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.
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.
A tuft of Batrachospermum on a submerged cobble in the littoral zone of Lamba Water, Shetland Isles, October 2016. Scale bar: approximately 1 centimetre.
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.
Colonies of Tolypothrix cf distorta (arrowed)) on rocks in the littoral zone of Loch of Girlsta, Mainland, Shetland Isles, October 2016.
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.
Autumn colours on the Durham riverbanks, October 2016.