Off grid, in tune …

A weekend camping at the Latitude Festival barely ranks as hardship on any meaningful scale, but it does provide a brief opportunity to reflect on what, for 361 days of the year, I take wholly for granted.  Water is one of the leitmotifs of this blog, creating the habitats that the creatures I write about inhabit.   Yet I barely pause for thought when turning on taps or watching used water drain away whilst I am at home.   Here, I am off-grid: if I want water I have to walk to a standpipe and fill a container; if I want to wash in hot water, I have to light my sturdy old Trangia to heat-up a saucepan; when I use the toilets, I have to walk 100 metres and hope that the previous occupant left the cubicle in a usable state.

Our sojourn under the Suffolk sun, in other words, is brief jolt into the extent of our disconnection from nature’s cycles.   One immediate consequence of having to plan ahead and put in some effort (tiny, compared to that required by a large part of the developing world) is that the quantity of water that we actually use drops precipitously.   Scale that up from the individual to a population, and I wonder how much of the UK’s water infrastructure would be unnecessary if everyone had to think as hard about water usage as Latitude’s campers?

We are a little closer to nature, a little less inclined to think of ourselves as separate from the wider whole, a little humbler …

To realise:
That we live in nature
But can never possess it;
We can guide and serve
But never control
This is the highest wisdom
Tao 51

Highlights of Latitude 2017?  Fleet Foxes’ first UK show since 2011 was worth the price of the ticket alone.  78-year old Mavis Staples on Sunday afternoon was magical.  Ventriloquist Nina Conti left me crying with laughter.  The desert blues of Tinariwen was memorable and, amongst the newcomers, I’ll definitely be watching out for Julia Jacklin in the future.

Tinariwen on the Obelisk Stage at Latitude 2017.

Damp days in search of desmids …

Seatoller, in Borrowdale, is the wettest place in England, so we should not have been surprised by the persistent drizzle that accompanied us as we set off hunting for desmids last week.  The combination of Borrowdale’s hard volcanic rocks and a damp climate combine to create ideal habitats for bog-loving desmids and I had intelligence that Dock Tarn, on the fells above Borrowdale, was a hot spot of desmid diversity.   Getting there, however, was no easy task.  Though just a couple of kilometres from Stonethwaite on the map, there were an awful lot of contour lines awfully close together between the beginning and end of our walk.   The footpath zig-zagged through ancient woodland clinging to a steep hillside until we emerged onto the moorland above.  We then made our way across a plateau covered with heather moorland until we saw the tarn stretching away into the mist in front of us.

You know you are in good desmid habitat when there is water percolating into your body from both ends: rain dripping down from the hood of your cagoule and dampness seeping in through your shoes.  They are organisms that love marshy, boggy conditions, especially in areas where the water is as soft as it is here.   The alternative to damp feet would be to either climb up from Borrowdale in Wellingtons or waders or carry them up that steep hillside in a rucksack.   However, I suspect that the mud at the bottom of the tarn was too soft and deep for Wellington boots and lugging waders up that hillside would have been hard work so damp feet was the price I had to pay.   I leaned out as far as I could from the shore to grab some of the sedge stems which had a visible coating of attached algae, and also squeezed the peaty water from a few handfuls of Sphagnum that I pulled from a boggy pool.  That would have to do on this particular morning as the rain was now soaking through my trousers and, in any case, there were places I needed to be later that morning.   I shoved the bottles containing my samples into my rucksack and followed the path back down the hillside.

Epiphytic algae growing around a sedge stem in the outflow of Dock Tarn, Cumbria, July 2017.   The width of the stem plus epiphytes is about half a centimetre.

Dock Tarn is one of a number of sites identified as an “Important Plant Area” (IPA) on the basis of the rich desmid flora, largely due to work over the years by David Williamson.   It qualifies as an IPA on four criteria: the presence of threatened species, high diversity, a long history of study and because it represents a “threatened habitat”.   David Williamson has recorded over 50 species from this location, 13 of which are candidates for a “potential Red Data List”.   A few of these are illustrated in the figures below.   One of the species in the first image, Haplotaenium minutum, belongs to a genus only recently separated from Pleurotaenium, which looks very similar to the untrained eye (the difference lies in the structure of the ridges on the chloroplast).  Looking at these long cylindrical cells serves to emphasise just how much dexterity Chris Carter needed to produce his Hilda Canter-Lund prize winning image.  Images in the second plate include two more species of the genus Xanthidium, which we met in “Desmids on the defensive …”.

