Blind to the obvious

I’ve moved just a few kilometres from the River Liza to the location for this post: Croasdale Beck, a stream which joins the River Ehen at Ennerdale Bridge.   Croasdale Beck has featured in a number of posts in the past (see, for example, “That’s funny …” and “Croasdale Beck in February”) partly because it continues to surprise me.   Maybe that reflects a level of complacency on my part: regular visits mean that I know what to expect which, in turn, means that I am alert to things that I do not expect.   Seeing something new in a stream I have never previously visited is evidence of life’s rich pattern; noticing something that was probably there on previous occasions but which I overlooked is a more profound and, somehow, humbling experience.  This post is about one of each of these sensations.

There are, for example, a number of turquoise-coloured boulders in the beck that were certainly not there when I first started visiting in about 2015.   Most of the stones in the beck are cobbles rather than boulders, so these stand out both for their size and colour.   The colour is, if you look closely, due to a thin surface film – a Cyanobacteria which I will call Lyngbya vandenberghenii although, because it is difficult to scrape off (the filaments live in amongst the rock crystals), and lacks any really eye-catching features, it is hard to be totally certain about this.   Presumably it likes the stability that boulders confer in this very flashy little stream.    I also see it in the River Ehen nearby but there its presence is easier to explain as it is confined to chunks of limestone washed in from the foundations of a section of the Coast-to-Coast walk.

Simulium argyreatum growing on a cyanobacteria-covered boulder from Croasdale Beck, Cumbria (shown in the photo at the top of the post).  The stone is about 30 cm across.   

Today, however, I’m interested in what is growing on top of the Lyngbya rather than in the Lyngbya itself: dense patches of what looks, with the naked eye, like small tan-coloured seeds.   These are the tiny larvae of Simulidae, whose adult phases are the annoying blackflies that swarm around streams on summer evenings.   They spin a web of silk on the substrate to which they anchor themselves using a ring of hooks at their posterior.   Their mouthparts include a pair of fans (one of which can be seen in the image below) and, by extending themselves above the stone, they can trap tiny particles (including algae) drifting in the current. They produce a secretion which makes the fans sticky and also have mandibles adapted to brush the trapped particles from the fans into their mouths.   Most descriptions of the Simulidae refer to this filter-feeding life-style but I’ve also seen them bent double so that their fans can brush up the algae which grow on the stone surfaces. 

Larvae of Simulum argyreatum on boulders in Croasdale Beck.  The upper photograph was taken in situ with the macro facility on my Olympus Tough camera (each is ~0.3 – 0.5 millimetres long) from a stone without the crust of Lyngbya whilst the lower photograph shows a magnified view of the feeding fan of one larva.

At some point, the larvae cease feeding and spin slipper-shaped cocoons with the closed end facing upstream and the open end downstream.   Six white ribbon-like gills protrude from the open end, ensuring a ready supply of oxygen to the pupa inside.   The adult develops inside this cocoon, eventually emerging with a duel raison d’être of having sex and irritating humans.  “Adult” hardly seems like the appropriate word: “perpetual teenager” seems more apt. 

Whilst the adult males feed on nectar, the females need a blood meal before mating, adding a dark Gothic twist to their natural history.  This difference arises from the roles each plays in reproduction: the male only needs the spurt of energy that the sugary nectar confers whilst the female needs the proteins and minerals from the blood in order to nourish the eggs.  In the south of England, bites from the Blandford Fly, a relative of the Simulium I watched in Croasdale Beck, can cause nasty rashes whilst in large parts of Africa the bites from other species of Simulium can inject the parasite responsible for Onchocerciasis, or river blindness.   This was a common disease in the region of Nigeria where we lived in the early 1990s so I’ve seen the damage that these flies can cause.   Much as we find black flies and midges to be a nuisance in this country, at least they are not vectors for potentially deadly diseases. 

At a deeper level, knowing about the life cycle of Simulium reminds us that we are not just observers of aquatic ecosystems, we are, indirectly, part of these ecosystems too.  We may like to think of ourselves as the ultimate predator (remembering that this power brings with it great responsibility) but sometimes, as here, we can be the prey too. 

Clusters of Simulium argyreatum pupae on the Lyngbya-covered surface of a boulder in Croasdale Beck.   Each is about 3-5 millimetres long. 

Reference

www.blackfly.org.uk

And thanks to Richard Chadd for identifying the Simulium from my photographs.

Some other highlights from this week:

Wrote this whilst listening to:  The late great Toots Hibbert, remembering, in particular, Toots and the Maytals’ set on the West Holt Stage on a glorious summer evening at Glastonbury 2010

Cultural highlights:  We’re in the Lake District this week and, having recently watched part of Simon Scharma’s BBC series on the Romantic Movement, I’m reflecting on the role that the landscapes around me played in catalysing the work of Wordsworth, Turner and others. 

Currently reading:  English Pastoral by James Rebanks, a thoughtful analysis of the state of British agriculture that does not shy away from criticism either of farmers or naïve ecologists.

Culinary highlight:  James Rebank’s thesis hangs on the necessity of animal husbandry to maintain healthy soils.  With that in mind, I ate a Lakeland lamb steak at the Shepherd’s Arms hotel in Ennerdale Bridge with a clear conscience. 

Belt and braces …

There was too much going on in the rock pools at Howick Bay to capture in a single post.  Just beyond the periwinkles quietly grazing on the turf of filamentous brown algae that I described in the previous post, for example, I photographed this vista.  In the foreground, there are buoyant ribbons of Ulva intestinalis (“gut weed”) rising above fields of the red algae Corallina officinailis, a red alga which deposits calcium carbonate in the cells to produce stiff, brittle fronds, unpalatable to most of the animals that share the habitat.   Then, in the background, there are fronds of the brown alga Fucus serratus (“serrated wrack”) which, in turn, bears massed filaments of yet another brown alga, possibly Pilayella – see “Epiphytes with epiphytes”).  That’s three distinct algal lineages in a single photograph. 

My observations of the biofilm sample I described in the previous post also revealed one other group: the Cyanobacteria and, more specifically, the Rivulariaceae.  We’ve met this family many times over the years (see “Both sides now” and references therein) and, whilst I knew that the family was also found in marine environments, I had not personally seen it before anywhere but in freshwaters.  The Rivulariaceae are “belt and braces” organisms, equipped with evolutionary adaptations to cope with both phosphorus and nitrogen deficiency.  This means that they are superbly equipped to cope with situations where nutrients are very scarce and, as a result, they can be particularly good indicators of the condition of the environment. 

Fragments of Rivulariacee colonies (probably Rivularia atra) from the biofilm at Howick Bay, Northumberland, August 2020.  20 micrometres (= 1/50th of a millimetre).  

