More algae from Shetland lochs …

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I’m taking you back in the Shetland Islands for this post, and onto the remote moorlands of northern Mainland.   When I visited this particular loch in 2016, I noticed a lot of slippery filaments of Batrachospermum attached to the sides of the cobbles in the littoral zone (see “Lucky heather …”).   This time around, I explored further around the edge of the loch and, in the south-west corner noticed prolific growths of algae in the shallow peaty water.  Closer inspection showed that these, too, were the red alga Batrachospermum and, though they were not fertile, Dave John suggests that they are likely to be B. turfosum Bory.

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Tufts of Batrachospermum turfosumin the littoral zone of Lamba Water, north Mainland, Shetland Islands, May 2019.   The picture frame is about 15 centimetres across. 

If you have a hand lens you can just about make out a bead-like structure when observing Batrachospermum in the field; however this becomes much clearer with higher magnification.   I think it looks like a bottle-brush when seen under the microscope at low magnification, with whorls of side-branches arising from the central filament.  At higher magnification, these filaments can be seen to have a bead-like structure, with cell size gradually reducing with distance from the centre.

What you cannot do in the field is separate Batrachospermumfrom the closely-related genus Sheathia(see “News about Batrachospermum… hot off the press”).   I usually tell people that, for a general overview of the condition of a stream or lake (for example, as part of the UK macrophyte survey technique), then simply recognising that you have “Batrachospermum” (meaning Batrachospermum or Sheathia) should be enough.   In my experience, the presence of Batrachospermumis usually a good indication that the water body is in a healthy condition.  However, I have been told that Batrachospermumis often found growing prolifically in very enriched conditions in southern chalk streams, which would challenge this assumption.   This may be because the species that are found in southern chalk streams are different to those that I encounter in my more usual haunts in northern England and Scotland.  But it is also possible that the factors I described in “The exception that proves the rule …” pertain in those cases too.

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Filaments of Batrachospermum turfosum from Lamba Water, north Mainland, Shetland Islands, May 2019.   The upper photograph shows a low magnification view of a filament (about 350 micrometres, or 0.35 millimetres, wide) whilst the lower image shows a whorl of side branches arising from the main stem.  Scale bar: 20 micrometres (= 1/50thof a millimetre).  

We often run into this dilemma with filamentous freshwater algae: it is reasonably straightforward to identify the genus but we need reproductive organs to determine the species.  As they seem to survive quite happily in the vegetative state our understanding of the ecology of individual species (rather than the genus as a whole) is scant so it is hard to tell whether there is value in that missing information or not.   In a few cases – this is one – better taxonomic understanding has revealed that we may not even be dealing with a single genus but the lists used for applied ecological surveys still persist with the old concepts.

This creates a toxic spiral of consequences: it is hard to split into species so most people don’t bother. Because we don’t bother, our interpretations are based on generalisations drawn from the behaviour of the genus.  This means we don’t generate the data needed to demonstrate the value (or otherwise) of the effort required to go from genus- to species-level identifications.   So we carry on lumping all records to genus (or, in this case, a pair of genera) and accept a few records that our out of line with our expectations as “noise”.  The situation is probably worse in the UK than in many places because there are very few people in universities specialising in these organisms and, as a result, no-one is producing the data that might break us out of this spiral.

We found Batrachospermum turfosum in a few other locations during our visit, but nowhere, even in nearby lochs, was it in such quantity as we saw in Lamba Water.   Chance might play a part in determining its distribution on a local scale but that ought to be the explanation of last resort rather than the go-to answer when we are worryingly short of hard evidence.

 

 

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Lucky heather …

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The interior of Shetland’s Mainland is rugged and remote and almost completely lacking basic tourist infrastructure such as footpaths that most hikers take for granted.  We located the approximate position of our destination on the skyline using our map then set off across heather-covered blanket bog, slithering down peat hags and across small streams until we reached our destination.  This was not a good time to find that I had left an important part of my sampling kit back in the car.

I searched every pocket of my cagoule and rucksack but I could not find my bag of toothbrushes.   These are the basic sampling tool of every diatomist, perfect for removing most algae growing on the surface of submerged stones.   Yet here I was, in one of the most remote corners of the country,  facing a beautiful small loch, but without any means of collecting a sample.   Jon, my co-worker on this trip, looked around us: “can’t you use a piece of heather?”

And so that is what I did: I pulled up a few shoots of heather, gripped them between two fingers and used these, toothbrush style, to clean the brown film off the surface of stones.   I picked out a few leaves and stems out of the final suspension and poured this into my sample bottle.   Problem solved.

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Using a piece of heather (Calluna vulgaris) to sample diatoms from a loch in Shetland, October 2016.  The top photograph shows Lamba Water, Mainland (photographed above), during the same sampling trip.

