Letter from Cyprus

When I stepped off flight EZY1973 from Manchester to Paphos on Saturday night I passed a personal milestone. Arriving in Cyprus means that I have now visited all 28 Member States of the European Union. Starting with (West) Germany in 1972 on an exchange visit before the UK was even a member of the European Economic Community, followed shortly after by a family holiday to southern Austria (where my father had been stationed just after the war) with a day trip to Slovenia (then part of Yugoslavia), the number started to increase in the late 1990s when I became involved in the work of CEN, the European Standards Agency and, from the mid-2000s onwards, with the intercalibration exercise associated with the Water Framework Directive. A few years ago I made a list and realised just how many I had visited, after which, I have to admit, my choice of conference and holiday destinations was driven by this rather childish whim. Latvia, Malta and Bulgaria, all subjects of posts on this blog, were ticked off, leaving just Cyprus. This year, a family holiday to celebrate my mother’s 80th birthday provided the opportunity and, after some shameless lobbying, we had booked a villa near Paphos via AirBnB and were on our way.

How Europe has changed in the 47 years since my first overseas trip. Twelve countries were behind the Iron Curtain, three of the remainder were right-wing dictatorships. Two have merged (East and West Germany) whilst seven have become disentangled from previous relationships (the Baltic States from the USSR, Slovenia and Croatia from the former Yugoslavia and the two former constituents of Czechoslovakia from each other). Cyprus, from where I am writing, was in political chaos in the early 1970s. A former British colony whose territory was argued over by Greece and Turkey, it was soon to be split into two, separated by a buffer zone. I used to browse my Collins World Atlas assuming national borders to be fixed and immutable; the older and wiser me wonders where (and when) the next changes will come from.

The intercalibration exercise, in particular, was an opportunity for an exchange of ideas and I counted co-authors from 23 of the 28 EU states on my publication list. Looking back, these papers show remarkable consistency in some aspects of ecology across Europe whilst, in other respects, I am much more cautious about assuming that knowledge gained in my damp corner of north-west Europe can be applied to warmer and more continental regions. This publication list includes, incidentally, two papers about Cyprus, despite never having either visited before or having a native Cypriot on my list of co-authors. In the first paper, we worked with an Austrian employed by the Ministry of the Environment but, for the second, the samples were collected and analysed by Italians and Germans whilst I helped out with data analysis. Scientific colonialism is not, perhaps, dead?

My favourite? I don’t think I should single one of the 28 out. The food and culture of the warm lands of the Mediterranean basin draw me but I think that the parched summer landscapes would lose their appeal if I was there for too long. I find the grey, damp climate of my own corner of Europe wearisome but the greenness of the Spring and Summer, and the Autumn colours almost compensate. My ideal, in other words, seems like it should be a semi-nomadic existence but that, too, would pale with time. The truth is that, for me, elsewhere, being wanted, is always more wondered at ….

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Natural lenses …

The photograph above is as about as far from Andreas Gursky’s careful constructions, described in the previous post, as it is possible to get.  It is a close-up of a green algal floc Heather noticed whilst on a walk around a local nature reserve.   I guess it fits the general description of “decisive moment” except that it takes a special sort of observer to find any interest at all in such an unprepossessing habitat.

Under the microscope, the floc turned out to be composed of filaments of Spirogyra, with a single helical chloroplast.  Members of this genus (and related genera such as Mougeotia) produce copious mucilage so are always slimy to the touch.  However, this mucilage makes it difficult for the waste gases produced by photosynthesis to diffuse away, leading to the production of bubbles within the mucilage mass.   The interest, today, however, was that these air bubbles are acting as tiny lenses through which it is possible to make out the individual filaments of Spirogyra.

The green floc beside a footpath in Crowtrees local nature reserve from which the other images in this post were derived. 

I should add the caveat here that the photograph was taken with the “super macro” facility of our Olympus TG2 camera but the end-product is, nonetheless, impressive.   It also offers us an insight into the world of the very earliest microscopists.  Anton van Leuwenhoek’s microscopes consisted of a metal plate which held a tiny sphere of glass which acted as a convex-convex lens capable of up to 266x magnification to a resolution of little  more than a micron (1/1000^th of a millimetre) (follow this link for more details).  To give an idea of what he might have seen with this, the right hand image below used 400x magnification.

