Diatom hunting in the Pirin mountains

I started 2018 peering down my microscope at a sample that I collected whilst in Bulgaria back in the summer.   I have written about my trip to the Pirin mountains before (see “Desmids from the Pirin mountains”) but the diatom sample that I collected from Lake Popovo had remained unexamined since I got back.

I had waded into the littoral zone of this steep-sided corrie lake and picked up a few of the smaller stones, which I had then scrubbed with the toothbrush stowed in my rucksack to remove the thin film of diatoms.  These, like most of the algae that I collect on my travels, get treated to a bath in local spirits to ease the journey back to the UK.  This is not an ideal preservative for soft-bodied algae but is not a problem when your primary interest is diatoms with their tough silica cell walls.  Once I got back, I had them prepared and mounted ready for inspection, but then got distracted by other things and have only just got around to having a proper look.

The two most abundant taxa were the Achnanthidium minutissimum complex (probably at least three species) and Cymbella excisiformis.  Together, these constituted over eighty per cent of all the diatoms in the sample.  Ten years ago, I would have called the organism I was calling Cymbella excisiformis by a different name, Cymbella affinis, but opinions have shifted more than once.  The original Diatomeen im Süsswasser-Benthos von Mitteleuropa has images of C. affinis that are actually C. tumidula, and also describes C. excisa as a separate species.   However, the most recent view is that C. affinis and C. excisa are two names for the same species, with C. affinis taking precedence.   To confuse matters yet further, the population illustrated below shows a gradation of features from “C. affinis” to “C. excisiformis”, suggesting that the use of length:width as a discriminating factor is over simplistic.  Krammer tried to explain his rationale for distinguishing between these species in his 2002 monograph but he uses the name “C. excisa” for the organism called “C. affinis” in our 2017 English edition.  Confused?  You will be ….

Cymbella excisiformis” from Lake Popovo, Pirin Mountains, Bulgaria, August 2017.   Based on Lange-Bertalot et al. (2017)’s criteria of length:breadth 4.2-5.3 in C. excisiformis compared to 3.1 – 3.8 in C. affinis, images a., b. and c. are C. excisiformis whilst d., e., f. and g. are C. affinis.   Scale bar: 10 micrometres (= 1/100th of a millimetre).

This is another good example of points that I have made several times before: that we should always try to identify populations rather than single cells, and that we should treat dimensions stated in the literature as indicative rather than definitive (see “More about Gomphonema vibrio”).    Length:width, in particular, can change a lot during the life-cycle of the diatom.

Species of Gomphonema were also present in the sample.  Though not numerically abundant (none constituted more than one per cent of the total count), they included some large cells which, in addition, have extensive mucilaginous stalks, so their contribution to total biomass is greater than their low abundance suggests.   I’ll write more about the ecology of these species in the next post.   Finally, I also found other Cymbella species, as well as some Encyonema and Encyonopsis, and a few valves of Eucocconeis flexella, a relative of Achnanthidium and Cocconeis which has a distinctive diagonal raphe.

Gomphonema spp. from Lake Popovo, Pirin mountains, Bulgaria, August 2017.   h., i.: G. acuminatum; j.: G. truncatum; k.: unidentified girdle view; l.: G. pumilum.  Scale bar: 10 micrometres (= 1/100th of a millimetre).

There is, at this point in time, no official Bulgarian method for assessing the ecological status of lakes using diatoms so I have evaluated Lake Popovo as if it were a low alkalinity lake in the UK instead.  Using the method we developed, this one sample has an Ecological Quality Ratio of 0.92, which puts it on the border between high and good status.   Looking around the lake, I see no reason why it should not be firmly in high status but, at the same time, I am using an evaluation method that was designed for lakes 2000 kilometres away, so maybe we should not expect perfect results.    However, I have performed similar exercises at other lakes far from the UK and also got similar results (see “Lago di Maggiore under the microscope”) which points to a basic robustness in this approach.

The outflow of Lake Popovo leads into a cascade that ends in the first of a series of lakes, the “Fish Popovski” lakes.   I wrote about the desmids in this lake back in September (see “”Desmids from the Pirin mountains”) and will return to this sample in order to describe the diatoms in another post.   But, meanwhile, the assemblage at Popovo reminded me of the littoral algae in another lake that I really should tell you about …

Miscellaneous diatoms from Lake Popovo, Pirin mountains, Bulgaria, August 2017.   m.: Cymbella sp.; n.: Encyonema neogracile; o. and p.: Eucocconeis flexella (raphe valve and girdle view respectively).  Scale bar: 10 micrometres (= 1/100th of a millimetre).

