Survival of the fittest (2) …

As well as the bright green flocs of Tribonema, the stream draining the Hadjipavlou chromite mine also had bright orange-red growths on some of the pebbles on its bed.  These seemed to be composed primarily of the Cyanobacterium Chamaesiphonthough I am still not sure what species.   Using the limited literature I have, from the UK and Germany, I would opt for either Chamaesiphon polymorphusor C. polonicus.   This particular alga was very easy to remove from stones, compared to other epilithic Chamaesiphon species (see “A bigger splash …”).  This is a feature of C. polymorphus, though the colour is more typical of C. polonicus*.  On the other hand, that bright colour could be the response to high solar radiation, so maybe my north European guides are not that reliable.  It could be something else altogether.

Chamaesiphon_polonicus_Troodos

Chamaesiphon growths on pebbles in the stream draining Hadjipavlou chromite mine in the Troodos mountains, Cyprus, March 2019.

Chamaesiphon_Troodos_Mar19

Colonies of Chamaesiphon from Hadjipavlou chromite mine under the microscope.   Scale bar: 10 micrometres (= 1/100thof a millimetre). 

In addition to the Chamaesiphon, there were a few diatoms, mostly Achnanthidium minutissimumand Meridion circulare.   These are typical species of metal-rich streams, as is the general lack of diversity that was evident.   There were also a few filaments of the cyanobacterium Phormidium, along with quite a few Paramecium and Vorticella.  As these are both heterotrophs that feed on organic matter, their abundance is probably at least partly a reflection of the long time that the sample spent in my suitcase between collection and analysis.  The latter is a fascinating organism to watch: it is a goblet-shaped cell with a fringe of cilia around the lip (or “peristome”).  These beat in unison to create water currents that draw small particles towards the cell.   These particles mostly at least an order of magnitude smaller than the algae)  are then collected in food vacuoles where they are digested.   A few of these vacuoles can be seen in the image of Vorticella below.

Vorticella is attached to its substrate by a stalk which contains contractile filaments, giving it spring-like qualities.  Watching a Vorticella is a beguiling experience, with the undulating rows of cilia drawing food into the vestibule (as the opening is known).  At intervals, the whole cell lurched across the field of view as the “spring” in the stalk suddenly contracted, shortening the stalk.  After this, the stalk would gradually extend again, the cilia not having missed a beat meanwhile.   This process may simply be a device that enables the Vorticellato exploit its locality to the full, as well as creating some additional turbulence to keep a steady flow of particles towards the peristome.  To be honest, I haven’t seen a more convincing explanation but, even if we don’t know why it does what it does, Vorticella is a fascinating organism to watch, whether or not I understand what is going on.

I’ll be coming back to talk more about the diatoms in a future post, and writing these posts has also reminded me that I’ve never written about the interesting mine sites almost on my own doorstep.  I cut my ecological teeth looking at these habitats back in the 1980s and they are striking examples of natural selection in action.   So, plenty of potential for more left-field natural history …

Hadjipavlou_organisims_Mar19

Other organisms present in the Hadjipavlou chromite mine. a. – d.: Meridion circulare; e. Phormidiumsp.; f. Vorticellasp.   Scale bar: 10 micrometres (= 1/100thof a millimetre). 

* Note: after I had written this post Brian Whitton confirmed that it was, most likely, Chamaesiphon polonicus.

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Survival of the fittest (1) …

Hadjipavlou_mine_March19

When I signed up to a trip to Cyprus in late March I was anticipating feeling some warm Mediterranean sun on my skin after the ravages of the British winter.  I did not expect snow and sleet.   However, as one of our destinations was the Troodos mountains, the location of Cyprus’ only ski resort, maybe it was a case of unrealistic expectations.   Fortunately, we realised our mistake just in time to pack some warm clothes, and the unseasonable weather did, at least, mean that the spring flowers at lower altitudes were, even by Cypriot standards, particularly impressive.

