Life out of water …

Last time I wrote, I mentioned that those diatom genera that did not have to be permanently submerged in order to thrive (so-called “aerophilous diatoms”) often appeared together in samples.   Having seen some Luticola muticaearly in my analysis of the sample from Castle Eden Burn, it was no surprise to find Diadesmisand Simonsenialater in the same analysis.   If anything, the biggest surprise was that I did not also find Hantzschia amphioxys, another habitué of the damp fringes of diatom society.

A quick analysis of my database puts these thoughts into context.   There are 6500 samples in my database, so we can see, from the total number of records of each of the aerophilous genera that these are relatively scarce in the samples I encounter.  That is largely because my sampling approaches are biased against the habitats where these thrive (more about this below).   Aerophilous diatoms are more common than you might think; it is scientists with a yearning to learn more about them that is in short supply.

Hantzschiaand Simonseniaare both less frequent and less abundant than the other two genera, never occurring in numbers exceeding ten per cent of the total but, when they form more than one per cent of the total, there is a very high chance that you will also find other aerophilous taxa in the sample.   Humidophilaand Luticolaare sometimes found in higher numbers, and when this is the case, then the proportion of other aerophilous taxa is also often high: 75 per cent of samples where Humidophilais abundant, for example, have at least one other aerophilous taxon present at one per cent or more.

Frequency of other aerophilous genera in samples with Hantzschia, Humidophila, Luticolaand Simonsenia.    Each genus is represented by two rows: records where it formed 10 per cent or more of the total number of valves and records where it formed more than one per cent.   Similarly, records for other aerophilous genera are also stratified into those where they comprise more than 10 per cent of the total and those where they comprise more than one per cent.  

Genus number of records   other aerophilous genera
>10% >1%
Hantzschia 147 >10% n/a n/a
>1% 0.50 0.70
Humidophila 248 >10% 0.25 0.75
>1% 0.09 0.29
Luticola 630 >10% 0.09 0.35
>1% 0.05 0.16
Simonsenia 61 >10% n/a n/a
>1% 0.50 1.00

Over the years, I have come to use this information informally as a way of knowing whether the results of an analysis are likely to be giving me useful insights into ecological condition.   Many of the samples I analyse are collected by other people and sent to me.   These samplers should have been working to protocols that ensure that they check that the stones they choose were fully submerged for some time prior to their visit.  However, the person collecting the sample may have to make a judgement about river and lake level fluctuations in the period before their visit.  Finding lots of cells of aerophilous taxa in a sample is a good hint that something is awry.

The German method for ecological status assessment actually uses the proportion of aerophilous taxa as a check on the reliability of an assessment.    I suspect that they are not the only ones, but They have a list of 46 species that they regard as aerophilous taxa, and use a threshold of five per cent in a sample as a threshold.   The genera I’ve discussed all feature prominently, along with representatives of 19 other genera. Most of these are represented by only one or two species, although there are seven species of Nitzschia, five of Pinnulariaand six of Stauroneis.   I suspect that some species on this list are more tolerant of desiccation than others. We do not know enough of the physiological mechanisms behind this tolerance but it would seem that a few genera (Hantzschia, Humidophila, Luticiola) have definitely got this hard-wired into their genotypes, whilst other genera have members which are mostly aquatic in their habit but with a few exceptions able to survive out of water for some time.   I, personally, would trust the five per cent threshold if it was restricted to the hardcore aerophilous genera, with other taxa on the list providing supporting evidence. I would also add the proviso that there should be more than one aerophilous taxon contributing to that five per cent.  I would be happier, too, if there were a few experimental studies behind these lists and thresholds but, as ever with the world of diatoms, taxonomists are several steps ahead of the physiologists and so we are heavily dependent on anecdotal information when interpreting results.

List of taxa regarded as aerophilous in the German system for assessing ecological status in rivers. 

