Entrances and exits …

Having shown in two recent posts how the presence of one alga influences the quantity of many others in the River Irt, I thought I should see if this relationship holds in other streams in the region.   As Gomphonema exilissimum was the “ecosystem engineer” in the River Irt, I started with Croasdale Beck because I knew that this, too, had abundant populations of Gomphonema at certain times of the year.   Whereas the River Irt flows out of Wastwater, Croasdale Beck tumbles straight off the west Cumbrian fells.  It is, as a result, a much flashier stream than the Irt, and this has a big effect on the stream’s algae.

Gomphonema in Croasdale Beck shows the same general annual pattern as it does in the River Irt but without the coupling to diatom biomass that I showed in “High-rise habitats” (there are weak relationships, but these are not statistically-significant).  The most abundant Gomphonema is different at the two sites I visit on Croasdale Beck: G. parvulum at the upper site and G. calcifugum at the lower one.  Neither grows on long stalks in Croasdale Beck although I have certainly seen relatives of G. calcifugum form long stalks elsewhere in northern England (see: “And the Oscar for the best alga in a supporting role goes to …”).  I suspect that the harsher conditions compared to the River Irt would mean that “high-rise” growth forms would get scoured away too frequently and that, in turn, means that there is less opportunity for other algae to exploit the habitat that a cushion of stalk-forming Gomphonema creates.   

Gomphonema parvulum (top row) and Gomphonema calcifugum (bottom row), the two most common species of Gomphonema in Croasdale Beck (seen in the photograph at the top of the post)

Both Gomphonema species in Croasdale are at their most abundant about now (just as in the River Irt).   As March passes to April so a different diatom, Odontidium mesodon will become abundant and then, during the summer, it will be Fragilaria that dominates (at least two species – F. gracilis and F. novadensis) before, towards the end of the year, Meridion constrictum will become abundant.   Platessa (P. saxonica and P. oblongella) show a weaker trend, with dropping to minima in mid-summer before rising again, whilst Achnanthidium shows no annual trend at all.  

Annual trends in relative proportions of six common diatom genera in Croasdale Beck.   Vertical lines divide the year into 12 months.  

The diatoms are, in other words, behaving just as the terrestrial vegetation.  Outside my window I can see crocuses where, a few weeks ago, I would have seen snowdrops.  Daffodils are also beginning to appear.   In nearby woodlands, I can see celandine, but this will soon be replaced by wood anenomes, bluebells and then wild garlic.  The processes that drive these changes in higher plants are hard-wired into the genomes.  We know much less about the reasons for changes in stream diatoms.  Maria Snell made a convincing case for seasonal changes in diatoms in a stream on the other side of Cumbria being the result of changes in nutrient supply.  However, I think it unlikely that Croasdale Beck experiences the same scale of nutrient flux.   We know that the rise and fall of Asterionella formosa (another late winter/spring diatom) in Cumbrian lakes is a much more nuanced story, with temperature playing a key role and there is no reason to assume that the same does not apply to stream diatoms too.   Nutrients will certainly be part of this tale, but there is a richer cast of characters than this simplistic interpretation allows. 

Cobbles from Croasdale Beck in February 2023, their upper surfaces glistening with a thick film of diatoms.

Why is seasonality in stream diatoms overlooked?   One possible reason is that most sampling frequencies are too low to detect patterns within individual streams.  Another, however, is that diatomists are not primed to look for this type of pattern.   The Freshwater Benthic Diatoms of Central Europe, the one-volume handbook that many of us use, describes over 800 common species, and includes ecological and habitat notes for all of these.   However, there is not a single comment on seasonality.  By contrast, preferences for chemical water quality are described in detail.   A benign explanation may be that seasonal preferences vary around Europe, but it is also possible that seasonality in diatoms is widely overlooked.   The two reasons – not being told to expect seasonal patterns and not sampling consistently at the same sites with sufficient frequency – are intertwined.

It is the inverse of Newton’s famous statement, “if I have seen further it is by standing on the shoulders of giants”.  What if those we thought of as “giants” were actually, themselves, only dwarves?   Maybe there are more patterns under our noses that earlier generations of diatomists had overlooked but which are ripe for a new generation to discover?   Wouldn’t science be boring if everything the “giants” of earlier generations told us turned out to be true and there was nothing left for us to discover? 

References

Maberly, S. C., Hurley, M. A., Butterwick, C., Corry, J. E., Heaney, S. I., Irish, A. E., … & Roscoe, J. V. (1994). The rise and fall of Asterionella formosa in the South Basin of Windermere: analysis of a 45‐year series of data. Freshwater Biology 31: 19-34.

Snell, M. A., Barker, P. A., Surridge, B. W. J., Benskin, C. M. H., Barber, N., Reaney, S. M., … & Haygarth, P. M. (2019). Strong and recurring seasonality revealed within stream diatom assemblages. Scientific Reports 9: 3313.

* All the world’s a stage,
And all the men and women merely Players,
They have their exits and their entrances ….
                        William Shakespeare, As You Like It Act 2 Scene 7

Some other highlights from this week: 

Wrote this whilst listening to: Lynyrd Skynyrd (pronounced ‘lēh-‘nērd ‘skin-‘nērd) following the death of their guitarist Gary Rossington. I’ve long been uncomfortable about a band that performed with the Confederate flag as a backdrop.  It raises similar issues for me as the film Tár, about the extent to which it is possible to separate an artist’s views from their work.  This week, however, I’ll give them the benefit of the doubt …

Currently reading: Lessons, by Ian McKewen

Cultural highlight:  Fergus McCreadie Trio at the Sage, Gateshead although, to be honest, I’m still on a high after the Vermeer exhibition at the Rijksmuseum 

Culinary highlight:   Slightly belated shout-out for Gertrude’s Restaurant and Bar in Amsterdam where we ate and drank last week.   “Small plates” and a bottle of an Alsatian Orange Gewürztraminer.  

And finally, two sketches made on my iPad after the Vermeer show.   My disappointment is that Vermeer’s “The Art of Painting” was too fragile to travel from Vienna.  Otherwise, I could have drawn someone photographing a painting of someone painting someone.  I had to make do with drawing someone photographing a painting of someone.

High-rise habitats …

In the previous post I said that I had looked at one patch of algae in the River Irt from four different perspectives.  I’ve actually looked at this patch from five perspectives, because I forgot to count the graphs that I included in Cold Comforts.   Graphs are visual representations of the algae but they are not figurative in the sense that the photographs I’ve used are.   They are abstract in the sense that they convey an essence of the subject matter whilst being independent of visual references.   In the case of these graphs, I was able to convey a sense of changes over time that would have been impossible without sophisticated time-lapse photography.