Several of the stones that I picked up from the littoral zone of Lamba Water had slippery, gelatinous tufts which, when examined closely with the naked eye could be seen to be made of bead-like filaments which I recognised to be the red alga Batrachospermum (see “Algae … cunningly disguised as frog spawn”).    Under the microscope, the beaded appearance resolved into tufts of branches arising from a single main axis which, at low magnification, looked like a bottle brush.   Most of my previous encounters with this genus have been in hard water but Lamba Water has relatively soft water (alkalinity: 7 mg L-1 CaCO3; conductivity: 117 mS cm-1) and a slightly acid pH (6.4) due to the surrounding peat which stained the water a dark brown colour.   Browsing through my Flora, I did notice that many of the species listed do appear to have very broad ranges for conductivity that suggest a low sensitivity for rock type compared to other types of algae.   I would not like to make too much of this as the data in the Freshwater Algal Flora of the British Isles are relatively sparse, but it is something that would be interesting to pursue in the future.

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A tuft of Batrachospermum on a submerged cobble in the littoral zone of Lamba Water, Shetland Isles, October 2016.  Scale bar: approximately 1 centimetre.

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magnification; right hand image at 400x (scale bar: 20 micrometres (= 1/50th of a millimetre).

One of the characteristics of Shetland is a very diverse geology packed into a relatively small area and the following day’s excursions took us to a very different lake on the other side of Mainland.   This was Loch of Girlsta, much deeper than Lamba Water (it is the only loch on Shetland with a population of Arctic Charr, I understand) and influenced by a narrow band of limestone (although most of the catchment seems to be the standard Shetland blanket bog).   By this time, we were having to contend with rain as well as strong winds and our time on site was limited.  I did, however, have a chance to spot some dark brown hemispherical colonies, mostly 3-4 mm in diameter, on some of the submerged stones.  Although the hemispherical colonies first made me think of Rivularia, when I was back in warm and dry conditions and had a chance to look at it under my microscope, it turned out to be Tolypothrix, the cyanobacterium that we last encountered in Ennerdale Water (see “Tales from the splash zone”) which is, chemically, quite similar to Loch of Girlsta, though perhaps with less peat in the catchment.   Both are in catchments with so little human influence that algae need to resort to nitrogen fixation in order to obtain the nutrients that they need to grow.

As an illustration of the extraordinary geological and ecological diversity that we encountered in such a small area, Loch of Benston, the final loch that we visited, was almost entirely underlain by limestone, and had extensive Chara beds.

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Colonies of Tolypothrix cf distorta (arrowed)) on rocks in the littoral zone of Loch of Girlsta, Mainland, Shetland Isles, October 2016. 

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Microscopic view of a false branch of Tolypothrix cf distorta from Loch of Girlsta.  Scale bar: 10 micrometres (= 100th of a millimetre).

Back on the mainland (the British mainland, that is, rather than Shetland’s Mainland), it was the autumn colours that struck me, after a few days north of the treeline on Shetland.   The drive back south from Edinburgh took me through the wonderful array of brown, red and yellow hues of the Borders and Durham, itself, always looks spectacular at this time of year.   The diatom samples that I collected with those bunches of heather now need to be processed and, I’m sure, there will be more tales from the northern isles to tell once I’ve had a chance to look at these.

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Autumn colours on the Durham riverbanks, October 2016.

 

Something else we forgot to remember …

The story of the mysterious red alga that I wrote about a couple of weeks ago (see “More than just an insignificant dot?”) has taken another intriguing turn.   Having decided that the alga was probably Audouinella pygmaea, I was shown a paper from 2011 by Orlando Necchi and Marianna Oliveira in which they consider the affinities of Audouinella species and came to the conclusion that Audouinella pygmaea only really exists in the imaginations of people who write identification guides. I’ve written before about the complicated life history of red algae (see “The schizophrenic life of red algae …”) and commented that it can be hard to differentiate between simple red algae such as Audouinella and stages in the life history of more complicated red algae.

Audouinella hermanii, the red alga that I was writing about in those earlier posts, does not present us with any serious problems, as it is possible to see all the reproductive structures, which enables us to distinguish between the (haploid) gametophyte filaments and the (diploid) sporophytes. However, reproductive organs have not been observed on populations of A. pygmaea, which presents us with some problems. Is this really an independent species of Audouinella or just a “chantransia” (gametophyte) stage of another red alga? Necchi and Oliveria took a number of populations of A. pygmaea and another species, A. macrospora (which has not been recorded from Britain or Ireland) and compared their genetic composition with other freshwater algae. What they found was that these chantransia stages were more closely related to known species from other red algal genera than they were to each other.   Their conclusion: “Audouinella pygmaea” does not exist in any meaningful sense. Rather, the populations we describe as A. pygmaea represent life history stages of other red algae. These life history stages are impossible to tell apart from one another using morphological criteria.   However, there is a good chance that a thorough search of the Anghidi Fawr stream upstream of where the sonde was placed will reveal another red alga – most likely Batrachospermum or Thorea – that was releasing the carpospores that produced the filaments that we named Audouinella pygmaea.