Howick Bay is about 70 kilometres north of Newcastle and the River Tyne.  Travel a further 100 kilometres north and you reach another River Tyne.  This one is shorter, gathering water from the Lamermuir Hills south of Edinburgh and flowing east across East Lothian before joining the North Sea in a large sheltered bay just north of Dunbar.   I’ve never been there but when I worked at Durham University colleagues used to trek up regularly to study the algae on the upper part of the shore.   They had found colonies of Rivularia growing in pools on the beaches of this bay and were curious to know more about the conditions that allowed it to thrive.  

They noticed that the Rivularia colonies thrived in pools on the upper part of the intertidal zone but also that there were large amounts of seaweeds (especially oarweed – Laminaria digitata) dumped at the top of the intertidal zone during extreme high tides. As this rotted, phosphorus and nitrogen leak out.  Much of the nitrogen is lost to the atmosphere as ammonia but the phosphorus concentrations were often much higher.  This is where Rivularia’s “belt-and-braces” strategy comes into play: the pale green heterocysts at the base of the filaments (see “Blue skies and blue flowers in Upper Teesdale” for clearer illustrations) capture atmospheric nitrogen and turn it into compounds that the organism can use whilst the long tapering hairs exude enzymes which scavenge the phosphorus (still often bound into molecules originating in the seaweed.   

I did not see intact colonies of Rivularia at Howick Bay; however, its presence here is very plausible: particularly as the seawater here is relatively clean with few obvious sources of nutrients.   I suspect that the situation at Tyne Sands is an extreme manifestation of Rivulaira’s ability to efficiently recycle phosphorus from the communities around and about.  As soon as the naturally sparse nutrient pool is supplemented by other sources (i.e. “pollution”), it will be out-competed by faster-growing algae and, eventually, disappear.  So these few fragments of Rivularia (or a close relative) are a good sign that this part of the Northumberland coast is in a relatively healthy state.  So too, for that matter, is the diverse assemblage of seaweeds that we found during our brief visit.   

However, you don’t need to be a trained ecologist to work out that there is something special about the Northumberland coast.  The stream of people making their way to the beach at Dunstanburgh, our fellow walkers along the coast path and the denizens of the pubs and cafés in Crastor had all worked this out for themselves.   There is, in fact, a growing field of research on the subject of “blue space”, arguing that aquatic environments have a particular restorative potential.   Maybe – just maybe – dabbling around in rock pools awakens some primeval instincts of foraging for shellfish.   Or, maybe it is just reawakening memories of beach holidays as a child.  

References

Khoja, T.M., Livingstone, D. & Whitton, B.A. (1984).  Ecology of a marine Rivularia population.  Hydrobiologia 108: 65-73.

White, M., Smith, A. Humphryes, K., Pahl, S., Snelling, D., Depledge, M. (2010).  Blue space: the importance of water for preference, affect and restorativeness ratings of natural and built scenes.  Journal of Environmental Psychology 30: 482-493.

Yelloly, J.M. & Whitton, B.A. (1996).  Seasonal changes in ambient phosphate and phosphatase activities in the Cyanobacterium Rivulaira atra in intertidal pools at Tyne Sands, Scotland.  Hydrobiologia 325: 201-212. 

Some other highlights from this week:

Wrote this whilst listening to:  Sitar virtuoso Anouska Shankar’s concert at the BBC Proms, dedicated to her father Ravi.  

Cultural highlights:  The 2018 film Can You Ever Forgive Me? with Melissa McCarthy and Richard E. Grant.  We saw it when it first came out but it stood up well to a repeat viewing this week.

Currently reading:  A Shepherd’s Life by James Rebanks, a very readable account of farming in the Lake District.   Of particular interest to me as much of our fieldwork is in the area, watched by the Herdwick and Swaledale sheep that he writes about.

Culinary highlight:  vegan chocolate brownie at the end of Southend Pier which was, it occurred to me afterwards, the closest I have come this year to having a meal “abroad”

 

Twisted tales …

Spirulina_ChrisCarter-

As opportunities for field work are still limited, I have returned to the banks of Lough Down for this post.   Lough Down, as some of you will have worked out for yourselves, is not somewhere that can be defined in terms of exact geographic co-ordinates, rather it is a state of mind.  However, that means that, in ecological terms, it is as diverse as I want it to be and, as such, it offers plenty of opportunities for writing about algae that I would not otherwise come across.   Thankfully, Chris Carter is another habitué of Lough Down and its environs, so I can use his pictures to illustrate these posts.

I used a Pasteur pipette to suck up a likely-looking patch of algae growing over some fine sediments in the littoral zone of Lough Down and brought this back to examine under my microscope.  When magnified, I was presented with the view of blue-green coloured helices twisting and turning across my field of view which means that this is almost instantly identifiable as the Cyanobacterium genus Spirulina.   It is, in effect, a helical cousin of genera such as Phormidium and Oscillatoria which we have encountered many times in this blog.   If you look closely, you’ll see that there are no heterocysts – the specialised cells responsible for nitrogen-fixation – whilst this particular population also has no gas vacuoles.  These are structures inside the cell which make the cells buoyant.  Many of the Spirulinaspecies found in warmer parts of the world have these, enabling them to live suspended in the water, whereas the temperate species tend to live at the bottom of lakes and ponds.  Whilst a few species definitely prefer freshwaters, most are associated with brackish and marine habitats, including saline lakes in Africa such as Lake Chad.

Spirulina is not a particularly common alga in UK and Irish freshwaters, but there is one habitat where it can be conspicuous: the shelves of health food stores.   All sorts of claims have been made for its health-giving properties – some supported by evidence, others not – earning it the epithet “superfood”.   There is, for example, evidence that women from communities around Lake Chad who regularly ate Spirulina (“Dihé”) had higher levels of Vitamin A than those who did not.   However, vitamin A deficiency is common in the region and the effects would not be pronounced in regions where there was a greater range of sources of vitamin A in the everyday diet.   On the other hand, Spirulina comes from the same sub-class as a number of Cyanobacteria known to produce neurotoxins, and there is some evidence (admittedly much less than for other genera) for it also producing toxins.   The aggressive marketing of Spirulina is enough to make me wary: there is no such thing as a “superfood”, except as one small part of a balanced diet.   Buy it and use it, by all means, but do not expect miracles.

