Algae from the Alto Duoro …

From the highlands of Serra da Estrela w headed north-west towards the vineyards of the Duoro Valley from which the grapes that make port are picked.  I’m supposed to be on holiday but, as the narrow road twists and turns down a steep hillside, with vineyards on both sides, I see a case study in how humans alter rivers and their catchments to suit their needs.  I wonder if the passengers on the cruise ships that move sedately through this beautiful landscape have any idea of just how difficult this same journey would have been just fifty years ago.   Now there are 51 large dams within the watershed, regulating the flow and, at the same time, generating much-needed hydroelectricity.   Before these were in place, the only way to get the port from the quintas in the Alto Duoro to Porto was to load the barrels onto a “barco rabelo”, and then to plot a perilous path through the rapids before using a combination of sail, oars and oxen to make the slow journey back upstream (you can see videos of these journeys on YouTube).

A replica of a barco rabelo moored in the Rio Duoro at Porto, September 2018.

The Rio Douro is a type of river that is rare in the UK but very common throughout the rest of Europe in that it crosses (and, for part of its course, forms) national boundaries.  There are a few rivers in Ireland which straddle borders (the Foyle is one, and some of the headwaters of the Shannon can be found in County Fermanagh) but, mostly, this is a complication that our river managers do not have to face.  By contrast, eighty per cent of the Rio Douro’s catchment lies in Spain (where it is called the Duero) and it is actually the largest watershed on the Iberian Peninsula.   The whole European project, and its environmental policy in particular, makes so much more sense when you are looking at a well-travelled river.

Our immediate objective was the Quinta do Bomfin at Pinhão, which produces grapes for Cockburns’, Dow’s and Taylor’s ports.  However, after a morning walking through the vineyards and following a tour of the winery (the robot that has replaced human grape treaders has, we learned, been carefully calibrated to match the pressure that a human foot exerts, lest the grape seeds are crushed, imparting bitterness to the resulting wine) plus some port tasting, the lure of the river was too strong.

A view across the Douro Valley from Quinta do Bomfin at Pinhão.   This, and the previous two photographs, were taken by Heather Kelly.

The river bank at Pinhão is lined with rip rap (loose stones) enclosed in mesh cages to protect it from erosion from the waves created by the many cruise ships that make their way up the river with tourists.   This, along with the floating jetties at which they embark and disembark, meant that it was not easy to get access to the river; however, I eventually found a small slipway close to the point where a small tributary joins.  There were a few loose stones with a green film in shallow water that I could just reach, plus some algal mats coating the concrete of the slipway at water level.   I managed to get small samples of each to bring back for closer examination, attracting the usual curious stares from passers-by in the process.

The mats on the slipway were composed of an alga (technically, a cyanobacterium) that has featured in this blog on several occasions in the past: Phormidium autumnale (see “In which the spirit of Jeremy Clarkson is evoked”).   This is the time of year when the Douro is at its lowest so living at this point on the slipway means that it spends a small part of the year exposed to the air, but most of it submerged.

Phormidium cf autumnale on a slipway beside the Rio Douro at Pinhão, September 2018.  The left hand image shows the mats on the lower part of the slipway; the right hand image shows individual filaments.  Scale bar: 20 micrometres (= 1/50th of a millimetre).

The stones beside the slipway had a thick greenish film which, when I looked at it under a microscope, turned out to consist largely of bundles of thin cyanobacterial filaments belonging to a relative of Phormidium: Homoeothrix janthina (kindly identified for me by Brian Whitton).   Homoeothrix differs from Phormidium in that the filament are often slightly tapered, rather than straight-sided and usually aggregated into colonies, often growing vertically towards the light rather than intertwined to form mats.   It is a genus that I see in the UK (including, sometimes, in the River Wear) but which I have not previously written about on this blog.   The photos below show tufts of filaments but it would be quite easy to imagine several of these clumps joined together to form a hemispherical colony, before I disrupted them with my vigorous sampling technique.