Dock tarn desmids: a. Netrium digitus var. latum; b. Tetmemorus brebissonii; c. Haplotaenium minutum.  Scale bar: 25 micrometres ( = 1/40th of a millimetre). 

The desmids in the lower plate, in particular, show one of their key characteristics very clearly: their cells are divided into two distinct lobes (“semicells”) joined by an isthmus (the word desmid comes from the Greek desmos, meaning “bond”).  The image of Staurastrum manfeldtii var. productum also shows a number of bacteria growing on the cell: these are probably growing within the mucilage that desmids secrete around themselves whilst there are distinct pyrenoids in the two Xanthidium species.  Their predilection for soft water means that they need the carbon-concentrating mechanisms that these contain if they are to thrive.   Not all desmids live in water as soft as this, and some are able to use inorganic bicarbonate to fuel their photosynthetic engine, but there will be little or no bicarbonatae in a habitat such as Dock Tarn.   I wrote about these carbon concentrating mechanisms in algae from Ennerdale Water (see “Concentrating on carbon …”) and the two filamentous algae that featured in that post, Mougeotia and Spirogyra, both belong to the same class within the green algae as the desmids (Conjugatophyceae or Zygnemtetophyceae).

There will be more about desmids on this blog over the next few months in preparation for a the weekend of 15-17 September when I am organising a joint meeting of the British Phycological Society and Quekett Microscopical Club in Windermere.  We’ll be visiting some other Lake District tarns known to be rich in desmids during this weekend and have Dave Johns and Allan Pentecost on hand, amongst others, to offer expert advice on what we find.  There are still a few places left, so hurry up to book your place.  I haven’t done a great job of selling the Cumbrian climate in this post but we have the use of the Freshwater Biological Association facilities, including a laboratory and the library, so no one need get damper than they want.   See you there…

More desmids from Dock Tarn: d. Euastrum cuneatum; e. Xanthidium cristatum var. uncinatum; f. Xanthidium antilopaeum; g. Staurastrum manfeldtii var. productum.   Scale bar: 25 micrometres
( = 1/40th of a millimetre). 

References

Coesel, P.F.M. (1994). On the ecological significance of a cellular mucilaginous envelope in planktic desmids. Algological Studies 73: 65-74.

Kiemle, S.N., Domozych, D.S. & Gretz, M.R. (2007). The extracellular polymeric substances of desmids (Conjugatophyceae, Streptophyta): chemistry, structural analyses and implications in wetland biofilms. Phycologia 46: 617-627.

Spijkerman, E., Maberly, S.C. & Coesel, P.F.M. (2005).  Carbon acquisition mechanisms by planktonicdesmids and their link to ecological distribution. Canadian Journal of Botany 83: 850–858.

 

Hilda Canter-Lund competition 2017 winners

The winner of the 2017 Hilda Canter-Lund photography competition is Chris Carter for his image of the desmid Pleurotaenium coronatum var. robustum.   This is the second time that Chris has won the competition and his fifth time on the shortlist, confirming an already impressive reputation as a photographer of the algal world.   This particular image is of a specimen that was collected whilst on holiday in Newfoundland, Canada, and preserved in formalin.  This led to the loss of chloroplast colour but which, in turn, made the pore field at the end of the cell more obvious.

The technical skill behind this image is not immediately obvious unless you know the genus Pleuotaenium typically consists of cylindrical cells several times longer than wide.  This particular specimen is 45 micrometres (about 1/20th of a millimetre) in diameter but is almost half a millimetre long.  The challenge was increased because the 100x magnification oil-immersion objective which he used has a very shallow depth of field.  Chris had to suspend the cell in dilute jelly in a cavity tank not much deeper than its length.  Having done this, he agitated the cell with a length of fine wire and once it was no longer horizontal he could manipulate it by gently sliding the coverslip relative to the cell.  The photograph which won the competition is one of many attempts and, even so, Chris commented that the cell is probably a degree or so away from vertical even here but, he went on: “I thought the lighting was actually quite attractive with the bronze hue of the preserved wall contrasting with a blue tinge from the light source; even the very slight tilt perhaps suggests a monster (or a something) rising out of the deep.”