The genus Gomphonema has featured prominently in the two earlier posts, so we’ll start with a closer look at how this changes over the course of the year.   This is mostly G. exilissimum but, as we saw in the previous post, other species are also present.   This graph shows a similar trend to the one showing chlorophyll concentrations on the riverbed over the course of a year, with the lowest values in the summer and higher values at the beginning and end of the year.   

The percent of total diatom valves belonging to the genus Gomphonema in the River Irt downstream of Wastwater (2019 – 2022).  The y axis is presented on a square-root transformed axis.   The photograph at the top of the post shows Cinderdale Bridge on the River Irt.

The question that arises is whether the Gomphonema is following a general trend in diatom biomass or whether it could actually be responsible for the annual fluctuations that we can see in biomass.   Over the course of the year, it rarely accounts for more than ten percent of all diatoms although, as we saw in the previous post, this equates to a larger proportion of total biovolume.   When we add in the stalks, then Gomphonema is by far the most abundant diatom.   The stalks do not contribute to the amount of chlorophyll that we measure, but they do create surfaces on and around which other algae can grow.   

The next step, therefore, was to look for relationships between the amount of Gomphonema and the amount of chlorophyll.   As you’ll see below, there is a positive relationship – more Gomphonema is associated with more chlorophyll.   If this was just a correlation with the annual trend in chlorophyll then we might expect to see this type of pattern in other common alga.  In fact, as the other three graphs below show, these do not show any relationship with biomass.   This is not conclusive, but it does hint to a role for Gomphonema in this particular stream as a creator of ephemeral habitats that other taxa can then exploit.   

Relationships between diatom biomass and Gomphonema (a.), Brachysira (b.), Achnanthidium (c.) and Fragilaria (d.) in the River Irt downstream of Wastwater (2019-2022).  Only the regression for Gomphonema is significant (adjusted r² = 0.44).

My interpretation is that many of the diatoms that I find in the River Irt are not particularly fussy about the substratum on which they grow, so I find them throughout the year, regardless of the biomass.   However, when Gomphonema exilissimum proliferates, the surface area available for other diatoms to colonise increases, leading to an increase in diatom biomass.   G. exilissimum has created opportunities for “high-density housing” – algal equivalents of tower blocks (“housing projects”, for North American readers).  

I suspect, too, that these Gomphonema-dominated communities make perfect meals for grazers once they get active in the spring.  The combination of crunchy protein-rich diatoms and lots of carbohydrates in the stalks creates a nutritious salad which, in turn, means that they do not last for very long.  These habitats are ephemeral, shifting in space and time.  That is probably one reason why diatoms are rarely considered to be “foundation species” in the generally adopted sense.  But in the brief window of opportunity when Gomphonema can thrive, they are every much as essential for the health of the overall community as the oak trees in an ancient woodland.

Some other highlights from this week: 

Wrote this whilst listening to: Hothouse Flowers and My Bloody Valentine: two very different bands sharing a common origin in Dublin in the early 1980s.  

Currently reading:   The Origins of Virtue by Matt Ridley.  

Cultural highlight: Transatlantic Sessions at the Sage, Gateshead, a coming together of Celtic and North American (mainly Appalachian) musicians exploring their common heritage.  Musicians included Liam Ó Maonlaí, leading me to explore Hothouse Flowers.

Culinary highlight:   Dinner at Khai Khai in Newcastle before heading to the Sage for Transatlantic Sessions.  Khai Khai is fast becoming our Indian restaurant of choice in Newcastle.

Ways of seeing …

I’m back at the River Irt, in the shadow of the Wastwater Screes, for this post.   I wrote about my visit in early December in “Cold Comforts”, then followed this up with “Temporary Foundations” in early January.   Together, these offer three “views” of the algae in the River Irt: first, as seen with the naked eye, then as observed through a microscope.   The third view was an imagined microscopic view had the catastrophic interventions required to transfer field growths to a microscope not been required.  Today, I offer a fourth view: that of the diatoms following standard cleaning procedures.   This is the approach adopted by most diatomists, prioritising the structure of the silica frustule (cell wall).  

In the earlier posts, I explained how the stalks of Gomphonema exilissimum formed a matrix within and around which other diatoms existed.   It is not always easy to see all the details needed for a confident identification when looking at fresh material, and a close look at cleaned material showed that, whilst this was the certainly the most abundant Gomphonema species, there were also several cells of two other species.  G. cymbelliclinumlooks very similar to G. exilissimum but there is a pronounced asymmetry along the long axis and the striae are also more radiate.   There were also a very small number of cells of G. hebridense. 

Gomphonema species from the River Irt, December 2022.   a. – f.: G. exilissimum; g., h. G. cymbelliclinum; i. G. hebridense.   Scale bar: 10 micrometres (= 100^th of a millimetre).   The photograph at the top of the post shows the River Irt at Lund Bridge, just downstream from the outflow of Wastwater.

However, although playing an important role as a “foundation species” in the biofilms of the River Irt, Gomphonema was not the most abundant genus in the sample.  That honour went to Achnanthidium, which accounted for 63 per cent of all the cells.  I spotted at least six species, five of which are illustrated below.  Two were common (A. minutissimum and A. siemenskae), two less so (A. caledonicum and A. neomicrocephalum) and two were scarce (A. “eutrophium”, A. lineare).   A. siemenskae has only recently been recognised in the UK.  Previously, it was “lumped” with A. caledonicum but some astute detective work by Ingrid Jüttner finally showed that it was distinct.   

Achnanthidium from the River Irt, December 2022.  a. – g. & k. – o.: A. siemenskae; h. – j.: A. minutissimum; p. A. eutrophilum; q., r. A. lineare; s., t. A. caledonicum.  Scale bar: 10 micrometres (= 100^th of a millimetre).  

Simply counting the number of individuals can be misleading, however.  Achnanthidium cells are smaller than Gomphonema exilissimum cells, and if we convert the number of cells to their volume, then Achnanthidiumdrops from representing 63 per cent of the total, to just 32 per cent.   G. exilissimum, by contrast, leaps from 13 per cent to 36 per cent.  The biovolume calculation is probably a better representation of how the two genera contribute to the primary productivity of the community but this is just based on the cell and excludes the stalk.  If we could include the stalks in the calculation, G. exilissimum would be even more dominant. 

The next most abundant species, assessed by numbers was Brachysira microcephala.  This is a curiosity for another reason: I calculate that it has changed names four times since I started looking at diatoms.  First, it was included in Anomoensis vitrea.  Next, freshwater species of Anomoensis were moved to a resurrected genus (originally created by Kützing in 1836) and it became Brachysira vitrea.  Then B. vitrea was split and forms found in soft water were placed in B. neoexilis.  Some people thought that there was no need to create this new species as a previously described species, B. microcephala, took priority.  Last year, however, Bart van der Vijver and colleagues showed that B. neoexilis and B. microcephala were two distinct species.   I think of this species as being more typical of lakes than rivers but this part of the River Irt is very close to the outfall of Wastwater, which may explain its frequency here.   We met this and some relatives from nearby Ennerdale Water in “Baffling Brachysira”.