Left: the rip rap at the edge of the Douro at Pinhão from which I sampled algae in September 2018; right: the stone after vigorous brushing with a toothbrush.

Bundles of filaments of Homoethrix janthina from the River Douro at Pinhão. Scale bar: 20 micrometres (= 1/50th of a millimetre).

Many of my posts try to make the link between the algae that I find in lakes and rivers and physical and human factors in those water bodies and their surroundings.  That is not an easy task in a large river basin such as that of the Douro as there is so much more of a hinterland including large towns in Spain such as Valladolid.   The river, to some extent, integrates all of these influences and, whereas the vines around Pinhão have their roots in nutrient-poor granite and schist soils, the river’s journey to this point has covered a range of different rock types, including chalky clay soils in the Spanish part of the catchment and the water reflect this.   This cocktail of physical alteration and pollution, shaken up with a dash of international relations, recurs in the largest rivers throughout Europe and is either a fascinating challenge for an ecologist or a complete pain in the backside, depending on your point of view.

I’ll come back to the Douro in a few weeks, once I’ve had a chance to have a closer look at the diatoms.  Meanwhile, I have one more stop on my travels along the Rio Douro, at the port lodges of Vila Nova de Gaia to try some vintage port …

Reference

Bordalo, A.A., Teixeira, R. & Wiebe, W.J. (2006).  A water quality index applied to an international shared river basin: the case of the Douro River.  Environmental Management 38: 910-920.

The end of the journey: port maturing in barrels at Cockburn’s lodge in Vila Nova de Gaia.

 

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Transitory phenomena …

Fieldwork in the River Ehen has been an unusually pleasurable experience over the past few months, even to the extent of abandoning waders altogether and wearing just a thin pair of neoprene beach shoes and shorts as I worked.   Curiously, there were few obvious signs of the prolonged period of low flow here, but that is partly due to the pumps installed by United Utilities to keep the river running whilst the lake was drawn down (see “Life in the deep zone …”).   I did, however, find some intriguing green patches on fine sediments at the margins.

Most of the bed in this part of the river consists of much coarser sediments than these which are, I suspect, silt and sand deposited on the occasions when Ben Gill (which joins the Ehen immediately below Ennerdale Water) is flowing.   Current velocity is lower at the edges of the river, allowing fine sediments to settle out and create temporary sandbanks.   One decent spate will be all that is needed, I suspect, to wash much of this downstream.  However, there has not been a period of prolonged high flow for several months and there is, as a result, a thin green mat of algae growing on the upper surface of this sediment.

Mats of Oscillatoria on fine sediments beside the River Ehen just downstream from Ennerdale Water, August 2018.   The total length of the mats in the left hand photograph is about one metre. 

I scraped up a small sample to examine under my microscope.  I was expecting to see the broad filaments of the cyanobacterium Phormidium autumnale which I often find at a site about five kilometres downstream (see “’Signal’ or ‘noise’?”) but what I saw was much narrower filaments, some of which were slowly gliding forwards and backwards.   These belong to a species of Oscillatoria, a relative of Phormidium that is common in the plankton.  A few species, however, do live on surfaces and can, as I could see in the Ehen, form mats.  I have, in fact, described a different mat-forming species of Oscillatoria (O. limosa) from the River Wear close to my home (see “More from the River Wear”) and this, too, had been favoured by a long period of warm weather and low flow.   The filaments in the River Ehen were much narrower – just a couple of micrometres wide – and had relatively long cells (two or three times longer than wide) but, in other respects, they clearly belonged to the same genus.

Microscopic views of Oscillatoria filaments from the River Ehen, August 2018.   The upper photograph was taken at medium magnification (400x) and the lower image was taken at 1000x.  The constant motion of the filaments means that it is not possible to use stacking software to obtain a crisp image.  Scale bar: 10 micrometres (= 1/100th of a millimetre). 

