Promising young algae …

Spring has arrived in Cassop Vale.  Leaves are appearing on many of the trees and the ground vegetation has the green flush of a new beginning.   More importantly, the herd of emo-fringed highland cows have been moved away, to give the plants more chance of flowering, and there is some warmth in the sun in the middle of the day.

From my point of view, the biggest change since I was last here is the appearance of an extensive floc of green algae covering much of the pond’s surface.   I had a hunch, from their appearance, that these would be predominately Spirogyra, but was not expecting the sight that greeted me when I put a small piece of a floc under the microscope. 

Flocs, predominately Spirogyra, in the margins of Cassop Pond, April 2021.

I find Spriogyra and its relatives quite regularly on my travels, but usually in the vegetative state.  It is relatively unusual to find them as they undergo sexual reproduction (see “Fifty shades of green …”).  But there was plenty of evidence of this process (termed “conjugation” in Cassop Pond’s green flocs.  There were plenty of vegetative filaments, each about 20 micrometres wide and with a single helical chloroplast.  But there were also many ellipsoidal zygotes apparent.   When I looked more closely, these were inside filaments which were linked to an adjacent filament by a narrow tube.   What started out as an early morning natural history trip has turned out to be the algal equivalent of Saturday night on Newcastle Quayside.   

For those of you unused to dating, Spirogyra style, here is a quick guide.   First, put on your best helical chloroplast (two or more, if you are daring), then head out to find a partner amongst the many other filaments in your particular floc.   Little is known about Spirogyra’s preferences, but we can assume that many species are not heterosexual, so don’t be shy: sidle up to any filament you fancy.   He/she/it might well play hard to get at first, so maybe you need to drop a hint.  Make sure your potential date gets a whiff of your aftershave (that’s what I assume “hormonal interactions between the paired filaments” means).  If he/she/it gets the hint, then you can indulge in a little mutual meiosis to get yourselves into the mood.    

Spirogyra from flocs in Cassop Pond, April 2021.   a. vegetative filament; b. two filaments undergoing sexual reproduction with zygotes in the lower filament.   Narrow filaments of Aphanizomenon gracile are also present.   Scale bar: 20 micrometres (= 1/50th of a millimetre).  

Now we’ve got that all-important emotional (okay … hormonal) connection, it is time to get physical.   An embarrassing bulge appears on the side of your filament but, fortunately, a similar one should appear on the side of your date’s filament at about the same time.   Eventually, these fuse to form a tube that links you both together.  The correct term for this is the “copulation canal” which is as frank as it is alliterative (it could also be called a “tupping tube”, I guess?). The protoplast of both cells now contracts and one (the “boy”, for want of a better analogy) crawls, amoeba-like, through the tube and fuses with the “girl” protoplast to form a zygote.  That’s as far as our frisky filaments in Cassop Pond have got.  If our phycological peep-show continued for longer, we would see the green zygotes gradually become brown in colour as thick, resistant walls grew around them, and the cell contents were processed into starch and lipid-rich food reserves.   They would then sink to the bottom of the pond and rest, dormant, until conditions were ripe for its germination.

Features of Spirogyra conjugation: a. a vegetative cell in one of the two aligned filaments; b. conjugation canals developing between the aligned filaments; c. a zygote.  Scale bar: 20 micrometres (= 1/50th of a millimetre).  

Why here, why now?   Nitrogen limitation has been quoted as one of the triggers for conjugation and the presence of a nitrogen-fixing cyanobacterium (Aphanizomenon gracile) plus nitrogen-fixing diatoms (Epithemia– see “Working their passage”) in the pond at the same time lends support to this hypothesis.  Also, the yellow-green appearance of the flocs is also a hint that they may be nitrogen-limited.   However, there are also reports of conjugation happening on a predictable annual pattern in some locations.  The two possibilities are not mutually exclusive, we should remember.  

Meanwhile, on dry land, there are plenty of other plants getting down to the complicated business of reproduction too.   We saw goat willow (Salix caprea) and hazel (Corylus aveana) as well as lesser celandine (Ficaria verna) in flower, and leaves of primroses yet to bloom.   You can read more about those here.   Just remember, when enjoying the sight of spring flowers, that the botanical bacchanalia takes place in less obvious ways in the water too.

Some other highlights from this week:

Wrote this whilst listening to:  Horses and Easter by the Patti Smith Group (see below).   And a 1977 BBC “Sight and Sound in Concert” recording of Jethro Tull, which I remembered seeing when it was first broadcast.