Brachysira microcephala from the River Irt, December 2022.  Scale bar: 10 micrometres (= 100^th of a millimetre).  

Finally, I have included a plate of the long, needle-like cells of Fragilaria tenera, a common species that has cropped up in many posts.   This was the fifth most abundant taxon when I just counted numbers of cells, but the long, thin cells each pack a lot of biovolume.   In Cold Comforts you can see it living as an epiphyte on the stalks of Gomphonema exilissimum, and I’ve also seen it growing on green algal filaments in rivers near here.   If Fragilaria tenera was a houseplant, the instructions would read “place in a well-lit environment and keep well-watered”.

This view of the diatoms of the River Irt is neater than the views I showed in Cold Comforts.   The photographs offer two-dimensional representations of three-dimensional objects which is fine if we want to peer at their fine details and try to match what we see with pictures in the scientific literature.   It is difficult, for example, to be aware of the full variety of forms of Achnanthidium (and, to a lesser extent, Gomphonema) in the earlier photographs but this extra information comes at a cost.   Nature is not as tidy as the plates I’ve presented in this post suggest.  The very untidiness, in fact, is an important part of the story.   I alluded to that in Cold Comforts and I’ll come back to this message again in the next post.

Fragilaria tenera from the River Irt, December 2022.  Scale bar: 10 micrometres (= 100^th of a millimetre).  

References

Jüttner, I., Hamilton, P. B., Wetzel, C. E., Van De Vijver, B., King, L., Kelly, M. G., … & Ector, L. (2022). A study of the morphology and distribution of four Achnanthidium Kütz. species (Bacillariophyta), implications for ecological status assessment, and description of two new European species. Cryptogamie, Algologie, 43(10), 147-176.

Van de Vijver, B., Schuster, T. M., Kusber, W. H., Hamilton, P. B., Wetzel, C. E., & Ector, L. (2021). Revision of European Brachysira species (Brachysiraceae, Bacillariophyta): I. The Brachysira microcephala-B. neoexilis enigma. Botany Letters, 168(4), 467-484.

Some other highlights from this week: 

Wrote this whilst listening to: Martha Wainwright and her father Loudon Wainwright’s songs about their dysfunctional relationship, ahead of a trip to see Martha Wainwright at the Sage, Gateshead next week.

Currently reading:   Kingdom of Characters by Jing Tsu, about the evolution and adaptation of Chinese writing to fit the needs of the modern world.

Cultural highlight: Cezanne exhibition at the Tate Modern  

Culinary highlight:   Haggis, neaps, and swede.  Belated Burns Night shorn of the ridiculous oratory.

Cold comforts …

Clouds were low enough to obscure the views that I used to illustrate my last post about Wastwater and Wasdale (see “Hunger games …”), so I have started this post with a photograph of the underwater landscape of the River Irt, rather than the distant mountains.  You should be able to see three distinct algal lineages here: diatoms forming the yellow-brown patches in the foreground and left-centre, cyanobacteria along with mosses forming black patches on the centre-right boulder and green algae in the right foreground and growing amidst the black cyanobacteria/moss patches.  The underwater landscape is verdant at the same time as the surrounding fields and fells are at their most depleted.

Is ”verdant” even the right word?  It comes from the French word for “green” yet green is just one of a number of hues on display.   All these, however, are the outcome of mixtures of green chlorophyll and other pigments, so we may have strayed from a literal definition of verdant whilst still being within the popular meaning of lush vegetation.  But, before we get lost in etymology, let’s think about why some rivers in the Lake District present this counterintuitive burst of colour in the depths of winter.

We do not yet have a definitive answer but suspect that the temperature of the water plays an important role.  The lushest algal growths are found in rivers immediately downstream of lakes which act, as it were, as huge “water-source heat pumps” – warming up gradually during the spring then cooling slowly throughout the rest of the year (see graph below).   The difference between the River Irt and nearby River Calder (which does not have a lake upstream) is small when measured as absolute temperature but nonetheless means that there is a third more heat energy in the River Irt every day at this time of year compared with the Calder.   It all adds up.

Water temperature (2021 & 2022) and benthic chlorophyll (2019-2022) trends in the River Irt downstream of Wastwater.

That’s not the whole story.   The flow regime in rivers downstream of lakes is not as harsh as it is in rivers without lakes upstream, and there must be differences in the intensity of grazing by invertebrates.   But small differences in temperature have effects on a wide range of processes in rivers, and there is no reason why it should not be an important factor in determining algal dynamics in Lake District streams either.

Gomphonema exilissimum in the River Irt (Lund Bridge), December 2022.   Scale bar: 20 micrometres (= 1/50^th of a millimetre).  

Do not misinterpret all this talk of the relative warmth of the River Irt in December.  Plunging an arm into a northern English river in December is not for the faint-hearted.  But you’ve got no other option if you want to know what organisms are responsible for those vivid yellow-brown patches on the stream bed.   Back in the relative warmth of my study, I examined these with my microscope and saw that the bulk of the diatoms belonged to a single species – Gomphonema exilissimum. – growing on long branched stalks.   Sometimes there were patches where other diatoms were prominent – Fragilaria tenera, Tabellaria flocculosa and Achnanthidium species.    But these were growing on and around the matrix of Gomphonema stalks.   Gomphonema, in this setting, is a “foundation species”, shaping the habitat in ways that let other organisms thrive.   We think of the trees of a forest as foundation species but these “bushes” of Gomphonema play similar roles in streams, albeit on much smaller scales.  

Gomphonema cf. exilissimum and Fragilaria cf. tenera in the River Irt (Lund Bridge), December 2022.  Scale bar: 20 micrometres (= 1/50^th of a millimetre).  

We could, perhaps, argue that the mosses and cyanobacteria play similar roles.  I’ve written about these before (see “As old as the hills …”) and also described how cyanobacteria can create conditions within which green algae can thrive in another stream in the western Lakes (see “Ever changing worlds …”).   These relationships all help to create the patchworks visible with the naked eye (see also “The multiple dimensions of aquatic biofilms”).   We need to think of the patterns not just in terms of variation across the stream bed, but also over time.  One big spate could roll the stones on which the algae grow or rip the filaments from the surfaces, leaving spaces for new species to invade.   It’s the ecological equivalent of Heisenberg’s Uncertainty Principle: we can predict that certain algae will live under certain conditions, but there is a limit to the accuracy of these predictions.   It is not that our measurements are necessarily flawed, just that this patchiness – across space, through time and at multiple scales – is an inherent property of the system that needs to be respected.   

