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.

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China’s lessons for the Western diet

mobikes_in_Chengdu

Just before I set off on my journey to China back in April I heard George Monbiot respond to the question  “what can we do to save the planet”.  His answer was “two things: eat a plant-based diet and avoid air travel”.  One ten-hour flight later I arrived in a country where it is notoriously difficult for a non-Mandarin speaker to avoid meat altogether so, it seems, I failed spectacularly on both counts.   The evidence behind Monbiot’s statements is strong yet I am not alone amongst academic environmental scientists in having a carbon footprint that is way above average.   For this to be justified I need to learn lessons as I travel that offset the environmental costs.  On this trip, those lessons came through the Chinese diet.

Whether we should eschew meat altogether is a moot point.  There are large parts of the UK where arable farming is not practical and livestock rearing makes practical sense, even if current economics leads to overstocking and what Monbiot has termed “sheepwrecking” of the uplands.   I’m more in favour of a substantial reduction in meat consumption, based on some realistic scenarios in a report produced by the French think-tank IDDRI (Institut du Développement Durable et des Relations internationals) and some other recent publications pointing out the environmental benefits of a less meat-rich diet.

Before I went to China I thought about this in terms of eating a higher proportion of vegetarian meals. After my trip I started to think more in terms of a lower proportion of meat in any given meal.  More importantly, meat does not have to dominate a plate but, rather, can act as a flavouring, enhancing the taste of dishes that were, essentially, vegetable-based.   Whilst it was not easy to get a meal that was dish that was through-and-through ‘vegetarian’ in China, few dishes were as meat-heavy as a typical meal in the West.  There are exceptions – Peking Duck being the obvious example – and two fortnight-long trips to this vast country does not make me an expert, but that is the impression that I have formed.

Kunming_hot_pot_April19

A Sichuan-style hot pot: note the liberal application of whole chillis. If you look very closely you will see Sichuan peppercorns between the chillis, just in case you were thinking that the seasoning was too tame.   The photograph at the top of the post shows Mobikes (and rival brands) for hire in the centre of Chengdu.   A monthly subscription costs less than a US dollar.

The other lesson I brought home from China is that they are not so focussed on the prime cuts and more use made of body parts that a Western cook might well throw away.   The cookery writer Fuchsia Dunlop explains this as a greater interest in the texture, rather than just taste, of food in China, compared to the west.   I’m not sure that duck intestines will appeal to everyone, but I also suspect that many will dismiss the idea without even trying.  But if we are to move to more sustainable diets that includes meat, then we will need to think about how to make use of the whole beast.  We may, actually, be exposed to more of this so-called ‘nose-to-tail’ eating than we think in the west as much of the meat that goes into highly-processed food comes from animal carcasses that have been mechanically-rendered.   The difference is that the Chinese actively embrace and take control of this concept (though they do seem to have an inexplicable fondness for luncheon meat).

Chengdhu_street_food_Apr19

Street food in Chengdu close to our Airbnb apartment: total price, including beer, was about £2 each. 

Back in Europe, I find myself less interested in a binary divide between ‘vegetarian’ versus ‘non-vegetarian’ as a result of this trip.   I did not have a Damascene conversion as such, as I have been trying to eat less meat for some time.  I’ve also tried to focus on the provenance of any meat that I buy but, when I did cook meat, it was usually a centrepiece of the meal.   Now, I find myself noticing how Italians toss pasta in a ragùsauce and serve what is, in effect, flavoured pasta rather than the British corruption of ‘spag bol’ where a pile of mince sits on top of the pasta.   That must be a better way to go.

How does this fit into a blog about natural biodiversity?   I often write about how the diversity of organisms is greatest in those lakes and streams that are in the most remote places.  The fertilisers that farmers use to boost production are a major source of nutrients in freshwaters.  These have significant effects on the communities that I see, and on the way that streams function.   One way that ecologists differ from other scientists is that they realise that they can never be wholly independent of the systems that they study. To comment on how agriculture influences freshwater is also to realise that, as a consumer of agricultural produce, I am part of the problem.  And, potentially, part of the solution too.