The motion that I could see is thought to be due to a layer of tiny fibres (“microfibrils”) which wind around the inner layer of the cell wall in tight spirals.   Movement is caused by waves that are propagated along these fibres, meaning that the filament actually rotates as it moves (though this is almost impossible to see with a light microscope).   The filaments can move either towards or away from light, depending on the intensity, at a speed of up to 11 micrometres per second (that’s about a millimetre a day or, for any petrolheads who are reading, 0.00004 kilometres per hour).  This allows the filaments can adjust their position so that they are neither in the dark nor exposed to so much light that they are likely to do damage to their photosynthetic apparatus (see “Good vibrations under the Suffolk sun” for more about this).   The result is that filaments will tend to converge, Goldilocks-style, at the point where light conditions are “just right”.  You can see some sediment particles settling on the top of the mat in one of the images and we can expect the filaments to gradually adjust their positions, incorporating these particles, over time.

Last year, I wrote about Microcoleus, a relative of Oscillatoria, which formed mats on saltmarshes and explained how this could be the first stage of colonisation of damp habitats by plants (see “How to make an ecosystem”).   We are seeing the same processes happening here, but the life expectancy of these mats is much lower.  They may well be gone next time I visit, depending on how the Cumbrian climate behaves over the next couple of weeks.   They are transitory phenomena, here today and gone tomorrow but, like the subjects of some of my other recent posts, particularly favoured by the long period of settled weather that we have enjoyed over recent weeks.

Reference

Halfen, L.F. & Castenholz, R.W. (1971).  Gliding motility in the blue-green alga Oscillatoria princeps.  Journal of Phycology 7: 133-145.

Note: you can read more about how the heatwave has affected fresh water in the Lake District in Ellie’s MacKay’s recent post on Freshwaterblog

How to make an ecosystem

I visited Scotland vicariously last week (meaning that I did not actually cross the border but a little bit of Scotland made its way south to me).   In this case, my wife had been reconnoitring potential sites for a field course along the Fife coast and had visited the sand dunes at Tentsmuir National Nature Reserve to see if the plant succession there would make a suitable exercise for her students.  Behind the sand dunes there was a low lying area of saltmarsh and, within that, large areas of algal mats.  I’m guessing that, having brought me a bottle of Highland Park whisky as a reward for not killing her houseplants during her previous trip to Scotland, she thought that my liver deserved a break.

Tentsmuir is a dynamic ecosystem, with sand dunes on the coastal side and, in places, a complete succession from colonising grasses on the seaward side to mature forest on the land.   However, there are also slacks behind the dunes which are periodically inundated by seawater, leading to the development of saltmarshes.   The periodic wetting and drying of saltmarshes is ideal for filamentous algae and these, in turn, create a mesh of interlocking filaments that binds the sand grains and traps organic matter.   Over the course of many tidal cycles, conditions become suitable for higher plants such as glasswort and sea asters.   I have a soft spot for saltmarshes and sand dunes as these are the habitats where I made some of my first forays as an ecologist (see “How to be an ecologist #4”); however, I have never looked in detail at the algal mats before.   So, I poured myself a glass of Highland Park, turned on my microscope and teased out a few of the filaments from my present.

Algal mats from saltmarsh at Tentsmuir National Nature Reserve.  The left hand picture shows a plant of Salicornia europaea agg. (Common Glasswort, or “samphire”) surrounded by algal mats (photo: Heather Kelly).  The right hand picture demonstrates how the mat retains its integrity after being removed from the saltmarsh.

The mat, in this case, seemed to be made up predominately of two types of alga: the yellow-green alga Vaucheria and the Cyanobacterium Microcoleus chtonoplastes.   I often see Vaucheria in freshwaters so it was the Microcoleus that attracted my attention.   It belongs to the same family as the Phormidium that we met in Mallerstang (see “The stresses of summertime …”) and we can see several of the same features: rows of almost identical cells and, in particular, no “heterocysts”, specialised cells that are responsible for nitrogen fixation.   Technically, the chain of cyanobacterial cells is referred to as a “trichome” and these are enclosed in a “sheath” (seen most clearly in genera such as Scytonema: see “Tales from the splash zone …”).  In Phormidium there is a single trichome per sheath but each sheath of Microcoleus contains several, often twisted around each other to form rope-like bundles.