That, however, only tells us part of the story of Anton van Leuwenhoek’s genius.   Whilst we should not underestimate the skill required to make the lenses and their mounts, the other essential element is curiosity.   Curiosity is, itself, multifaceted: in a few weeks we will probably make a trip out to an old quarry where we know we will find several species of orchids, and maybe some excursions to locations new to us but where others have reported interesting assemblages.  That’s one type of curiosity.  However, simply looking harder at the habitats all around us involves a different type of curiosity: a recognition that there is more to know even about things we think we already know about.   The former broadens our experiences, the latter deepens them …

The algal floc at Crowtrees local nature reserve in close-up: left: an extreme macro view of a single bubble from the image at the top of the post and, right: filaments of Spirogyra photographed under the microscope.  Scale bar: 20 micrometres (= 1/50^th of a millimetre).

3 minutes 59.4 seconds …

Back in 1995 I interviewed a number of eminent people about their first academic publications as part of an occasional series for the Times Higher Education Supplement.  I wrote about one of the more daunting of these in “An encounter with Enoch Powell”.   The hour or so I spent with Sir Roger Bannister, who died a couple of days ago, could not have been more different.   He was best known for three minutes 59.4 seconds on a running track in Oxford in May 1954 but went on to have a successful career as a neurologist and eventually became master of Pembroke College, Oxford.  He was, despite this sporting and academic prowess, one of the most charming people I have met.

One of the secrets of his success on the running track was that he was, to all intents and purposes, a sports scientist before that term had been coined.  He took time out from his medical degree to do research on the physiology of breathing and, more particularly, how the point of exhaustion could be delayed by feeding his subjects with different concentrations of oxygen.   As a medical student working in straightened times just after the war, his first task was to build his own equipment, including the treadmill on which he and an assortment of colleagues and friends ran in order to generate the data he needed.  Building this kit involved trips to RAF bases to strip meters and other parts from decommissioned bombers (John Hapgood, former Archbishop of York and also a physiologist by training told me a very similar story).

Whilst his experiments were not directly relevant to his running (his actual training time amounted to less than an hour a day), there was, clearly, a benefit from understanding how his body worked.  However, whilst a runner cannot alter the concentration of oxygen that he breathes, a mountaineer can, and Bannister’s work was used by the team that conquered Everest the following year (he commented that he was surprised at how unfit some of the Everest team were by the standards of track runners).

Whatever his other achievements, however, it was that afternoon in Oxford in May 1954 that defined Roger Bannister.  Three minutes 59 seconds works out at just over a quarter of Andy Warhol’s quotient of fifteen minutes of fame and would have ensured Bannister’s place in the history books.   However, as the obituaries in the newspapers show, he achieved far more than that in his life.   And he was a gentleman too.

If you have the patience to battle with News International’s paywall, you can read my original article by following this link.

More about Platessa oblongella and Odontidium mesodon

As my last post used the conventions of figurative art to describe algal ecology, I thought I would stick to graphs – science’s very own school of abstract art – for this one.   I spent some time in “Small details in the big picture” discussing the ecology of Platessa oblongella (including P. saxonica) but without saying very much about the types of streams where these species were found.  So I am going to take a step away from the Ennerdale catchment in this post and, instead, collate environmental data a large number of sites to get a broader understanding of their habitat preferences.  As these species are often associated with Odontidium mesodon (see “A tale of two diatoms …”), I will summarise the preferences of this species at the same time (but see Annex 1 for a graph of this species’ preferences for still versus standing water).

The first set of graphs show the response of these species to pH and alkalinity and establish both as species typical of circumneutral soft water.  Platessa oblongella can be abundant in more acid conditions (i.e. to the left of the green vertical lines) but most of the records where it is abundant have pH values between 6.5 and 7.5.   Note that P. oblongella can also be found in humic waters, where lower pH thresholds apply (see Annex 2).