Pleurotaenium coronatum var. robustum.  The top left image is an apical view, showing the pores and the radial ring of tubercules (knobbly projections).  The lower image shows the cell in plane view.   All images by Chris Carter.

Chris Carter, Hilda Canter-Lund prize winner, 2013 and 2017.

The second prize this year was also awarded to a former winner.  Tiff Stephens won the competition last year with her photograph of Durvillaea antarctica in the intertidal zone of the sub-Antarctic Snares Islands.  This year, it was her photograph of the red alga Bonnemaisonia clavata that caught the judge’s eye.   This is a very different style of photograph to her winning entry from last year, taken using an Olympus DP20 camera on a dissecting microscope.   The row of spheres along the secondary axis (“stem”) contain female reproductive cells and the prominent branchlet in the centre right is 1.5 mm long.

“Cystocarp Central”: Tiffany Stephen’s winning entry for the 2017 Hilda Canter-Lund photography competition. 

Though the style of the picture is very different to last year’s entry, it shares with that image an encapsulation of the “decisive moment” (see “How to win the Hilda Canter-Lund competition”). Tiff comments that many of her images are “opportunistically taken while sprinting around doing fieldwork”.  In this particular case, she was on a fun dive outside of Victoria, British Columbia (Canada), collecting seaweeds to look at later, with a view to possibly making herbarium pressings.   She saw dense lumps of Bonnemaisonia clavata, a species with which she was not familiar, at depths between 5 and 10 metres on semi-exposed reefs and collected some to have a closer look later.

The two images represent the two extremes of photographing the microscopic world: Chris applied a great deal of technical skill and ingenuity to create an aesthetically-pleasing image from difficult subject matter whilst Tiff saw an elegant composition drift into view as she scanned around recently-collected field material.  Both photographers have an “eye” for a good composition and the patience and technical skill needed to capture a fine image when the occasion final presented itself.   They are also – and this is important – keen field scientists, grabbing samples out of sheer curiosity and then marvelling as new and fantastical worlds open up to them under the microscope.  Both worthy winners and, with John Huisman (winner in 2014, shortlisted five times), now form algal photography’s “superleague”: the people to beat in 2018!

Tiff Stephens surrounded by Macrocystis in Alaska earlier this year.  Follow Tiff on Twitter at @tiffanybot to see more examples of her photography.

Where’s the Wear’s weir?

There was minor excitement in Durham – and some consternation amongst the rowing fraternity – when river levels dropped rapidly overnight last week.  The river had been very low for some time but was 20 cm lower on Wednesday morning (28 June) due, we learned, to a failure in a sluice gate on the weir just below Prebends Bridge.   It does not look very dramatic in the picture above (a temporary – but not wholly effective – repair had been effected a couple of days earlier) but, as the hydrograph below shows, it was enough to alter the levels to a point where rowing becomes difficult.  The following two days were wet and miserable and the rain caused levels to increase again (note the steep rise on the evening of 29 June as floodwater washed down from Weardale) before gradually tailing off over the next few days.  My photograph was taken in the afternoon of 2 July when levels were back to normal.

“Normal” is, however, a tricky word to apply to any river, so diverse are the alterations to which they are subject.  For me, the ponded section of the Wear upstream of the weir is all I have known and the view of the cathedral looming over the Fulling Mill and its weir is the quintessential impression of Durham, immortalised in J.M.W. Turner’s paintings.  Without that weir there would be no rowing on the river – an important “ecosystem service” within the city (see “Bring on the dambusters …”) – yet that dip in the hydrograph on Tuesday morning offers us a rare glimpse into what the river would have looked like in summers in the far past.  Rowers would be not be very happy were this to pesist but perhaps canoeists would prefer faster-flowing water?  Maximising the ecosystem services that a river provides often involves a trade-off between competing needs.