I was in Cyprus primarily as a camp follower on a reconnaissance trip for a geology and botany excursion next year.   Cyprus is, to put it in layman’s terms, the outcome of a collision between the African and European continental plates.   The Troodos mountains are a geologist’s paradise, having a wide range of features arising from this and from associated volcanic activity.   As the molten rocks cooled, minerals precipitate out and the resulting geological strata reflect differences in the melting points of these minerals.   Some of these minerals, such as chromite, are commercially valuable and have been mined for centuries.   Indeed, the name Cyprus itself is derived from cuprous, the Greek word for copper, which was mined here since 4000 BC.

The Hadjipavlou mine is set amidst pine forests close to the highest point of the Troodos.  It was an active chromite mine from 1950 to 1954 and from 1979 to 1982 but was abandoned when cheaper sources of chromite became available in South Africa.   Over a million tonnes of ore were extracted in the period when the chromite mines in the area were active, but now there are few obvious signs apart from this adit driven into the hillside.   A small stream bearing water that has percolated through the rocks and collected in the mine’s galleries emerges from the mine entrance and tumbles down the hillside to join the stream below.   This, on closer inspection, has some quite interesting microbial growths.

First of all, having been told that this is a chromite mine, you might expect the water to carry toxic concentrations of heavy metals.   So you might also be surprised to see abundant growths of bright green algae thriving in the stream immediately downstream of the mine entrance.   This is, in fact, a common phenomenon in mine waters and happens, we think, because the fast-growing algae evolve metal tolerance whilst the animals that feed on them are slower to adapt.   This is, literally, survival of the fittest and, with nothing to eat them, the algae grow prolifically.

These filaments belong to the genus Tribonemawhich, despite being bright green in colour, actually belongs to the yellow-green algae, the Xanthophyta, rather than to the green algae.  This group is actually more closely related to the diatoms than to the green algae, though it can be hard to understand why simply by peering through a microscope.  One useful test is to add a little iodine  solutionto the slide: this binds to the starch inside green algae cells, staining them a dark brown colour.   The Xanthophyta, by contrast, do not have starch as their storage product so the cells are not stained by iodine.   The only other member of this group that I have discussed in this blog is Vaucheria, a very different alga (see “Who do you think you are?”).

Tribonema_affine_Troodos

Tribonema cf affinein the channel draining the Hadjipavlou chromite mine in the Troodos mountains, Cyprus, March 2019.   a. close-up of the alga in situ; b.  microscopic view of filaments; c. fragments of disintegrated filaments showing the H-shaped cell endings.  Scale bar: 10 micrometres (= 100thof a millimetre).   

Tribonemahas simple, unbranched filaments with two or more plate-like chloroplasts arranged around the cell periphery.   One other feature is the arrangement of the cell wall, which tends to consist of two overlapping halves.  When filaments disintegrate (as they often do) the fragments have an H-shape, with each end forming half the cell wall of a different cell.   The cells are, in fact, cylindrical but this is not apparent with the flattened perspective of a high magnification objective.   This feature is not universal in the Xanthophyta, nor is it unique to this group (a few green filamentous algae show the same characteristic) but it is a useful hint that you may be looking at Tribonema.

Whilst lush growths of algae is a common feature of streams draining mines, the species that form these growths can vary.   In the northern Pennines, I am used to seeing green algae in these habitats, but there are at least three different genera that I find.  Typically there is just one filamentous alga in this location, and they tend to be  constant over time: they are reliable sources for material for undergraduate practical classes as a result.  There is more to this story but I will have to come back to it at some point in the future.  .

There is also more to the algal flora of the Hadjipavlou chromite mine but, again, that will have to wait for another post.  I should also confess that, although I visited the mine briefly last year, these samples were collected by Heather, whilst I was sitting snugly below the snow line.

Hug a Brexiteer …

Green_line_Nicosia

I was hoping to start this blog, written on the original date for Brexit, noting that, in contrast to most other UK citizens, I had begun the day outside the EU but had, during the course of the morning, re-joined the Union.  The delay in the date for Brexit messes up that neat little opener but the experience of walking across the Green Line in Nicosia, from the Turkish Republic of Northern Cyprus to the Republic of Cyprus is a sobering reminder of the way that festering resentments within communities can spiral out of control.