Name Authority
Achnanthes coarctata (Brébisson) Grunow in Cleve & Grunow 1880
Chamaepinnularia parsura (Hustedt) C.E.Wetzel & Ector in Wetzel et al. 2013
Cosmioneis incognita (Krasske) Lange-Bertalot in Werum & Lange-Bertalot 2004
Denticula creticola (Østrup) Lange-Bertalot & Krammer 1993
Diploneis minuta Petersen 1928
Eolimna subadnata  (Hustedt) G. Moser, Lange-Bertalot & Metzeltin 1998
Fallacia egregia (Hustedt) D.G. Mann 1990
Fallacia insociabilis (Krasske) D.G. Mann 1990
Fistulifera pelliculosa (Brébisson ex Kützing) Lange-Bertalot 1997
Halamphora montana (Krasske) Levkov 2009
Halamphora normanii (Rabenhorst) Levkov 2009
Hantzschia abundans Lange-Bertalot 1993
Hantzschia amphioxys (Ehrenberg) Grunow 1880
Hantzschia elongata (Hantzsch) Grunow 1877
Hantzschia graciosa Lange-Bertalot 1993
Hantzschia subrupestris Lange-Bertalot 1993
Hantzschia vivacior Lange-Bertalot 1993
Humidophila aerophila (Krasske) Lowe, Kociolek, Johansen, Van de Vijver, Lange-Bertalot & Kopalová, 2014
Humidophila brekkaensis (J.B.Petersen) D. Lowe, Kociolek, Johansen, Van de Vijver, Lange-Bertalot & Kopalová, 2014
Humidophila contenta (Grunow) Lowe, Kociolek, Johansen, Van de Vijver, Lange-Bertalot & Kopalová, 2014
Humidophila perpusilla (Grunow) Lowe, Kociolek, Johansen, Van de Vijver, Lange-Bertalot & Kopalová, 2014
Luticola cohnii (Hilse) D.G. Mann 1990
Luticola dismutica (Hustedt) D.G.Mann1990
Luticola mutica (Kützing) D.G. Mann 1990
Luticola nivalis (Ehrenberg) D.G. Mann 1990
Luticola nivaloides (W.Bock) J.Y.Li & Y.Z.Qi 2018
Luticola paramutica (W. Bock) D.G. Mann 1990
Luticola pseudonivalis (W.Bock) Levkov, Metzeltin & A.Pavlov 2013
Luticola saxophila (W.Bock ex Hustedt) D.G.Mann 1990
Mayamaea nolensoides (W. Bock) Lange-Bertalot 2001
Melosira dickiei (Thwaites) Kützing 1849
Muelleria gibbula (Cleve) Spaulding & Stoermer 1997
Neidium minutissimum Krasske 1932
Nitzschia aerophila Hustedt 1942
Nitzschia bacillarieformis Hustedt 1922
Nitzschia disputata J.R. Carater 1971
Nitzschia harderi Husedt 1949
Nitzschia modesta Hustedt 1950
Nitzschia terrestris (J.B. Petersen) Hustedt 1934
Nitzschia valdestriata Aleem & Hustedt 1951
Orthoseira dendroteres (Ehrenberg) Genkal & Kulikovskiy in Kulikovskiy et al. 2010
Orthoseira roseana (Rabenhorst) Pfitzer 1871
Pinnularia borealis Ehrenberg 1843
Pinnularia frauenbergiana E. Reichardt 1985
Pinnularia krookii (Grunow) Hustedt 1942
Pinnularia largerstedtii (Cleve) Cleve-Euler 1934
Pinnularia obscura Krasske 1932
Simonsenia delognei (Grunow) Lange-Bertalot 1979
Stauroneis agrestis J.B. Petersen 1915
Stauroneis borrichii (J.B.Petersen) J.W.G.Lund 1946
Stauroneis gracillima Hustedt 1943
Stauroneis lundii Hustedt 1959
Stauroneis muriella J.W.G. Lund 1946
Stauroneis obtusa Lagerstedt 1873
Surrirella terricola Lange-Bertalot & Alles 1996
Tryblionella debilis Arnott ex O’Meara 1873