River levels in the River Wear at New Elvet (NZ 272    ) from 27 June to 2 July.  The orange line indicates the point at which flooding may occur.   From: https://flood-warning-information.service.gov.uk/station/8288425

I saw the opposite situation on the River Tees at Egglestone, just downstream from Barnard Castle.   Turner visited this location as part of the same trip that took him to Durham in 1797 and he sketched the view of Egglestone Abbey which he later worked up into a painting and engraving.   In his pictures you can see an old paper mill, what appears to be a weir across the Tees and open ground on the steep land in front of the abbey itself.   The view today is quite different: the mill is still there, albeit in a dilapidated condition and there is thick woodland on the river banks which completely obscures the view of the abbey.   There is also no sign of the weir but the mill race that diverts river water through the mill can still be seen, though water only flows through when the river is high.

I did wonder if this meant that the weir had been completely washed away since the mill had fallen derelict but another possibility is that the weir is artistic license on Turner’s part.  He made his sketch in 1797 but there is no obvious weir in the drawing that has survived.  The painting on which the engraving is based dates from about twenty years later, and it is possible that the weir was added to the composition, based on memories of other localities that he visited on that trip (including Durham).   The presence of a weir also cannot be confirmed from a painting by Thomas Girtin from about the same time but it is possible that he, too, worked up his watercolours some time after his sketching trips and relied on hazy memories.  And, as we know that Girton and Turner were acquainted, Turner may have fed off Girton’s interpretation of the scene, compounding the intital error.

Egglestone Abbey near Barnard Castle.  Engraved by T. Higham after J.M.W. Turner. 1822.   Image released under Creative Commons CC-BY-NC-ND (3.0 Unported)

The other possibility is that we are not looking at the same river as Turner or Girtin.   The river we look at today is downstream of major reservoirs at Cow Green and on two tributaries, the Greta and Balder, none of which were present when they visited.   Cow Green, in particular, was designed with regulation of the water supply in mind, in order to ensure that there was enough for the industries in Teesside.  One consequence is that there is more water in the Tees during the summer now than when Turner and Girtin visited.   Maybe a weir would have been necessary at that time to keep the water level high enough to feed the mill race during the summer?

So here, as in the Wear, “normal” is a difficult word to apply.   First impressions are that the river is now in a more natural state than two hundred years ago because an impediment to natural flow has been removed.  When we look more closely, however, we see that the river we see today is, in fact, a different type of “abnormal” to that which Turner and Girton sketched.   But we also need to remember that Turner and Girton’s interpretations are not entirely trustworthy guides to the past either.  There is much to be said for walking backwards into the future but occasionally this may mean that we trip ourselves up …

The view across the River Tees towards Abbey Mill and Egglestone Abbey from approximately the same place as Turner’s view.  The mill is just visible amongst the trees in the middle of the picture.

Reference

David Hill (1996).  Turner and the North.   Yale University Press, New Haven and London.

 

Unlikely neighbours …

One of the lessons I learned from writing “A tale of two diatoms …” is that we can often learn more about the ecology of a species by contrasting its behaviour with that of another species rather than by just relating the distribution of that species to features of its environment.  I came across another example of this when I was writing up the results of the latest “ring-test” that UK diatom analysts undertake to maintain their competence.

The sample came from a stream in east Devon (the one that had a walk-on part in “The challenging ecology of a freshwater diatom”).  This stream receives effluent from a small sewage works but our sample comes from just upstream of this works.   We know that the stream downstream of the sewage works is quite polluted but were also interested in the condition of the stream above the works.   This has proved to be challenging and, it seems, there are some pollution sources, including septic tanks and runoff from fields, that mean that the stream already shows signs of impact before it reaches the sewage works.   There are, however, mixed messages when we look at the aquatic flora, and some of the diatoms that are abundant are characteristic of low or only slight enrichment.