There are few certainties in UK politics at the moment but, based on voting patterns in the referendum, it is very likely that over 40 per cent of the population is going to be dissatisfied with the outcome of the Brexit negotiations.   I have made my own views clear in this blog and I know that some of my readers disagree with my views.   This post is not about the rights and wrongs of Brexit but about the aftermath, and how the country as a whole treats that large proportion who will almost certainly be disappointed by the outcome.

The situation in Cyprus is complex but there are parallels to Brexit in that, after 1945, the key political question concerned a union (with Greece in this case) that would have left a significant minority of the population feeling disenfranchised.  On the other hand, there is one key difference from the UK in 2019 in that the disenfranchised minority were ethnically distinct.  In 1974 the failure to find a mutually-acceptable settlement led eventually to invasion by Turkish forces and the partition of the island which persists to this day.   We in the UK should be thankful that there is no such clear “them” and “us” distinction as our politicians pick their way through the morass of possibilities.

But the absence of a physiognomic, linguistic or religious differentiator in the Brexit debate does not mean that differences – and resentments – will not persist long after a final settlement is agreed.  That means the country, once it has resolved the present Brexit stalemate, will need to think seriously about a reconciliation process to heal the divisions.   Time, alone, will not necessarily be enough; indeed, time may even sharpen the divisions, especially if the economy is not buoyant in the post-Brexit years.  I live in a liberal bubble where almost everyone I encounter is pro-EU and opposed to Brexit; however, if the UK does end up leaving the EU, there is no point in brooding over what might have been.  We will need to pick ourselves up, dust ourselves down and move on.   And hug a Brexiteer.  Judging by the press reports, many of them are going to be just as disappointed as the Remainers.   At least we will have that in common

 

More about measuring biomass …

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

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

cyanos_in_Ehen

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

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

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

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

The complexities of measuring mass…

Benthotorch_in_action

Once upon a time, measuring the quantity of algae growing on the beds of streams and rivers was a painstaking, slow process that invariably revealed large amounts of spatial and temporal variation that, very often, obscured the ecological signals you were looking for. That has changed in the last decade thanks to the availability of field fluorimeters such as the BenthoTorch.  This makes it much quicker and easier to measure chlorophyll concentrations, the usual proxy for algal quantity.  Thanks to devices such as this it is now much easier to discover that your ecological signal is masked by spatial and temporal variation.

We’ve generated a lot of data about the fluxes of algae in the River Ehen using a BenthoTorch over the past five years and are in a position where we can start to make some generalisations about how the quantity of algae vary over the course of a year.  In broad terms, the results I showed in “The River Ehen in January” back in 2014 have not varied greatly over subsequent years, with peak biomass in mid-winter and low biomass in the summer (due, we presume, to intense grazing by invertebrates).  Curiously, we see a much less distinctive seasonal pattern in the nearby Croasdale Beck, but that is a story for another day….

The BenthoTorch uses an algorithm to partition the fluorescence signal between three major algal groups and, though this is not without issues (see below), I thought it might be interesting to see how these groups varied with biomass trends, and consider how this links to ecological theory.  The first group I’m considering are the green algae which, in this river, are mainly filamentous forms.   The general pattern, seen in the graph below, is for a gradual increase in the proportion of green algae, which fits with the current understanding of thicker biofilms having greater structural complexity with filamentous algae out-competing attached single celled algae to create a “canopy” of algae that are more effective at capturing light and other resources.  The relationship is, however, strongly wedge-shaped so, whilst many of the thickest biofilms have a lot of green algae, there are also thick biofilms where green algae are scarce or even non-existent.  Croasdale Beck shows a similar, but less pronounced, trend.

green_algae_in_Ehen

Relationship between the proportion of green algae and the total quantity of benthic algae (expressed as chlorophyll concentration) in the River Ehen (a.) and Croasdale Beck (b.).   The blue lines show quantile regression fits at p = 0.8, 0.5 and 0.2.   The image at the top of the post shows Ben Surridge using a BenthoTorch to measure algal biomass beside Croasdale Beck in Cumbria.