Lake Popovo, photographed from close to the location from which my sample was collected.  The brass plate on the rock at the right hand side gives the altitude as 2234 metres above sea level.  The photograph at the top of the post shows Lake Popovo against a backdrop of the Pirin mountains.

References

Hofmann, G., Werum, M. & Lange-Bertalot, H. (2011).   Diatomeen im Süßwasser-Benthos von Mitteleuropa. A.R.G. Gantner Verlag K.G., Rugell.

Krammer, K. (2002).  Diatoms of Europe volume 3: Cymbella.   A.R.G. Gantner Verlag K.G., Ruggell, Germany.

Lange-Bertalot, H., Hofmann, G., Werum, M. & Cantonati, M. (2017).   Freshwater Benthic Diatoms of Central Europe: Over 800 Common Species Used In Ecological Assessment (edited by M. Cantonati, M.G. Kelly & H. Lange-Bertalot).   Koeltz Botanical Books, Schmitten-Oberreifenberg.

The UK lake diatom assessment method is described in:

Bennion, H., Kelly, M.G., Juggins, S., Yallop, M.L., Burgess, A., Jamieson, J. & Krokowski, J. (2014).  Assessment of ecological status in UK lakes using benthic diatoms.  Freshwater Science 33: 639-654.

Details of the calculation can be found in the UK TAG method statement.

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The kindness of strangers …

A matter of days after we arrived in Nigeria (see “How to make an ecologist #11”) a battered old Peugeot 504 station wagon pulled up alongside us as we walked from our hotel to get a bush taxi across Jos to the university campus. A North American voice called through the open window (we were later to discover that it never closed properly) and asked if we wanted a lift. We clambered in gratefully, the vehicle crunched into gear and pulled out into the traffic again. As the car lurched forward a whisky bottle rolled across the foot well and the driver, a lean man in his fifties, introduced himself as Alvin, a worker with CUSO, the Canadian equivalent of the Peace Corps or VSO. The whisky bottle, he explained, contained local honey (invariably sold with honeycomb and a few dead bees included). By the time we had made the mile or so journey to the centre of town where our routes diverged, he had invited us back to his house for dinner the following evening.

A week at the Plateau Hotel had been enough to exhaust our enthusiasm for their rather limited menu so we accepted with alacrity and, the following evening, his Peugeot grumbled up the driveway to the Plateau Hotel to collect us for the short drive to his house on the edge of the town where we met his wife Sylvia and ate her home-cooked food. They had had a furniture business in Kenora, Western Ontario, we learned, but had sold up to take a career break teaching in a technical college. Officially, Alvin taught woodwork (which he wryly summarised as showing students how to make long pieces of wood shorter) but he had an unofficial sideline in demonstrating how random acts of kindness made the world a better place. They and we bonded despite the age difference and, at weekends, we joined them in their elderly Peugeot to explore the region.

Fishermen on the River Benue, early 1990.   The photograph at the top of the post shows rock formations near Riyom, south of Jos (but taken some months later, during the wet season).

A few days ago  we heard news that Alvin had died after a long battle with cancer. Once our initial sadness had passed, we found ourselves smiling again as memories that had faded with time reasserted themselves. One trip, in particular, summed-up Alvin’s indomitable attitude, taking us south off the Jos Plateau into the heat of the northern Nigerian plain. I can’t remember the motivation for this trip, only that we spent the night in a guest house belonging to a mission, but only after a hair-raising crossing of the Benue River. Our first approach to the river was presaged by a sudden improvement in the road surface as we drove up an incline towards a very modern-looking bridge before Alvin stood on the brakes to bring us to a halt just before the road ended abruptly with just a few traffic cones between us and a vertical drop.

From this narrow escape we made our way on smaller roads to the ferry, where a narrow barge barely wider than the car itself was tied up with some planks bridging the gap to the steeply-sloping riverbank. At this point, the rest of us climbed out declaring our intention of recording the occasion on film, leaving Alvin to line-up the car at the top of the slope and then to slither down, across the rickety planks and onto the barge.  We followed him onto the barge and were shown into the open boat lashed to the side, from which the ferryman started up the outboard motor and pointed the ferry towards the line of trees that marked the opposite shore.

Boarding the ferry across River Benue, Nigeria, 1990.

We shared the broad river channel with a few small boats carrying foot passengers and a skiff from which a local fisherman and his son were casting seine nets.  There are reports of manatee and hippopotami from the river, though we did not see any, and there are almost certainly crocodiles too, though they kept out of sight.  Our ferry moved slowly diagonally upstream across the broad river channel towards the southern shore where the exercise was repeated (the river bank on this side was far less intimidating) and we were in Benue State.  This was the heartland of the Tiv ethnic group whose distinctive round huts were the subject of one of my very first watercolours.   The Tiv are the fourth largest ethnic group in Nigeria, a farming people, proud of their yams.  Inside the round huts it is easy to imagine the scenes related by the anthropologist Laura Bohannan in her fascinating article Shakespeare in the Bush.

