Bollihope Bhavacakra*

My explorations of the biology of Ulothrix zonata have taken me from Bollihope Burn in Weardale (see “Bollihope Burn in close-up”) to upper Teesdale (see “The intricate ecology of green slime”) and one of the outcomes is this representation based on the diatom-smothered filaments that I observed in Bollihope Burn, close to the sink hole.   The picture illustrates the suggestion that I made in the post about Bollihope Burn – that the switch from “vegetative” to “reproductive” mode leads to less energy being available for the alga to manufacture the slime that it needs to stop epiphytes gaining a foothold.   By intercepting the limited light that penetrates into the water, these algae can shade the host plant to such an extent that it cannot gain the energy it needs to grow.   The mucilage is the equivalent of the “anti-fouling paint” that mariners use to stop barnacles encrusting their hulls.

My image shows a single healthy filament of Ulothrix zonata at the bottom right of the image and, on the left, two filaments of cells that are producing flagellated gametes that will eventually be released.  I write “gametes” with mild trepidation, as they may also be nascent zoospores associated with the asexual phase (see below).   A third filament, in the background, is composed mostly of empty cells that have already released their gametes.   There are no “male” or “female” gametes; any two can combine to form a zygote, so long as they come from different filaments.   This zygote then attaches to the substratum and does little more over the summer.

In my image, the Ulothrix filaments have been colonised by needle-like cells of Fragilaria gracilis, Achnanthidium minutissimum cells on short stalks, and a couple of cells of Gomphonema pumilum.   There are also a couple of cells of Ulnaria ulna and some zig-zag colonies of Diatoma tenuis.   The effect of these cells on the appearance of the Ulothrix zonata is marked, smothering the filaments entirely so that, with the naked eye, the assemblage appears brown rather than green.

The diagram below summarises the life cycle of Ulothrix zonata and emphasises the point that the green filaments that most people associate with this alga are only a small part of the story.  The cell contents divide in one of two ways.  The first produces zoospores, each with four flagellae, which are released, settle and grow directly into a new vegetative filament.  The second, however, produces a number of cells which are smaller but otherwise look similar to the zoospores except that each has two rather than four flagellae.  These gametes then fuse with gametes produced by another filament to produce a “zygote” which, in turn, germinates to produce several (typically eight) zoospores, each with four flagellae, from which new vegetative filaments grow (see illustration of putative “germlings” in “The intricate ecology of green slime”).

The life-cycle of Ulothrix zonata, following Lokhorst and Vroman (1974).   “2n” refers to diploid stages; “n” refers to haploid phases (note that the vegetative filament is also haploid).

The asexual phase can be produced at any time, but is stimulated by high temperatures; the sexual phase, however, is more strictly regulated.   The formation of gametes only occurs under “long day” conditions, which means that it will happen as daylight hours extend in the spring.   By contrast, the division of the zygote requires short day conditions and low temperature, meaning that the zygote is relatively inactive over the summer months, only dividing to produce zoospores, and ultimately, new filaments, in late autumn and winter.   This creates a useful niche for the organism during a period of the year when nutrients are relatively plentiful in upland rivers (as they are washed off the land following rainfall) and grazers are relatively inactive.   It also means that this apparently simple green filament actually has some sophisticated controls that regulates how and when it divides.

I’ve talked about algal life cycles in the past, commenting that the concepts behind these are not always easy to grasp (see “Reflections from the trailing edge of science …”).   The problem is that undergraduates of my generation were taught this as part of a broader overview of plant evolution and the variations between patterns in different groups tended to befuddle rather than enlighten students already struggling to grasp the big picture.   The interesting twist to my explorations of Ulothrix zonata is that it has shown how the idiosyncrasies of an organism’s life-cycle can have a practical significance that helps the organism survive in a particular habitat.   Knowing about the life cycle can, in turn, inform our understanding of processes occurring within a stream or river.  The problem is that these topics have largely fallen off the agenda both for teaching and research, so we are generally limited to interpreting descriptions from old journals, and often forget completely the role that these factors may play in creating the mosaic of algae in a stream.

Reference

Lokhorst, G.M. & Vroman, M. (1974).  Taxonomic studies on the genus Ulothrix (Ulotrichales, Chlorophyceae) III.  Acta Botanica Neerlandica 23: 561-602.

* “Bhavacakra” is a symbolic representation of the cyclical nature of existence used in Tibetan Buddhism.  The title of this post is also an affectionate tribute to Brian Moss, who died a few days ago.

Hilda Canter-Lund competition shortlist 2016

Organising the annual Hilda Canter-Lund competition to find the best photograph of algae is one of the pleasures of my year and the shortlist for the 2016 prize is now online.   Choosing a shortlist this year was more difficult than usual, but we finally arrived at a set of images that spans marine and freshwater habitats and feature organisms which range in size from microscopic single cells to giant kelps.