I should mention, in closing that “Spirulina”, as commonly understood, is actually two genera: Spirulina and Arthrospira.  Much of the material sold as health food actually belonging to the genus Arthospira, which is broader than Spirulina and has more distinct cross-walls.   Looking at the Freshwater Algal Flora of the British Isles, I see a record for Arthrospira jenneri from a pond just a short cycle ride from my house from 1938.  Maybe I should make a trip one day soon to see if it is still there …

References

McCarron, P., Logan, A. C., Giddings, S. D., & Quilliam, M. A. (2014). Analysis of β-N-methylamino-L-alanine (BMAA) in Spirulina-containing supplements by liquid chromatography-tandem mass spectrometry. Aquatic Biosystems. https://doi.org/10.1186/2046-9063-10-5

Roy-Lachapelle, A., Solliec, M., Bouchard, M. F., & Sauvé, S. (2017). Detection of cyanotoxins in algae dietary supplements. Toxins. https://doi.org/10.3390/toxins9030076

Soudy, I. D., Minet-Quinard, R., Mahamat, A. D., Ngoua, H., Izzedine, A. A., Tidjani, A., … Sapin, V. (2018). Vitamin A status in healthy women eating traditionally prepared Spirulina (Dihé) in the Chad Lake area. PLoS ONE. https://doi.org/10.1371/journal.pone.0191887

Wrote this whilst listening to: Bob Dylan’s Live at Budokan, Slow Train Coming and Saved.  Also, Big Thief’s new single Love in Mine.  Still not sure how I missed their set at Green Man 2019.

Cultural highlights:  Enjoyed the film Peanut Butter Falcon, an indie hit last year which we missed first time around.   Also discovered a podcast on Spotify called Winds of Change by American journalist Patrick Radden Keefe.  It might be about American soft power and psy-ops at the end of the Cold War or it might just be a loopy conspiracy theory.  Not sure I know myself yet.

Currently reading:   Just about to start Sarah Walter’s The Paying Guest.

Culinary highlight:   Either a Yotam Ottolenghi recipe for tamarind and tomato braised chickpeas from the Guardian [https://www.theguardian.com/food/2020/may/09/tamarind-tomato-braised-chickpeas-savoury-porridge-browned-butter-lime-rice-pudding-yotam-ottolenghi-thrifty-recipes] or an improvised East-meets-West better-than-it-sounds risotto topped with steamed sea bass with ginger and spring onions.

Whatever doesn’t kill you …

Potamogeton_epiphytes_April20

The previous post focussed mostly on the higher plants that I found in the short stream that connects White’s Level with Middlehope Burn.  I mentioned the mass growths of algae that I found growing immediately below the entrance to the adit, but I did not talk about them in any detail, instead spinning off on a tangent while I mused on why the water cress had a purplish tinge.

When I did find time to examine the algal floc, I found it to consist of a mix of three different algae, the most abundant of which was Tribonema viride, but there were also populations of a thin Microspora (not illustrated) and Klebsormidium subtile.   I talked about Tribonema in the drainage from the Hadjipavlou chromite mine in Cyprus last year (see “Survival of the fittest (1)”) and both Microspora and Klebsormidium are also genera that are known to frequent these habitats.  Indeed, there is evidence that the populations that grow in these extreme habitats have physiological adaptations that help them to cope with the conditions.  Brian Whitton, my PhD mentor, led several studies on these adaptations in the streams of the northern Pennines in the 1970s, and Patricia Foster did similar studies in Cornwall at about the same time.   There is probably a mixture of physiological strategies involved, including the production of low-molecular weight proteins, which bind the toxic metals, and the production of extracellular mucilage.  Most of the populations I find in such habitats have a distinctly slimy feel due to the production of extracellular polysaccharides, and it is possible that these play a role in trapping the metal ions before they can get into the cell and cause damage.

Tribonema_viride_WhitesLevel_Apr20

Filamentous algae from the drainage channel below White’s Level, upper Weardale, April 2020.  a., b. & c.: Tribonema cf. viride, showing the characteristic H-shaped cell ends.   d.  Klebsormidium cf. subtile.  Scale bar: 10 micrometres (= 100th of a millimetre).   The picture at the top of the post shows an artist’s impression of Chamaesiphon cf. confervicolus on the upper surface of a Potamogeton polygonifolius leaf. 

I also had a look at the algae growing on the submerged leaves of Potamogeton pergonifolius in the channel between the adit and Middlehope Burn.   One easy way of examining them is to add a small amount of stream water then shake the leaves vigorously in a plastic bag.  The result is a brownish suspension of algae that can be sucked up with a Pasteur pipette and placed on a microscope slide.  When I did this, I found a community that was dominated by a short cyanobacterium, closest in form to Chamaesiphon cf. confervicolus.  The other abundant alga in the sample was Achnanthidium minutissimum, which is often common in minewaters, along with smaller numbers of a few other species.  The total number of species in the sample was just 12, which is low by the standards of streams without metal pollution, but such suppression of all but the hardiest species is another characteristic effect of heavy metal pollution.

I’ve added a “cf” (from the Latin conferre, meaning “compare to”) to my identification of Chamaesiphon confervicolus because this is the closest name, based on a comparison with images in the Freshwater Algal Flora of Britain and Ireland.  However, it is not an exact match.  Whether this is because the metals have strange effects on Chamaesiphon (as we saw for diatoms in “A twist in the tale …”) or whether our knowledge of the species within this genus is imperfect is not clear.  But discretion is the better part of valour in this instance.  Chamaesiphon species fall into two groups: those that live on stone surfaces (see “Survival of the fittest (2)”) and those that live on algae and plants, such as the one we see today (another is illustrated in “More from the River Ehen”).   They consist of a single, elongate but gently tapering cell, attached at one end to the plant and enclosed in a sheath.   The upper end of the filament forms small spherical buds (technically “exospores”).  One reason that I am wary of calling this population C. confervicolus is that most illustrations of this species show a stack of exospores in the sheath, whereas the White’s Level population all had just a single exospore.

Chamaesiphon_confervicolus

Chamaesiphon confervicolus, growing on Potamogeton polygonifolius in White’s Level outflow, April 2020.   Note the exospores at the end of the cell.  f. and g. show the sheath very clearly.  Scale bar: 10 micrometres (= 100th of a millimetre). 