The second graph shows that this pattern of a gradual increase in proportion is also the case for diatoms and, once again, there is a broad wedge of points with an upward trend.  But, once again, there are also samples where biomass is high but diatoms are present in very low numbers or are even absent.   What is going on?

The problem is clear I think, if one looks at the final image in “The only way is up …” where the very patchy nature of algal communities in the River Ehen (and, indeed, many other rivers).   There are plenty of algae on this boulder, but not organised in a homogeneous manner: some zones on the boulder are almost pure diatom whilst others are almost pure green algae (and there are also zones that are almost pure Lemanea– I’ll come to that in a future post).   We try to sample the stones as randomly as possible so you can see the potential for getting very different numbers depending on where, on a stone, we point the BenthoTorch’s sensor.

diatoms_in_the_Ehen

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

With experience, you can make an educated guess about the types of algae present in a biofilm.  I’ve tried to capture this with my watercolours, using washes of raw sienna for the diatoms and a grass-green for the green algae, which roughly matches the colour of their respective growths in the photo in my earlier post.   The two groups of algae a are relatively distinct on that particular boulder.   The top row roughly matches the upper “edge” of the graph showing variation in diatoms, whilst the bottom row emulates the upper “edge” of the graph showing variation in green algae.  These are the two extreme situations; however, we also often see darker brown growths in the field, which can be recreated by mixing the raw sienna and grass-green together.  When I peer through a microscope I often see green algae smothered in diatoms: genera such as Oedogoniumare particularly prone as they have less mucilage than some of the others we find in the Ehen. Their filaments often host clusters of Fragilariacells as well as Achnanthidium minutissimum, whilst stalked Gomphonemaand chains of Tabellaria flocculosaoften grow through the tangle of green filaments.   The dark brown colour is deepened yet further by the colour of the underlying rock, so my effort on white watercolour paper is a little misleading.

colour_patches

A colour chart showing how different proportions of green algae and diatoms influence the colour of biofilms.

The final graph shows how, as the average biomass increases in the River Ehen, so the variability in biomass also increases.   The River Ehen is one of the cleanest rivers I know but I suspect that this pattern in benthic algal quantity could be reproduced in just about any river in the country. What I would not expect to see in any but the purest and most natural ecosystems is quite so much variation in the types of algae present.   Once there is a little enrichment, so I would expect the algae to become more of a monoculture of a dominant filamentous alga plus associated epiphytes.  Like much that happens in the microscopic world of rivers, it is easier to describe than it is to measure.

That, however, is only part of the story but I’ll come back to explain the patterns in the other main groups of algae in the Ehen and Croasdale Beck in my next post.

mean_biomass_by_stdev

The relationship between mean chlorophyll density and the standard deviation (based on measurements from five separate stones) for samples from the River Ehen and Croasdale Beck. 

 

Secular icons?

paintings_at_botanic_gardens_Mar19

I’ve got two pictures on display as part of an exhibition at Durham University Botanic Gardens, both showing abstract or semi-abstract views of algae.  One is my sextych of the alga Apatococcus(see “Little round green things …”) and the other is a triptych based on Haematococcus, an alga which I wrote about in “An encounter with a green alga that is red” back in 2013.   Both pictures were painted for my final degree show back in 2008 and both addressed questions about the boundaries between abstract and representational art.

The point that I was trying to make with these images is that the boundary between abstract and representational art depends partly on what the viewer knows about the subject matter and, in the case of algae, this is usually not very much.  In cases such as these, the legend becomes very important as a means of bridging the gap between abstraction and reality by providing just enough information to help viewers make sense of the content (see “How to win the Hilda Canter-Lund Prize (2)”).   In the case of microscopic images, this should always include some indication of scale, written in terms that non-biologists can easily understand (I would always write “1/100thof a millimetre”, rather than “10 micrometres”, for example).