Distribution of Odontidium mesodon and Platessa oblongella (including P. saxonica) to pH and alkalinity in UK streams.   Vertical lines for pH indicate threshold values that should support high (blue), good (green), moderate (orange) and poor (red) ecological status classes.  See Annex 2 for more explanation.

The second set of graphs shows how these species respond to inorganic nutrients.   Both are most abundant when inorganic nutrients are present in low concentrations, though the trend is stronger for phosphorus than it is for nitrate-nitrogen.   The graphs for Platessa oblongella, however, both have a few outliers.   I have seen P. oblongella in a few situations where I did not expect it – I remember finding it in the Halebourne, a stream draining heathland around Aldershot and Bagshot in Surrey, where the water was well buffered (mean alkalinity: 61.3 mg L^-1 CaCO₃) and nutrient concentration were high (mean total oxidised nitrogen: 4.01 mg L^-1; dissolved phosphorus: 0.25 mg L^-1) and Carlos Wetzel and colleagues note some other anomalous records from the literature in their paper (cited in my earlier post), including a few from high conductivity and even brackish environments.   So we should treat these plots as indicative of the ecological preferences rather than definitive.

Distribution of Odontidium mesodon and Platessa oblongella (including P. saxonica) to nitrate-N and dissolved phosphorus in UK streams.   Vertical lines indicate threshold values that should support high (blue), good (green), moderate (orange) and poor (red) ecological status classes.  See Annex 2 for more explanation.

The final pair of plots show how the relative abundance of these two species changes over the course of the year.  These plots show the months when each taxon is abundant, by the standards of that taxon.  Because Platessa oblongella tends to be very numerous in samples, the threshold for this taxon (the 90^th percentile of all records) is higher than that for O. mesodon.   This reveals a very clear pattern of O. mesodon thriving in Spring whilst P. oblongella is abundant throughout the year, but with a slight preference for summer and autumn.  We need to reconcile these patterns with the observations in A tale of two diatoms that show that P. oblongella is associated with thinner biofilms than O. mesodon and try to work out whether season is driving the patterns or whether the seasonal patterns are the manifestation of other forces.   My suspicion is that P. oblongella is a classic pioneer species but also has a low-growing prostrate habit which means that it should be resistant to heavy grazing, which may confer an advantage in the summer and autumn when grazers are most active.  However, I may be getting ahead of myself, as we are in the process of analysing data on grazer-algae interactions in the River Ehen and Croasdale Beck that may throw more light on this.  There are clearly more layers to this story yet to be revealed …

Distribution of Odontidium mesodon (i.) and Platessa oblongella (j., including P. saxonica). The solid lines represent relative sampling effort (i.e. the proportion of samples in the dataset collected in a particular month) and the vertical bars represent samples where the relative abundance of taxon in question exceeded the 90^th percentile for that taxon (20% for P. oblongella/P. saxonica and 5% for O. mesodon).

Reference

The dataset used for these analyses is that used in:

Kelly, M.G., Juggins, S., Guthrie, R., Pritchard, S., Jamieson, B.J., Rippey, B, Hirst, H & Yallop, M.L. (2008). Assessment of ecological status in UK rivers using diatoms. Freshwater Biology 53: 403-422.

Annex 1: Odontidium mesodon’s preference for still or standing water

As I included a graph showing the preference of Platessa oblongella / P. saxonica for still or standing water in “A tale of two diatoms …”, I have included a similar graph for Odontidium mesodon here.   I have not included any data from the streams that flow into Ennerdale Water’s north-west corner in this graph as this would give a distorted picture.  To date, I have only seen a single valve of O. mesodon during analyses of 14 samples from these streams but I have not yet sampled these in spring which, as the graph above shows, is the time when O. mesodon is most abundant.   Like Platessa oblongella, O. mesodon is predominately a species of running, rather than standing waters.

Differences in percentage of Odontidium mesodon in epilithic samples from Ennerdale Water and associated streams.  Data collected between 2012 and 2018.

