Living rocks, gently rolling … A trope in film noir where the protagonist is seduced by a femme fatale which came to mind when I was in Ambleside earlier in June. There were signs of a surface cyanobacterial scum in Windermere when we were sampling with our students (similar to the one described in the addendum to “A hitchiker’s guide to phytoplankton …”), feeding into broader concerns about the state of England’s largest lake. Yet, a day later, I was being wooed by cyanobacteria in a very different habitat, just a few kilometres from the side of Windermere. One minute, I’m the hard-boiled algal detective, trying to make sense of a problematic situation. The next, I’m running off with a Manic Pixie Dream Alga. Followers of the blog are shouting at their computer screens: “don’t do it, Martyn, they’re cyanobacteria …. they’re baaaad”. “They’re not bad”, I reply, “just misunderstood. They need to be given another chance …”. And off I go again, chasing my latest cyanobacterial seductress … This latest tryst happened at an abandoned quarry at Whitbarrow, on the narrow belt of limestone that runs along the southern edge of the Lake District. I’ve had flings here before (the most recent is described in “Cyanobacteria inside their comfort zones …”) but on my latest trip, my eye was caught by some small pebbles on the bed of a seepage. These were not just any old pebbles, there was a distinct brownish film on their upper surfaces that suggested that there was a microbial community here and observation under the microscope revealed this to be Cyanobacteria, probably _Rivularia_ or, possibly, _Calothrix_. **Oncoids on the bed of a seepage at Whitbarrow Quarry, Cumbria, June 2025. The photograph at the top of the post shows the limestone cliffs at the edge of the quarry.** The story of oncoids goes something like this: “Teesdale’s unseen natural history …” explained how Cyanobacteria such as _Rivularia_ formed hemispherical colonies and the previous post (“A garden of sub-visual lifeforms …”) commented on how these colonies led to the precipitation of calcite (described more fully in Allan Pentecost’s publication listed below). The _Rivularia_ colonies that I described from Upper Teesdale are, in other words, miniature freshwater stromatolites. If this process continued indefinitely, these tiny hemispheres would grow into substantial structures such as those seen in Shark Bay, Western Australia. But Upper Teesdale is a very different place to the sheltered environment of Shark Bay, and periodic storms disrupt this process of stromatolite formation and the largest we see there are rarely more than a centimetre across. Now imagine a situation where there is some periodic but gentle disturbance, such that the colony is turned over but not washed away completely. The Cyanobacteria continue to grow but the light is now on the other side so the original hemispherical colony starts to become spherical. But then it is turned again, perhaps showing a different face and the process is repeated. As the colony grows, so the innermost parts of filaments are starved of light and die off, leaving behind the calcite deposited around them. Repeat these cycles over decades or even centuries and the original hemisphere, a few millimetres in diameter, becomes a round object a centimetre or more across, with a solid core and just a thin layer of actively growing filaments on the outside. It is these that we refer to as “oncoids” or “oncolites”. Think of them as mini-stromatolites, “living fossils”, if you will, that connects us with the pre-Cambrian world when Cyanobacteria ruled the world and, through their photosynthesis, created the oxygen-rich atmosphere that allowed life as we know it to evolve. That’s why I can never resist the flirtations of an attractive Cyanobacterium. **_Rivularia_ filaments from the surface of an oncoid from Whitbarrow Quarry, June 2025. Scale bar: 20 micrometres (= 1/50th of a millimetre). ** The problem with making Cyanobacteria the pantomime villains of campaigns for better water quality is that the essential roles that Cyanobacteria play (and played) in ecosystems is overlooked. I would go as far as to say that Cyanobacteria are routinely “othered” in the way that migrants are in other political contexts, as a means of distilling complex environmental problems into simplistic political messages. Cyanobacteria do what evolution has made them extremely capable of doing only because we, and the governance systems within which we function, create conditions where they can flourish. In the process (and, again, just like migrants), their positive contributions are downplayed. I dream of a day when, instead of this demonisation, the rare sighting of a Cyanobacterium such as _Anabaena_ can be celebrated, and the beauty of these ancient organisms fully appreciated. **Reference** Pentecost, A. (1981). The tufa deposits of the Malham District, North Yorkshire. Field Studies 5: 365-387. Some other highlights from last week: **Wrote this while listening to:** Alanis Morisette’s set at Glastonbury **Currently reading:** Tony Parson’s _Man and Boy_. **Cultural highlight:**_The Anatomy of Painting_ , Jenny Saville’s show at the National Portrait Gallery. **Culinary highlight:** Tasting menu at _Bamboo Mat_ , a restaurant serving Nikkei – a fusion between Japanese and Peruvian cuisines. Sharp, clean flavours, ideal for a hot summer’s evening. Enjoyable stroll back to the station through the Olympic Park, albeit set to a soundtrack of Iron Maiden playing at the nearby London Stadium. ### Share this: * Click to share on X (Opens in new window) X * Click to share on Facebook (Opens in new window) Facebook * Like Loading... ### _Related_

Lovely blog from #MartynKelly #cyanobacteria #algaedon microscopesandmonsters.wordpress.com/2025/07/01/living-rocks-...

@davidho Better or worse than depression about coral reef dying when it got too hot and algal components had to be ejected? #algaedon