Jamie Canepa’s image Adaptation in Action (left above) continues a trend in the competition of showing symbiotic relationships between algae and other organisms, in this case sea anenomes, photographed near Cape Sebastian in Oregon.   John Huisman (right above), a former winner, shows a different type of relationship, with a filament of the Xanthophyte genus Vaucheria that has been parasitized by a rotifer (“Unwelcome guests: Vaucheria gall”).

The organism exploiting algae in Dani Machlis’ image(left above) is humans (“algae tubes”).  He shows algae being grown for the biotechnology industry (in this case, a flavour and fragrance company based in Israel).  Leah Reidenbach’s image (“A white Christmas in the Sea”) returns us to the natural world, showing sunlit blades of the giant kelp Macrocystis pyrifira at Monterey Bay, California.  The white flecks in her image are “marine snow”, microscopic particles of organic material that become stuck together to form visible flecks of “snow” partly due to natural polymers produced by algae.  Leah’s image, therefore, spans some of the smallest and largest members of the algal world.

Tiffany Stephens takes us to the edge of Antarctica for a beguilingly simple yet elegant composition (“Swell Life”) showing the intertidal zone of Snares Island, 200 km south of New Zealand, dominated by the brown alga Durvillaea antarctica.  Finally, Petr Znachor’s image pulls us back from the macroscopic to the microscopic world, and from marine to freshwaters with his image “Freshwater phytoplankton dominated by desmids” showing algae found in a routine sample from a reservoir in the Czech Republic.  This near-abstract composition is very much in the style of Hilda Canter-Lund herself.

I get real pleasure from watching the entries for each year’s competition arrive in my in-box, because the competition sits at the junction between art and science and I can be both entranced and educated by a single picture.   The diversity of the algae, along with their worldwide distribution, means that no-one has such a comprehensive grasp of the field that they cannot be surprised by a particularly intriguing image.  And the range of patterns within the algae allows photographers to push at the boundaries between “representation” and “abstraction” and submit entries that are far from run-of-the-mill natural history photography.   The final twist comes from seeing which of these images will gain the ultimate accolade.  The Council of the British Phycological Society vote to decide the winner and it is never easy to predict which of the shortlisted images will attract the most votes.   The result for this year’s competition should be in before too long; meanwhile, have another look through the shortlist, and choose your own favourite …

What has the EU ever done for us?

This is the text of an article published in the Quaker magazine The Friend on 12 May as part of my contribution to the debate on the UK’s membership of the European Union:

I should declare my interest in the outcome of the EU referendum: my work involves helping clients (government agencies, mostly) translate European environmental legislation into practice.  I once tried to explain this to Enoch Powell.  His put his face close to mine and, eyes blazing, spat contemptuously “what business of theirs is it if we poison our rivers?”

It was a fair question.  If I was a Dutchman, I would have pointed out that all of our major rivers rose elsewhere and received effluents from sewage works and industries in several other EU States before crossing into their territory.   Were I Swedish, I could point to the role of EU legislation in reducing emissions from power stations elsewhere in the European Union, leading to less air pollution blowing over their territory.  But what about the UK?   We have a short land border with the Republic of Ireland, mostly running through rural areas.  Other than that, the patterns of North Sea currents mean that our coastline is less affected by pollution from the River Rhine than by our own rivers, and the prevailing winds from the Atlantic mean that it is our pollution that blows to continental Europe and Scandinavia, not the other way around.  There is, relatively speaking, less direct benefit to the UK’s environment than is the case for many other countries.

Environmental management can be summarised as devising a path from where we are to where we would like to be.  That destination might be expressed in the language of science but it is tangled up with a slew of social and cultural factors.   Ambition, in many cases, is tempered by what is perceived to be the Art of the Possible, framed by a collective vision.   An environmental regulator responsible for a densely-populated region with a long history of urban and industrial development will, rightly, gain a sense of achievement from any significant movement towards a cleaner environment.  And the Environment Agency in England has made considerable progress over recent years.  But “better than before” is not the same as “good enough” and where European Union legislation goes beyond what the UK alone can achieve it is by establishing this collective vision.

But regulation of the environment the UK as a whole suffers from a more systemic problem: the lack of clear policy separation between agriculture and the environment.   It is, of course, foolish to pretend that environmental policy does not have implications on agriculture, or vice versa.  The problem is that the ambition for the environment can never be entirely separated from issues of farm income or food security.  What may be presented as joined-up thinking on rural affairs may also end up as a fudge.  Far better to lay out the ambition and then make cogent arguments for why that ambition may need to be balanced by pragmatism.