Having got to Tiv country on the Saturday evening we had to turn our eyes back towards Jos if we were to be back in time for work on Monday.   We took a more circuitous, albeit faster, route this time, crossing the river by the modern bridge and heading back along roads lined with mahogany plantations.   We stopped at a roadside stall beside one of these and haggled for a small pestle and mortar, which our Nigerian friends dismissed as hilariously inadequate and which imparted a tinge of brown boot polish to our first few batches of pounded yam.   And then Alvin was changing down the gears so that the Peugeot could haul itself back up to the milder climate of the Jos Plateau and we were passing familiar landmarks again.

A reconstruction of the Tiv village at the Museum of Traditional Nigerian Architecture in Jos, circa 1990. 

Recalling Alvin and Sylvia at this time of year is apt, as hospitality to strangers is an integral part of the Christmas story.  They helped us find our feet and we, in due course (I hope) followed their example with other new arrivals.   After leaving Nigeria they moved to Minnesota, to be close to their children, where we visited them in November 2012 (I watched Bill Clinton’s first election victory from their front room).  Distances were too great to see them regularly but we kept in touch by letter and email.   Though I had not seen him for over twenty years, I felt the bonds we forged in Nigeria were strong and knowing that he is no longer here to share his dry humour and practicality is enough to give me pause for thought.

In pursuit of Bulgarian diatoms …

Our visit to Rila Monastery was one of the cultural highlights of our trip to Bulgaria in the summer (see “The art of icons …”) with the added bonus that it is set amidst some spectacular scenery.   The monastery was founded by St Ivan Rilski (“St John of Rila”) in the 10th century, though the present structures date from the 19th century.   St Ivan, I gleaned from my reading, shared a love of nature with St Francis and St Cuthbert and Rila’s remote location reflects his desire to live the life of a hermit.

Beyond the monastery the road twists and turns amidst the forest that lines the valley.   Occasionally, the canopy is broken by meadows and orchards of apricot and plum trees.  The apricots were ripe for harvest and at an easy height for foraging as we passed by.   We were too late in the year to find many wild flowers in these meadows but the absence of any of the paraphernalia associated with intensive agriculture made us suspect that these would have been a riot of colour in the spring.    Eventually, we came to a small hamlet set amidst a wider area of meadows, where we refuelled at a small café serving the delicious local bean soup (“bob chorba”) before making our way across the meadow to the stream.

A haystack in a meadow near Rila Monestery, August 2017.

The Rila stream itself flowed through a densely-wooded channel, with a variety of substrates from coarse sand to moss-covered boulders.   The larger stones were mostly granite, reflecting the underlying geology of the region, which almost certainly means that the water was very soft.  The surrounding vegetation and low population density also mean that the water is probably as pure as we are likely to find anywhere in Europe.   I had a toothbrush and sample bottle in the bottom of my rucksack and scrubbed a few cobble-sized stones to remove the thin surface film and stowed this for the journey back down the valley.

Sampling Rila stream at Kirilova meadows, a few kilometres upstream from Rila Monestery in August 2017.   The photograph at the top of the post shows the scenery around Kirilova meadows.

It has taken until now for me to get around to looking at this sample, which turned out to have a large population of Gomphonema rhombicum, along with quite a lot of Achnanthidium minutissimum and relatives, confirming my suspicion of a circumneutral, low nutrient environment.   G. rhombicium is a relatively uncommon diatom, so I was intrigued to have a closer look.  It has a similar outline to G. pumilum, which is very common, but is larger and has a distinct broad lanceolate axial area and, consequently, relatively short striae.   The axial area broadens out a little further at the central area, where there is also a single stigmoid.  I wish now that I had had a look at the sample before digestion as many of the larger Gomphonema species have long mucilaginous stalks, whereas G. pumilum and relatives tend to be attached to the substrate by short mucilaginous pads.   I can find nothing in the literature that alludes to the habit of the living cell and, on this particular occasion, am in no position to judge the shortcomings of my peers.

By coincidence, the type location for Gomphonema rhombicum is given as “Appleby, Westmoreland”, which is just over an hour’s drive from where I live.   The most obvious place to hunt for G. rhombicum would be the River Eden; however, the scant details on the ecology of G. rhombicum that I can find suggest a preference for softer water than found here.  This is a geologically-complex area so there is a possibility of suitable habitat existing in a stream in the vicinity.  If the Eden was the location from which the original population of G. rhombicum was collected, then I suspect that it may have been a casualty of the agricultural intensification that has taken place in this area since it was first described.