I’ll end where I started: this is all happening in the midst of a northern English winter.  The trees are bare and the water is cold.  We watch the weather forecasts closely, and plan our fieldwork for the short gaps when water levels are low enough to permit safe wading.  When we get to the rivers, though, we find richer growths – both in quantity and diversity – than we see at any other point in the year.   We can only wonder …

Some other highlights from this week: 

Wrote this whilst listening to:   The Specials, following the untimely death of Terry Hall.  In particular, their most recent album, Protest Songs:1924 – 2012. 

Currently reading:   Henning Mankell’s The Pyramid, short stories featuring the Swedish detective Kurt Wallander.

Cultural highlight: non-existent.  A combination of winter lurgies and too much work to finish before the Christmas break

Culinary highlight:  homemade mince pies.   

The diatoms of Lago Trasimeno

Back in October I wrote, somewhat apologetically, about my inability to switch off completely whilst on holiday (see “Reflections from Lago Trasimeno”).  The flip side of that condition is that I can continue to revisit a holiday two months after I have packed my flip-flops and sunhat away for the year.   On a damp, cold winter afternoon I can travel, virtually, back to warmer climes simply by peering through a microscope.   Somehow, the presence of particular assemblages of diatoms synergises with the memory of being there to take me to a flow state, where time melts away and space ceases to have any relevance.  For a couple of hours, at least, I can feel the Umbrian sun on my face again. 

Looking at the diatoms of Trasimeno not only took me back to the summer, it also linked Trasimeno to some other places I have visited and written about here.  It recalls Cassop Pond and Croft Kettle in my own neighbourhood (see “The diatoms of Cassop Pond” and “More about Croft Kettle”), but also turloughs in the west of Ireland (see “Famous for 15 minutes …”), small lochs in the Shetland Islands and shallow lakes in Greece that I have been studying.   Genera such as Epithemia, Rhopalodia and Mastogloia all crop up together in these hard water habitats, irrespective of geography.   

Diatoms from Lago Trasimeno.  a., b. Diatoma moniliformis; c. Tabularia fasiculata; d. Cocconeis placentula.  Scale bar: 10 micrometres (= 1/100^th of a millimetre).   The photograph at the top of the post shows Lago Trasimeno from Passignano sul Trasimeno, September 2022.

I found 32 species in the sample I collected on the shore of Isola de Maggiore, and could have found more had I been inclined to spend more time.   I always prefer to spread my effort over several samples from different locations or collected on different dates rather than to “mine” a single sample to exhaustion.   32 is a respectable haul for a single sample: not especially species rich but, at the same time, not depauperate either.  

About ten percent of these belong to the genera Epithemia and Rhopalodia which are capable of nitrogen fixation.   These are relatively large diatoms, so they will represent a greater proportion of the biomass and biovolume than a simple count of individuals suggests.  No great surprise, perhaps, that Lago Trasimeno in September, is short of nitrogen as these are also ideal conditions for the bacteria which break down the nitrogen compounds that run off the surrounding farmland and release it back to the atmosphere.   My earlier post on the algae of this lake pointed out the abundance of the cyanobacterium Gloeotrichia, another nitrogen-fixing organism, again emphasising the nitrogen-limited state of the lake at this time of year. 

More diatoms from Lago Trasimeno.  a. Navicula crptotenelloides; b. Navicula cryptotenella; c. Navicula cf. microdigitoradiata; d. Navicula duerrenbergiana; e. & f. Mastogloia baltica (two focal planes); g. Haslea spicula; h. Cymbella neocistula; i. Encyonema caespitosum; j. Seminavis strigosa; k. & l. Amphora sp.; m. & n. Amphora pediculus.   Scale bar: 10 micrometres (= 1/100^th of a millimetre). 

About a third of the diatoms belonged to genera such as Navicula and Nitzschia that are capable of movement.   Large numbers of these can often be signs of human disturbance, but not always.  In this case, I suspect that the naturally hard water leads to the precipitation of calcium carbonate, which smothers surfaces and challenging any organism living there.  Being able to constantly adjust position means that a motile diatom has an advantage over its sessile cousins.   A further twist to the story is that 20% of the diatoms are tolerant of saline conditions, which ties in with some evidence that the concentration of ions in the lake is increasing (see references in earlier post).   The two most likely reasons are abstraction of water from the lake for irrigation and climate change so this, too, is a potential sign of human disturbance.   Greater evaporation also makes it more likely that calcium carbonate will precipitate at the same time as the lake water gets more salty.   My interpretation of conditions, based on a single sample, is that the water is getting close to being “brackish” rather than strictly “fresh”.  If trends for global warming continue, then shallow lakes in warm regions such as this will become more salty, with implications for the ecosystem services that they provide to the region.  

Diploneis cf. elliptica, photographed at three focal planes.   Scale bar: 10 micrometress (= 1/100^th of a millimetre)

I’ve found at least one of the motile diatoms – a small Nitzschia – in brackish lakes in Greece too.  It does not correspond to any Nitzschia I’ve seen described (“e.” in the plate of Nitzschia and Tryblionella below), so one challenge for the next few months is to try and find out some more about this, comparing Italian and Greek populations and digging a little deeper into the literature. 

More diatoms from Lago Trasimeno.  a. Epithemia sorex; b., c. Epithemia adnata; d., E. frickeri; e., E. turgida.  Scale bar: 10 micrometress (= 1/100^th of a millimetre).

This slide is my “souvenir” from Trasimeno.  We associate the word souvenir with knickknacks and trinkets, but the word has its roots in the French word meaning “remember”.  Peering through a microscope on a cold winter day in northern England is enough to transport me back to sunny days in Umbria.  At the same time, the diatoms that I see bring me back to my own locale because I can find several of them in a pond that is walking distance from my house.   At the same time, finding salt-tolerant diatoms so far from the sea is a reminder of the encroaching reality of global warming.   All these pictures combine to tell a story … happy memories, certainly, but no guarantee of a happy ending.

More diatoms from Lago Trasimeno: a. Nitzschia acicularis; b. Nitzschia filiformis var. conferta; c. Nitzschia cf. palea; d. N. palea var. tenuirostris; e. Nitzschia sp.; f. Tryblionella sp.   Scale bar: 10 micrometress (= 1/100^th of a millimetre)

Some other highlights from this week: 

Wrote this whilst listening to:   Low’s Christmas and Sufjan Stevens’ Songs for Christmas.  Two very leftfield Christmas albums. 

Currently reading:   more Nadime Gordimer.  This time it is Livingstone’s Companions, a book of short stories.

Cultural highlight:   A recreation of local artist Norman Cornish’s house and studio at Beamish Museum in County Durham.

Culinary highlight:  “dirty broccoli” – broccoli roasted with a peanut and chilli marinade.  