That, to me, is the biggest advantage of the EU to the UK: it brings a clear ambition for sustainable development, based on a continent wide view, independent of views of other sectors.   My point is not that these other viewpoints are not important, or that there may be situations where they have to take priority.   It is that we must not let these sectors influence the setting or implementation of environmental targets.   The accommodations that are necessary to make high principle rub up against reality can be dealt with by derogations within the legislation (as is the case in the Water Framework Directive, for example) rather than by fudges during the process of policy development.

But this debate is less about the minutiae of legislation, whether environmental, trade or any other sector, than it is about how the UK sees itself in relation to the rest of Europe.  The logic of pulling back from international co-operation at a time when national boundaries seem to be increasingly irrelevant, defeats me.  The environment epitomises this: a crude analysis suggests that the UK gains fewer tangible benefits than some other countries, yet this misses the point.  The true benefit of Europe to the UK’s environment is not measured by the absence of negative effects, so much as by the share that we hold in a collective vision that is greater than the sum of its parts.

An abandoned lead mine draining into the River Nent in Cumbria: one of many challenges facing the UK environment where we benefit from engagement with the European Union.

Older … but not necessarily wiser?

A stream flowed through Gubeikou, the village beside the Great Wall where we stayed.  It ran in an artificially-straightened channel, crossed by several small bridges, fords and stepping stones and, when I first saw it, a high percentage of its surface area was covered by floating mats of algae.   This, of course, piqued my interest.   However, when I returned the following morning equipped with rudimentary sampling equipment, the locals were busy clearing these flocs out of the stagnant areas.  The prospect of trying to communicate my interest in algae despite an almost total lack of Mandarin was too much and I skulked off, returning later to find a few of these flocs, along with some submerged leaves smothered in algae in a couple of sheltered backwaters.   Even so, the sight of a wuharin (foreigner) peering intently at the less-savoury aspects of their local stream attracted plenty of curious stares from passing locals.

A floc composed of leaves from an aquatic monocotyledon and associated algae in the stream at Gubeikou, Beijing Province, China, April 2016.

Local liquor is the travelling diatomist’s best friend, as it can be pressed into use as a preservative.  However, I did not add any baijiu to this sample, as this would have damaged the green algae that dominated the flocs.   Instead, I stuck the samples into a corner of my suitcase and hoped for the best.   This was rather optimistic on my part as, ten days later, when I finally had a chance to get the sample under my microscope, the green alga had disappeared completely and the sample was dominated by diatoms, particularly chain-forming araphid species, of which I could make out at least two species, even in this raw state.

A chain of diatoms, possibly Staurosira binodis associated with a green algal floc collected from Gubeikou stream, April 2016, along with (at the bottom of the picture), an out-of-focus chain of a smaller diatom.  Scale bar: 20 micrometres (= 1/50^th of a millimetre). 

What I saw when I peered down my microscope at the samples, once they had been properly prepared and mounted, encapsulated many of the challenges faced by the modern diatomist.   Had I collected this sample thirty years ago, I would have confidently named most of what I could see.  The prevailing assumption was that diatom species were mostly cosmopolitan and I would have picked up a copy of Hustedt’s 1930 Flora from my bookshelf and matched the shapes that I saw in my Chinese sample with the illustrations.   However, looking at the sample through a mind conditioned by the developments over the past thirty years, I see subtle deviations from the outlines with which I am familiar, and I start to wonder …

It doesn’t help that the most abundant group in the sample from the algal floc were chain-forming araphids of the genera Staurosira and Pseudostaurosira, a group where there is much uncertainty over species and generic limits even within the geographical areas that I do know quite well.   The sample does, nonetheless, illustrate a principle that I discussed last year as, once again, we see several of these closely-related forms occurring together in the same habitat(see “When is a diatom like a London bus?”).   It suggests to me that, whatever the subtleties exist in species composition, the same general factors are ordering the community, whether in western Europe or China.   The sample from the submerged leaves had a quite different composition, dominated by Nitzschia species.  Some of the species looked familiar but at least two of those are known to be complexes that have still only been partially unravelled.

Chain-forming araphid diatoms associated with a green algal floc in the stream at Gubeikou, Beijing Province, China, April 2016.  a., b.: Staurosira cf. binodis; c.,d.: Pseudostaurosira cf. elliptica; e.,f.: Fragilaria capucina.   Scale bar: 10 micrometres (= 1/100^th of a millimetre).