Cultural highlights:   The film Black Bear – a rather dark and challenging, but ultimately rewarding, film.

Currently reading:  Just Kids, by Patti Smith.  Best read with Horses and Easter as a soundtrack.  The geographer in me also reads it with a map of New York to hand, as it is a book with a very strong sense of place.

Culinary highlight:.our local Indian restaurant makes a rather good lamb shank, cooked in aromatic spices which, with basmati rice and a side order of bhindi, is just about unbeatable.

Of microbes and mountains …

I spent a few anxious days last week watching the weather forecast in anticipation of fieldwork.   It was not clear from the forecast whether there would be enough rain to lift river levels to a point where I could not safely collect samples or if, rather than rain, there would snow, which may make the roads slippery but would, at least, mean that river levels were low.  The best I thought I could expect was to be working in near freezing conditions amidst flurries of snow, so it came as an unexpected surprise to find clear skies and sunshine even if April water temperatures were still bitingly cold.   The photograph at the top of the post shows Wastwater, looking towards Scafell Pike and Great Gable on a cold but still April morning, but the focus is on the River Irt, about 500 metres or so downstream from the outfall from the lake.   The landscape overlooking the lake is spectacular but, on a different scale, the subaquatic landscape that I see when I peer at the bed of the River Irt through my aquascope, is equally spectacular, albeit on a vastly smaller scale. 

Underwater landscape in the River Irt, April 2021, with green algae (a.), mosses mixed with Cyanobacteria (b.) and diatoms (c.).   The foreground of the picture frame is about a metre in width.

The flocs of green algae are mostly composed of Spirogyra whilst the mosses and cyanobacteria combos in the background are the same as those that I wrote about in “Tangled up under blue skies” a couple of months back.   The diatoms in the front foreground are the most intriguing.   Here, as at several other locations, we could see and feel distinct biofilms on rocks, but our measurements of chlorophyll concentrations were nearly always very low.  The answer became clear when I looked at some of the biofilm under my microscope: the dominant diatom in these biofilms was a long-stalked form of Gomphonema; probably the same one that I wrote about in “Diatoms and the space-time continuum” a few years back.   The biofilm that covered the patches where other algae and mosses were not dominant was composed mostly of the polysaccharide stalks, with the photosynthetic cells forming a surface layer.  From the point of view of any subaquatic grazer, this roughly equates to a piece of bread with a thin smear of marmite on top.   However, the tangled mass of stalks also works well as a means of trapping organic and inorganic particles that are in transit through this part of the river, and most of the invertebrates that live on stream beds are not particularly fussy about precisely what is on the menu.   I have no data to back this up, but my hunch is that these diatoms make a bigger contribution to the diet of these bugs through these trapped particles than they do through the energy that they have created from trapped sunlight.  

Gomphonema on long stalks, along with a few Achnanthidium, from the River Irt, April 2021.  Scale bar: 10 micrometres (= 1/100th of a millimetre).  

With samples from the River Irt safely packed into the cool box, our field work was finished and, as it had already spilled into the weekend, we felt no compunction about heading back to explore the mountains that loomed over Wastwater.   Our target today was Great Gable, a steep pull up from Wasdale, but a climb that rewarded us with striking views of the lake and the famous screes.   Having started our walk with blue skies and cotton wool clouds, it also gave us a panoramic view of the changing weather as clouds blew in and showers fell along the west Cumbrian coastal plain.   We encountered a few flurries of snow as we approached the summit of Great Gable, but not enough to obscure a view which extended to Windermere to the east, Skiddaw, Helvellyn and Blencathra to the north-east and Crummock Water and the Liza valley to the north.  Somewhat to my surprise, Ennerdale Water was not quite visible from the summit.

The view back along Wasdale towards Wastwater from the flank of Great Gable, April 2021.

We made a steep descent to Styhead Tarn, then followed the track back to Wasdale, passing a group of intrepid mountain cyclists on the way up variously pushing and carrying their bikes.  We could still see showers in the distance but the snow flurries we encountered on the way up did not seem to have come to much.  Consequently, it was a surprise to us when, having driven out of Wasdale and back to our accommodation in Ennerdale, we saw the flanks of the hills around Great Gable to be covered with snow.   Last April, we were basking in unseasonably warm weather at the start of the first lockdown; a year on there is snow, and not just on the high fells either.   Nature continually surprises us, on a whole range of scales, from the minute to the enormous.  That’s what keeps pulling us back.