More than just hitchhikers …

The Iroquois people of North America believed that the earth rested on the back of a giant turtle swimming around in a vast ocean.   It sounds quaint and fanciful but, during my visit to the Croatian Biological Congress, I learned that marine turtles do, in fact, carry worlds around on their backs, albeit on a somewhat smaller scale than envisaged by the Iroquois.    The image at the top of the post shows a turtle at Pula Aquarium’s Marine Turtle Rescue Centre, with several barnacles clearly visible but Sunčia Bosak of the University of Zagreb gave a fascinating talk on yet smaller organisms living on turtles.   She focussed on the diatoms but also talked about bacteria and a range of other organisms.

I’ve written many times about epiphytes on this blog – organisms that live on the back of other plants (most recently, “Springtime surprises …”).  In the same way, smaller organisms can hitch a ride on the back of animals and studies have shown that these are not just common but, in many cases, the hitchhikers have strong preferences for exactly this type of habitat.  Luc Denys, from Belgium, has found unique genera that live only on the backs of whales and there is now also evidence that some species and genera found on the backs of marine turtles are also restricted to this unusual habitat.  

In a slight deviation from the Iroquois creation myth, diatoms were found not just on the shell (carapace) of the turtle, but also on the skin.   Furthermore, different diatoms were found on skin and shell, and yet more differences were revealed when turtles from different parts of the world were compared.   The diatoms that seem to live exclusively on turtles were more abundant on skin whereas the assemblages on shells were dominated by a range of generalist species.   

The next twist to this story comes with a very recent paper (published in October 2022) that shows that not only do turtles have distinct assemblages of diatoms on their skin and shell, but that these diatoms, in turn, each have distinct assemblages of bacteria.  I’ve talked before about how loose associations between the protozoan and Ophyridium and diatoms can benefit both (see “Intimate strangers …”). In brief, the hitchhikers extend the “metabolic toolkit of the host, giving it greater resilience to the uncertainties of life in the oceans.  Because they, in turn, host a range of bacteria, the turtle-squatting diatoms take this to the next level, facilitating a rich external “microbiome” to complement the gut microbiome whose importance in humans is now recognised.  

This is all part of an emerging field that is, ostensibly, about how species interact with each other in ways other than traditional view of “nature red in tooth and claw”. There are many studies now showing co-operation amongst organisms that challenge received wisdom not just in science.  “Survival of the fittest” contributed not just to an understanding of nature in the late 19^th and early 20^th century, it also knitted in with ideas such as Nietzsche’s Übermensch to underpin political views that dominated much of the 20^th century.   How might a more co-operative view of nature synergise with politics?   How does this challenge the harsh right-wing political views that dominates modern politics?    This type of speculation may seem to be a long way from scraping diatoms off the back of a turtles in the Adriatic, but it is one of a number of studies all pointing to a more co-operative view of species interactions.   Maybe there is a lesson we should all learn from that.  

References

Denys, L. (1997). Morphology and taxonomy of epizoic diatoms (Epiphalaina and Tursiocola) on a sperm whale (Physeter macrocephalus) stranded on the coast of Belgium. Diatom Research 12: 1-18.

Filek, K., Lebbe, L., Willems, A., Chaerle, P., Vyverman, W., Žižek, M., & Bosak, S. (2022). More than just hitchhikers: a survey of bacterial communities associated with diatoms originating from sea turtles. FEMS Microbiology Ecology 98: fiac104.

Holmes, R. W. (1985). The morphology of diatoms epizoic on cetaceans and their transfer from Cocconeis to two new genera, Bennettella and Epipellis. British Phycological Journal 20: 43-57.

Kanjer, L., Filek, K., Mucko, M., Majewska, R., Gracan, R., Trotta, A., Panagopoulou, A., Corrente, M., DiBello, A. & Bosak, S. (2022). Surface microbiota of Mediterranean loggerhead sea turtles unravelled by 16S and 18S amplicon sequencing. Frontiers in Ecology and Evolution doi: 10.3389/fevo.2022.907368

Van de Vijver, B., Robert, K., Majewska, R., Frankovich, T. A., Panagopoulou, A., & Bosak, S. (2020). Geographical variation in the diatom communities associated with loggerhead sea turtles (Caretta caretta). PloS one 15:  e0236513.

Another highlight of Pula Aquarium: a Noble Pen Shell (Pinna nobilis) sanctuary – hosting populations of this large (up to one metre) rare bivalve endemic to the Mediterranean Sea.  

Some other highlights from this week: 

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

Currently reading: Barry Unsworth’s Morality Play.  3^rd time I’ve read this book which sits with Umberto Eco’s Name of the Rose as masterpieces of Medieval whodunnits, whilst at the same time rising above the limits of this genre.

Cultural highlight:   Midsummers Night Dream at Newcastle Playhouse, featuring Nadine Shah as Titania.   Brilliant production.

Culinary highlight:  sustainably sourced roast saddle of venison from The Wild Meat Company

All change …

For the first time since the start of the pandemic I’m travelling to a conference, to give a plenary talk about the UK’s experience with applying metabarcoding to ecological assessment.   I’ve not written about this on the blog for some time (see “Dispatches from Plato’s cave …”) so I’m taking the opportunity of preparing a talk, and sitting around in transit lounges, to summarise some of my thoughts.  I’ve also put in a few of my photos from this trip to break up the text.

The UK was the first country in Europe where the regulatory bodies got involved, alongside academics, in the application of metabarcoding to environmental regulation.  From the outset, we have had funding from the government agencies responsible for regulation, and had their representatives looking over our shoulders as results started to emerge.  That was mostly a constructive relationship between research scientists, but we had more than our fair share of tense moments, sometimes feeling like pawns in wider inter- and intra-agency squabbles.  What I came to realise, however, was that these discussions about the science often missed broader issues about how the new technology would affect whole organisations.  The introduction of metabarcoding, I came to see, was a case study in managing change in organisations that make decisions using ecological data.  

I wrote about this in an online paper a few years ago, and some of my reflections gained further traction when I listened to an episode of Tim Harford’s excellent Cautionary Tales podcast [https://timharford.com/2019/12/cautionary-tales-ep-6-how-britain-invented-then-ignored-blitzkrieg/].  This is about tank warfare rather than ecology, explaining how, he following the invention of the tank, commanders in the British army tried to fit it into the existing approaches to warfare rather than redesigning battle formations to make full use of the tank’s capabilities.   It was left to the German army to do this more radical restructuring in the 1930s, resulting in the “Blitzkrieg” tactics that overrun much of Europe in matter of weeks in 1940.  Harford related these changes back to a paper on business strategies for managing change.   This classified change in two ways: whether or not the core concepts and components that underlay processes in an organisation were changed by a new innovation, and whether or not this affected the linkages between these, which can be visualised as a table:   

Over the course of this podcast, I realised that the same analysis could be applied to the work that we were doing.  Until our metabarcoding projects, the Environment Agency had been using light microscopy to analyse diatoms for about 20 years, using an index that I developed in the early 1990s.   That first version had undergone several changes over the years as our understanding techniques and taxonomy has developed, but these could all be regarded as “incremental innovation” insofar as each development reinforced the way that the data produced was used by the organisation as a whole.   Environment Agency managers, meanwhile, were tinkering with linkages, moving from a structure where almost every area had in-house capability combined with local knowledge to one where diatom analyses were focussed around a few “hubs”.  That counts as an “architectural innovation” because the pathway from sample collection to the use of the data in decision-making changed.  