Reference

Schaumburg, J., Schranz, C., Steizer, D., Hofmann, G., Gutowski, A. & Forester, J. (2006).  Instruction protocol for the ecological assessment of running waters for implementation of the EC Water Framework Directive: macrophytes and phytobenthos.  Bavarian Environment Agency

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Tales from a dry river bed …

Two weeks ago I stood in a dry stream bed at Castle Eden Dene, wondering at the absence of water yet also conscious that many of the stones that littered the surface had a slipperiness that suggested not only that they had been wet relatively recently, but also that the surface biofilms (which impart this slipperiness) might still be intact.   A first look at a portion of this film under my microscope suggested that this might well be the case: I could certainly see some diatoms, and some green algae cells, but most were very small and that there was also a lot of particles, both inorganic and organic, that made viewing these algae quite difficult.   Since then, I’ve prepared a permanent slide from this material, so I can now take a closer look and get a better idea of what diatoms thrive in a dry stream bed in mid-winter in northern England.

A quick analysis of the sample found 34 species, of which four were abundant (comprising over 60% of the total) and the remainder were relatively infrequent.   The most abundant species was Amphora pediculus, which I’ve written about before, and which was not a surprise, as it is a species that thrives in the hard water that I would have expected in a stream draining a limestone catchment.  The other three common species wereHumidophila contenta, Luticola muticaand Simonsenia delognei, all of which are known to survive in habitats that are not permanently submerged.   These are relatively uncommon in the typical samples that I encounter but when they do occur in large numbers, they are often found together.   It is another facet of the “London Bus” paradigm that I described in the previous post, except this time it is a characteristic assemblage of species from different genera, rather than from a single genus or family.

Castle_Eden_diatoms_Jan19

Some of the diatoms from Castle Eden Burn, January 2019: a. Nitzschia nana; b. – g. Luticola mutica; h. – k. Humidophila contenta.   Scale bar: 10 micrometres (= 1/100thof a millimetre). 

Diatoms in the genus Humidophilahas changed names twice over the course of my career.   Back in the 1980s, species from this genus, as well as Luticolawere considered to be part of the Navicula which was regarded as a “dump for all bilaterally symmetrical [e.g. boat-shaped] raphid diatoms lacking particularly distinctive features” according to Frank Round, Dick Crawford and David Mann.    They split several groups of species away from Naviculato create new genera, one of which was Luticola.  In other cases, to resurrect old genera that had been subsumed into Naviculain the first half of the 20thcentury.  One of these resurrected genera was Diadesmiswhich differed from “true” Naviculain several respects, not least of which was a tendency to form ribbon-like colonies.   A more recent study suggested that Diadesmis, itself, needed to be split, with several species being moved to yet another new genus, Humidophila.   Unfortunately, the criteria on which this was based are not easily seen with the light microscope.  However, one by-product of this split was that all the species within the genera that are associated with damp, rather than fully-submerged habitats, ended up in the new genus rather than in Diadesmis.   That lends weight to the split, suggesting that there is more to the separation than just minor differences in the details of the cell wall.

The final species that was common in Castle Eden Burn was Simonsenia delognei.   This is another small diatom and, as I could not get good photographs from this sample, I have included photographs from another site to show what it looks like.  It is a very delicate diatom, easily overlooked when scanning a slide, particularly as it usually only occurs in small numbers.  That, again, might be because I usually look at samples from fully-submerged habitats.   Here, it formed about 12 per cent of the total number of valves, which is four times as many as I have previously found.

Simonsenia_delognei.jpg

Simonsenia delogneifrom Ballyfinboy River, Co. Tipperary, August 2014.   Scale bar: 10 micrometres (= 1/100thof a millimetre).  Photographs: Lydia King.