The picture at the top of this post shows an artist’s impression of the Chamaesiphon cf confervicolus on the upper surface of the Potamogeton leaf.   I wanted to get some idea of the size, shape and arrangement of the epidermal and stomatal cells on the Potamogeton leaves and resorted to the tried and tested technique of painting a layer of clear nail varnish onto the leaf surface, then peeling this off when it had dried.  This had the added (and unexpected) benefit of also pulling of the epiphytes, giving some idea of their arrangement on the leaf surface at the same time.   One extra observation that this yielded was that upper surface was dominated by Chamaesiphon, growing in clusters, whilst the lower surface had greater representation of diatoms.   I’ve also tried to portray the chloroplasts in the stomata guard cells.  Plant epidermal cells generally do not contain chloroplasts, as their purpose is to protect the mesophyll cells that are the main centres of photosynthesis.  Guard cells of stomata, however, need energy to open and close the stomata so these are the exception to this rule.  I had not even been sure that I would see stomata on the upper surface of the cell, as these are mostly found on the underside of leaves; however, Potamogeton appears to have stomata on both surfaces.  As ever, there is a certain amount of evidence along with a dose of extrapolation.   Imagined, but not imaginary …

You can find a description of the terrestrial plant life of Slitt Mine and its environs in this post on Heather’s blog.

References

Foster, P.L. (1982).  Metal resistances of Chlorophyta from rivers polluted by heavy metals. Freshwater Biology 12: 41-61.

Harding, J.P.C. & Whitton, B.A. (1976).  Resistance to zinc of Stigeoclonium tenue in the field and the laboratory. British Phycological Journal 11: 417-426.

Robinson, N.J. (1989).  Algal metallothioneins: secondary metabolites and proteins.  Journal of Applied Phycology 1: 5-18.

Say, P.J., Diaz, B.M. & Whiton, B.A. (1977).  Influence of zinc on lotic plants. I. tolerance of Hormidium species to zinc.  Freshwater Biology 7: 357-376.

Sorentino, C. (1985).  Copper resistance in Hormidium fluitans (Gay) Heering (Ulotrichaceae, Chlorophyceae).  Phycologia 24: 366-368.

(Note that Hormidium is the old name for the genus Klebsormidium.  There is an orchid genus called Hormdium and, as this was described first, it takes priority.)

 

Some other highlights from this week:

Wrote this whilst listening to: Bob Dylan’s New Morning and Pat Garrett and Billy the Kid.   Also, Samuel Barber’s Prayers of Kirkegaard.

Cultural highlights:  The Netflix series Unorthodox, about a young woman fleeing a Hassidic community in New York.

Currently reading:  Agatha Christie’s A.B.C. Murders.

Culinary highlight:   Arroz con leche (Spanish rice pudding) served with peaches poached in madeira.

Shuffling the pack

Microcystis-Ladybower_CCarter

The next group of algae I’m going to consider in my review of higher taxonomy and systematics, the Cyanobacteria, or “blue-green algae”, present some significant challenges.  Not least of these is a shift over the past forty years from being classified according to the rules of botanical nomenclature to being classified according to the International Code of Nomenclature of Bacteria.  The former assumed species could be defined from field material on the basis of morphology, with “type specimens” preserved in herbaria; the latter uses axenic (i.e. pure) cultures as the basic taxonomic unit, and allows a wider range of attributes than just morphology.   In recent years, as those who follow this blog will know, properties such as gene sequences have also been used to define species although the Code of Botanical (now Biological) Nomenclature still requires a description of the any new species that are described, with an expectation that the morphology will take a prominent role in that description.  As this post will show, morphology is no longer such a reliable indication of how Cyanobacteria are organised as it was in the past.

For practical purposes, many Cyanobacteria fall into the same size range as other algae, live in communities that include many protist groups and can be identified using similar techniques as would be employed to identify other algae.  They also have a form of photosynthesis that produces oxygen as an exhaust gas, in contrast to other bacteria which are capable of photosynthesis. This means that a default view of the Cyanobacteria as “algae” is a reasonable starting point for a field ecologist.   However, at an intercellular scale, the Cyanobacteria are very different to other algae, and we should never lose sight of the fact that they actually belong to a different Domain to other algae.

The problems are clear when I compare the morphology-based classification that I used when I first taught classes on algae in 1990 with the classifications that are accepted now.  Then, Cyanobacteria were divided into three or four orders, typically:

  • Chroococcales – single cells or cells loosely-bound into irregular gelatinous colonies
  • Oscillatoriales – filamentous forms lacking heterocysts
  • Nostocales – filamentous forms with heterocysts

The high-level classification, in other words, was based solely on whether or not the organism formed filaments and, if so, whether or not it possessed heterocysts (specialised cells responsible for nitrogen fixation).  This made logical sense when your primary source of insight is morphology.  Unfortunately, more recent studies have shown that it bears little relationship to the genetic relationships amongst the organisms that have been revealed over the past thirty years or so.   A more recent organisation is given in the diagram below.

First, note that this shows subclasses, rather than orders, within the class “Cyanophyceae” (the only class in the division Cyanophyta).   There is rarely unanimity amongst experts on the appropriate organisation of high-level classifications so just bear with me on this one.   Of the four sub-classes, one, Nostocophycidae, contains a single order (Nostocales) which includes all the heterocyst-bearing forms.  No change there.   However, the other two classes diverge very much from the older classifications in that they both contain a mixture of filamentous and non-filamentous forms.

Cyanobacteria_subclasses

The organisation of the Cyanobacteria (blue-green algae) division into four sub-classes.  Filled boxes indicates the classes that are represented in UK and Irish freshwaters.   Organisation follows Algaebase.   The image at the top of this post shows a Microcystis bloom at Ladybower Reservoir (photo: Chris Carter)

The Oscillatoriophycidae is a good example, with five sub-classes, four of which are represented in the UK and Ireland.  Two of these have featured in several posts (see Appendix) so you can see for yourself just how different they are in appearance.  The Oscillatoriales includes filamentous forms without heterocysts whilst the Chrococcales has taxa that either exist as single cells or in masses loosely-bound within gelatinous colonies.    A similar situation exists within the Synechococcophycidae; indeed, some genera that would formerly have been considered to be relatives of taxa within Oscillatoriales (e.g. Schizothrix and Heteroleibiana) are now included in families in this group.   There is, however, still more work to be done to unravel all the relationships within this sub-class.   The current understanding is that there is a single order (“Synechococcales”) but a great number of families.  Similarly, all the heterocystous forms are grouped into a single order, the Nostocales, within the Nostocophycidae, also divided into a large number of families.

Oscillatoriophycidae_orders

Organisation of the Oscillatoriophycidae showing the orders that include genera found in UK and Irish freshwaters.  

I always stress that taxonomy and identification are two distinct crafts: the taxonomist calls on a wide range of tools to find natural groupings of species at different levels whilst an ecologist only needs a parsimonious route to an unambiguous identification.  For the purposes of identification, recognising whether an organism is filamentous or not is a logical early step, even though both options will contain representatives of both Oscillatoriophycidae and Synecchococcophycidae.   We need to recognise that some of the characteristics that contribute to our taxonomic understanding (gene sequences, arrangement of thylakoids) are useless from the point of view of someone trying to name an organism encountered in a field sample but, at the same time, the taxonomist’s standpoint will not necessarily capture all of the features that explain how an organism contributes to energy and nutrient flow within ecosystems.