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Smog over Chengdu, photographed from our Airbnb apartment near Zongfu Road.

 

When the going gets tough …

Castle_Eden_Dene_May19

Two months after the visit I described in the previous post I was back at Castle Eden Dene.    The trees were now in leaf and the floor of the forest was carpeted with wild garlic.   The stream, however, had disappeared below the surface and, once again, I could walk along the channel without getting my feet damp.

Having found a rich crop of diatoms on my last visit when the stream was dry I was intrigued to see what was growing on the stones this time, so I used a toothbrush and some water that I had brought along to scrub a few and collected the dislodged material in my white tray.   I was intrigued to see that the suspension that collected in my tray had a distinct green tinge and, when I got a drop of it under my microscope, found it to be dominated by small green cells.  These were superficially similar to the cells of Desmococcus and Apatococcus that I found on the fence in my garden (see “Little Round Green Things …”) but this is a difficult group with not many clear morphological features with which to distinguish genera so I sent a sample off to Dave John for his opinion.

His view is also that groups such as this are almost impossible to identify unless you grow them in the laboratory or have access to DNA sequencing facilities.   He commented that Desmococcus and Apatococcus both have distinctive 2- or 4-celled packets of cells, which were not common in the Castle Eden Dene sample.  Likely candidates are the generaPleurastrumand Pseudopleurococcus, both of which are subaerial or terrestrial.   Perhaps “Little Round Green Things” is as close as we need to go in this particular instance?

CED_biofilm_May19

A distinctly-green suspension of the biofilm on stones at Castle Eden Dene in May 2019 (left) along with a magnified view showing some of the green cells which dominated the sample (right).  Scale bar: 20 micrometres (1/5thof a millimetre).   

A short distance further on I found some mats of entwined filaments on the tops of stones which also piqued my curiosity.   Under the microscope, and with the addition of a drop of water to rehydrate them, these filaments revealed themselves to belong to Vaucheria (see “Who do you think you are?”).   Technically speaking, Vaucheria is not filamentous but “siphonous”, meaning that there are no cross walls but, instead, the organism consists of branching tubes containing many separate nuclei and chloroplasts.  The cell walls of Vaucheria, however, rupture easily releasing the chloroplasts and giving the appearance of an empty sausage skin. In this case, there are still quite a few chloroplasts but a healthy Vaucheria filament has a uniformly dense green appearance that none of those that I saw in Castle Eden Burn possessed.

There was more than just vegetative filaments of Vaucheria here: scattered amongst them were some larger, spheroid or jar-shaped cells, which are part of Vaucheria’s sexual reproduction apparatus.   I’ve talked before in this blog about how sexual reproduction is relatively rare in the filamentous algae that we find in lakes and streams (see “The perplexing case of the celibate alga …”) and Vaucheria is another case in point.   Put simply, many algae do not bother with sexual reproduction when conditions are favourable and they can grow through simple cell division.   If you subjected a Vaucheria filament to Freudian analysis, it would probably tell you that one outcome of sexual reproduction was a 50% dilution of its unique genotype. So why bother if you don’t have to?  On the other hand, sexual reproduction in these organisms usually results in a zygote with a thick wall that is capable of resisting tough conditions.   The complete absence of water in Castle Eden Burn would be one such circumstance.   To put it another way, when the going gets tough, the algae get frisky.

CED_Vaucheria_mat_May19

Mats of Vaucheria growing on a small boulder in Castle Eden Dene in May 2019.  The picture frame in the left hand image is approximately 30 centimetres. 

CED_Vaucheria_May19

Cell walls of Vaucheria, with a few chloroplasts still present, from Castle Eden Burn, May 2019.  Scale bar: 20 micrometres (= 1/50thof a millimetre). 