That there are patterns in the distribution of diatoms seems to be beyond dispute. There has been an enormous amount of research on this topic in recent years, much of it in reaction to a paper by Bland Findlay and colleagues who argued that biogeographic concepts were of limited applicability to microscopic organisms.   Yet we also know that some species are cosmopolitan, and the situation is further complicated because most diatomists base deductions about distribution on morphological criteria (what the [dead cell] looks like) and assume that this aligns with the biological species concept (ability of interbreeding pairs to produce fertile offspring) without further testing (the papers listed below are amongst the exceptions).   Finally, the limited geographical scope most studies, coupled with the prevailing belief that biogeographical variation exists, means that it is too easy to assume that a species has a restricted distribution.  It raises interesting questions about what we mean by a term such as “species” when considering diatoms, but that question will have to wait for another day.

My bigger concern is that the diatomist sees ecology in terms of nouns, whereas the dynamic systems that we study (and whose condition we are expected to advise upon) are perhaps better envisioned as a series of verbs.   Seen like this, the taxonomic complexity that diatomists love to unravel distils down into little more than a source of energy for the next trophic level.   Biogeographic differences only become important when they affect this flow of energy and, as we are often dealing with subtle variations in shape and size of cells, I doubt that all this taxonomic work will lead to radically different conclusions about the state of the environment.   But I may be wrong.  The problem is that this leads into a vicious circle: to answer questions about the extra information contained in all this diversity, we first have to unravel this diversity.  But this, in turn, takes up time that could be spent asking equally valid questions about ecosystem functioning.  Yet the unstudied diversity may, itself, be a confounding variable in studies on ecosystem functioning.   I’d like to think that diatomists get wiser as they get older; however, I am not fully convinced that this is always the case …

Nitzschia species associated with submerged monocotyledon leaves in Gubeikou stream, Beijing Province, China, April 2016.   a., b.: Nitzschia cf fonticola; c., d.: Nitzschia amphibia (girdle and valve views respectively); e.: Nitzschia palea sensu lato.  Scale bar: 10 micrometres (= 1/100^th of a millimetre).

Reference

Findlay, B.J., Monaghan, E.B. & Maberley, S.C. (2002). Hypothesis: The Rate and Scale of Dispersal of Freshwater Diatom Species is a Function of their Global Abundance.  Protist 153: 261-273.

Rimet, F., Trobajo, R., Mann, D.G., Kermarrec, L., Franc, A., Domaizon, I. & Bouchez, A. (2014).  When is sampling complete? The effects of geographical range and marker choice on perceived diversity in Nitzschia palea (Bacillariophyta).   Protist 165: 245-59.

Trobajo, R., Mann, D.G., Chepurnov, V.A., Clavero, E. & Cox, E.J. (2006).  Taxonomy, life cycle and auxosporulation of Nitzschia fonticola (Bacillariophyta).  2: 1353-1372.

Trobajo, R., Clavero, E., Chepurnov, V.A., Sabbe, K., Mann, D.G., Ishihara, S. & Cox, E.J. (2009) Morphological, genetic and mating diversity within the widespread bioindicator Nitzschia palea (Bacillariophyceae). Phycologia 48: 443-459.

Reflections from the Great Wall

After three days amidst the urban sprawl of Beijing I was ready for an opportunity to breathe some fresh air into my lungs.  This desire was more than amply fulfilled by the next stop on our itinerary: two hours drive to the north of the city, to a small guest house in a village called Gubeikou beside the Great Wall.   My original objective was to find a part of the Great Wall away from the most touristy areas (where the Wall is, in any case, largely a reconstruction rather than original).   Gubeikou surpassed that expectation: the scenery was fantastic and, apart from a custodian, who collected a 25 Yuan fee from us at an isolated milecastle, we walked the wall in complete solitude.

Whenever we paused for breath, we could see the wall snaking across the rugged terrain for as far as the eye could see in both directions. The scale is staggering: I live close to Hadrian’s Wall in the north of England, which is 118 kilometres long; the Great Wall, by comparison, extends for 8,850 kilometres: 75 times further.   The oldest parts of the Great Wall were 700 years old when the Romans started building Hadrian’s Wall, although most of what we see today dates from the Ming Dynasty (14^th century).  Our circumstances – alone in this vast landscape but with the wall ever-present to determine our path – created near-meditative conditions, giving me ample space for my mind to roam and reflect.

Last year I read Nick Lane’s excellent book The Vital Question in which he explained how the membranes around cells are used generate the energy that the cells need.   This, in turn, is necessary if we are to understand how – and where – life evolved.   Nick Lane managed to do this in a way that I, who had been turned off biochemistry at school and university, could understand.   I read his book, however, at the time that tens of thousands of migrants were flowing across Europe, and the analogies between the semi-permeable membranes around cells and the more-or-less permeable borders around countries were hard to avoid.   The Great Wall is nothing, if not a border, yet this is not just a means of excluding people: borders can also help to define the identities of those inside and, by controlling what comes in and out, influence the economy.  Cells generate energy by maintaining gradients across membranes such that the electrons from which that energy is derived flow naturally into the cell.   Maintaining this differential is essential if the cell is to keep conditions inside favourable.   And so it is for countries and their borders.