Annex 2: notes on species-environment plots

These are based on interrogation of a database of 6500 river samples collected as part of DARES project.  Vertical lines show UK environmental standards for conditions necessary to support good ecological status: blue = high status; green = good status, orange = moderate status and red = poor status.  Note that there are no environmental standards for alkalinity and the vertical lines show a rough split of the gradient into low alkalinity (“soft water”: < 10 mg L^-1 CaCO₃), low/moderate alkalinity (³ 10, < 75 mg L^-1 CaCO₃), moderate/high alkalinity (³ 75, < 150 mg L^-1 CaCO₃) and high alkalinity (“hard water”: ³ 150 mg L^-1 CaCO₃).

pH thresholds are for clear water (see UK TAG’s Acidification Environmental Standards.  The corresponding thresholds for humic waters are lower (high/good: 5.1; good/moderate: 4.55; moderate/poor: 4.22; poor/bad: 4.03).

Phosphorus thresholds are based on UK TAG’s A Revised Approach to Setting WFD Phosphorus Standards.   Current UK phosphorus standards are site specific, using altitude and alkalinity as predictors.  This means that a range of thresholds applies, depending upon the geological preferences of the species in question.  The plots here show the position of boundaries based on the average alkalinity and altitude measurements in the DARES database.

Note, too, that phosphorus analyses use the Environment Agency’s standard measure, which is unfiltered molybdate reactive phosphorus.  This approximates to “soluble reactive phosphorus” or “phosphorus as orthophosphate” in most circumstances but the reagents will react with phosphorus attached to particles that would have been removed by membrane filtration.

Nitrate-nitrogen: There are, currently, no UK standards for nitrates in rivers.  Values plotted here are derived in the same way as those for phosphorus (see “This is not a nitrate standard”)

 

Algae behaving selfishly …

My most recent trip to Ennerdale Water was on a wonderful windless winter day, offering perfect reflections of the snow-dusted peaks beyond the lake. It was a cold day but I was well wrapped-up and could enjoy both the long-distance views and the close-ups of nature around the lake’s margins.   One of the small streams that I crossed as I skirted the perimeter of the lake had patches of green algae growing on its submerged stones and even a quick examination showed it to be coarser than the green algae that covered most of the larger stones on the lake bed itself, as well on those in the River Ehen, just below the outfall.   When I managed to get specimens under my microscope I saw that the algae on the lake bed was Spirogyra (which I have seen here before; see “A lake of two halves”) whilst that in the inflow stream was Oedogonium.

I’ve written about Oedogonium before, and lamented the problems we face when we try to identify the species within this large genus (see “The perplexing case of the celibate alga”).   Ironically, a couple of weeks after I wrote this, I encountered a population of Oedogonium in another Cumbrian stream that did have sexual organs (see “Love and sex in a tufa-forming stream”).  However, this was the exception that proves the rule, as I have not seen a sexually-mature population of Oedogonium since.  The population I found beside Ennerdale was not sexually mature either but it did show a different, but equally effective, means of going forth and multiplying.

In the left hand diagram below we see a vegetative cell from an Oedogonium filament that has split open, allowing a vesicle to be extruded within which a single zoospore has formed.   This has a ring of flagella at one end, resembling a monk’s tonsure (you can just see these flagella in the photograph).   The other two photographs show the monk’s bald pate, though the fringe of flagella is not very clear.    The transparent vesicle swells and eventually ruptures, releasing the zoospore, which swim around for an hour or so, before settling on a new substratum and growing into new filaments.

Zoospores of Oedogonium from a stream flowing into Ennerdale Water, January 2018.   Scale bar: 25 micrometres (= 1/40^th of a millimetre). 

In my material, the new filaments were mostly attached to mature Oedogonium filaments; however, this is probably partly an artefact and, in the field, they would almost certainly also settle on rocks and other surfaces too.   You can see, in the diagram below, how the “bald” end of the zoospore has started to differentiate into a holdfast that will secure the cell to the substrate whilst, over time, the other end will start to divide to produce the first cells of the new filament.  The whole process is described in a series of papers by Jeremy Pickett-Heaps (see reference list below).