However, the structures did not really match any pictures that I could find of oogonia or antheridia in Vaucheria.  I passed my images around some friends, and Gordon Beakes suggested that we might be looking at sporangia of chytrids, a group of fungi that have a string of previous convictions for infecting algae (see “Little bugs have littler bugs upon their backs to bite ‘em ….”).  As I was taking the photographs below, a cloud of tiny spores was released, prompting me to call out “come quickly if you want to see an alga ejaculating” before remembering that we had visitors in the house who might think this a little weird (and not just because I had not yet realised that they were, in fact, fungi).   I even took a video.  I’ll upload it to the Dark Web at some point.  There must be a site for fungal-themed pornography out there, if only I took the time to look…

CED_Vaucheria_oospores

Sporangia of chytrids on Vaucheria filaments from Castle Eden Burn, May 2019.  The one on the right was releasing spores (arrowed) at the time the photograph was taken.   Scale bar: 20 micrometres (= 1/50thof a millimetre).  

Out of my depth …

Castle_Eden_Dene_March19

I was about to start writing up an account of my latest visit to Castle Eden Dene, when I realised that I had forgotten to describe my previous visit, back in March.   I’ve already described a visit in January, when the stream was dry (see “Castle Eden Dene in January” and “Tales from a dry river bed”) and promised regular updates through the year.   It seems that, amidst all the travel that filled my life over the last three months, I overlooked the post that I should have written about the visit that I made in early March.

Whereas the river was dry in January, rain during February meant that, when I returned to the Dene on 11 March, some rather turbid water was flowing down the channel on its short journey to the North Sea.   There is, finally, something more like a stream habitat from which I can collect some diatoms.

Many of the diatoms that I found in March belonged to taxa that I had also seen in January; however, the proportions were quite different.   In some cases, species that were common in January were less common now (e.g. Humidophila contenta*) but there was a small Nitzschia species with a slightly sigmoid outline that was very sparse in the January sample but which was the most abundant species in the March sample.  I’ve called this “Nitzschia clausii” but the Castle Eden Dene population does not fit the description of this perfectly.   A lot can change in a couple of months, especially when dealing with fast-growing organism such as these, as my posts on the River Wear showed (see “A year in the life of the River Wear”).  Castle Eden Burn’s highly variable discharge just adds another layer of complication to this.

CED_diatoms_Mar19

Diatoms from Castle Eden Dene, March 2019:   a. – e.: Nitzschia cf clausii; f. Tabularia fasiculata; g. Tryblionella debilis; h. Luticola ventricosa; i. Luticola mutica; j. Ctenophora pulchella.  Scale bar: 10 micrometres (= 1/100thof a millimetre).   The picture at the top of the post shows Castle Eden Burn at the time that the sample was collected.   

Nitzschia clausii is described as being “frequent in brackish freshwater habitats of the coastal area and in river estuaries, as well as in inland waters with strongly increased electrolyte content”.   A couple of the other species from this sample – Ctenophora pulchella and Tabularia fasiculata (both illustrated in the diagram above) – have similar preferences.    My experience is that we do often find a smattering of individuals belonging to “brackish” species in very hard water, as we have in Castle Eden Burn.  Average conductivity (based on Environment Agency records) is 884 µS cm-1; however, values as high as 1561 µS cm-1.   The fluctuating discharge plays a role here, as any evaporation will serve to concentrate those salts that are naturally present in hard freshwater.   This should probably not be a big surprise: life in brackish waters involves adapting to fluctuating osmotic regimes so species that can cope with those conditions are also likely to be able to handle some of the consequences of desiccation.

Average values of other chemical parameters from 2011 to present, based on Environment Agency monitoring are: pH: 8.3; alkalinity: 189 mg L-1 CaCO3; reactive phosphorus: 0.082 mg L-1; nitrate-nitrogen: 1.79 mg L-1; ammonium-nitrogen: 0.044 mg L-1.   There is some farmland in the upper catchment, and the burn also drains an industrial estate on the edge of Peterlee but, overall, nutrient concentrations in this stream are not a major concern.   The Environment Agency classifies Castle Eden Burn as “moderate status” due to the condition of the invertebrates but does not offer any specific reason for this. I suspect that the naturally-challenging habitat of Castle Eden Burn may confound assessment results.