I’m quite intrigued, now, to see how the algal communities change over the course of the year. Are these diatoms that can tolerate drying ever-presents or will their proportions fluctuate over the course of the year as the stream comes and goes?   And what is it that makes some diatoms cope with these dry periods?   The ability to live out of water is associated with a few genera in particular, so what is it about their genetic make-up that lets them thrive.  What about Amphora pediculusand the other diatoms that I associate with submerged habitats? Am I looking at dormant but viable cells (I did not see many healthy chloroplasts when I made my initial observations) or are these diatom carcasses strewn across an arid desert?    At the risk of sliding into metaphor-overload, does this mean that Humidophila, Luticolaand Simonseniaare the cacti of the diatom world?

References

Lowe, R.L., Kociolek, P., Johannsen, J.R., van de Vijver, B., Lange-Bertalot, H. & Kopalová, K. (2014).  Humidophilagen. nov., a new genus for a group of diatoms (Bacillariophyta) formerly within the genus Diadesmis: species from Hawai’I, including one new species.  Diatom Research29: 351-360.

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

A twist in the tale …

hamsterley_forest_jan19\

After my sojourn in East Durham, described in the previous post, I have travelled back to the Pennines for this one, crossing the River Wear at Wolsingham before driving up onto the fells and finally dropping down to the woodlands that are Hamsterley Forest.  This is a large man-made plantation, dating from the 1930s and popular for recreation. In January, however, the forest is quiet, and I only have a few mountain bikers and a lone dog walker for company as I peer into the peaty waters of Euden Beck.   This stream rises on the open fells of Hamsterley Common, between Weardale and Teesdale, before flowing through the forest and joining Spurl’s Wood Beck just downstream from where I am standing, to become Hamsterley Beck.  This then joins the Wear a few kilometres downstream from Wolsingham.

eudon_beck_jan19

Euden Beck, just above the forest drive in Hamsterley Forest, January 2019.  The photograph at the top of the post shows a view towards Hamsterley Forest. 

There is a mixture of diatoms growing on the stones here but I am most interested in the genus Fragilaria today.   One of the curiosities of this genus is that we often find several representatives growing at the same site at the same time, reminiscent of the old adage about London buses (“you wait ages, and then three come along at once”).   I’ve written about this before (see “Baffled by the benthos (2)” and “When is a diatom like a London bus?”) and Euden Beck is another good example of this conundrum in practice.

Today, I could see quite a few cells of Fragilaria teneraand smaller numbers ofF. gracilisplus a newly-described species that I will talk more about later in the post.  Fragilaria teneraforms long, needle-like cells, often clustering together to form sea urchin-like masses growing out from either a filamentous alga or particle to which they are attached (see “Food for thought in the River Ehen” for an illustration).  Most of the ones that I saw in my samples from Euden Beck were either single cells or pairs of cells, presumably following a recent division. Note how the second cell from the left in the figure below is not as straight as the others.   This is something that I often see with Fragilaria populations in streams in the northern Pennines, and indicates that there may be heavy metal pollution in the water.  There are a lot of abandoned lead mines in the northern Pennines and, sure enough, when I looked at a large scale map, I found one that I had not previously noticed in the upper part of Euden Beck’s catchment.

fragilaria_tenera.euden_jan19

Live cells of Fragilaria tenera(a. – d.) and F. heatherae from Euden Beck, January 2019.   a., b. and e. are valve views; c. and d. are girdle views.  Scale bar: 10 micrometres (= 1/100thof a millimetre). 

The next image shows these valve abnormalities even more clearly, with almost all of the cells showing aberrations in their outline.   These images are from an older sample; the curiosity here is that whilst most of the Fragilaria tenera valves were twisted, fewer of the valves of Fragilaria gracilisare twisted, whilst few of the valves of the third Fragilaria species show any abnomality in their outline at all.   This species is very common in northern Pennine streams, and I have often seen distorted valves of this species in streams polluted by mine discharges.  This makes the discrepancy between the outlines of this and Fragilaria tenera in Euden Beck particularly intriguing.

fragilaria_tenera_rt#55

Fragilaria tenera from a sample collected from Euden Beck in June 2012.  Scale bar: 10 micrometres (= 1/100thof a millimetre).   Photographs: Lydia King.