Microcoleus cf chthonoplastes from the saltmarsh at Tentsmuir National Nature Reserve, August 2017.  Scale bar: 10 micrometres (= 100th of a millimetre).

Although I mentioned that Microcoleus lacked heterocysts, this does not mean that it is not capable of nitrogen fixation.   The reason that cyanobacterial cells need heterocysts is that the nitrogenase enzyme only works in anerobic conditions.  The oxygen that is produced as a result of photosynthesis is, therefore, a toxin that needs to be kept away from nitrogenase. Heterocysts have thick cell walls and less chlorophyll as means of keeping the nitrogenase in an oxygen-free environment.  However, some non-heterocystous cyanobacteria, including Microcoleus, are able to fix nitrogen at night (when the photosynthetic apparatus is not pumping out oxygen) .   As there seems to be no protection for the enzyme inside the cells, it is possible that the daily destruction of enzyme is offset by renewed synthesis when light levels fall and there is no more oxygen being produced internally.   Nitrogen-fixation is already an expensive process for cells, requiring a large amount of energy, and this will increase the cost further.  However, in the case of the saltmarsh at Tentsmuir, there is a large amount of habitat available and few other organisms capable of exploiting it, so perhaps this is an investment worth making?

The benefits of that investment then “trickle down” (or up, depending on your point of view) through the ecosystem.   The cyanobacteria “fix” carbon and nitrogen and, in effect, create the soil within which other organisms thrive.  Janet Sprent, of the University of Dundee, calculated that, assuming nitrogen to be the limiting nutrient, then the fixation by Microcoleus and other cyanobacteria in such habitats could probably support the biomass of higher plants that is usually observed.  They are, in other words, a self-perpetuating “green manure” that creates a habitat within which other organisms can thrive.  In turn, by binding sand, they help to stabilise coastal features and, in turn, protect other coastal habitats and the communities that live amongst these.

References

Malin, G. & Pearson, H.W. (1988).  Aerobic nitrogen fixation in aggregate-forming cultures of the nonheterocystous Cyanobacterium Microcoleus chthonoplustes. Journal of General Microbiology 134: 1755-1763.

Omoregie, E.O., Crumbliss, L.L., Bebout, B.M. & Zehr, J.P. (2004).  Determination of nitrogen-fixing phylotypes in Lyngbya sp. and Microcoleus chthonoplastes cyanobacterial mats from Guerrero Negro, Baja California, Mexico.  Applied and Environmental Microbiology 70: 2119-2128.

Sprent, J.I. (1993).  The role of nitrogen fixation in primary succession on land.  pp. 209-219.  In: Primary Succession on Land (edited by J. Miles & D.W.H. Walton), Blackwell Scientific Publications, Oxford.

Sroga, G.E. (1997).  Regulation of nitrogen fixation by different nitrogen sources in the filamentous non-heterocystous cyanobacterium Microcoleus sp.  FEMS Microbiology Letters 153: 11-15.

Tales from the splash zone …

ennerdale_161005_2

Mougeotia was not the only alga that intrigued me in Ennerdale Water during my recent visit (see “Fifty shades of green …”).   Alongside the green tufts, and also just at water level, there were dark spots and patches on the rock that yielded to a gentle scrape with my finger nail.   The colour suggested Cyanobacteria, so I popped a little into a sample bottle to examine later.

stigonema_ennerdale_oct16

Patches of Stigonema mamillosum and Scytonema cf crustaceum growing at water level on granite boulders on the southern shore of Ennerdale Water, October 2016.   The scale bar is approximately one centimetre.

The surprise, when I looked down my microscope, was not that it was cyanobacteria, but that there were at least three genera mixed together.   The first of these was Scytonema cf crustaceum, characterised by a thick brown sheath and the presence of double “false branches”, formed when both ends of a broken filament continue to grow and, eventually, burst out of the sheath (see “Poking around amongst sheep droppings”).   In the image below you can see the narrow blue-green filament of cells within the much broader sheath.