Wrote this whilst listening to:  Déjà vu, by Crosby, Stills, Nash & Young.

Cultural highlights:   The film The Mauritanean, about the longest serving prisoner at Guantanamo Bay.  

Currently reading:  Spring Has Not Been Cancelled: David Hockney in Normandy, by Martin Gayford.  Reflections on landscape painting by an undisputed master.

Culinary highlight: probably has to be the sandwiches we ate on the way up Great Gable, mostly because of the spectacular views that accompanied them.

Snow over the fells to the south of Ennerdale Water: Heather’s photo taken on the evening of 10 April after our ascent of Great Gable (just out of frame).

A multicoloured rock stop …

Our route to Cassop Pond is rural but certainly not natural.   That’s the way with much of County Durham’s landscapes: the economic history of the area is based around extractive industries and those parts that were not mined for coal were most likely quarried. That’s particularly the case in the immediate vicinity of our house, overlooked by the scarp face of the Permian limestone.  There is a large working quarry beside the footpath we follow but, even when we have left that behind, it took some time to realise that another path we followed, overhung by trees on both sides to form a natural tunnel, was an ancient, long-abandoned wagonway.  This leads to the edge of Cassop Vale, where there are also signs of quarrying but, en route, passes through what is either another abandoned quarry or a man-made cutting for the wagonway.  Or both.  Why not get a return from the back-breaking endeavours of flattening out the route that rock-laden wagons will have to take?  

Splashes of colour on the exposed rock in the cutting also drew our attention.  Some of this was the orange-yellow of the alga Trentepohlia aurea that I have written about before (see “Fake Tans in the Yorkshire Dales”).  However, there were also patches with a brick-red colour that, under the microscope resolved into a different species, Trentepohlia umbrina (see “Cassop Vale, Febrary 2021”).   Above there are blackish patches of Gloeocapsa alpina (see “The mysteries of Clapham Junction …”) and, if you look closely, you’ll see some green patches too (see “Little round green things …”).  That’s at least four different terrestrial algae within about a metre of one another.

The quarry / cutting bordering the wagonway near Cassop Vale (NZ 3369 3820).   The image on the right shows a close-up of the exposed limestone.   a. orange patches of Trentepohlia aurea; b. brick-red patches of T. umbrina; c. black patches of Gloeocapsa alpina.

I confess to having walked along this footpath several times without ever really noticing what was right in front of my eyes.  That brings to mind a quotation from Henry David Thoreau: “It’s not what you look at that matters, it’s what you see”.   Seeing is a process that is as much to do with the brain as it is to do with patterns of light falling on the retina.   And, at the same time as I notice that there are four species of algae on this outcrop, I have to acknowledge that there is so much more to this narrow track than I have realised.  I am aware of the rich diversity of limestone plants, largely because Heather points them out.   We notice several of the birds, either by sight or by their song and she is getting better at spotting and naming butterflies.  Then there are the fungi: the larger ones on trees we notice but we read Merlin Sheldrake’s Enchanted Lives recently and this made us conscious of the rich diversity of this group – and their many important roles in ecosystems.  

Gloeocapsa alpina from the rock face near Cassop Vale.   Scale bar: 10 micrometres (= 100th of a millimetre).  

Our local countryside, in other words, offers us both a sense of stability, via nature’s predictable rhythms, but also the opportunity to encounter the unexpected.   The unexpected arises from two directions.   The first is an intrinsic capacity for nature to change and surprise us – for a species of plant or bird to disappear or another to appear at a location for the first time.  But there is also a capacity that lies more with us, as observers, than with the habitat itself.  That is for us to notice details that had been there all along but which we had overlooked, perhaps because we were rushing along, perhaps because we lacked the awareness that allowed the patterns that fell on our retinas to make the necessary connections in our brain.   Noticing that we’ve noticed something that we should have noticed before is doubly important, especially when this happens in our own backyards, because it makes us realise how little we know, even about the habitats we think we know best.

Wrote this whilst listening to: various live sets on YouTube by P.J. Harvey.

Cultural highlights:   Brilliant new film, Munari, about a Korean family’s attempts to farm in a remote corner of Arkansas.   Little House on the Prairie, but with Asian, rather than European settlers.  

Currently reading:  Lila, by Marilynne Robinson.  

Culinary highlight: homemade samosas, eaten al fresco on Stannage Edge, Derbyshire with daughter and partner: our first face-to-face meeting this year.