Working on the principle that we usually pass only a handful of people during our walks in Upper Teesdale we decided that this counted as “social distancing” and headed off to the hills. Whether this is still deemed to be acceptable behaviour this week is another matter, but I can report that Teesdale in midweek was certainly far less crowded than the tourist honey-pots that were the focus of so much bad press over the weekend. But I digress.
Our regular beat follows the Pennine Way for a long stretch with the River Tees on our left and the looming cliffs of Falcon Clints on our right. Just before the Pennine Way gets to this section, however, the valley is broader, with a flat floor that is used as grazing land by Widdybank Farm. A small stream, Fold Sike, flows off Widdybank Fell and crosses the Pennine Way at an oblique angle before joining the River Tees. I’ve walked past it many times, mentally noting prolific growths of a broad leafed Potamogeton as I press on, but little else. Today, however, my eyes were caught by light-coloured crusts on many of the basalt stones just below the surface of this shallow stream. If you look closely at these crusts you’ll see that they are not homogeneous: there are distinct nodules on their surfaces and they are more prominent on the edges, rather than the tops, of the stones. You’ll also see a distinct green tinge in some areas.
Potamogeton and Homoeothrix crustacea growing in Fold Sike, Upper Teesdale (NY 834 292) in March 2020. The photograph at the top of the post shows the view looking back down the valley from Fold Sike with Widdybank Farm in the distance.
A basalt cobble from the bed of Fold Sike showing the surface nodules and the greenish tinge to the crust.
This crust is distinctive: I know from previous encounters that it is formed, primarily, of the cyanobacerium Homoeothrix crustacea, a member of the Oscillatoriales (see “Shuffling the pack”). I also know that it is a beast to photograph, having very narrow filaments and, in this case, also is extensively calcified. I describe the process of calcification of Chara in “Everything is connected” and the same principles are likely to apply here too. the I did try to dissolve away the calcite with some vinegar, but without much success in this case. I’ve included some photographs of another species below, and you can see yet another species of Homoeothrix in “Algae from the Alto Duoro”. The microscopic image shows the characteristic tapering filament combined with the absence of a heterocyst. In the far past, Homoeothrix was thought to be a heterocyst-free relative of Calothrix, rather than a tapering relative of Oscillatoria and Phormidium.
Some images of Homoeothrix: a. Homoeothrix crustacea encrusting a boulder (approximately 40 cm across) from a calcareous stream in Cumbria, UK; b. filaments of H. fusca from a crust on Whitbarrow tufa stream, Cumbria (scale bar: 100 micrometres, 0.1 millimetre); c: close-up of a single trichome from the same stream. Note the distinctive tapering and absence of a heterocyst (scale bar: 10 micrometres, one hundredth of a millimetre).
The greenish patches on the surface of the crust were mostly composed of the green alga Bulbochaete (discussed in more detail in other posts – see “A winter wonderland in the River Ehen“) and I also saw a number of diatoms, principally Achnanathidium minutissimum and Delicata delicatula. The latter, formerly included in Cymbella, is a common species in streams hereabouts, though relatively uncommon in the UK as a whole. I also saw a few trichomes of a member of the Rivulariaceae, though did not find any intact colonies. Were this a warm, shallow maritime environment a few dominant calcifying algae that create a habitat for a range of other species would be called a “reef”. That word stretches the imagination when applied to a small windswept sike in upland County Durham, but the processes are the same even if scale and context are very different. However, what with all the travel restrictions and closed borders at the moment, this might be the closest any of us will get to a coral reef for quite some time …
Delicata delicatula (?) from Fold Sike, March 2020. Scale bar: 10 micrometres (= 1/100th of a millimetre).
Some other highlights from this week:
Wrote this whilst listening to: Bob Dylan’s first two albums. One of my projects for the next weeks is to listen to all Bob Dylan’s albums sequentially. Tony Allen and Hugh Masekela’s latest album, Rejoice, is also well worth a listen.
Cultural highlights: The Perfect Candidate. A Saudi film about a female doctor battling misogyny to get elected to the local council. Under normal circumstances we would probably have ventured up to the Tyneside Cinema in Newcastle to see this. Instead, we streamed it via Curzon Home Cinema.
Currently reading: Still ploughing through Hilary Mantel’s The Mirror and The Light. Oddly, despite the enforced isolation, I don’t seem to be finding much time to read at the moment.
Culinary highlight: The bad news is that Durham Indoor Market has finally succumbed to the inevitable and closed its doors, taking with it most of our opportunities to buy non-supermarket food. That means that the risotto we cooked with a stock made from the leftovers from last weekend’s prawns probably wins the “culinary highlight” this week, if only because it may be some time before we can make another.