Why did I see zoospore formation in this particular sample?   I don’t know for sure but it may be because I let a longer than usual time elapse between collecting and examining the sample.   This one had sat around in a cool box and fridge for four days, whereas I usually manage to check them within 24 hours.   Neglect can be a useful tool in the phycologist’s arsenal, as many freshwater algae see no need to indulge in anything more taxing than routine cell division for as long as the habitat keeps them replenished with whatever light, nutrients and other resources that they need.   Only when this is no longer the case do the algae start to channel resources into survival strategies.

Oedogonium zoospores germinating into new filaments, both epiphytic on mature filaments.   From a stream flowing into Ennerdale Water, January 2018. .   Scale bar: 25 micrometres (= 1/40^th of a millimetre). 

Although I used the phrase “go forth and multiply” in an earlier paragraph, these Oedogonium cells are actually “going forth” rather than “multiplying” as the process we are watching only produces a single new cell.  However, were this zoospore to be released in a stream rather than a sample bottle, then there is a good chance that it would have been washed downstream and that a few of the many zoospores might have settled on a suitable habitat away from the constraints of their former home.   Asexual reproduction is a dispersal mechanism that results in the spread of genetically-identical copies of the parent cell.  For a sessile organism, this strategy allows a single genotype to move on from less-favourable locations and to exploit the potential of nearby locations.

The word “reproduction” is misleading as the mixing of genetic material that we associate with sex doesn’t take place.  The end product is a clone of a successful Oedogonium filament growing somewhere else.   However, taking the “sex” out of “asexual” removes a huge potential for innuendo, and readers who have battled this far through a post on nondescript green filaments deserve a reward.  So let’s finish with Woody Allen’s definition of masturbation as “sex with someone you love” and suggesting that the cytological huffing and puffing involved in zoospore production may not have the romance of sex but nor does it lead to any of the complications which result from sex either.   The alga gets offspring that are 100% identical to itself, just slightly further downstream and there is no risk of mixing with inferior genotypes.   That’s about as “selfish” as the “selfish gene” can get.

References

Pickett-Heaps, J. (1971).   Reproduction by zoospores in Oedogonium. I. Zoosporogenesis.   Protoplasma 72: 275-314.

Pickett-Heaps, J. (1971).   Reproduction by zoospores in Oedogonium. II. Emergence of the zoospore and the motile phase. Protoplasma 74: 149-167.

Pickett-Heaps, J. (1972).   Reproduction by zoospores in Oedogonium. III. Differentiation of the germling.  Protoplasma 74: 169-173.

Pickett-Heaps, J. (1972).   Reproduction by zoospores in Oedogonium. IV. Cell division in the germling and the possible evolution of the wall rings.   Protoplasma 74: 195-212.

See also “The River Ehen in March” for some further perspectives on asexual reproduction in algae.

View from near our sampling site on Croasdale Beck, looking towards Ennerdale Bridge, January 2018.

 

Rolling stones gather no moss …

Back in early July I mused on how rivers changed over time (see “Where’s the Wear’s weir?”) and reflected on how this shapes our expectations about the plants and animals that we find.  In that post, I compared a view of the River Tees today with the same view as captured by J.R.W Turner at the end of the 18^th century.   The photograph above is taken about 40 kilometres further upstream from Egglestone Abbey and shows the River Tees as it tumbles along in a narrow valley between Falcon Clints and Cronkley Scar.   I’ve written about this stretch of river before (see “The intricate ecology of green slime” and “More from Upper Teesdale”) and it is an idyllic stretch.   It all looks, to the uninitiated, very natural, almost untouched by the hand of man.

However, a couple of kilometres beyond this point we turn a corner and are confronted by a high waterfall, Cauldron Snout, formed where the river cascades over the hard Whin Sill.   Scrambling up the blocky dolerite is not difficult so long as you have a head for heights but, on reaching the top, a wall of concrete comes into view.  This is the dam of Cow Green Reservoir, constructed between 1967 and 1971 and highly controversial at the time.  The purpose of the reservoir was to regulate the flow in the River Tees, in particular ensuring that there was sufficient flow in the summer to ensure a steady supply for the industries of Teeside (most of which have, subsequently, closed).  My first visit to Cauldron Snout was in the early 1980s on a Northern Naturalist Union field excursion led by David Bellamy.  As we scrambled down Cauldron Snout, Tom Dunn, an elderly stalwart of the NNU, told me how much more impressive Cauldron Snout had been before the dam was closed.