Any flow depends on a differential, and the movement of migrants is no different.   There are economic migrants (differential in income), refugees from conflicts (differentials in security) and hybrids of the two.   As last summer wore on, political rhetoric also flowed yet reason, I realised, was largely on the side of the migrants.   There was an inevitability to their movement that the political Right, in particular, just did not get.  I had sympathy with the UK government’s policy of putting money into support for refugees in the middle East.  Reduce the differential (i.e. make people feel more secure in the middle East) and the flow should dwindle; however, the momentum last year was too great and the efforts too late.  I had great respect for Angela Merkel and many Germans who were prepared to welcome migrants.   But there are many in Europe – including the UK – who see the solution only in terms of reduced permeability of borders.   What events of the past year have shown is that national borders are flimsy membranes that take great energy to maintain and which have the potential to generate enormous tensions.  Yet these same economic consequences reduce the differential, and that is one way that the flow of economic migrants to Europe will be slowed.   On the other hand, acknowledging that the flow of migrants into a region will have economic consequences is offering the advantage to the nationalistic elements who play on the fears of populace.

These thoughts were put into context by yet another excellent book, Peter Frankopan’s The Silk Roads, which outlines the long history of east-west movement of people and trade between Europe and Asia, and their consequences.  It helps us set the movements we have witnessed over the past year or so into a much broader historical perspective, partly by emphasising how transitory many national boundaries are, but mostly by illustrating how many other mass migrations have taken place over time.  Some were generated by natural events such as famines; others were the consequences of human actions (the Mongol invasions are a good example).   Once again, we see disequilibria in security or basic human needs precipitating movements that seem to be almost unstoppable.   The problem is that such events are sporadic, once a century or less and, as such, difficult to learn practical lessons from.   Our politicians, with their typically short-term vision, enter crisis mode if it happens on their watch, then try to hold back the flow, rather than adapt to the inevitable.

As the poet Steve Turner once wrote: “History repeats itself.   Has to.   No-one listens.”

References

Frankopan, P. (2015).  The Silk Roads.  A New History of the World.  Bloomsbury, London.

Lane, N. (2015).  The Vital Question: Why Is Life the Way It Is?   Profile Books, London.

The final line is the poem “History Lesson” by Steve Turner

Finally, our accommodation in Gubeikou was at the Great Wall Box House, which we can thoroughly recommend.  One wall of the courtyard is, in fact, part of the Great Wall itself.  The rooms are clean and comfortable and they provide excellent vegetarian food and advice on the best routes to explore the Wall in the vicinity.

 

The intricate ecology of green slime …

The first really warm weather of the year was a perfect excuse to visit Upper Teesdale and remind the world that spring gentians are not the only botanical wonders in this part of the world.   Our route to the gentians follows the course of the Tees up from Langdon Beck, alongside Falcon Clints (pictured above) and finally a scramble up beside Cauldron Snout to Widdybank Fell.  Along the way we saw birds eye primrose and butterworts growing alongside the path and, up on Widdybank Fell the spring gentians were approaching their best, and we saw some blue moor grass (Sesleria caerulea) too.  But my eyes were focussed beyond the terrestrial vegetation, and soon homed in on some green films in the river as we were sitting down to eat our lunch.   I had not come prepared for fieldwork today, so had to lean out precariously from the bank to grab a sample which I then had to store in an empty Twiglets bag for the journey home.

Sampling algae in the River Tees near Falcon Clints, May 2016

I had a hunch that I had found some more Ulothrix zonata (see “Bollihope Burn in close up …”) but could not be sure in the field.  The film of algae on the rock surface was slimy, and, as far as I could tell with the naked eye, unbranched, but there are other algae that share these properties and I could not know for sure until I had a specimen under my microscope.   This means that algal natural history lacks the immediacy that is associated with larger organisms and one of my campaigns this year is to see just how much can be achieved with field microscopes.  Today, however, was supposed to be a day off.  Hence the need to requisition a Twiglets packet.

Ulothrix zonata on the surface of a submerged boulder in the splash pool below Cauldron Snout, Teesdale, May 2016.   In contrast to my usual close-up views of the algal world, this was taken with a 300 mm telephoto lens.