I say “Fragilaria gracilis” with a modicum of trepidation as a recent study in which I have been involved, suggests that there may well be at least two species.  These are, as far as we can tell, indistinguishable using characteristics that can be seen with the light microscope though we know that they are genetically quite distinct, and both are widespread, turning up not just in the UK but in other parts of Europe too.

The third species, to the best of our knowledge, does not match the description of any other Fragilaria species, and we are in the process of publishing it as a new species, Fragilaria heatherae.   We have found it a number of samples, not just from the UK but also from sites elsewhere in Europe.   These, by comparison with the other two species, show very little distortion at all.   Whilst several authors have noted this phenomenon in the past, the physiological cause is still not understood. My guess is that the metal ions are displacing a metal co-factor in an enzyme that is involved in the process of laying down the silica cell wall.   Fragilaria seems to be particularly susceptible, but this may be because their long needle-like cells show the distortions more clearly than in some genera but, based on the evidence from Euden Beck, there are clearly differences in susceptibility between species.

Once again, I seem to be ending a post having asked more questions than I have answered. That is always frustrating but another way of looking at this is to realise that the frontiers of ecology are only ever a short drive away from where you are now.  It is very nice to cross oceans to visit rain forests and coral reefs, but there are adventures to be had closer to your doorstep.

fragilaria_gracilis_rt#55

Fragilaria gracilis from a sample collected from Euden Beck in June 2012.  Scale bar: 10 micrometres (= 1/100thof a millimetre).   Photographs: Lydia King.

fragilaria_heatherae_rt#55

Fragilaria heatherae” from a sample collected in Euden Beck in June 2012.  Scale bar: 10 micrometres (= 1/100thof a millimetre).   Photographs: Lydia King

References

Duong, T.T., Morin, S., Herlory, O. & Feurtet-Mazel, A. (2008). Seasonal effects of cadmium accumulation in periphytic diatom communities of freshwater biofilms.  Aquatic Toxicology90: 19-28.

Falasco, E., Bona, F., Ginepro, M., Hlúbiková, D., Hoffmann, L. & Ector, L. (2009). Morphological abnormalities of diatom silica walls in relation to heavy metal contamination and artificial growth conditions.  Water SA35: 595-606.

McFarland, B.H., Hill, B.H. & Willingham, W.T. (1996). Abnormal Fragilaria spp. (Bacillariophyceae) in Streams Impacted by Mine Drainage. Journal of Freshwater Ecology 12: 141-149.

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, 

 

Return to the Serra da Estrela

towards_manteigas

Back in October I wrote about the algae and other plants that I had found in a small stream draining the Serra da Estrela mountains in Portugal (see “Notes from the Serra da Estrela”).  I’ve now had a chance to look more closely at the diatoms that I found there, and can offer a few thoughts on the ecology of the stream.

I collected two samples from the stream: one by brushing the top surface of the granite stones with a toothbrush and the other from the darker patches that I described in the earlier post.   These were a mix of algae and mosses, with the former dominated by cyanobacterial filaments and diatoms.   I merged the two samples prior to digesting them, but the biofilm on the submerged rocks was very thin so it is the diatoms from the dark patches that dominate the slide that I prepared from this stream.   As my preliminary observations suggested, motile diatoms were very abundant in this sample, with Surirella roba, Navicula angustaand N. exilis all common, along with some Pinnularia and Nitzschia.   I do not often find motile diatoms to be quite so abundant in fast-flowing upland streams, but I suspect that this is because I look in the wrong places.   Our standard sampling method involves scrubbing the tops of submerged stones which, in this type of stream at least, are not situations where motile diatoms thrive.  By contrast, the tangle of cyanobacterial filaments and dead organic matter creates a very different environment, where an ability to adjust position in order to move away from densely-shaded areas and, perhaps, from situations where bacteria and fungi had used up all the available oxygen, was an advantage.