I’ve also been given some data on discharge by the Environment Agency which shows how patterns vary throughout the year.  The two sampling locations are a couple of kilometres above and below the location from which I collect my samples and both have more regular flow.  However, we can see a long period between April and September when discharge is usually very low.   The slightly higher values recorded in July are a little surprising, but are spread across a number of years.   It is also, paradoxically, most common for the burn to be dry in July too: clearly, a month of extremes.  As my own visits have shown, it is possible for the burn to be dry at almost any time of the year, depending on rainfall in the preceding period   The dots on the graph (representing ‘outliers’ – records that exceed 1.5 x interquartile range) show that it is also possible to record high discharges at almost any time during the year too.  I should also add that, as I am not a hydrologist, I am rather outside my comfort zone when trying to explain these patterns.  I would have said ‘out of my depth’ though that’s not the most appropriate phrase to use in this particular situation.

CED_discharge

Discharge in Castle Eden Burn, as measured by the Environment Agency between 2007 and present.   Measurements are from NZ 4136 2885 (‘upstream’) and NZ 45174039 (‘downstream’).  

* Note on Humidophila contenta:it is almost impossible to identify this species conclusively with the light microscope as some key diagnostic characters can only be seen with the scanning electron microscope.   However, all members of this complex of species share a preference for intermittently wet habitats so these identification issues are unlikely to lead to an erroneous ecological interpretation.  It is probably best to refer to this complex as “Humidophila contenta sensu lato” rather than “Humidophilasp.” order to distinguish them from those species within the genus that can be recognised with light microscopy.

Reference

Lange-Bertalot, H., Hofmann, G., Werum, M. & Cantonati, M. (2017).  Freshwater Benthic Diatoms of Central Europe: over 800 Common Species Used in Ecological Assessment. English edition with updated taxonomy and added species.  Edited by M. Cantonati, M.G. Kelly & H. Lange-Bertalot.  Koeltz Botanical books, Schmitten-Oberreifenberg.

When is an icon not an icon?

Florence_from_Fiasole_May19

Yet another change in location, this time to Florence for a wedding, but with some time set aside to gorge myself on early Renaissance painting.   That means traipsing around a lot of churches (because much of the best Italian art remains in situ) and a long queue to get into the Ufizzi gallery (because some of it doesn’t), emerging at the end footsore and with more questions than answers.

Having immersed myself in Eastern Orthodox imagery earlier this year (see “Secular icons?”) my first response on looking at the earliest works by Giotto and Cimabue was “those are icons”.  Stylistically and in subject matter, there is nothing to distinguish them from contemporary Eastern Orthodox icons: the flat, gilded backgrounds, the poses of the Madonna and child, and the saints, are all identical.  That made me wonder if the Medieval believers had approached these images in the same way that an Orthodox Christian would have done, in which case we need to think of the Renaissance not just in the conventional art-historical terms (epitomised by Kenneth Clark’s Civilisation) but also in terms of a change in belief.    This is important because, in most cases the artists would have been working to strict instructions from their clerical paymasters and would not have had much latitude to experiment with new designs.

A case in point is Giotto’s Madonna and Child with four saints, which looks very much like a row of icons on an Orthodox iconostasis. Except that this was originally altarpiece and that, itself, tells a story.   The Orthodox iconostasis stands between the priest who conducts the eucharist and the congregation whereas a Catholic altarpiece sits behind the altar, so that the congregation (that part beyond the rood screen at least) can see the ceremony and, in particular, the part when the priest elevates the host.   Theological developments in the 13thcentury, therefore, drove changes in the arrangement of church furniture and, in turn, led to some of the changes that we see in art during this period.