Arch of the Sergii, a Roman triumphal arch in Pula, dating from approximately 27 BC.  The photograph at the top of the post shows the first century Roman Arena.

When we started the metabarcoding project, there was an assumption that, at some point, metabarcoding would replace analysis by light microscopy, much as you might upgrade a component in your computer: the old component is taken out, the new one dropped in, and everything proceeds as before. In Henderson and Clark’s terminology, this was a “modular innovation”.   Unfortunately, this turned out to be a naïve assumption. Replacing light microscopy by metabarcoding has implications that go beyond the analysis of samples and is, in fact, another example of “architectural innovation”.  The “linkages” (how data/information flowed through the organisation) also need to change if full value from the new method is to be obtained. Here are three examples:

• Area staff found they had much less agency in the production of data in the metabarcoding era.   There were often long lags between samples being collected and results being available because samples were batched up and sent to remote laboratories where finite analytical capacity created a bottleneck at the times of year when samples were collected.   Previously, area staff could either prioritise particular samples themselves (if they were investigating a local river, for example) or telephone the people that were doing the analysis and ash them to fast-track these samples. 
  
• Time spent collecting and analysing samples is valuable unstructured learning that gives ecologists the experience that they need to interpret data.   You slowly learn to associate particular organisms with certain habitats and, gradually, build up a “sixth sense” about when you have encountered an unusual sample.  This was particularly the case in the UK system where a biologist might have had quite detailed knowledge (invertebrates, macrophytes, diatoms) of a single catchment.   In the metabarcoding era, the first time a biologist encounters an organism is as an entry in a spreadsheet or database containing processed sequencing output.   One option is to automate data interpretation; however, this raises more questions.  What is gained and, more importantly, what is lost by not having expert field ecologists involved at this stage?
  
• Finally, metabarcoding for ecological assessment is still a very young science and new developments appear regularly in the literature.  However, you cannot keep tinkering with a system that, ultimately, drives multi-million pound/dollar/euro investment decisions.  The regulators want to “lock down” a particular method in the interests of stability and transparency.  However, in the time it takes to pass all the stages of approval in government bureaucracy, improvements on the method are likely to have become available.  Given that we know that there is always uncertainty in predictions of ecological status, any improvement ought to bring us, incrementally, towards more robust decisions.  Too much faith in “stability” simply entrenches avoidable errors.   There is, in the UK, recognition of a need to embrace “incremental innovation” within regulation, but the process is not very systematic and certainly not regular enough.   At the moment, the mantra of “stability” is putting the cart before the horse, and some genuinely bad decisions will slip through the net as a result.   

I tried to capture some of these issues in the title of my paper.  Characterising molecular ecology as “fast-moving” is not controversial.   Characterising environmental regulation as “slow-moving” might appear pejorative but there are good reasons why this should be the case.  None of us would be happy if the speed limits changed overnight on our local roads without good reason and due warning and the same applies to environmental regulation.   This mismatch between science and regulation, however, means that the gap between what is possible and what is allowed is set to widen.  Up to now, we have been expected to squeeze the science into outdated regulatory models.  What we need to think about now is how regulation can evolve to embrace this new potential.

References

Henderson, R.M. & Clark, K.B. (1990).  Architectural innovation: the reconfiguration of existing product technologies and the failure of existing firms.  Administrative Science Quarterly 35: 9-30.

Kelly, M. (2019). Adapting the (fast-moving) world of molecular ecology to the (slow-moving) world of environmental regulation: lessons from the UK diatom metabarcoding exercise. Metabarcoding and Metagenomics, 3, e39041. [https://mbmg.pensoft.net/article/39041/]

Santa Maria Formosa, a Byzantine chapel dating from the 6^th century.   The best views are from beside a busy road in bright sunlight.   The view from a nearby café was not as good but I was able to sit in the shade and sip beer whilst I sketched.

Some other highlights from this week: 

Wrote this whilst listening to: The Rest is Politics podcast with Alistair Campbell and Rory Stewart.  Strictly speaking, writing this blog was delayed while I absorbed unfolding political events in the UK.  The implications of economic and fiscal policy will have knock-on effects for all government departments and, therefore, for the subject I write about here.

Currently reading: Act of Oblivion, latest novel from Robert Harris book, set at the time of the Restoration and the revenge enacted on those responsible for the execution of Charles I.  

Cultural highlight:  See How They Run, whose plot involves murders on the set of Agatha Christie’s The Mousetrap.   Gentle, old-fashioned humour channelling the Ealing Comedies of yore.

Culinary highlight:  Currently in Croatia and eating hotel buffet food, which is plentiful though hardly a “highlight”. It has, however, removed any inclination to search out any IrIstrian cuisine that might otherwise replace this as the top gastronomic experience of my trip.

It’s an ecosystem, stupid …

Our garden acquired a small pond earlier this year (see “The story of a pond”) and, five months on, the pond has acquired its first obvious algal growth.   Typing “algae” and “garden pond” into Google returns almost 10 million “hits”, and I’m guessing that the generally negative tone of the top hits will continue all the way down.  The Royal Horticultural Society set the tone with: “Algae can be a major problem in ponds, causing discoloured water, green scum at the pond edges, or dense mats of green growth under the surface. If conditions are favourable, algae will spread quickly and can harm aquatic life”.   Suffolk Wildlife Trust, by contrast, adopt a more balanced attitude: “Algae are important members of a healthy, well-balanced pond ecosystem, providing food for species at the lower end of the food-chain. To deal with algae effectively is not to eradicate it, but to prevent, or control, its excessive growth”.

The flocs in our pond were composed of Oedogonium, a green unbranched filamentous alga often encountered in this blog (see, for example “Under the weather”).   Both the websites I mentioned point to nutrients as a major cause of algae “problems” but the Oedogonium in our pond was covered with needle-like cells of the diatom Fragilaria gracilis, a species that favours nutrient-poor conditions.  Our garden receives no artificial fertiliser so there is little scope for enrichment. 

A more likely reason for the appearance of algal flocs is the warm sunny weather.  Although our pond is shaded, it still receives some direct sunlight, and the water temperature is now over 20^o: ideal conditions for any plant to grow.   We should not really be surprised that a fast-growing organism grows particularly fast when conditions are ideal.   I talked about this in Summertime Blues, describing the effects of the 2018 heatwave on the River Wear.   If climate predictions are correct then we will be experiencing more visible algal growths in the coming years in both ponds and rivers, regardless of how carefully we manage nutrients.   