Calothrix-stagnalis_CCarter

Calothrix stagnalis: a member of the Nostocales.  Note the heterocysts at the base of the filaments (photo: Chris Carter)

References

Mai, T., Johansen, J.R., Pietrasiak, N., Bohunciká, M. & Martin, M.P. (2018).  Revision of the Synechococcales (Cyanobacteria) through recognition of four families including Oculatellaceae fam. nov. and Trichocoleraceae fam. nov. and six new genera containing 14 species.  Phytotaxa 365: 1-59.

Palinska, K.A. & Surosz, W. (2014).  Taxonomy of cyanobacteria: a contribution to consensus approach.  Hydrobiologia 740: 1-11.

Appendix

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

Group Link
Synechococcophycidae
Synechococcales Chamaesiphon: A bigger splash

Heteroleibleinia: River Ehen … again

Oscillatoriophycidae
Chrococcales Aphanothece: No excuse for not swimming …

Gloeocapsa: The mysteries of Clapham Junction …

Oscillatoriales Microcoleus: How to make an ecosystem

Oscillatoria: Transitory phenomena …

Phormidium: In which the spirit of Jeremy Clarkson is evoked …

Pleurocapsales Watch this space …
Spirulinales Spirulina/Arthospira: Twisted tales …
Nostocophycidae
Nostocales Nostoc: How to make an ecosystem (2)

Rivularia: Both sides now

Scytonema, Stigonema, Tolypothrix: Tales from the splash zone

Some other highlights from this week:

Wrote this whilst listening to: Leonard Cohen’s posthumous album Thanks for the Dance.   And, as I used it to name a post, Joni Mitchell’s Both Sides Now.

Cultural highlights:  David Hockney: Drawing from Life at the National Portrait Gallery.   Great examination of the importance of drawing and observation to artistic practice.   By coincidence, another post I’ve cited is named after one of Hockney’s paintings

Currently reading: Robin Wall Kimmerer: Gathering Moss (Oregon State University Press).  A collection of essays on the natural and cultural history of mosses.

Culinary highlight: dinner at The Sichuan on City Road in London.

Hockney_drawings

Close to the edge in Wastwater …

Wastwater_190610

I’m back in the Lake District for this post, standing beside Wastwater, the most remote and least disturbed of England’s lakes and, especially obvious on a sunny day in June, the most spectacularly-situated.  I stood on the western shore looking across to the screes and, beyond to the mass of Scafell Pike, England’s highest peak, looming up in the distance.

When I was done admiring the scenery I adjusted my focus to the biology of the lake’s littoral zone and some dark brown – almost black – marks on the boulders in the littoral zone.  In contrast to the grand vista stretching away to the north, these were beyond unprepossessing and my attempts to photograph them yielded nothing worth including in this post. However, I had seen similar looking marks in Ennerdale Water and there is a photograph in “Tales from the splash zone …” that should give you some idea of what I was seeing.

Under the microscope, my expectations were confirmed.  As in Ennerdale Water, these patches were composed of Cyanobacteria – gradually tapering trichomes of Calothrix fusca and more robust trichomes of Scytonema calcareum, both encased in thick, brown sheaths which, when viewed against the granite boulders on which they lived, resulted in the dark appearance of the growths.  To the untrained eye, these barely look like lifeforms, let alone plants yet they offer an important lesson about the health of Wastwater.

Calothrix_fusca_Wastwater_June19

Calothrix cf fusca from the littoral zone of Wastwater, June 2019. Scale bar: 20 micrometres (= 1/50thof a millimetre)

Though hard to see amidst the tangle of filaments in these population, both Calothrix and Scytonema have specialised cells called “heterocysts” that are capable of capturing atmospheric nitrogen (you can see these in the photographs of Nostoc commune in “How to make an ecosystem (2)”.   Nitrogen fixation is a troublesome business for cells as they need a lot of energy to break down the strong bonds that bind the atoms in atmospheric nitrogen together.   That means that plants only invest this energy in nitrogen fixation when absolutely necessary – when the lack of nitrogen is inhibiting an opportunity to grow, for example.   The presence of these Cyanobacteria in Wastwater is, therefore, telling us that nitrogen is scarce in this lake.

The dogma until recently was that phosphorus was the nutrient that was in shortest supply in lakes, so attention has largely focussed on reducing phosphorus concentrations in order to improve lake health.   Over the last ten years, however, evidence has gradually accumulated to show that nitrogen can also be limiting under some conditions.   That, in turn, means that those responsible for the health of our freshwaters should be looking at the nitrogen, as well as the phosphorus, concentration and, I’m pleased to say, UK’s environmental regulators have now proposed nitrogen standards for lakes.   That marks an important shift in attitude as, a few years ago, DEFRA were quite hostile to any suggestion that nitrogen concentrations in freshwaters should be managed.   In this respect, the UK is definitely out step with the rest of Europe, most of whom have nitrogen as well as phosphorus standards for freshwaters.

Scytonema_crustaceum_Wastwater_June16

Scytonema cf calcareum from the littoral zone of Wastwater, June 2019. Note the single and double false branches.   Scale bar: 20 micrometres (= 1/50thof a millimetre)

Wastwater flows into the River Irt and, a few kilometres down from the outflow, I found another nitrogen-fixing Cyanobacterium, Tolypothrix tenuis.  Once again, I could not get a good photograph, but you can see images of this in an earlier post from the River Ehen in “River Ehen … again”.   Nitrogen fixing organisms, in other words, are not confined to the lakes in this region, which raises the question why the UK does not have nitrogen standards for these as well (see “This is not a nitrate standard …”).   In rivers such as the Irt and Ehen that are already in good condition, it might only take a small increase in nitrogen concentration for the ecology to change.   Whether the loss of these nitrogen-fixing organisms will be noticed is another question.

For now, I am just happy to see that nitrogen in lakes has finally made it to the regulatory agenda.  It has taken about 15 years for the science to percolate through the many layers of bureaucracy that are an inevitable part of environmental management.  Give it another decade and maybe we’ll get nitrogen standards for rivers too.

References

Maberly, S. C., King, L., Dent, M. M., Jones, R. I., & Gibson, C. E. (2002). Nutrient limitation of phytoplankton and periphyton growth in upland lakes. Freshwater Biology. https://doi.org/10.1046/j.1365-2427.2002.00962.x

Moss, B., Jeppesen, E., Søndergaard, M., Lauridsen, T. L., & Liu, Z. (2013). Nitrogen, macrophytes, shallow lakes and nutrient limitation: Resolution of a current controversy? Hydrobiologia. https://doi.org/10.1007/s10750-012-1033-0

P.S. any guesses as to which 1970s prog rock group I was listening to over the weekend?  The clue is in the title.