Cleaned valves of Gomphonema rhombicum from Rila stream at Kirilova meadows, August 2017.  a. – g. show valve views; h. shows a girdle view.  The scale bar is 10 micrometres (= 100th of a millimetre).

That leaves me with just one option: a return to the Rila National Park.  I think I can just about live with that.   We stayed at Hotel Pchelina, a few kilometres down the valley from Rila Monestery and our dinner that evening was the most delicious grilled trout that I have ever tasted.  If a return visit was needed to solve the mystery of Gomphonema rhombicum’s habit then I think that is a hardship with which I can just about cope …

Reference

Iserentant, R. & Ector, L. (1996).  Gomphonema rhombicum M. Schmidt (Bacillariophyta): typification et description en microscopie optique.   Bulletin Français de la Pêche et de la Pisciculture 341/342: 115-124.

Ecology’s bear necessities

I found an old box of slides recently, which took me on a nostalgic journey back to British Columbia in 1980 and, in particular, to a weekend fishing trip with my cousin Steve.  We travelled north from Terrace, where he lived, along a series of unsurfaced roads through dense pine forest, passing the ethereal moonscape of Nisga’a Memorial Lava Bed to the Nass River where we cast lures and caught the salmon which became our dinner a few hours later.   The following morning we followed the road past an impressive Piedmont glacier, through the small town of Stewart and, a couple of miles beyond, passed an unmanned border post and entered Alaska.

The tiny settlement of Hyder sat just beyond the border, beyond which the forests close in again around the gravel track that followed a small stream into the hills.   When we pulled up beside the road and got out, however, the overwhelming sensory experience was not the landscape or even the sound of the stream tumbling out of the hills towards the fjord behind us.  It was the stench of rotting fish.   We were witnessing the spawning and subsequent death throes of the Pacific Salmon.   Unlike the Atlantic Salmon (Salmo salar) which can repeat their migration from the sea to freshwater several times, Pacific Salmon (Onchorhynchus spp.) spawn only once in their lifetime.   Exhausted after the exertions of the migration and what is euphemistically referred to as “big bang reproduction”, the salmon become easy prey for bears, one of whom emerged from the forest a hundred metres or so upstream of where we were standing.

My first encounter with the USA.   The border is at the point where the metalled road ends and the gravel track starts.  The building on the left is the US Customs post.   

You can just make out the bear in the photograph at the top of the post (I’ve also circled in another version at the end).  At the time, my camera was a Kodak Instamatic, which had a semi-wide-angle lens.   We all have two appendages dangling from our hips that make up for many of the deficiencies of a wide-angle lens but, on that stream bank in Alaska, I decided that discretion was the better part of valour.   We watched from afar and the multisensory memory is rather more vivid than the somewhat faded Kodachrome slide that I found in the loft.

That would have been the end of the story except that, in the early years of the new millennium, scientific papers started to appear which turned this spectacle from an item on the wildlife tourist’s bucket list to an integral component of the engine that drives the forest ecosystems of the Pacific Northwest.    These forests, like most natural systems, are hungry for nutrients such as nitrogen and phosphorus and the salmon are, in effect, unwitting suppliers of the fertiliser that the trees need.   The Pacific Salmon spend up to five years in the ocean before moving to their spawning grounds.   Those strong muscles that they need to swim upstream and leap up waterfalls are largely protein which is built from nitrogen-containing molecules.  And nitrogen is, coincidentally, the nutrient that trees need most.

A view across Nisga’a Memorial Lava Bed in the Nass River valley, British Columbia.  The lava was the result of a volcanic eruption in about 1700.  This and other photographs in this post were taken with my Kodak Instamatic, which partially explains their poor quality.

By fishing the dying salmon from streams such as this (and even grabbing the leaping salmon before they get to their spawning grounds – see some spectacular footage from David Attenborugh’s Nature’s Great Events here) the bears become the agents by which the salmon’s nutrients are transferred from the Pacific Ocean to the forests.    It has been estimated that up to a quarter of the nitrogen needs of the forest around these streams is supplied in this way.   Indeed, some have suggested that this transfer of nutrients may be so essential to the functioning of this forest ecosystem that the salmon and bears are, in effect, “keystone species” and that their interaction has an effect that is greater than their contributions individually.