Flocs of Oedogonium in our garden pond, August 2022.

So what should we do about it?   A garden pond differs from almost every other habitat with which I deal in that one person has complete agency to enact appropriate changes.  Common sense says that a light-touch hands-off approach should suffice, in order to let natural processes determine outcomes.   However, a garden pond is also an extraordinarily small habitat, so there is limited scope for a full range of organisms to create a balanced ecosystem.  The answer is to extend the principles that we apply to the rest of the garden to the pond itself: inspired by large-scale rewilding experiments such as Knepp we’ve adopted a light-touch approach to our lawn (see: “No mow May”).   For this to work, however, we need to acknowledge that a small garden cannot support the large herbivores that would naturally manage vegetation at places such as Knepp, and occasionally mow the grass to simulate their effects.

The same principle applies in a garden pond.   This is not large enough to support a balanced ecosystem where pike predate on smaller fish which, in turn, eat the invertebrates who graze on the algae.   So, instead, we need to act as the primary “grazer”, manually removing the filamentous algae at intervals using a cane or a rake.   They can then be tossed onto the compost heap or used directly as mulches on the flower beds.   The RHS website cautions that “this will only be a temporary solution” but then so is mowing your lawn.   That’s what happens when you create habitats but omit some key ecosystem components.   

Filaments of Oedogonium, along with epiphytic Fragilaria gracilis from our garden pond.   Scale bar: 20 micrometres (= 1/50^th of a millimetre)

The Suffolk Wildlife Trust cautions against manually removing filamentous algae growths as these can harbour larvae of great crested newts but this is more of an issue earlier in the year.   It does bring us full circle, however, reemphasising the point that algae are a natural part of the pond ecosystem.  Learn to love and appreciate them.  Better that than the appalling suggestion on the RHS website that adding dyes to the water will “prevent” algae.   It is an approach that may appeal to antediluvian horticulturists and golf-course groundsmen who still insist on “tidiness” but if you have the tiniest shred of interest in the natural world, you had better remember that algae are the engine rooms of natural aquatic ecosystems and treat them with the respect that they deserve.

P.S. I should add that “we”, when referring to gardening activities, is a euphemism for Heather.  I’m a non-executive director at best in that department. 

Some other highlights from this week:

Wrote this whilst listening to: Sweet Season by the American percussionist Glen Velez.  Also, several Richard Thompson records, following an excellent gig at Whitby Bay Playhouse.   Highlights include I Want to See the Bright Lights Tonight, from 1974, and some very old Fairport Convention songs including Who Knows Where the Time Goes?   It seemed wholly appropriate for a 73-year old to sing this wistful song until you remember that he and his Fairport compatriots wrote and sang these wise-beyond-their years lyrics when they were in their early 20s. 

Currently reading: Reluctant Saint by Donald Spotto, a biography of St Francis ahead of a trip to Asissi in September.   Just finished Delia Owen’s Where the Crawdads Sing.

Cultural highlight:  Brian and Charles: a new British comedy loosely-based on the Frankenstein story which, by coincidence, uses Who Knows Where the Time Goes over the closing credits.

Culinary highlight:  After my eulogy to Casa Mama in the previous post, I discovered St Pancras Square and Coal Drops Yard just behind King’s Cross Station.   Meals at Morty & Bob’s and BAO King’s Cross [ bracketed a meeting in London.

Famous for 15 minutes …

My trip to the Burren seems like an age ago now, but I’ve finally got around to looking at the diatoms in the Ophyridium versatile colony that I collected from the shore of Lough Gealáin (see “Intimate strangers …”).   In my earlier post I commented on the presence of many small diatoms, mostly Encyonopsis, that I could see but not easily photograph.  Now that I have got a properly cleaned sample, I can look at it under high magnification and try to put names onto the organisms present.  

My brief analysis found 32 species of diatom and confirmed that Encyonopsis was the most abundant genus.   In fact, I found at least five different species of Encyonopsis in the sample, the most abundant of which was E. cesatii.   There were, in addition, quite a lot of Delicatophycus delicatulus (hard to differentiate from Encyonopsis at lower magnifications), as well as Cymbella and Cymbopleura species.  All of these would have been classified as “Cymbella” thirty years ago, but taxonomic revisions, of the types discussed in the previous posts, have exploded this genus.   Quite what it is about this family that helps them to thrive in Ophyridium colonies is not clear.  

The genus Encyonopsis, itself, has also exploded into many parts.   In the first edition of the Süsswasser-flora von Mitteleuropa from 1930, Hustedt described two species of Cymbella that would now be regarded as species of Encyonopsis.   In the second edition (1986), there were three Cymbella species that fit the current definition of Encyonopsis but Algaebase now lists 149 valid species names for the genus.   To return to the theme of the previous post, we have learnt to look at Encyonopsis differently over the past 30 years.  And, having done so, we begin to make sense of their distribution patterns, as Bryan Kennedy showed in a recent paper based on data from Irish lakes. 

Quite what it is about this family that helps them to thrive in Ophyridium colonies is not clear.  Encyonopsis species tend to be highly motile, so would be well-adapted to moving through the gel matrix of the Ophyridium colony.  However, Cymbella species tend to attached to surfaces via stalks, a very different strategy.  Are they temporary residents on the outside of colonies whilst the Encyonopsis lives within?   

Diatoms from an Ophyridium versatile colony at Lough Gealáin, May 2022.   a. – j. morphotypes of Encyonopsis cesatii; k. – m.  E. cf. krammeri; n. – p. Delicatophycus delicatulus.  Scale bar: 10 micrometres (= 1/100^th of a millimetre).

Other diatoms found within the colonies include a species of Epithemia, last encountered in Cassop Pond (see: “The diatoms of Cassop pond”). Its presence here may well suggest that the Ophyridium colony is short of nitrogen for at least part of the time.   I also found several valves of Denticula tenuis, a species that can survive periods of desiccation.   All are telling me fragments of a bigger story without necessarily telling me the same story.  Just as Andy Warhol said “in the future, everyone will be world-famous for 15 minutes” so, in the microscopic world, every diatom has its brief moment when conditions are just so, before there is a change in circumstances and another diatom moves centre stage.   One of the explanations for the incredible diversity of diatoms is simply that their environments are never in equilibrium for long enough for “survival of the fittest” to have any traction.  Instead, we have a basketful of species, each with a different “superpower”, just waiting for their time to come.

Diatoms from an Ophyridium versatile colony at Lough Gealáin, May 2022.   a. – b.  Epithemia cf. alpestris; c. – f.  Cymbella subhelvetica; g. – i. Denticula tenuis; j. Navicula subalpina; k. Brachysira vitrea; i. Cyclotella meneghiniana; m. – n. Aulacoseira distans.  Scale bar: 10 micrometres (= 1/100^th of a millimetre).