Also present was Stigonema mamillosum, a representative of a genus with a more advanced morphology than other Cyanobacteria, with branched filaments that can be several cells thick (see “More from the River Atma”), and Calothrix sp., which has tapering filaments in a much thinner sheath.   All three genera have the capability to fix atmospheric nitrogen, so thrive in nutrient-poor habitats such as Ennerdale (see also “Both sides now …”).   Calothrix, in addition, is able to scavenge phosphorus from the water, releasing enzymes from the long colourless hairs (just about visible to the right of my photograph).

scytonema_crustaceum_oct16_

Scytonema cf crustaceum from the littoral zone of Ennerdale Water, October 2016.   Scale bar: 20 micrometres (= 1/50th of a millimetre).

stigonema_mamillosum_oct16_

Stigonema mamillosum and Calothrix sp from the littoral zone of Ennerdale Water, October 2016.   Scale bar: 20 micrometres (= 1/50th of a millimetre).

I found superficially-similar growths on rocks on the north east side of the lake, but it was clear, even from the appearance in my sample bottle, that this was something different.  The tangles of filaments from the southern shore of the lake, where I had started, had no other form when suspended in water, than an amorphous blob.  However, the material from the north-east side formed distinct “tufts”.   The superficial similarities continued when I peered down the microscope: once again the chains of blue-green cells were enclosed within a thick brown sheath and, once again, there were false branches.  This time, however, the false branches were single, not double, and formed acute angles with the “parent” filament, rather than the near perpendicular double false-branches that we saw in Scytonema.   These features are characteristic of Tolypothrix (Brian Whitton suggests T. distorta) and it is these acute branches that impart the “bushy” appearance to the colony.   Like the cyanobacteria that I found on the southern shore, Tolypothrix is capable of nitrogen fixation so, its presence here is confirmation of the nutrient poor status of the lake.

tolypothrix_ennerdale_oct16

Tolypothrix distorta (var. penicillata?) from the littoral zone of Ennerdale Water, October 2016.  a: low power view of a tuft of filaments (approximately 5 mm in length); b: filaments showing single false branching (x100 magnification); c: medium power (x400) view of false branch.   Scale bar: 20 micrometres (= 1/50th of a millimetre).

Nitrogen-fixation involves busting apart the strong bonds of atmospheric nitrogen in order that the cell can use the nitrogen to build the proteins that it needs to function.  This requires a lot of energy and, as a result, the investment is only worthwhile if other sources of nitrogen are very scarce.   That energy could, otherwise, be diverted to more useful purposes.  The presence of so many different types of nitrogen-fixing organism around Ennerdale is sending out a clear sign that this is a nitrogen-poor habitat.  Algae such as Mougeotia cannot fix nitrogen, and they presumably have to make other sacrifices (a slower growth rate, perhaps?) in order live alongside these Cyanobacteria.   As far as I know, the energy costs of scavenging phosphorus from organic compounds in the water has not been calculated but the same principle must apply: the cell has to create more of the phosphatase enzymes than normal, in order to produce a surplus that can leak through the cell membrane and react with organic molecules in the vicinity.   Again, that all requires energy that can be used for other purposes.  In contrast to nitrogen fixation, this is an ability that Cyanobacteria share with some other algae including, possibly, Mougeotia.

Finding these algae in a one of the most remote lakes in the country, where the impact of humans is very low, I start to wonder how many of our other lakes would have had such an assemblage of organisms before agricultural intensification and the rise in population numbers.   Nature is, naturally, parsimonious in the way it distributes the inorganic nutrients plants need.   Necessity, we are told, is the mother of invention and the diversity we see in near-pristine habitats such as Ennerdale Water is as much the result of plants and algae finding their own individual solutions to grabbing their share of the scant resources available.   There’s enough here for a BBC natural history documentary … apart from an anthropomorphic mammal or bird.  Which is another way of saying … no chance …