One feature of the stream that was quite unusual was a relatively large number of cells of Reimeria uniseriata, a relative of Reimeria sinuata which is quite common.  Both of these are illustrated below: note that R. uniseriata tends to be slightly larger and has distinctly punctate striae.  However, when I looked at the distribution of these species in response to water chemistry, I could see few differences, with most of the records suggesting a preference for water with low or slightly elevated phosphorus concentrations.   Reimeria sinuata is more common than R. uniseriata and when the latter is found, the former is usually present too.  They seem to be able to share their habitat quite comfortably.

Reimeria sinuata from Polly Brook, Devon, December 2016.   a. – f.: valve views; g.: girdle view focussed on ventral side.  Scale bar: 10 micrometres (= 1/100th of millimetre).  Photos: Lydia King.

Reimeria uniseriata from Polly Brook, December 2016.  h., i.: valve views; j.: girdle view focussed on dorsal side; k., l.: girdle views focussed on ventral side.   Scale bar: 10 µm (= 1/100th of millimetre).  Photos: Lydia King.

In other words, we cannot learn very much from looking at differences in the distribution of these two species of Reimeria, given our current state of knowledge.  There is, however, one other “compare and contrast” within the data that I collected from Polly Brook that is more intriguing.   If Reimeria sinuata, in particular, usually indicates a healthy stream, possibly with a little nutrient enrichment, Rhoicosphenia abbreviata is more often associated with enriched conditions.   We have met this diatom before (see “Cladophora and friends” amongst other posts) and I have explained that it is often found growing as an epiphyte on other algae.  We rarely see situations where both species are abundant at the same time, as the graph below shows.

The relative distribution of Reimeria sinuata and Rhoicosphenia abbreviata in the 6500 UK stream and river samples in the DARES dataset.   The horizontal and vertical lines indicate 10% relative abundance of each species.

When I started looking at stream algae there was a prevailing assumption that there were strong causal relationships between the species of diatom that were found at a site and the level of chemical pressures.  In the case of phosphorus, in particular, I am now not convinced that the evidence supports this whilst, at the same time, am more convinced that we should be able to, at the very least, describe what a healthy stream algal community looks like and give reasons.  I use the word “describe” because I think that many of us have been preoccupied with counting and measuring, often at the expense of a qualitative understanding.  These two species illustrate my point as when I look down a microscope and see Reimeria sinuata, I can usually assume that the stream where it was growing was reasonably healthy, even if the nutrients are a little higher than would be ideal.  On the other hand, seeing lots of cells of Rhoicosphenia makes me suspect that there has been a breakdown in the functioning of the healthy community.  These conclusions would be irrespective of what the chemistry or the values that biological indices told me.

Two species is barely enough to base a credible assessment upon but we could stir more into the mix: I often find Reimeria sinuata with Achnanthidium minutissimum, and that, in in summer especially, suggests strong top-down control by grazers, which means that pathways of energy flow have not been disrupted.   And Rhoicosphenia, as I have already mentioned, is associated with Cladophora which, in abundance, suggests a breakdown in these pathways, as shown by Michael Sturt and colleagues from University College, Cork, a few years ago.   That Polly Brook has both Reimeria and Rhoicosphenia in abundance suggests that it might just be at the tipping point between these two states.

The naïve answer to making sure that the upper stretches of Polly Brook do not cross this threshold would be to manage the nutrients.  However that is not quite as easy as it sounds in an agricultural catchment.   It could be that managing other aspects of the riparian environment are equally effective at keeping the stream in a healthy condition but that takes us into areas where the evidence is still accumulating.  It could be that the simplistic determinism that drove much of the development of biological assessment methods actually held back the gathering of that evidence for a long time.  Reimeria sinuata – and it’s cousin, R. uniseriata – stand as two reminders that there is more to the management of aquatic ecosystems than strong correlations.

Reference

Sturt, M.M., Jansen, M.A.K. & Harrison, S.A.C. (2011).  Invertebrate grazing and riparian shade as controllers of nuisance algae in a eutrophic river.  Freshwater Biology 56: 2580-2593.

Sticky water …

It seems strange to be writing about an alga that thrives in winter in the middle of one of Britain’s rare heatwaves but I came across two papers recently that shed some light on the ecology of Ulothrix zonata.  This is a species that has intrigued me for some time, having a very distinct preference for times of the year when our rivers are at their coldest and I have tried to unravel the reasons for this in some earlier posts (see “Bollihope Bhavacakra” and “The intricate ecology of green slime …”).