Brian Moss used to use this as a pithy illustration of the need to take a very broad view when managing ecosystems.   We all know that rivers flow into the sea but it is not always so obvious how the oceans can have an effect on terrestrial vegetation far inland.   Similarly, we understand how water flows across land and into stream channels but perhaps we have a hazier awareness of the movements in the opposite direction – from the river channel into the depths of the forest.   Salmon spawning in the Pacific Northwest is one of the world’s great wildlife spectacles, but it should also give us cause to pause and consider the complexities of interactions within natural habitats and, in turn, the dangers of meddling.

One more prosaic lessons that I learned from this short trip: if you are going to the USA, take a passport. Actually, I didn’t need one going into Alaska, but when we returned the Canadian border official had rolled out of bed after his Sunday lie-in  and almost didn’t let me back in!

Another species of hairy wildlife in search of salmon, this time on the Skeena River, British Columbia.   On this particular occasion, the salmon did not oblige and I had my first and only encounter with Kentucky Fried Chicken instead.  

References

Helfield, J.M. & Naiman, R.J. (2006).   Keystone interactions: salmon and bear in riparian forests of Alaska.  Ecosystems 9: 167-180.

Naiman, R.J., Bilby, R.E., Schindler, D.E. & Helfield, J.M.  (2002).  Pacific salmon, nutrients, and the dynamics of freshwater and riparian ecosystems.  Ecosystems 2: 399-417.

Quinn, T.P., Carlson, S.M., Gende, S.M. & Rich, H.B. (2009). Transportation of Pacific salmon carcasses from streams to riparian forests by bears.  Canadian Journal of Zoology 87: 195-203.

The scene near Hyder, Alaska, this time with the bear circled, just in case you didn’t believe me.

Notes from Berlin

Whenever I pass though Liverpool Street Station on the eastern side of London, I always take a moment to pause beside “Kindertransport – the arrival” sculptures by Frank Meisler.   They show Jewish refugee children arriving in Britain with their small amounts of luggage, fleeing from Nazi persecution.   In this age of fear and distrust of migration, they remind me that these fluxes are nothing new, and remind me that we need to show generosity towards the helpless and dispossessed.  As I walked past Friedrichstrasse station during a visit to Berlin last week I saw a companion piece to the Liverpool Street sculptures.  However, the statue at Friedrichstrasse (“Züge in das leben, Züge in den tod, 1938 – 1945” – literally: “trains to life, trains to death”, also by Frank Meisler) differs in one important respect: the German children at the start of their journey are facing in two directions: some are awaiting the Kindertransports to the west but two are heading towards the death camps.

Züge in das leben, Züge in den tod, 1938 – 1945.  Bronze sculpture by Frank Meisler at Freidrichstrasse station, Berlin (photo taken in low light – apologies!).  The photograph at the top shows “Kindertransport – the arrival, also by Frank Meisler, at Liverpool Street Station, London.

Berlin does not flinch at confronting its recent past.   I spent the hour or so between the end of my meeting and my trip out to the airport at “Topographie des Terrors” – a museum on the site of the former Gestapo and SS Headquarters.  It was a reminder of what the children depicted in Meisler’s sculptures were fleeing from.  After a gruelling hour, I was ready for a change of atmosphere and turned towards the Martin Gropius Bau – one of Berlin’s best galleries, just a short distance away.  By coincidence, one of the exhibitions was a series of etchings by Lucien Freud, himself a Jewish refugee (though not part of the Kindertransport).   Freud’s portraits have an intensity that can be unsettling to a viewer; however, seen immediately after my immersion in Nazi atrocities, they had the opposite effect.  I was left wondering how my reactions would have differed had I seen the exhibition before, rather than after, Topographie des Terrors.  The irony of a Jewish refugee’s art being exhibited so close to the former headquarters of the powers that forced him to flee in the first place did not escape me either.

A year ago, I was here on the night that Donald Trump was elected president of the USA (see “Remembrance in Berlin”).   This time, my visit started just a day after the AfD (“Alternative for Germany”) won 74 seats in the Bundestag at the federal elections, becoming the third largest party.   Anger at Germany’s own tolerant policy to refugees was one of the reasons that they did so well, particularly in the former eastern states.   As I write, I am not sure how this meshes with my statement about Berlin’s ability to confront the less savoury aspects of its past.  There is a willingness to do this within the Federal government, and the middle-class, well-educated Germans I meet share a desire to look back objectively.  The rise of AfD is worrying partly because it has happened in a country that has tried so hard to learn from its past.   Let’s hope that Germany does not forget to remember ….

The Martin Gropius Bau rising above a section of the Berlin wall.  Topographies des Terrors is behind the wall.  The right hand image shows the row of cobblestones marking the path of the wall in places where it is no longer standing.