Blooms from above

Dianchi_lake_cyano_bloom

Saturday’s excursion saw us travelling to the southern end of the Kunming metro and joining a procession of locals trekking up the wooded slopes of the Xī Shān hills to the settlement of Lóng Mén (‘Dragon’s Gate’), which gave us some spectacular views over Diān Chí (Dian Lake) stretching away into the distance, After a lunch of fried noodles from one of the many takeaway stalls at Lóng Mén, we travelled back down to lake level by cable car, which gave us our second panoramic view of Cyanobacteria in three days.   The lake, China’s eighth largest, had a very conspicuous Cyanobacterial bloom that serves as the ‘yin’ to the Green Lake’s ‘yang’.

The environmental problems of Diān Chí are well known with an article in Newsweek describing it as the ‘ground zero of China’s toxic algae problem’.  The problems starts with Diān Chí’s location on a high plateau (1886 m above sea level) in Yunnan, which means that it has a relatively small catchment area relative to its size (40 km long, about 300 square kilometres area and with an average depth of 4.4 metres).   The city of Kunming sits at the north end of this lake and now has a population of over six million people.   For a long time, their untreated sewage was pumped directly into the lake, leading to high concentrations of phosphorus which, in turn, fertilised the lake water, allowing blooms of Microcystis aeruginosa to develop.   Many genera of Cyanobacteria, including Microcystis, produce potent toxins that attack the liver or nervous system, and which can cause skin rashes.

Unfortunately, the city of Kunming depended upon Diān Chí for its water supply in its past but now, due to this contamination, it has to rely upon reservoirs upstream of the city.  It has, according to the Newsweek article, invested $660 million dollars to reduce industrial pollutants, building sewage treatment works, intercepting polluted water and banning detergents containing phosphorus but that, as my photograph from the cable car shows, has had little effect.   There are two reasons for this.  The first of these is a reluctance to control fertiliser use in the productive agricultural areas to the west of the lake (China is not unique in this respect; a similar tardiness can be found in the West, where agriculture is a potent political lobby).  The second is that much of the phosphorus that was pumped into the lake in the past is still there, sitting in the sediments and being constantly recycled by the algae.  In small lakes it might be possible, albeit expensive, to dredge out this sediment but on a lake the size of Diān Chí this is an unimaginable prospect.

Another paper that I found online demonstrated a dramatic loss of higher plants and fish from Diān Chí. Since the 1950s, over half of all native higher plant species have been lost, along with 84 per cent of native fish.  Diān Chí also had a number of unique species, which evolved in this remote habitat, but 90 per cent of these, too, have been lost since the 1950s.  That is a catastrophe in biodiversity terms, but the collapse of the lake ecosystem also led to the loss of valuable commercial fisheries.  In the past, some of the fish and shellfish that we ate in local restaurants might have been bought from fishermen who worked the lake; now they have to be imported.

Dianchi_reaeration_equipment

A view from the cable car over Diān Chí, with yellow rafts bearing reaeration apparatus visible on the lake surface.  The picture at the top of the lake shows one edge of the Cyanobacteria bloom, with clearer water along a channel flushed by inflow from a lagoon.

We can see, in other words, another interesting case study in competing ecosystem services emerging. We might imagine a time in the far past when there was a balance between the use of the lake as a supply of resources (drinking water, fish and shellfish, irrigation water) was not compromised by the use of the lake’s natural biogeochemical cycles to break down any waste products that flowed in from the catchment.   More likely, human and animal wastes would have been recycled more directly as manure for local agriculture so, again, some sort of equilibrium would have pertained.   Now, we see the ‘provisioning’ services compromised due to the overuse of the ‘regulating’ services and, at the same time, opportunities for ‘cultural’ services such as recreation are also much reduced.

Thinking more widely, what about the ecosystem services lost due to the construction of the new water supply reservoirs around Kunming?   But then, rather than end on an overly sanctimonious tone, to what extent have we in the West, ‘solved’ some of our own environmental problems in recent decades through the contraction of our own manufacturing industries in the face of competition from countries such as China?  \

view_along_Dian_Chi

A view south along Diān Chí with the far shore, 40 km away, just visible in the distance.

References

Liu, J., Luo, X., Zhang, N. & Wu, Y. (2016).  Phosphorus released from sediment of Dianchi Lake and its effect on growth of Microcystis aeruginosaEnvironmental Science and Pollution Research23: 16321-16328.

Wang, S., Wang, J., Li, M., Du, F., Yang, Y., Lassoie, J.P. & Hassan, M.Z. (2013).  Six decades of changes in vascular hydrophyte and fish species in three plateau lakes in Yunnan, China.  Biodiversity and Conservation222: 3197-3221.

Zhu, L., Wu, Y., Song, L. & Gan, N. (2014).  Ecological dynamics of toxic Microcystis spp. and microcystin-degrading bacteria in Dianchi Lake, China.  Applied and Environmental Microbiology80: 1874-1881.

Notes:many authors, Western and Chinese, refer to ‘Dianchi Lake’.  However, as ‘chí’ means ‘lake’, I have just referred to ‘Diān Chí’ throughout.  See “Lake lakelake lake” for more about this. “La Grande Assiette de Lac Léman”  describes a similar conflict between ecosystem services in Lake Geneva, albeit with more positive outcomes.

 

Algae in a stone forest

Shilin_panorama_#1

A change in location from the previous post: this one is being written on the roof terrace of a guest house in Kunming, in Yunnan Province, China, whilst sipping a cup of the local pu’er tea.   I’m in China with my family visiting my eldest son who works in Chengdu, a sprawling metropolis of 11 million people in Sichuan Province, and have escaped to the warmer climate and more sedate environs of Kunming (only 6 million people) for a few days.  We’ll then move on to Dali (a mere village, by comparison, with less than half a million people) before returning to Chengdu.

From Kunming we travelled about 120 km southeast to Shílín, the site of a strange Karst phenomenon known as the “stone forest”, a collection of upright pillars of limestone often with other limestone blocks perched precariously on top.   In geomorphological terms, we are looking at a limestone pavement on a huge scale, but with substantial erosion of the “grykes” (the gaps between the “clints”).   Geologically, it is a little more complicated than that, with the Permian limestone being later overlain by basalt which was subsequently eroded away to leave a red soil.  However, that is enough to give you some context for what follows.

