologists can get quite misty-eyed at the mention of large woody debris because of the important role it can play in supporting biodiversity.   This example in the River Ehen is a good example of how natural treefall creates patches within a stream that creates a set of conditions enabling a range of species to thrive.   I’ve focussed on one of our larger freshwater algae in this particular example, but there is evidence of similar benefits working on invertebrate and fish populations too.   One day, probably after an exceptional flood, I’ll come back and find that this fallen tree has been washed downstream and these patches of finer sediments, along with the algae and plants that they support, have been eroded away.   Patches exist in time as well as in space: you just need to think in another dimension.  

The problem is that this type of woody debris makes rivers look untidy and owners and bailiffs are prone to remove it.   Anything that holds back water can cause localised flooding, which may be a problem for the owner of adjacent land; however, slowing down the flow is, generally, beneficial for communities downstream.   So that’s another reason why we should not pull out fallen tree trunks.   Once upon a time, a fallen tree trunk was only ever seen as a nuisance, now it is a “public good” with at least two tangible benefits for streams and rivers.   “Tidiness”, however, is not one of those but, then, look at an ecologist’s study or even the boot of his or her car, and you will see that it is rarely a trait that we endorse either.   


Thompson, M.S.A., Brooks, S.J., Sayer, C.D., Woodward, G., Axmacher, J.C., Perkins, D.M. & Gray, C. (2019).  Large woody debris “rewilding” rapidly restores biodiversity in riverine food webs.  Journal of Applied Ecology 55: 895-504.  

Some other highlights from this week:

Wrote this whilst listening to:  Stevie Wonder.  Because, halfway through Lockdown 2.0, we neeed cheering up.  

Cultural highlights:  To the Ends of the Earth: a Japanese film about a team making a travel documentary in Uzbekistan.   If Lost in Translation is about westerners discombobulated by Japanese culture, then this is (Lost in Translation)2.  Many of the scenes were set around locations in Tashkent and Samarkand that we recognised from our visit in 2017. 

Currently reading:   Why I No Longer Talk to White People About Race by Reni Addo-Lodge.

Culinary highlight:   A toss-up between Bouillabaisse and a water cress and horseradish risotto. 

Worst case scenarios …

After last week’s post from the Lake District I have travelled vicariously to the headwaters of the River Wye to report on a paper looking at the effect of liming on the ecology of headwater streams.   These areas are located in mountainous areas with soft water and, in many cases, extensive afforestation.  Although acidification due to “acid rain” has decreased in recent decades, ecosystem recovery is slow, hindered by accumulated acidity in the soil, as well as by the many conifer plantations.   One way to speed up this process is to spread lime in the headwater catchments in order to provide more buffering and to raise the pH and our paper (I played only a minor role in data analysis) followed the chemical and ecological changes that ensued.

For me, the study is interesting as a road-test of our Diatom Acidification Metric (DAM), developed with funding from Environment Agency.   What we expected to see was a gradual increase in the value of DAM following liming, indicating a shift from an acidified flora to one closer to what would be expected in a stream of that type.  And, indeed, that is what happened although, as is usually the case, there was a lot of noise in the relationship.  Values of DAM for samples collected following periods of high flow, for example, tended to be lower than those collected during periods of low flow. That is because hydrogen ions are washed out of soil during rainfall and make their way into the streams, depressing the pH.    

Adding lime to acid grassland in the upper Wye valley.  The photograph at the top of the post shows coniferous plantations in the upper Irfon valley.  Both photos courtesy of Ingrid Jüttner.

These discrepancies are, however, the whole point of monitoring such as this.  If there was a wholly predictable and stable relationship between biology and pH, we would not need to measure both: simply measuring pH would give you all the information you need.  Because pH is naturally variable, a single measurement of either biology or chemistry isn’t particularly helpful.   Even if you measured pH in a stream monthly, your estimate of typical conditions would still only be based on reliable insights from just three per cent of the year.  The rationale for biological monitoring has always been that the organisms are exposed continually to stream conditions and so give better insights than isolated visits to measure chemistry.

However, when we compared the diatom results with measured pH, we found that the average result for diatoms consistently over-estimated the condition of the streams.  The UK’s standards for pH and acid neutralising capacity (ANC) were set based on knowledge of the toxicity of pH to salmon fry.   This life stage is extremely sensitive so a single pulse of acid water could be enough to kill any fry exposed to it.   We got a much better fit between the diatoms and measured pH and ANC when we used the minimum value of DAM recorded at a site, rather than the average, as this gives a better indication of the “worst case” to which the fry will be exposed.   

Relationship between mean and minimum phytobenthos EQR (Ecological Quality Ratio) and mean pH and ANC in the upper Wye and Irfon catchments.  Horizontal and vertical lines indicate thresholds for high (solid) and good (dashed) status.  The regression line fitted by locally weighted scatterplot smoothing (LOESS) is shown as a solid line and the dashed diagonal line indicates the regression line fitted to the 10th percentile of the data.  More details in Jüttner et al. (2020).  

The problem is that routine assessments in the UK are based on just two diatom samples, and you’ll need to be very lucky to capture the whole range of conditions with such a lean strategy.   When designing a case study, however, there is no excuse for not having at least three or four replicates.   The more you have, the greater the chance of the lowest of them indicating the worst-case scenario for the stream you are monitoring.

There is one other possibility, which may work better if you have a small number of samples: subtract about 0.2 from the mean value of DAM.  That is about enough to correct it from giving an accurate insight into the condition of the diatoms to giving an insight into the overall state of the stream biota.  That should give you enough insight into what is happening on the 97% of the days when no-one collected a chemical sample.  From this, you should be able to work out what is going on in a stream and, more importantly (and as our paper shows) demonstrate when genuine improvements have been made.


Juggins, S., Kelly, M., Allott, T., Kelly-Quinn, M. & Monteith, D. (2016).  A Water Framework Directive-compatible metric for assessing acidification in UK and Irish rivers using diatoms.  Science of the Total Environment 568: 671-678. 

Jüttner, I., Kelly, M.G., Evans, S., Probert, H., Orange, A., Ector, L. & Marsh-Smith, S. (2020).  Assessing the impact of land use and liming on stream quality, diatom assemblages and juvenile salmon in Wales, United Kingdom.  Ecological Indicators https://doi.org/10.1016/j.ecolind.2020.107057

Some other highlights from this week:

Wrote this whilst listening to:  Benamin Britten’s War Requiem, as it is Remembrance Sunday.

Cultural highlights:  About Endlessness, a strange film by Ron Andersson in which a series of apparently mundane events are elevated to high art through a series of beautifully-lit and  carefully-crafted vignettes.

Currently reading:  Walking to Jerusalem by Justin Butcher, an account of a pilgrimage from London to Jerusalem to commemorate the 100th anniversary of the Balfour Declaration.  

Culinary highlight:   Pumpkin pie.