surirella_roba_unhais_sep18

Surirella robafrom the stream at Unhais de Serra, September 2018; a. – f.: valve views; g. – i.: girdle views. Scale bar: 10 micrometres (= 1/100thof a millimetre). The photo at the top of the post shows the view along the valley of the Rio Zêzere towards Mantiegas in the Serra da Estrela.

misc_diatoms_unhais_sep18

Miscellaneous diatoms from the stream at Unhais de Serra, September 2018: a. – d.: Cocconeis placentula, complete frustule, rapheless valve and two raphe valves; e. – g.: Navicula exilis; h. N. angusta; i. – k.: Pinnularia subcapitata, two valve views and a girdle view.  Scale bar: 10 micrometres (= 1/100thof a millimetre). 

A chain-forming species of Fragilariawas abundant in the original sample although, by the time I had prepared a slide, the chain had disintegrated into individuals or pairs of cells.  These all belonged to a member of the Fragilaria capucinacomplex, though I am not sure which one. There were also a few cells of the free-living (i.e. non-chain-forming) Fragilaria gracilis.    Eunotia minoror a close relative was also present, sometimes also forming short chains and, finally, I found a number of cells of Cocconeis placentula(possibly var. klinoraphis).

These are all diatoms that I would expect to find in a stream draining a hard rock such as granite in an area that is remote from any industrial or mining influences that might lead to artificial acidification.   There are mines in the area, but these are further south.  These do have a measurable effect on the biology of local streams, as the references at the end of this post attest.   However, this particular stream appears to be in rude health.

A curious side-effect of the years that I have spent looking at diatoms is that a sample such as this can evoke the environments from which it came: an assemblage of soft-water circumneutral diatoms conjures, in my mind, a particular landscape.   The label on the slide, of course, takes me straight back to our time in the Serra da Estrela but, in a more general sense, the diatoms capture an essence that transcends any one particular time or place.   Analysing diatom slides can become an escape from the humdrum and a chance to remember warmer days …

fragilaria_unhais_sep18

Fragilaria species from the stream at Unhais de Serra, September 2018: a. – g.: chain-forming member of Fragilaria capucina complex (a.-c.: valve views; d.-g.: girdle views); h.-j.Fragilaria gracilis.  Scale bar: 10 micrometres (= 1/100th of a millimetre).

eunotia_cf_minor_unhais_sep18

Eunotiacf. minorfrom the stream at Unhais de Serra, September 2018: j. – n.: valve views; o. valve view of a related species; p. girdle views. Scale bar: 10 micrometres (= 1/100thof a millimetre). 

References

Luis, A.T., Teixeira, P., Almeida, S.F.P., Matos, J.X. & Silva, E.F. (2004).  Environmental impact of mining activities in the Lousal area (Portugal): Chemical and diatom characterization of metal-contaminated stream sediments and surface water of Corona stream.  Science of the Total Environment409: 4312-4325.

Silva E.F., Almeida, S.F.P., Nunes, M.L. & Fredrik, A.T.L. (2009). Heavy metal pollution downstream the abandoned Coval da Mó mine (Portugal) and associated effects on epilithic diatom communities.  Science of the Total Environment407: 5620-5636.

A year in the life of the River Wear …

After six bimonthly visits to the River Wear at Wolsingham during 2018, I can now step back and have a look at the complete dataset to see what patterns emerge.   Over the course of the year, I have visited the site six times and recorded a total of 107 species: 5 Cyanobacteria, 32 green algae, 69 diatoms and one red alga.  The true figure is probably higher than this, as the green algae include a number of “LRGT” (see “Little round green things …”) and certainly did not receive the same level of attention as the diatoms.