The pictures below reiterate the comments I made in my earlier post about the problems we have appreciating the three-dimensional structure of microscopic algae when removed from their natural habitat: the left hand image was taken underwater with my Olympus TG2 camera in macro mode and shows the filaments supported by the fast-flowing water of the Tees; the right hand view shows them collapsed into a gungy green slime on top of a cobble that I have removed from the edge of the river.   It is equivalent to looking at a mass of wracks and kelp smothering a rocky shore at low tide and trying to imagine these as the vertical fronds of a “kelp forest” at high tide.

Ulothrix zonata in the River Tees, near Falcon Clints, May 2016.  Left: close-up view of filaments in situ, taken underwater with an Olympus TG2 camera; right: a cobble removed from the margins of the river.

Looking down the microscope, there were definite signs that this was late season Ulothrix, even if it was not so overgrown as the population I had seen at Bollihope Burn.   First, the chloroplasts were not in a particularly healthy state – earlier in the year they would encircle most of the cell, whereas now they seem to be shrivelled and fill less than half of the cell length.  Second, there were several cells in “reproductive” mode, forming zoospores. And, third, there was an abundance of epiphytes, particularly on those that had already released their zoospores.   Had I come earlier in the year, I would have expected to see filaments virtually free of attached algae.  Now, they were abundant.   Many of the epiphytes were diatoms, similar to those I described from Bollihope Burn, but there were a few groups of a different alga, which I initially thought was either Characium or  Characiopsis but which is more likely to be a germling of Ulothrix zonata that has grown from one of the zoospores.

There are nuances to the natural history of this nondescript green slime.   Studies in the North American Great Lakes have shown that it thrives in high light conditions, in the shallow littoral (less than a metre deep in the littoral) and grows best when the temperature is less than five degrees.   This gives it a window of opportunity in our northern England streams, thriving in the late winter and spring before tree cover reduces the light available.  It is not the only alga that likes cool temperatures, and the quid pro quo of this habit is that it needs to produce copious mucilage in order to stop epiphytes growing on the cell wall and blocking out the light that it craves.   As days get longer and the water becomes warmer, so the organism shifts to a reproductive mode, producing zoospores and, from those, zygotes, that can hunker down and survive the inhospitable conditions that we call “summer”.

Oh yes, we saw a ringed plover too.  Almost forgot.

Ulothrix zonata from the River Tees, near Falcon Clints, May 2016.  Left: vegetative cells with degrading chloroplasts; right: “dead” cells with epiphytic cells that are probably germlings produced by U. zonata zoospores.   Scale bar: 25 micrometres (=1/40^th of a millimetre).

References

Auer, M.T., Graham, J.M., Graham, L.E. & Kranzfelder, J.A. (1983).   Factors regulating the spatial and temporal distribution of Cladophora and Ulothrix in the Laurentian Great Lakes.  Pp. 135-145.   In: Wetzel, R.G. (editor) Periphyton of Freshwater Ecosystems.   Dr W. Junk, The Hague.

Graham, J.M., Kranzfelder, J.A. & Auer, M.T. (1985).  Light and temperature as factors regulating seasonal growth and distribution of Ulothrix zonata (Ulvophyceae).  Journal of Phycology 21: 228-234.

 

David Attenborough: psalmist for our secular age?

David Attenborough, doyen of TV Natural History programmes, celebrates his 90^th birthday today.  I have occasionally been rude about Attenborough and TV nature programming in general in this blog (see “Africa”) but I cannot deny that his ground-breaking series “Life on Earth” had a deep influence on me, and my generation of ecologists, when it was first aired in the 1970s.

I have a theory that David Attenborough is the modern-day successor to King David, the Biblical Psalmist.  Leave aside the disputes about who actually wrote the Psalms for the moment, and just consider his series, Life On Earth, Life in the Undergrowth, The Blue Planet and all the rest – as modern, secular responses to the experiences which inspired the Psalms.   The Biblical David praised with harp and lyre; our modern David uses the television camera.  The awe in a world that the former ascribed to God, the latter attributes to evolution.   We understand creation to be a more dynamic entity than our forebears could ever contemplate and, as such, King David’s God-as-a- noun becomes modern David’s god-as-a-verb:  As scientists, we strive for objectivity in our professional writings yet most biologists I have met still admit to awe when contemplating nature and, in this, there is, perhaps, a vestigial spirituality which the psalmists would recognise?    Even Darwin occasionally lapsed into near-psalmody, most memorably in the “tangled bank” passage right at the end of Origin of the Species.

Souvenirs of my life on earth: a termite colony in Yankari game park, Nigeria, 1990.  The top picture shows a lion, also at Yankari.