Now look back at the picture at the top of this post.   The dark patches on the tops of the boulders emerging from the water are growths of the moss Schistidium rivulare, which thrives on the tops of stable boulders that are occasionally submerged.    The old adage “a rolling stone gathers no moss” is, actually, true, leaving me wondering how much less of this moss an walker beside this river in the mid-1960s might have seen.   How many more powerful surges of storm-fuelled water would have there been to overturn the larger boulders on which Schistidium rivulare depends?   Bear in mind, too, that two major tributaries, the Rivers Balder and Lune, also have flow regimes modified by reservoirs and the potential for subtle alteration of the view that Turner saw at Egglestone increases.   I wrote recently about how differences in hydrological regime can affect the types and quantities of algae that are found (see “A tale of two diatoms …”).   I may have stood at exactly the same place where Turner had sat when he drew the scene at Egglestone, but I was looking at a very different river.

The dam of Cow Green Reservoir looming above the top of Cauldron Snout in Upper Teesdale National Nature Reserve, Co. Durham, July 2017.  The picture at the top of this post shows the Tees a couple of kilometres downstream from Cauldron Snout.

Trevor Crisp from the Freshwater Biological Association showed that the consequences of Cow Green Reservoir on the River Tees extend beyond alterations to the flow.  Impounding a huge quantity of water in one of the coolest parts of the country also affects the temperature of the river, due to water’s high specific heat capacity.  This means that there is not just a narrower range of flows, but also a narrower range of temperature recorded.   The difference between coolest and warmest temperatures in the Tees below Cow Green dropped by 1 – 2 °C, which may not seem a lot, but one consequence is to delay the warming of the river water in Spring by about a month, which delays the development of young trout.  However, Crisp and colleagues went on to show that any reduction in growth rate due to lower temperatures was actually offset by other side-effects of the dam (such as a less harsh flow regime) to result in an increase in the total density of fish downstream.   Others have shown significant shifts in the types of invertebrate that he found in the Tees below Cow Green, with a decrease in taxa that are adapted to a harsh hydrological regime, as might be expected.   Maize Beck, a tributary which joins just below Cauldron Snout, and which has a natural flow regime, shows many fewer changes.

One conclusion that we can draw from all this is that healthy ecosystems such as the upper Tees are fairly resilient and can generally adapt to a certain amount of change, as Trevor Crisp’s work on the fish shows us. The big caveat on this is that the upper Tees is relatively unusual in having no natural salmon populations, as the waterfall at High Force presents a natural obstacle to migration.  Had this not been present, then all potential spawning grounds upstream of the reservoir would have been lost.   A second caveat is that there is still a lot that we do not know.   The studies of the river that followed the closure of the dam focussed on lists of the animal and plant species found; a modern ecologist might have put more effort into understanding the consequences for ecological processes, the “verbs” in ecosystems, rather than in the “nouns”.  Who knows how different energy pathways are now, compared to the days before regulation, and what the long-term consequences of such changes might be?  Schistidium rivulare is a good example of the limitations of our knowledge: its presence offers insights into the hydrology of the river, but we know relatively little about the roles that these semi-aquatic mosses play in the river ecosystem.   Knowing that there is much that we do not know should, at least, keep us humble as we struggle to find the balance between preserving natural landscapes and their sustainable use in the future.

Note

Twenty years ago, I would have recognised Schistidium rivulare, if not in the field, then at least after a quick check under the microscope.  Now, however, my moss identification skills are rusty and I had to turn to Pauline Lang to get this moss named.   I mentioned in “The Stresses of Summertime …” how the ecologist’s niche becomes the office not the field.  One danger is that we remain familiar with names (as I am with S. rivulare and other aquatic mosses) but, through lack of practice, lose the craft that connects those names to the living organisms.