Haematococcus_MGK

Haematococcus. Triptych.   2008 50 x 130 cm Acrylic, resin and PVA on canvas.

This issue of viewers being able to “unlock” the meaning of images extends beyond the abstract/representational boundary that I encounter when displaying images of the microscopic world.  Exactly the same challenges occur when, for example, secular western Europeans look at eastern Orthodox icons, a subject that occasionally creeps into this blog (see, for example, “Unorthodox icons”.   My own curiosity about this art form led me to spend a week studying icon painting at the Quaker College in Woodbrooke, in the suburbs of Birmingham.  About ten minutes away from Woodbrooke there is the Serbian Orthodox church of St Lazar (built after the second world war by Yugoslav refugees with financial support from the Cadbury family, the Quaker philanthropists who also established Woodbrooke).

I talked a little about the practice of icon painting in “The art of icons …”.  Today, I am more interested in the symbolism.   A secular westerner can look at many of the icons I’ve depicted and broadly catagorise the contents: most would recognise that Fr Nenad, the priest of the Selly Oak Orthodox church, is holding an icon that depicts the crucifixion, for example, or that the icon just to the left of the centre of the doors in the iconostasis in the lower image depicts the Virgin and Child.  However, the symbolism goes much deeper.   I have a spotter’s guide to icons (sad, I know …) and it lists twenty eight different variants on the basic depiction virgin and child, differing in the physical relationship of Mary and Jesus, their facial expressions and the setting.  Each of these have a slightly different meaning for the Orthodox faithful.   The westerner sees “virgin” and “child”, the eastern Orthodox devotee sees so much more.

St_Lazar_Bournville

The Serbian Orthodox Church of the Holy Prince Lazar in Selly Oak, Birmingham with, right, Father Nenad displaying an icon of the crucifixion. 

What’s all this got to do with painting algae, you may ask.   Scientific illustratation and icon painting are two branches of applied art, where the subject matter serves a higher purpose.  Both, in their own way, try to help viewers understand their place in the world.  If you are not religious, you may not be comfortable with this comparison but, for most of Europe, east and west, until the Enlightenment, this would have been the case.   In both cases, however, the image cannot be viewed in isolation, the viewer needs the appropriate “keys” to unlock meaning.   Even then, the viewer is not a passive observer.   The icon requires a response from the viewer, it is the focus for contemplation and meditation and, I suggest, scientific images, when displayed as “art” should play a similar role, inviting viewers to reflect upon the mysteries of the natural world and demanding a response.

St_Lazar_iconostasis

The iconostasis at the Serbian Orthodox Church in Selly Oak.

The only way is up …

Ehen_Mill_Feb19

How does an alga move upstream?   I’m curious because, I am now seeing populations of Lemanea fluviatilisabout four kilometres further upstream in the River Ehen than when I first started my regular visits in 2013.   I can explain the presence of the organism partly through changes in the hydrology of the river: a small tributary, Ben Gill, that had been diverted into the lake in Victorian times was reconnected to the river in 2014 and this introduced periodic pulses of intense energy to the river that had immediate effects on the substrate composition.  Lemanea fluviatilisis a species that thrives in the fastest-flowing sections of streams so I am quite prepared to believe that even a small shift in the hydrology of this very regulated river might make the habitat more conducive.

But that does not explain how it got there in the first place.   If the alga was occurring a few kilometres further downstream we would not have any such problems: the upstream populations would provide innocula and, if the habitat conditions changed at the downstream location, then some of those propagules might be able to establish at the downstream locations.   But what about movement in the other direction?