Reference

Kennedy, B., Buckley, Y., & Allott, N. (2019). Taxonomy, ecology and analysis of type material of some small Encyonopsis with description of new species in Ireland. Phytotaxa 395: 89-128.

Some other highlights from this week:

Wrote this whilst listening to: Gris Gris, 1968 album by Dr John who I saw in similarly hot weather at Glastonbury in 2010.

Currently reading: Sagittarius Rising by Cecil Lewis.

Cultural highlight:   In the Heights, also set in a heatwave.   

Culinary highlight:  riding out the heatwave with homemade gazpacho.   The culinary low point of my week was learning that Casa Mama, my trusty Italian trattoria that, for a quarter of a century, fuelled me with pasta, pizza and red wine before boarding a train at King’s Cross station, has closed.   There are two types of Italian restaurant: the ones where the waiters say “prego” when they put food in front of you and the ones that don’t.   Casa Mama was in the former category, and all the better for it.

Reflections from remote lochs …

Naturalists make a big thing out of rarity – that an organism is considered scarce is one of the most basic reasons for wanting to protect and encourage those populations that remain.  But rarity is an elusive concept to pin down for all sorts of reasons, one of which is that the people who are likely to notice rare species are, themselves, scarce.   So it is that relative rarity of different orchid species is quite well understood, but rareness is harder to assess for freshwater algae because there are fewer people who study these organisms in sufficient detail.  A limited number of interested naturalists multiplied by a limited number of habitats where the organism is found inevitably results in a poor understanding of its distribution.   

Look at the paperclip-shaped object in the bottom right image of the figure below.   I found a lot of these in a sample from the littoral zone of a small loch in Shetland and it took me some time to associate them with the small elliptical diatom valves that cropped up in the same sample (the plate shows lots of the valves but only one of the paperclip-shaped girdle bands whereas, in reality, there were far more of these than there were valves).    The penny dropped, eventually, and I realised that I was looking at a very rare diatom, Oxyneis binalis var. ovalis.   These are relatives of Tabellaria (see “The bluffer’s guide to Tabellaria …”) and, like this genus, have several girdle bands, each with a silica plate (“septum”) between the two valves.   Indeed, until relatively recently, Oxyneis species were considered to be part of Tabellaria.

Oxyneis binalis var. elliptica from Lamba Water, Shetland Isles, October 2021.  Top row: valve views; bottom row left: partially intact frustule in girdle view (note the large number of girdles); bottom right: single girdle band in valve view.  Scale bar: 10 µm (= 100^th of a millimetre).  

I’ve looked at several samples from this loch over recent years and have not noticed this species before.  I use the word “noticed” deliberately, as I’m now worried that I’ve overlooked it in the past.  However, I’ve also looked at samples collected after the one where I first found it and did not find it there, despite being aware of the likelihood that it might be there.  That means that we need to add an extra coefficient to my equation: a patchy distribution over the course of a year further reduces the chance that it will be noticed by one of a limited number of naturalists who just happens to visit one of the limited number of locations. 

Two intact frustules of Oxyneis binalis var. elliptica in a cleaned sample from Lamba Water, Shetland Isles, October 2021.   Scale bar: 10 µm (= 100^th of a millimetre).

By coincidence, at about the same time as I was finding Oxyneis binalis var. elliptica in the Shetland Isles, Chris Carter send some photographs from a population of Oxyneis binalis var. binalis collected by Chris Johnson from Lochan an Fheòir on the Isle of Harris, in the Outer Hebrides.  This species has a distinct “dumbbell” shape and, once again, many more girdle bands than valves.  The literature hints that Oxyneis binalis var. binalis tends to form straight chains whilst O. binalis var. elliptica forms zig-zag chains.   However, our photos offer only limited support for this and, in any case, many of the chains will disintegrate on preparation.  That both these specimens come from remote peripheries of our archipelago only seems to emphasise their rarity.

Oxyneis binalis from Lochan an Fheòir on the Isle of Harris, colllected by Chris Johnson and photographed by Chris Carter.  a., b.: two focal planes showing girdle and valve face; c., d.: two focal planes of a girdle band; e., f.: two focal planes of a girdle view of a partially-intact frustule beside a valve view.  Scale bar: 10 µm (= 100^th of a millimetre).

Live cells of Oxyneis binalis from Lochan an Fheòir on the Isle of Harris.

Should we even be concerned about rarity?   All I’ve said so far equates rarity with quantities – numbers of organisms and numbers of habitats, complicated by the numbers of biologists actually interested enough to do the counting combined with an element of chance.  Anna Kondratyeva and colleagues from the Sorbonne in Paris think that this is a naïve way of thinking about ecological diversity and ask questions about what unique characteristics these “rare” organisms bring to ecosystems.   If they are just variants on themes already well represented by other organisms in a habitat, then does rarity matter?  On the other hand, if they exhibit “functional originality” (i.e. they bring distinctive characters to an ecosystem, influencing the way that energy flows through trophic levels) then they are more than just a tick on a naturalist’s recording sheet; they are active contributors to the uniqueness of a particular habitat.   The problem we have is that we don’t know enough about the inner workings of individual diatom species to have much of an idea about what Oxyneis binalis brings to a habitat that species of Tabellaria do not.   It encapsulates the diatomist’s dilemma: we know the shape of everything and the meaning of nothing …

References

Three of these papers give background information on what makes Oxyneis different from Tabellaria, one includes some earlier records from the Shetland Isles and the final reference explains the theory behind “rarity” and “originality” 

Carter, J. & Bailey-Watts, A.E. (1981).  A taxonomic study of diatoms from standing waters in Shetland.  Nova Hedwigia 33: 513-630.

Flower, R.J. 1989. A new variety of Tabellaria binalis (Ehrenb.) Grun. from several acid lakes in the U.K. Diatom Research. 4: 21-23.

Kingston, J.C. (2000).  New combinations in the freshwater Fragilariaceae and Achnanthidiaceae.  Diatom Research15: 409-411.

Kondratyeva, A., Grandcolas, P. & Pavoine, S. (2019).  Reconciling the concepts and measures of diversity, rarity and originality in ecology and evolution.  Biological Reviews 94: 1317-1337.

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

Some other highlights from this week:

Wrote this whilst listening to:  Radiate Like This, latest album by Warpaint

Currently reading:   PJ Harvey’s Orlam: poetry in Dorset dialect.

Cultural highlight: a visit to Yorkshire Sculpture Park on a sunny Sunday afternoon, enjoying, in particular, the tranquility within James Turrell’s Deer Shelter Skyspace.   .   

Culinary highlight: Vegan peanut butter and banana brownies