Curiously, this brings us back close to the situation almost 100 years ago as, reading my trusty old copy of West and Fritsch I read that the freshwater species we now call Audouinella were then placed in the genus Chantransia and that “C. pygmaea is probably a stage in the life-history of Batrachospermum moniliforme Roth.”   Another case, perhaps, of things we forgot to remember?

Reference

Neechi, O. Jr. & Oliveira, M.C. (2011). Phylogenetic affinities of “chantransia” stages in members of the Batrachospermales and Thoreales (Rhodophyta). Journal of Phycology 47: 680-686.

West, G.S. & Fritsch F.E. (1927). A Treatise on the British Freshwater Algae.   Cambridge University Press, Cambridge.

News about Batrachospermum … hot off the press

Two developments since I wrote my post on Batrachospermum (“Algae … cunningly disguised as frog spawn”): first, two of the images (my field view and Chris Carter’s microscopic shot) are going to appear in a book “Freshwater Life in South Africa” and, second, the genus Batrachospermum has been split into two.   This presents a slight problem as I no longer have the field material and so cannot determine whether the images are of true Batrachospermum or of the new genus Sheathia. However, as the book is intended for a lay audience, the nuances of red algae taxonomy can be sidestepped and, in any case, the key ecological “message” in this case is mostly obtained by recognising the genus (or, as we should now say, genera).

The paper is Molecular and morphological evidence for Sheathia gen. nov. (Batrachospermales, Rhodophyta) and three new species by Eric Salomaki and colleagues and it can be found in the latest issue of the Journal of Phycology (volume 50, pages 526-542).   It is a very neat study, collecting specimens of Batrachospermum from all over the world and subjecting these to molecular analyses. The outcome was a molecular “tree” that indicated quite clearly that one group of taxa within the genus was genetically quite distinct from the others.   So far, so good, but do these genera have any characteristics other than just different DNA?   The answer turns out to be that the main axis of cells in Batrachospermum is composed of cylindrical cells whilst that of Sheathia is a mixture of cylindrical and bulbous cells. Although red algal taxonomists already knew that there was a group of Batrachospermum species with this property, it was only when the morphological and molecular evidence was combined that there was a strong case for splitting these off into a new genus.

Seven species of Batrachospermum are listed in the Freshwater Algal Flora of the British Isles. Of these, three have now been transferred to Sheathia.   As I said in my earlier post, genus level identification is usually adequate for the purposes of general ecological assessment, so most of our current records will not allow us to differentiate between these two genera. The ecological notes in the Flora are not particularly helpful but do suggest that there is quite a lot of overlap in the preferences of the various species, so I doubt whether this split will result in a change in the way we interpret data. On the other hand, as we re-organise our synapses to accommodate this change, maybe someone will have a flash of inspiration to prove me wrong.

Oh yes, and I will need to update my lecture notes too.

Algae … cunningly disguised as frog spawn?

A couple of kilometres from Whitbarrow Quarry there is a spring that we always visit during the “Introducing Macroalgae” course because it usually yields a range of larger algae that we like to ensure that all the students can recognise. One of these forms tufts of filaments that are very slippery to the touch. There is a slight resemblance to frog spawn in both appearance and texture: under a hand lens the filaments can be seen to have a beaded appearance and this plus the texture creates a superficial resemblance to frog spawn. It is, in fact, another red alga, Batrachospermum which, like Lemanea (see “Lemanea in the River Ehen”) has an olive-green rather than red colour. I’ll explain more about that in the next post. I have also included one of Chris Carter’s photographs to show the structrure of Batrachospermum at higher magnification: the “beads” are composed of tufts of branchlets arising from a central filament.

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Left hand image: Batrachospermum sp. growing at Burn Head, near Whitbarrow in Cumbria; right-hand image: filaments of Batrachospermum in the palm of my hand. Each of the “beads” is about half a millimetre across.

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Batrachospermum sp. from Bodmin, Cornwall. Photograph by Chris Carter

I usually associate Batrachospermum with healthy ecological conditions: low nutrients, clear, cool water and diverse invertebrate communities. However, when I told the group on our course this, one of the participants said that he sometimes found it in quite polluted conditions. Interestingly, the same thing happened on a presentation of the course a few years ago and both the contradictory examples were from chalk streams in southern England. I went back to the published literature to reassure myself and, sure enough, these also referred to Batrachospermum as a species associated with good ecological conditions. There must be, however, some rare combination of conditions that enables Batrachospermum to occasionally proliferate in very enriched conditions. What we have, I suspect, is a common situation in ecology: we base our inferences about preferences on statistics rather than ecophysiology. This means that we assume that an association between a genus or species and a set of environmental conditions represents the realised niche of the species, without always understanding the nuances of ecology and physiology that determine these niches.

Next time: a red alga that really is red.