There has been relatively little published on this topic in recent years.  I have a review by Jørgen Kristiansen from 1996 that considers the dispersal of algae but most of the references that he cites are quite a lot older than this and I have not seen much published subsequently.   He lists our options: dispersal by water, by organisms, by air currents and by human activity.   Let’s consider each in the context of Lemaneain the River Ehen.   Lemanea, like most red algae, has a complicated life cycle with the potential for dispersal in both the haploid and diploid phases, but that is probably more detail than we need right now.  We’ll just outline the options in broad terms:

Water:the linear flow of the river means that it is almost impossible for the downstream population to provide inocula for the new upstream locations.  It may be possible for populations from further upstream in the catchment to seed the new locations.  I have not seen Lemaneain any of the streams that flow into Ennerdale Water (from which the Ehen emerges) but my knowledge of the catchment is not exhaustive.   Likelihood: very low to low.

Lemanea_at_Mill_Feb19

Young shoots of Lemanea fluviatillis(bottom right) growing on a submerged boulder in the River Ehen at a location where I have not previously seen it.   These are growing alongside thick growths of diatoms (yellow-brown in colour) and patches of green filamentous algae.

Organisms:much of the older literature is concerned with the possibility of living algae or their propagules being transported in mud attached to bird’s feet or feathers and this cannot be ruled out.   There is also a recent study showing how mink may act as a vector for Didymosphenia geminata in Chile.  The Ehen also has aquatic mammals (such as otters) that could be acting as vectors for Lemanea, as well as migratory fish such as salmon and trout that could move propagules upstream.   There is also some evidence that some algae can survive passage through mammalian and invertebrate guts, and this, too, may provide a means for Lemaneato spread upstream.    Likelihood: low to medium.

Air currents / wind:quite a lot has been written about airborne dispersal of algae, with even Darwin making a contribution (see reference in Kristiansen).  The key hazard in airborne dispersal is desiccation so, in the case of Lemanea, the most likely lifecycle stages that could be dispersed in this way would be the diploid carpospores or haploid monospores. This, however, would assume that there were times during the year when the relevant life-cycle stages were exposed and, as Lemaneais a species that I usually find in the Ehen only fully-submerged, this is not very feasible.  Likelihood: low.

Human activity:there is evidence that Didymosphenia geminatacan be transported between sites attached to waders and new records often correspond with patterns of recreational use (references in Bergey & Spaulding – see below).   When we work in the Ehen we prefer to move downstream in order to minimise the risk of moving organisms on our kit, and we also clean our kit before we start.   However, a lot of people work in this part of the Ehen and it only takes one dirty wader to introduce a propagule.   Likelihood: low to medium.

We’ll almost certainly never know for sure why Lemanea fluviatilisis now thriving four kilometres further upstream than it was five years ago.  It is, however, worth bearing in mind that, given enough time, even a low probability may yield a positive result.   So none of the four hypotheses can be ruled out for sure.   Three of the possibilities are entirely natural, with one – movement by the stream itself – being constrained by the direction of flow.  Biological vectors look like a very plausible means of moving algal propagules around catchments but, for this to work, we need wildlife-friendly corridors around the river to support the animals and birds.  The upper Ehen has these, but many other rivers do not.

Actually, having a number of options all with a relatively low likelihood adds to the sense of mystery that every ecologist should have when they approach the natural world.  When cause and effect are too predictable, we tend to focus on engineering the right “solution”.  The truth, in our muddled and unpredictable world, is often that nudging several factors in the right direction will give us a more resilient outcome, even though we may have to wait longer for it to happen.

Reference

Bergey, E.A. & Spaulding, S.A. (2015). Didymosphenia: it’s more complicated.  BioScience65: 225.

Kristiansen, J. (1996).  Dispersal of freshwater algae – a review.  Hydrobiologia336: 151-157.

Leone, P.B., Cerda, J., Sala, S. & Reid, B. (2014).  Mink (Neovision vision) as a natural vector in the dispersal of the diatom Didymosphenia geminataDiatom Research29: 259-266.

Raven, J.A. (2009).  The roles of the Chantransia phase of Lemanea (Lemaneaceae, Batrachospermales, Rhodophyta) and of the ‘Mushroom’ phase of Himanthalia (Himanthaliaceae, Fucales, Phaeophyta).  Botanical Journal of Scotland46: 477-485.