The photograph at the top of the post gives you some idea of what the stone forest looks like, and also some idea of the crowds to be expected at mainstream tourist attractions in China.  At times, the mass of people and, in particular, the overlapping amplified commentaries from tour guides, dressed in the costumes of the local Sani ethnic minority, made the experience almost unbearable.  But then, as is often the case, you turn a corner, the hubbub dies away, and you are able to enjoy the ethereal landscapes almost undisturbed.  In our case, however, we turned a corner too many, found ourselves outside the officially-sanctioned tourist beat and were unceremoniously ejected by an officious security guard.

Once we had talked our way back into the park through the main entrance, using Ed’s Mandarin skills, the park was noticeably quieter.   Most of the organised tours squeeze the stone forest and a local cave network into the same trip so the morning crowds had been hustled back onto their coaches, and the whole experience in the park was much more pleasant.   Walking through the Major Stone Forest gives you an ants-eye experience of living in a limestone pavement habitat, with the clints towering above you and only occasional glimpses of sunshine.   The park authorities have provided a concrete path and steps to lead you through but it is, at times, an arduous trek with some narrow and low gaps through which to squeeze.   This, in turn, lets you get up close to the limestone and, in my case, gets the phycological antennae twitching …

Shilin_panorama_#2

The Major Stone Forest at Shílín from the inside.   The photo at the top of the post shows the Major Stone Forest from the main public viewing area.

The limestone from which the stone forest is made is largely slate-grey in colour, rather than the creamy beige that I normally associate with this rock.   Only after reading one of the interpretation boards in the park did the penny drop, and I realised that I, and thousands of other tourists, had each spent 130 RNB to stare at algae.   After my brush with officialdom in the morning I was not in the mood to scrape at the rocks to collect a sample but am guessing we are looking at the Cyanobacterium Gloeocapsa alpina or something similar (see “The mysteries of Clapham Junction …”).   We were visiting the park close to the end of the long dry season but for the next few months the climate here will be much damper, creating a more conducive environment for these microorganisms to grow.

A few of the rock faces, particularly those associated with seepages, had multicolour streaks, with the grey supplemented with pinks and greens.  The former may well be other Cyanobacteria (possibly Schizothrix) and the greens could be Apatococcus, Desmococcus or a relative (see “Little round green things …”).  There were also a few orange-red patches of Trentepohlia (see “Fake tans in the Yorkshire Dales”).   All of these are forms are familiar to me from the UK and, whilst it would be rash to assume that the species were identical to those I find back home, the genera are generally cosmopolitan, so some extrapolation can be permitted.

Shilin_algae_Apr19

Algal crusts on rocks in the Major Stone Forest at Shílín, April 2019. The left hand image shows a mixture of Cyanobacteria and (possibly) green algae on a vertical surface associated with a seepage; the right hand image shows Heather photographing a growth of Trentepohlia nearby.

Trentepohlia_Shilin_Apr19

Trentepohlia growths inin the Major Stone Forest at Shílín, April 2019.  The picture frame spans about 10 centimetres. Photograph: Heather Kelly.

I did hunt around for some verification for these names but it is not possible to access Google Scholar in China without a VPN.  I am limited to whatever Bing throws up, and have not yet been able to find any papers on the algae of Shílín.  What I did find, during these searches, however, was an article about the world’s largest Haematococus farm, which is very close to here.   I’ve described Haematococcus in earlier posts (see “An encounter with a green alga that is red”) and mentioned that it was the source of the food colouring astaxanthin.   The combination of the limestone geology, warm weather and the huge market for food additives in China makes this possible.  Travelling in China with two vegetarians makes me realise that, even in this enormous, technocratic country, the market for natural products is growing.

Shilin_panorama_#3

 

 

More about measuring biomass …

The previous post showed how the proportions of green algae and diatoms changed as the total quantity of algae in the River Ehen waxed and waned over the course of a year.   The BenthoTorch, however, also measures “blue-green algae” and so let’s look at how this group changes in order to complete the picture.

Before starting, though, we need to consider one of the major flaws of the BenthoTorch: its algorithms purport to evaluate the quantities of three major groups of algae yet, in my posts about the River Ehen I have also talked about a fourth group, the red algae, or Rhodophyta (most recently in “The only way is up …”).  Having pointed a BenthoTorch at numerous stones with thick growths of Audouinella,we can report that Rhodophyta seem to be bundled in with the blue-green alga signal, which is no great surprise given the similarity in their pigments.  It is, however, one of a number of examples of the need to interpret any BenthoTorch results with your brain fully engaged, and not just to treat outputs at face value. Similar questions need to be asked of the Xanthophyta and Chrysophyta, though the latter tend not to be common in UK streams.

cyanos_in_Ehen

Relationship between the proportion of “blue-green algae” (Cyanobacteria and Rhodophyta) and the total quantity of benthic algae (expressed as chlorophyll concentration) in the River Ehen (c.) and Croasdale Beck (d.).  The blue lines show quantile regression fits at p = 0.8, 0.5 and 0.2.  

In contrast to the green algae and diatoms, the Cyanobacteria/Rhodophyta signal shows a strong negative relationship as biomass increases though, again, there is enough scatter in this relationship to make it necessary to approach this graph with caution.  I suspect, for example, that the data points on the upper right side of the data cloud represents samples rich in Audouinella, which tends to occur in winter when biomass, generally, is much greater.   On the other hand, Croasdale Beck, in particular, has a lot of encrusting Chamaesiphon fuscus colonies which are pretty much perennial (see “a bigger splash …”) but whose relative importance in the BenthoTorch output will be greatest when the other two groups of algae are sparse.   I suspect that encrusting members of this genus are favoured by conditions that do not allow a high biomass of other algae to develop, as these will reduce the amount of light that the Chamaesiphonreceives.

Thicker biofilms in the River Ehen often have some narrow Phormidium-type filaments as well as small bundles of nitrogen-fixing Calothrix, but the overall proportion is generally low relative to the mass of diatoms and green algae that predominate.    But that is not really telling us the whole story.  I finished my previous post with a graph showing how the variation in biomass increases as the biomass increases.  The heterogeneity of stream algal communities, however, cannot be captured fully at the spatial scale at which the BenthoTorch works: there is a patchiness that is apparent to the naked eye: one of our sites has distinct mats of Phormidium autumnale towards one margin, and dense Lemaneagrowths in the fastest-flowing sections, largely attached to unmovable boulders, which makes biomass measurement very difficult. I’ve also written about distinct growths of Tolypothrix and its epiphytes (see “River Ehen … again”), another alga which forms discrete colonies at a few locations. I try to collect a random sample of stones from a site but there are constraints, including accessibility, especially when the river rises above base flow.   In the River Ehen we also have to take care not to disturb any mussels whilst removing stones.