This crude enumeration of species, however, disguises some interesting seasonal patterns with, as I described in “Summertime Blues” and “Talking about the weather …”, abundant growths of green algae during the heatwave and associated low flow periods.  This can be seen clearly in the bar chart showing the seasonal changes in the river: diatoms predominate in the early part of the year whilst green algae are very scarce.  The bloom of the green filamentous alga Ulothrix zonata that I expected to see in March was missing due, I suspected, to the hard weather we experienced in late Feburary (see “The mystery of the alga that wasn’t there …”) but, by the summer, the river had taken on a very different complexion and was dominated by small green algae.   The last sample of the year, collected in November, showed a return to diatom dominance with a late autumn showing of Ulothrix zonata(see “The River Wear in November …”).

wear_summary_2018

Relative proportions (by approximate biovolume) of the main groups of algae found in the River Wear at Wolsingham during 2018.  

Looking back at records of a similar exercise in 2009, I see that the beginning and end of the year were quite similar, with thick biofilms dominated by diatoms; however, the algae in the summer of 2009 were very different to those I found in 2018.  My 2009 exercise involved visits every month rather than every other month and I see that I recorded more Cyanobacteria in June and July 2009 than I found in Summer 2018.  These were mostly filaments of Phormidium retziiand tufts of Homoeothrix varians, which I assumed to be a consequence of intense grazing (there is evidence that invertebrates find Cyanobacteria to be less palatable than other algae).  By July, Cyanobacteria comprised over half the total biovolume of algae; however, there was a major spate soon after my visit.  I was surprised to find, when I visited in August, a noticeably thicker biofilm smothering the rocks and, when I looked closely, this was dominated by the small motile diatom Nitzschia archibaldii.   The Cyanobacteria had disappeared almost completely.   I attributed this change to the invertebrate grazers being washed away by the spate, allowing the algae to grow unhindered.  As the biofilm grew in thickness, so the algal cells start to shade each other, and a diatom that can glide through the biofilm has an advantage over any that are stuck to one place.  Diatoms remained dominant for the remainder of the year, although my November sample came just after another storm and the stones I sampled were completely bare.

wear_summary_2009

Relative proportions (by approximate biovolume) of the main groups of algae found in the River Wear at Wolsingham during 2009.   A sample was collected in November but no living algae were recorded from it.

Overall, however, the similarities between the years outweighed the differences in the summer assemblages, whilst the composition of communities between late autumn and late spring was remarkably similar across the two years.   The changes in summer 2018 extended beyond just a shift in the balance of algae in favour of greens: there were also changes in the composition of diatoms too.  In fact, the changes in diatoms proved to be quite powerful mirrors of the changes in the community as a whole.  I have demonstrated this in datasets spanning a number of sites in the past but it is reassuring to see that they are also reflecting patterns within one site.   On the other hand, if I only had examined the diatoms, I would have missed some of the most interesting changes in the river over the course of the year.

Another observation is that no single sample from 2018 contained more than a quarter of the total algal diversity that I recorded over the course of the year.  Every month saw some new arrivals and some departures (or, more likely in some cases, a few taxa that were present had dropped below my analytical detection limit).  Some of these were expected (the seasonal dynamics of Ulothirx zonata, for example); others not (e.g. dominance by Keratococcus bicaudatusin the summer).  I discussed this in “A brief history of time-wasting …” and, in honour of that post, am not going to repeat myself here. In an age when our environmental regulators are cutting back on the amount of data that they gather, I shall go into 2019 reflecting on Yuval Noah Harari’s comment that “the greatest scientific discovery was the discovery of ignorance”.

A day out in Wasdale

Irt_LundBridge_Nov18

A few days after my trip to Weardale I found myself beside the River Irt, a few hundred metres below the point where it flows out of Wastwater, in the western part of the Lake District.   Whereas the River Wear drains a catchment underlain by Carboniferous rocks, including a high proportion of limestone (see “Co. Durham’s secret Karst landscape”), the Irt’s catchment is largely underlain by ancient volcanic rocks, resulting in much softer water.   I was curious to see how different the algae were here compared to those in the Wear.