The lead authors on these papers are based at Irkutsk, beside Lake Baikal in Siberia, so are in a good position to contemplate the effects of cold conditions on algae.   Whereas I complain about plunging my hand into cold water in northern England to collect Ulothrix zonata, they had to Scuba dive under the ice of Lake Baikal in water only just above freezing point.  They have found two adaptations in the Lake Baikal populations of U. zonata to cold conditions.  The first of these is that the ratio of polyunsaturated to saturated fatty acids are higher in these populations than in those of other Ulothrix species.   This sounds as if it could be an algal equivalent of the “blubber” that insulates sea mammals but the truth is rather more mundane: it is part of a series of adaptations of the cell membrane that allows the organism to keep functioning despite the harsh conditions.

Living underwater is, in many ways, the easy option for a plant in Siberia, where the average outside temperatures in winter are less than -10 °C, and the record low is almost -50 °C.  Terrestrial plants adapt to such harsh environments simply by shutting down operations.   However, whilst the surface layers of Lake Baikal freezes, life below the ice can continue and there are several studies about the rich algal life within this enormous lake (which contains a fifth of the planet’s fresh water).   Enough sunlight can penetrate through the ice to sustain growth, albeit at a slow rate but, on the other hand, the cold water creates problems of its own.   In particular, the density of water increases as temperature drops, making it more viscous.  We might not notice that cold water is more gloopy than warm water but that is because how we experience viscosity is partly a function of our size.  What might be an insignificant change to a human can be a big deal to a microscopic alga.

The cell membrane is composed largely of lipids and, like margarine, these are soft in warm environments (such as frying pans) but hard in cold environments (such as refrigerators or Lake Baikal).  The problem for cells is that there are other molecules embedded in the lipid layers which help the cell obtain the raw materials it needs, and these will not be able to function if the lipids in the membrane are too rigid.   Molecules of saturated fats pack together more compactly than those of polyunsaturated fats which means that a membrane with lots of these is more rigid than one with a high ratio of polyunsaturates.   Consequently, if an organism is to thrive in cold environments then it is beneficial for it to have a high ratio of polyunsaturated to saturated fats in the lipid molecules.

Water is one of the molecules that submerged algae need to shift into their cells to keep their cellular machinery running as this is one of the raw materials of photosynthesis.   There is no shortage of water on the outside of the cell.  However, having a membrane composed largely of hydrophobic lipids means that this is not straightforward and one of the molecules that is embedded in the lipids belongs to a group of proteins called “aquaporins”.  These are shaped in such a way that there is a narrow channel in the centre (like the hole in a doughnut) through which water molecules can pass in single file.

Aquaporins are well known in animal, plant and bacterial cells but it is only recently that they have been found in algae too.   Aleksey Permyakov and colleagues showed that Ulothrix zonata populations from Lake Baikal and streams in the vicinity had more aquaporins in winter than the summer, which they interpreted as an adaptation that ensured a steady supply of water to the cell despite the higher viscosity of the water.  This is also the first time that algal cells have been shown to be able to regulate the amount of aquaporin in membranes in response to their environment.

These two observations together suggest how cold-tolerant algae may have to invest some of their hard-earned energy in modifying their membranes to help them thrive.  I suspect that this is part of a complex network of interactions here: survival in such extreme conditions is possible because the slow rate of growth in very cold water is offset by an even slower rate of grazing and other processes which remove algal biomass.  Diverting energy and resources to make more aquaporins, in turn, means that photosynthesis is not limited by a shortage of raw materials.   It is a fine balance but, if an organism can get this right, then there is an opportunity to thrive with relatively little competition from other organisms.  It is another reminder that ecology is a science that depends on a 365 day perspective and that we should not assume that a few fieldtrips when the weather is most clement will reveal all of its riches.

References

Osipova, S., Dudareva, L., Bondarenko, N., Nasarova, A., Sokolova, N., Obulinka, L., Glyzina, O. & Timoshkin, O. (2009).  Temporal variation in fatty acid composition of Ulothrix zonata (Chlorophyta) from ice and benthic communities of Lake Baikal.  Phycologia 48: 130-135.