Giotto_Madonna_&_Child_Ufizzi

Giotto: Madonna and Child with St Nicholas, St John the Evangelist, St Peter and St Benedict the Redeemer.  Tempera on wood, 1337.   Ufizzi Gallery, Florence.

It is not just the position of the image that changed in Catholic churches during Medieval times: subject matter also changes from schematic images painted to prescribed formulae to styles that demanded more mental engagement by the viewer.  Look at Gentile da Fabriano’s altarpiece depicting the Adoration of the Magi, painted about a century after Giotto’s Madonna and Child.   The Madonna and child are still present but are now set in a context that would allow the viewers to imagine that they were participants at the original event.   Note, too, how the subjects in the picture are dressed in contemporary attire and original audiences might also have recognised the patron and members of his family painted into the front of the crowd.   At one level, these altarpieces function as a “poor man’s bible”, bringing elements of the Gospel to the largely illiterate congregations but, at the same time, they are also drawing the viewers into the story, ensuring that they are not just passive observers and, in turn, demanding a response.

Adoraton_of_Magi_Fabriani_Ufizzi

Gentile da Fabriano’s Adoration of the Magi.  Tempera on wood, 1420. Ufizzi Gallery, Florence.

As the fifteenth century progresses, we see the influence of the Renaissance in the images growing. In particular, a better understanding of linear perspective allowed artists to place the characters in their paintings in more plausible settings, drawing the viewer into the pictorial space.   Fra. Angelico’s Annunciation is painted onto a wall at the top of a staircase leading to monk’s cells in the Convent of San Marco, so the engagement with the viewer would be brief: no more than a short pause and a prayer before moving on.   The quiet scene depicted here is, perhaps, better suited to a monastery’s cloisters than the busy-ness that we saw in the Adoration of the Magi but, by focussing on just two people, pictures of the Annunciation create spaces that need to be filled if the illusion of pictorial depth is to be maintained.   And so we see, in the background of both Fra. Angelico’s and Leonardo’s Annunciations, the first tentative steps at depicting landscapes.

Annunciation_Fra_Angelico

Fra. Angelico’s Annunciation at the Convent of San Marco, Florence.  Fresco, 1437-1446.

Annunciation_Leonardo

Leonardo da Vinci’s Annunciation. Oil and tempera on wood, 1472-1474.  Ufizzi Gallery, Florence.

The painting style may have developed through the early Renaissance but one feature that all these pictures still share with their Gothic predecessors, and with Byzantine icons, is that they are still “applied art”: each was painted with a particular purpose in mind, whether for a church or a monastery, and 21stcentury notions of aesthetics have to bear this in mind.   On our trip to Florence this aspect was exemplified by Ghirlandaio’s The Last Supper, also at the Convent of San Marco.  This is in rather better condition than Leonardo’s depiction of the same scene in Milan (which is about a decade younger) but is similar in other ways (some think that Leonardo may have been inspired by Ghirlandaio’s treatment of the subject) and, significantly, was also painted life-size onto the wall of a refectory.   Once again, we can see clever use of linear perspective to create an illusion of depth and, in the background, trees that suggest that, instead of looking at a flat wall we are, in fact, looking into an extension of the room that we are in which, in turn, has windows that look out onto a garden.   That gives us an important clue to unlocking the meaning of the image.

The Refectory where we find The Last Supper is now the gift shop for the San Marco museum, but there are wooden benches along two of the walls where you can sit down and try and put yourself into the place of the monks and their visitors who would have eaten their meals here.   The painting creates the illusion that they were eating in a room that seemed bigger than it really is, and where there were a dozen or so extra guests whose presence was a constant reminder of one of the most important events in the Gospels.  This is the acme of Renaissance thinking: scientific and mathematical principles being utilised to create a work of art that, in turn, synergised man’s relationship with God.   C.P. Snow described what he saw as a profound gulf between arts and sciences in the Two Cultures, written in 1959.  Even then he could conceivably have extended this observation to three cultures by including religion too.  That would have been an anathema in the fifteenth century, when the boundaries between art, science and spirituality were much more fluid.  We’ve learned a lot in the intervening five hundred years but, at the same time, there is much that we have forgotten to remember.