To be strictly accurate, the biblical David did not spend much time contemplating nature (look at Job chapters 38-40, if you want a biblical writer contemplating the wonders of the natural world).  Some of my favourite Psalms are those in which the author sits on a dark hillside and contemplates the night sky.   This was cosmology in its most primeval form: gazing in awe at the world around and beyond us, and contemplating its origins, our place in it, and its (and our) ultimate fates.   If this is what a man writes staring up at the cosmos with his naked eyes writes, what would he have written, had he had a telescope?

And just as Biblical David found reassurance in the form of God, so modern-day David offers reassurance in the form of science.   His confident delivery offers us a somewhat optimistic view of a world whose mechanisms are understood by scientists.  To my mind, this means that the complexity – and our lack of understanding – of the more prosaic “back room staff” of ecosystems is underplayed.  This, however, would distract from the visual splendours that keep the viewers entranced.   The scientist, as portrayed by Attenborough (he always looks the part!) needs to slot neatly into the hole where, in pre-Enlightenment times, God sat.

The poetry of the Old Testament extends into the writings of the prophets, and so it is today.  It should be no surprise that the medium that has done so much to reveal the wonders of the natural world to us is also an effective platform for highlighting the threats that the world faces.  Again, I have my concerns (see “The one where the author gets sentimental about pandas … almost”) but Attenborough has probably done as much as anyone in the English-speaking world to get climate change and habitat loss, in particular, onto the political agenda.   This means that he is more than just a David for our age; he is also a Jeremiah.   If, however, the authorities of our time decided that Attenborough, like Jeremiah, should be tossed into a well, we can be reassured that he would probably find enough of interest at the bottom to make yet another programme …

Souvenirs of my life on earth: mudskippers in a mangrove swamp near Oron, southern Nigeria, 1990.   You can also see some chocolate-brown diatom films on the mud surface.

 

Bollihope Burn in close-up

Bollihope Burn does not disappear dramatically down a single swallow hole in the way that Gaping Gill swallows up Fell Beck on the slopes of Ingleborough.  Rather, there is a gradual diminishment of flow, as the river percolates through the joints in the limestone, before the remnants of the stream swirl down a final sinkhole (see “Co. Durham’s secret Karst landscape”).   I was intrigued to see how the organisms that inhabited Bollihope Burn reacted to these stresses so got down on my knees close to this final sinkhole to get a closer look.

My waterproof Olympus TG2 (see “Getting close to pearl mussels with my underwater camera”) set to super-macro mode is equivalent to putting my head under the surface of the water and then peering at the rock through a magnifying glass … but gets fewer odd looks from passers-by.   Fortunately, this is an isolated corner of Weardale and passers-by were limited to a few rabbits, because sticking a camera into a stream to take a photograph of a stone is, itself, odd enough to attract stares from most people.

These close-up views of freshwater algae in their natural habitat continue to surprise me.  It is only in the last few years that waterproof digital cameras with macro facilities have fallen to an affordable price.  Before this, underwater photography required special kit that few freshwater biologists could afford.  Yet, removing a stone to photograph the algal growths meant that the algae were never photographed in their natural habitat, and were deprived of the buoyancy that the water afforded them.   I have plenty of photographs of green or brown gunk composed of different algae but, with the algae removed from their context, these photographs offer few insights into the biology of the stream bed.  The photograph below, however, shows a community with a distinct structure – a “turf” of near-vertical filaments waving in the gentle eddies of the stream as it swirls around before disappearing down the swallow hole.

A cobble in Bollihope Burn, close to the swallow hole, covered by a short “turf” of algae, April 2016.   Scale bar: approximately two centimetres.

Under the microscope, the structure of this “turf” starts to reveal itself.   The filaments appear to be aggregations of diatoms around dying filaments of the green alga Ulothrix zonata.   This is an alga that is common in Pennine streams in the winter and early Spring but which disappears as the weather starts to warm up. It often forms very conspicuous green patches on the river bed for a short period of time, as in the following picture, which I took a few kilometres away from my current location, in the River Wear at Wolsingham.   The difference in appearance between the alga in the two photographs is mostly due to the Bollihope population being smothered with diatoms whilst the Wolsingham population was virtually a pure growth of Ulothrix.   This may be partly due to the Bollihope picture being taken taken two months later than the Wolsingham image.   Ulothrix zonata produces copious quantities of mucilage and the Wolsingham population was slimy to the touch.  I rarely see epiphytes on this or any other slime-producing algae in their healthy state.   However, Ulothrix is a species that thrives in cold water.   Indeed, a study has shown that when the water starts to warm up and the day length increases, the Ulothrix filaments switch into their dispersal and reproductive modes and that is what may be happening here.   As the rate of photosynthesis declines, so there is less carbohydrate from which the slime molecules can be made and, as a result, less of a deterrence to any diatom looking for a perch.   From now until next winter, Ulothrix zonata will not be very obvious in the streams that I visit.  This is because the zygotes which are produced by sexual reproduction lie dormant until day length decreases and temperature drops.   At this point, they germinate and divide to produce zoospores which, in turn, grow into new Ulothrix zonata filaments.