Permyakov, A., Osipova, S., Bondarenko, N., Obolinka, L., Timoshkin, O., Boedekker, C., Geist, B. & Schäffner, A.R. (2016).  Proteins homologous to aquaporins of higher plants in the freshwater alga Ulothrix zonata (Ulotrichales, Chlorophyta).  European Journal of Phycology 51: 99-106.

The photograph at the top shows Ulothrix zonata growing on the bed of the River Wear at Wolsingham, Co. Durham in February 2009.

Hilda Canter-Lund competition shortlist 2017

The shortlist for the annual Hilda Canter-Lund competition to find the best algal photograph has just been uploaded to the British Phycological Society website and here is a quick guide to the images.  No less than three previous winners have made it to the shortlist again, along with three newcomers, so it looks like being a particularly intriguing year.

2013 winner Chris Carter has made it to the shortlist for the fifth time with an apical view of the desmid Pleurotaenium coronatum var. robustum with an image that combines aesthetics and technical ability in his own inimitable manner (above left).   The desmid genus Pleurotaenium typically has cylindrical cells several times longer than wide, so getting a good image of one end of a cylinder that is about 1/20th of a millimetre in diameter is quite an achievement.   He is joined on the shortlist by 2016 winner Tiff Stephens, who switches style this year to offer a macroscopic view of female reproductive cells of the subtidal red seaweed Bonnemaisonia clavata, collected off the coast of Vancouver Island in Canada (above right).   The prominent branchlet in the centre-right with its own side branches is 1.5 mm long.

John Huisman shares with Chris Carter the honour of being the most shortlisted photographer in the competition, with five nominations including the winning entry in 2014.   His image this year shows the green alga Ulva stenophylloides, at the centre of a diverse assemblage (above left), photographed whilst snorkelling off the coast of Western Australia.   Heather Spalding, by contrast, makes her first appearance on the shortlist, with a view of Chara zylanica beds in a brackish lagoon in Hawaïi (above right).  Note the small snail making its way across the plants in the foreground, reminding us of the important role that macroalgae play in structuring ecosystems.

We go back to Australia – the D’Entrecasteaux Channel in Tasmania actually – for the next entry: Luis Henriquez’s image of a young plant of the brown alga Carpoglossum confluens emerging from a bed of Caulerpa trifaria (above left). As well as providing a striking image, Luis’ image also tells a story of marine eutrophication as the slow growing brown algae such as Carpoglossum are struggling to compete with the fast growing green algae such as Caulerpa.   Finally, Alizée Mauffrey brings a completely different style to the competition, with a collage of images of seaweeds exhibiting different functional traits (above right).   As well as telling a story about how different morphological, phenological and physiological traits combine to equip each species to inhabit a particular niche, Alizée also creates a pleasantly abstract composition.   She is also the first person to submit an image produced using a flatbed scanner rather than a camera (for more examples of this technique, see An Ocean Garden by Josie Iselin).

This shortlist is unusual in that there is only a single true micrograph and a single freshwater alga (both represented by Chris Carter’s image).   A number – using both the light microscope and scanning electron microscope – were submitted but the judges who selected the shortlist felt that most did not quite make the grade.  It was a close call in a couple of instances (and, in at least one case, some minor adjustments to contrast might have persuaded us) but that is the sad truth.  It may simply be that taking a really good image using a high power microscope is a more technically demanding task than photographing macroalgae in situ?   If nothing else, this does show just how good a photographer Hilda Canter-Lund was.

The final step in the competition is for the council of the British Phycological Society to vote for the winning entry.  After that, a second (but equal) prize will be awarded for the best of the shortlisted entries in a contrasting style (i.e. a micrograph is a photo of a macroalga wins and vice versa).   Both winners should be announced within the next couple of weeks so keep an eye on www.brphycsoc.org for the announcements.  And, while you are there, browse through the archives of pictures that we’ve accumulated since the competition started in 2009 and enjoy some of the remarkable and beautiful organisms that they portray.