References

Armitage, P.D. (2006).   Long-term faunal changes in a regulated and an unregulated stream – Cow Green thirty years on.  River Research and Applications 22: 957-966.

Crisp, D.T. (1973).  Some physical and chemical effects of the Cow Green (upper Teesdale) impoundment.  Freshwater Biology 7: 109-120.

Crisp, D.T., Mann, R.H.K. & Cubby, P.R. (1983).  Effects of regulation on the River Tees upon fish populations below Cow Green Reservoir.  Journal of Applied Ecology 20: 371-386.

Lang, P.D. & Murphy, K.J. (2012).  Environmental drivers, life strategies and bioindicator capacity of bryophyte communities in high-latitude headwater streams.  Hydrobiologia 612: 1-17.

A hidden world in a salty puddle …

An exchange of emails amongst a group of us preparing an obituary for Hilary Belcher led me to a short paper written by herself and Erica Swale on diatoms from a salty puddle close to a bridge under the M11 motorway in Cambridgeshire.  They had noticed some brown patches that looked like diatoms on the bottom of this puddle in 1979 and took a sample home to examine under the microscope. What they saw was an assemblage of diatoms that was more suggestive of a brackish habitat than freshwaters, leading them to conclude that the road salt that was spread on the M11 in winter was draining off the road and creating these mini salt lakes.  These were not one-off observations: they returned several times to find similar assemblages of diatoms in the same puddles.   Of these, only Surirella brebissonii is common in freshwaters.  Entomoneis and Cylindrotheca are two genera that I have written about before, both from marine or brackish habitats (see “A typical Geordie alga …” and “Back to Druridge Bay”).

Some diatoms associated with a puddle close to the M11 in Cambridgeshire: A: Entomoneis paludosa var. salinarum; B: Surirella brebissonii; C: Tryblionella hungarica; D: Nitzschia sigma; E: Nitzschia vitrea; F: Cylindrotheca closterium; G: C. gracilis.  From Belcher and Swale (1993).

I do occasionally find diatoms from marine habitats in rivers, and often suspect road salt to be the culprit.  One of the most extreme cases I encountered was a sample from the Ingrebourne, a small stream close to my childhood home where Bacillaria paxillifer constituted a third of all the diatoms present.  Bacillaria paxillifer is an intriguing diatom (see “The paradox that is Bacillaria” and links) but one that is very definitely a species that prefers saline rather than fresh water.  The Ingrebourne passes under the M25 motorway within about a kilometre of its source and crosses the busy A12 trunk road just upstream of the sampling location, so periodic pulses of salt are a possibility.

The ephemeral nature of these events, however, make them hard to prove and we are left with scattered notes such as this one in a small natural history journal.   These journals are, in many cases, struggling to survive in the modern age and I guess blogs such as this are taking over from them as records of botanical observations that are not structured in a way that makes publication in a mainstream scientific journal a possibility.  Hilary Belcher and Erica Swale made a number of substantial contributions to algal research over the course of their careers, but they were also consummate observers and recorders of their local environment – the wellspring from which an understanding of the natural world ultimately flows.

I am thankful to Hilary in one other way: she and her partner Erica Swale wrote a small (47 page) booklet with clear line drawings of the most common freshwater algae that was a required purchase for all undergraduates (and demonstrators) attending Brian Whitton’s algae practicals at Durham and it was through this book that I started to learn how to identify algae.  There are, I notice, just 17 genera of diatoms illustrated in this book but there was enough here to start putting names onto the shapes that floated – or flitted – through my field of view as I struggled to learn the rudiments of the craft.

Left: Hilary Belcher on a sampling trip to the Thames in the early 1990s (photo: Alison Love) and, right: the cover of her introductory guide to freshwater algae, co-authored with Erica Swale.

Reference

Belcher, H. & Swale, E. (1993).  Some diatoms of a small saline habitat near Cambridge.  Nature Cambridgeshire 35: 75-77.

A full appreciation of the life and work of Hilary Belcher, compiled by Jenny Bryant, will appear in the next edition of The Phycologist.