Growths of Ulothrix zonata on cobbles in the River Wear at Wolsingham, February 2009. 

The photographs taken under the microscope illustrate this well.  On the left hand side there is one of the few healthy looking Ulothrix filaments that I found, with a chloroplast wrapped around the inside of the cell wall   On the right hand side you can see that the chloroplasts have gone, replaced by dark green blobs which are (I think) bundles of gametes awaiting release.   More significantly, you can also see several diatoms around the Ulothrix filament, taking advantage of it to lift themselves up above the rock surface.

The paradox is that these algae are entering their senescent phase just as most of the plant life in Weardale is flourishing.   This is probably not a coincidence: life in cold water means fewer grazing invertebrates and less shade to intercept the precious winter sunlight.   I suspect that algae, once masters of the planet, have gradually adapted and evolved to live a subordinate life, flourishing in those periods of the year when most of us are content to stay indoors.

Ulothrix zonata from Bollihope Burn, April 2016.  The left hand image shows a healthy vegetative filament; the right hand image shows zoospore production and colonisation by diatom epiphytes. 

References

Graham, J.M., Graham, L.E. & Kranzfelder, J.A. (1985).  Light, temperature and photoperiod as factors controlling reproduction in Ulothrix zonata (Ulvophyceae).  Journal of Phycology 21: 235-239.

van den Hoek, C., Mann, D.G. & Jahns, H.M. (1995).  Algae: an Introduction to Phycology.  Cambridge University Press, Cambridge.

Co. Durham’s secret Karst landscape

When I was at school in London, a field trip to see the classic limestone scenery that is a standard part of the geography curriculum involved a major expedition: a week-long journey to the Craven district of Yorkshire where we had our first opportunity to see features described in our textbooks and on the blackboard for ourselves.  Now, an inhabitant of northern England for over half my life, I can get to a miniature “Karst” landscape with a drive of under an hour drive from my home.

Bollihope Burn rises on the moorland between Weardale and Teesdale, and looks like many other small tributaries of the Wear as the water tumbles through a series of riffles towards its confluence with the River Wear near Frosterley.   As is the case for many streams in this area, there are spoil heaps and other relics of the lead mining industry close by the water and, were I to look closely, I am sure that I would see evidence for their malign effect on the ecology of the stream.   A couple of kilometres above the confluence with the Wear there is, however, a rather more serious problem for the fish and other aquatic life: a complete absence of water.   Scrabbling down the bank into the dry stream bed and walking upstream for a short distance, I can start to hear the sounds of a babbling brook again and, on turning a corner, see the stream as it disappears through a series of swallow holes.

Bollihope Burn at approximately NZ 034 362, as it disappears down a swallow hole, with the dry river bed beyond.

Walk a short distance downstream and more “Karst” landscape features are on display.   The dry river channel continues over a waterfall and then in a steep gorge, which once was an underground cavern created as the water eroded away the limestone.  Just at the point where the stream should have tumbled over the waterfall, the limestone is darker and close examination reveals a patterning of lighter-coloured fossils.   This is the famous but misnamed “Frosterley Marble”; it is, in fact, a dark-coloured variant of the Great Limestone that is common in the Pennines.   The most prominent fossils in the rock are corals and crinoids, reminding us of the origin of these rocks in shallow, warm tropical seas of the Carboniferous period over 300 million years ago.

Bollihope Burn showing the dry waterfall in the foreground and the collapsed cavern in the background.

A polished block of Frosterley marble beside Bollihope Burn, April 2016.

The fine grain of this particular means that it can be cut and polished to give the appearance of marble, although a geologist would reserve this word for particular metamorphic variants of limestone.   There is no true marble in northern England, and the Frosterley marble is a fine substitute, cropping up in several places including, most famously, Durham Cathedral, where columns (probably quarried from the bed of Bollihope Burn) support the roof of the Chapel of Nine Altars and the rood screen.   Much great architecture (and certainly that which blends most sympathetically with the landscape) is really just a rearrangement of local geology.

However, I did not make this journey to muse about landscapes and geomorphology.   The time has come to unpack my sampling equipment and take a closer look at the life in Bollihope Burn.   That will be the subject of my next post …

Pillars of Frosterley marble in Durham Cathedral.  Left: in the Chapel of Nine Altars; right: part of the rood screen between the nave and choir.