Whilst our sampling cannot really be described as “random” I do think that there is sufficient consistency in the patterns we see for the results to be meaningful. We could spend a lot more time finessing the sampling design yet for little extra scientific gain.   I prefer to think of these measurements as one part of a complex jigsaw that is slowly revealing the interactions between the constituents of the dynamic ecosystem of the River Ehen.   The important thing is to not place too much faith in any single strand of evidence, and to have enough awareness of the broader biology of the stream to read beyond the face value indications.

Castle Eden Dene in January

castle_eden_burn_jan19

The story so far: in 2018 I made bi-monthly visits to the River Wear, my local river and tried to capture, in my posts, the changes in the algae that occurred over the course of 12 months (follow the links in “A year in the life of the River Wear” to learn more).  It was an interesting exercise, partly because last summer’s exceptional weather led to some intriguing changes over the course of the year.   Consequently, as 2019 dawned, I thought I should find a different type of stream within a short drive from my home and try again.  So, bearing in mind that Wolsingham is south and west from where I live, I turned in the opposite direction and drove due east instead, stopping on the edge of the brutal concrete housing estates of Peterlee, a most unprepossessing location for a National Nature Reserve.

My journey has brought me right across the Permian limestone that dominates the eastern Durham landscape. Its escarpment rises up close to my home, and I have written about the algae that live in the ponds at the foot of it (see “A hitchhiker’s guide to algae…”).  On the other side, however, the limestone ends in a series of cliffs overlooking the North Sea and small streams have cut into the limestone to create a series of wooded valleys, or “denes”.   I’ve come to Castle Eden Dene, the largest of these: if you want a cultural reference point, watch the film “Billy Elliott”, set just a few miles further north along the coast, or read Barry Unsworth’s The Quality of Mercy.

We made our way down the footpath into the dene on a crisp and very cold winter morning, past the old yew trees from which the name is derived, and myriad ferns.   A deer bounded across the path ahead and disappeared into some scrub, and then we turned a corner and looked into Castle Eden Burn, which runs along the bottom of the dene.   To my surprise, the stream was dry.   This is a valley that cuts through limestone, so it is common for the stream to be dry in the summer, but I had not expected it to be dry in the middle of winter.  Thinking back, however, I realised that there has not been much rain for some weeks, and this may have meant that the water table, still low, perhaps, after last summer’s dry weather, is too low for the stream to flow.

blunts_burn_jan19

Diatoms and cyanobacterial colonies in Blunt’s Burn, Castle Eden Dene, January 2019.   The top photograph shows diatom growths on bedrock; the lower image shows Phormidium retzii colonies, each about two millimetres across.   The photograph at the top of the post shows a yew tree overhanging Castle Eden Burn. 

A few hundred metres further down the dene, we finally heard the sound of running water where a small tributary stream, Blunt’s Burn, joined the main burn.  Judging from my OS map, it drains a good part of Peterlee so it might not have very high water quality.  It was, however, a stream and it did, as I could see with the naked eye, have some distinct diatom-rich growths.    These, I discovered later, were dominated by the diatoms such as Navicula tripunctataand N. lanceolata which are typical of cold weather conditions (see, for example, “The River Wear in January”).   A closer look showed that the orange-brown diatom growths were, in places, flecked with dark brown spots.  Somehow, I managed to get my cold fingers to manipulate a pair of forceps and pick up a few of these spots for closer examination.

blunts_burn_diatoms

Diatoms from Blunt’s Burn, January 2019: a. Navicula tripunctata; b. N. lanceolata; c.Gyrosigma cf. acuminatum; d. Nitzschiacf. linearis (girdle view); e. N. linearis(valve view).  Scale bar: 10 micrometres (= 1/100thof a millimetre).

I had a good idea, when I first saw these spots, that they were colonies of a filamentous cyanobacterium and, peering through my microscope a few hours later, once I had warmed myself up, I was relieved to see that I was right.  I picked out a dark patch and teased it apart before putting it onto a slide with a drop of water.  Once I had done this, I could see the tangle of filaments along with a mass of organic and inorganic particles and lots of diatoms.   The filaments themselves were simple chains of cells (a “trichome”) of Phormidium retzii, surrounded by a sheath.   There were also, however, a few cases, where I could see the sheath without the Phormidium trichome, and in some those I could also see diatom cells.

There are some diatoms that make their own mucilage tubes (see “An excuse for a crab sandwich, really …”) but Nitzschia is not one of those most often associated with tube-formation (there are a few exceptions).    On the other hand, there are some references to Nitzschiacells squatting in tubes made by other diatoms.   Some of those who have observed this refer to Nitzschia as a “symbiont” but whether there is any formal arrangement or is just a by-product of Nitzschia’s ability to glide and seek out favourable microhabitats, is not clear.  There are, as far as I can see, no references, to diatoms inhabiting the sheaths of Cyanobacteria, though Brian Whitton tells me he has occasionally seen this too.

We made our way back along the dry bed of Castle Eden Burn.  Many of the rocks here were quite slippery, suggesting that there had been some water flowing along it in the recent past.  That encouraged me to scrub at the top surface of one with my toothbrush and I managed to get a sample that certainly contains diatoms though these were mostly smaller than the ones that I found in Blunt’s Burn, and there was also a lot of mineral matter.   I’ll need to get that sample prepped and a permanent slide prepared before I can report back on just what diatoms thrive in this tough habitat.  Watch this space …

blunts_burn_phormidium

Cyanobacterial filaments from Blunt’s Burn, Co. Durham, January 2019: a. a single trichome of Phormidium retzii; b. and c. empty sheaths colonised by cells of Nitzschia; d. aPhormidiumfilament with a sheath and a trichome but also with epiphytes and adsorbed organic and inorganic matter.  Scale bar: 10 micrometres (= 1/100thof a millimetre).   

References

Carr, J.M. & Hergenrader, G.L. (2004).  Occurrence of three Nitzschia(Bacillariophyceae) taxa within colonies of tube-forming diatoms. Journal of Phycology23: 62-70.

Houpt, P.M. (1994). Marine tube-dwelling diatoms and their occurrence in the Netherlands. Netherlands Journal of Aquatic Ecology28: 77-84.

Lobban, C.S. (1984). Marine tube-dwelling diatoms of the Pacific coast of North America. I. BerkeleyaHasleaNitzschia, and Navicula sect. Microstigmaticae.  Canadian Journal of Botany63: 1779-1784.

Lobban, C.S. & Mann, D.G. (1987).  The systematics of the tube-dwelling diatom Nitzschia martiana and Nitzschia section Spathulatae. Canadian Journal of Botany.  65: 2396-2402,