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Domenico Ghirlandaio’s The Last Supper in the Small Refectory at the Convent of San Marco, Florence.  Fresco, 1486.

Santa_Croce_from_Palazzo_Vecchio_May19

The church of Santa Croce rising above the rooftops of central Florence in May 2019.    The photograph at the top of the post shows a view of Florence from Fiesole.

More algae from Shetland lochs …

Lamba_Water_May19

I’m taking you back in the Shetland Islands for this post, and onto the remote moorlands of northern Mainland.   When I visited this particular loch in 2016, I noticed a lot of slippery filaments of Batrachospermum attached to the sides of the cobbles in the littoral zone (see “Lucky heather …”).   This time around, I explored further around the edge of the loch and, in the south-west corner noticed prolific growths of algae in the shallow peaty water.  Closer inspection showed that these, too, were the red alga Batrachospermum and, though they were not fertile, Dave John suggests that they are likely to be B. turfosum Bory.

Batrachospermum_Lamba_Water_May19

Tufts of Batrachospermum turfosumin the littoral zone of Lamba Water, north Mainland, Shetland Islands, May 2019.   The picture frame is about 15 centimetres across. 

If you have a hand lens you can just about make out a bead-like structure when observing Batrachospermum in the field; however this becomes much clearer with higher magnification.   I think it looks like a bottle-brush when seen under the microscope at low magnification, with whorls of side-branches arising from the central filament.  At higher magnification, these filaments can be seen to have a bead-like structure, with cell size gradually reducing with distance from the centre.

What you cannot do in the field is separate Batrachospermumfrom the closely-related genus Sheathia(see “News about Batrachospermum… hot off the press”).   I usually tell people that, for a general overview of the condition of a stream or lake (for example, as part of the UK macrophyte survey technique), then simply recognising that you have “Batrachospermum” (meaning Batrachospermum or Sheathia) should be enough.   In my experience, the presence of Batrachospermumis usually a good indication that the water body is in a healthy condition.  However, I have been told that Batrachospermumis often found growing prolifically in very enriched conditions in southern chalk streams, which would challenge this assumption.   This may be because the species that are found in southern chalk streams are different to those that I encounter in my more usual haunts in northern England and Scotland.  But it is also possible that the factors I described in “The exception that proves the rule …” pertain in those cases too.

Batrachospermum_turfosum_Lamba_Water

Filaments of Batrachospermum turfosum from Lamba Water, north Mainland, Shetland Islands, May 2019.   The upper photograph shows a low magnification view of a filament (about 350 micrometres, or 0.35 millimetres, wide) whilst the lower image shows a whorl of side branches arising from the main stem.  Scale bar: 20 micrometres (= 1/50thof a millimetre).  

We often run into this dilemma with filamentous freshwater algae: it is reasonably straightforward to identify the genus but we need reproductive organs to determine the species.  As they seem to survive quite happily in the vegetative state our understanding of the ecology of individual species (rather than the genus as a whole) is scant so it is hard to tell whether there is value in that missing information or not.   In a few cases – this is one – better taxonomic understanding has revealed that we may not even be dealing with a single genus but the lists used for applied ecological surveys still persist with the old concepts.

This creates a toxic spiral of consequences: it is hard to split into species so most people don’t bother. Because we don’t bother, our interpretations are based on generalisations drawn from the behaviour of the genus.  This means we don’t generate the data needed to demonstrate the value (or otherwise) of the effort required to go from genus- to species-level identifications.   So we carry on lumping all records to genus (or, in this case, a pair of genera) and accept a few records that our out of line with our expectations as “noise”.  The situation is probably worse in the UK than in many places because there are very few people in universities specialising in these organisms and, as a result, no-one is producing the data that might break us out of this spiral.