The river bed at this point is dominated by boulders of granite, which host a patchwork of mosses, filamentous algae and discrete growths of diatoms (visible on the right-hand side of the figure below).  Between these there were areas of pebbles and gravels, suggesting good habitat for freshwater mussels.   The patches of filamentous algae (mostly no more than a couple of centimetres in length) were a mixture of Mougeotiaand Zygnema, similar to the forms that I find in the River Ehen, a 30 minute drive to the north.   These two species differ in the form of their chloroplasts (Mougeotiahas a flat plate whilst Zygnemahas two star-shaped chloroplasts, attached by thin cytoplasmic strands to resemble an animal skin stretched on a frame) but are closely-related, both belonging to the family Zygnemtaceae.

Irt_substratum_Nov18

An underwater photograph of the substratum of the River Irt in November 2018 showing patches of filamentous green algae, mosses and (on the right-hand side) diatoms growing on granite boulders.

Irt_greens_Nov18

Filamentous green algae from the River Irt, November 2018.   The upper photograph shows cells from a filament of Mougeotiawhilst the lower image shows two filaments of Zygnema. Scale bar: 20 micrometres (= 1/50thof a millimetre).

In between the tufts of filamentous algae were apparently bare patches of rock (they almost certainly had a very thin biofilm that would be hard to sample in isolation from the lusher algal growths that shared their habitat) and some conspicuous orange-brown growths of colonial diatoms.  These turned out to be almost pure growths ofGomphonema hebridense, or a close relative (I can’t give a definitive answer until I have examined cleaned material), growing on long mucilaginous, sometimes branched, stalks to create a veritable “bush” of diatoms.  There were a few other species of diatom growing within this bush, most notably some cells of Achnanthidium (cf.) caledonicumthat seemed to be growing on short stalks attached to the Gomphonemastalks, but also a few cells of Gomphonema capitatum(which also grows on long stalks) and some chains of Tabellaria flocculosa.

Gomphonema hebridenseis a diatom that I have written about several times before, as it is also common in the River Ehen, and also presents a number of interesting challenges to taxonomists (see “Diatoms and dinosaurs”). Whatever future studies reveal, however, the presence of colonies of this (or these) species that are visible with the naked eye is something I associate with only the cleanest rivers in the country during the cooler times of year.  It should not have been a great surprise to me to find it flowing out of one of the most pristine lakes in England (see “The Power of Rock …”).

Gomphonema_Irt_x1000_Nov18

A close up of cells within a colony of Gomphonemacf hebridense.  Several mucilaginous stalks are also visible as well as (top left) a cell of Achnanthidiumcf caledonicum.   Scale bar: 10 micrometres (= 100th of a millimetre).

The predominance of boulders over smaller, more easily moved stones, suggests a river that has more energy than the River Ehen, one of my regular Lake District haunts.   Both flow out of lakes whose catchments include some of the wildest and most mountainous terrain in the country.   Lakes tend to act as shock absorbers in catchments, slowing down the water that pours off the fells after heavy rain.   Streams in this part of the world that have no such impediments to flow tend to have rocky, mobile beds and relatively sparse algal communities.   By contrast, the Irt and Ehen just below their respective lakes have relatively lush growths of algae.   The substrates of the two rivers, however, are very different: the Ehen having very few boulders in comparison to the Irt, due to the presence of a weir at the outfall. This allows Ennerdale Water to be used as a water supply for the towns of north west Cumbria but, at the same time, turns the lake into an even more effective hydrological shock absorber.  Yet more of the energy that should be washing smaller stones down the river is no longer available except after the most exceptional storms.

That’s my working hypothesis, then: the Irt is a river that is subject to just enough high energy events to move the rocky substrates around yet no so many that rich algal communities cannot develop between these.  The Ehen, by contrast, has fewer events, leading to fewer opportunities for the algae to be scoured away, whilst unregulated streams such as Croasdale Beck (see “What a difference a storm makes …”) have such regular scouring spates that the algal communities are usually sparse.   I might be wrong, of course and I might be back in a years time with a better hypothesis.  Until then …