We found Batrachospermum turfosum in a few other locations during our visit, but nowhere, even in nearby lochs, was it in such quantity as we saw in Lamba Water.   Chance might play a part in determining its distribution on a local scale but that ought to be the explanation of last resort rather than the go-to answer when we are worryingly short of hard evidence.

 

 

Notes from Windermere

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Just before the trip to the Shetland Islands I wrote about in the previous post, I spent two days in the Lake District teaching a course on identifying macroalgae for the Freshwater Biological Association.  It coincided with a period of gorgeous weather, showing Windermere at its absolute best (as the photo at top of the post shows).  Only a month ago my wheels were spinning in the snow on Whinlatter Pass (see “How to make an ecosystem (2)”).

Looking up Windermere towards the high peaks of the Lake District’s volcanic centre, I find myself reflecting on how geology creates the diversity in landscapes and aquatic features that, in turn, creates variety in the microscopic flora and fauna (see “The Power of Rock”).   A nuanced understanding of the aquatic world requires one to view the grand panorama at the same time as focussing on organisms that are scarcely visible with the naked eye.

One of the locations that we visited during the course was Cunsey Beck, which flows out from Esthwaite Water and, a few kilometres later, into Windermere.   Esthwaite is one of the more productive of the lakes in this region and we usually find a healthy crop of algae in the beck.   This year was no exception and, amongst the different forms we collected were some long straggly growths that had a slighty gelatinous feel.  Back at the laboratory we put part of one of these growths under the microscope and saw a large number of individual cells set in a jelly matrix.   This identified the alga as Tetraspora gelatinosa, a green alga that I have written about before (see “More from the Atma River …”) although not for some time.

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Tetraspora gelatinosafrom Cunsey Beck, Cumbria, May 2019.   The picture frame is about five centimetres wide.

The genus Tetraspora gets its name from a mode of division that leaves many of the daughter cells in groups of four (visible in the lower illustration).  These, in turn, are embedded in mucilage, and repeated divisions can lead to growths becoming visible with the naked eye.   Three species have been recorded from Britain and Ireland, of which the Cunsey Beck population is most likely to belong to T. gelatinosa.   In the past, it might have been called Tetraspoa lubrica, which has a more tubular thallus; however, this is now thought to just be a growth form of T. gelatinosa that is associated particularly with fast-flowing rivers.  As far as I can tell, no-one has performed any detailed molecular genetic studies on this genus to better understand the relationships between these different growth forms so we will have to go with current convention for now.

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Tetraspora gelatinosaunder the microscope.   Cells in the foreground are about ten micrometres in diameter.   Photograph by Hannah Kemp.

I’ve seen Tetraspora in a wide range of habitats – on stones in fast-flowing, relatively soft water rivers in Norway and growing on plant stems in the littoral zone of hard water ponds in Ireland.   Most of my records are from the spring, though I should add that spotting some of the smaller gelatinous colonies (barely more than near-transparent dots on the stone surface) does take some practice and I suspect that I have missed it on a few occasions too.

The microscopic image of Tetrasporawas taken during the course using a Carson Hookupz, a neat device which allows a smartphone to be attached to a microscope (or any other optical device).   It takes a little fiddling to get the set-up right but, once this has been achieved, the quality of pictures we obtained was excellent.   My microscope engineer tells me that he is selling large numbers of these to schools and colleges as it means that students can capture images during practical classes that they can subsequently use in reports or just (as was the case during our course) as an aide mémoire.

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The Carson Hookupz 2.0 as it comes out of the box (left) and (right) in action during the Identifying Macroalgae course at the Freshwater Biological Association.

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Looking north from Miller Ground towards the central Lake District peaks as the sun sets.  The photograph at the top of the post was taken from nearby but shows the view in early morning.