Looking east across Lily Tarn, Loughrigg Fell, near Ambleside in Cumbria, May 2015.
I was in the Lake District earlier this week, teaching a course at the Freshwater Biological Association (of which, more later). En route, I stopped off at Ambleside, and climbed up onto Loughrigg Fell in search of algae. Why here? Well, this was one of a small number of locations identified as an “Important Plant Area” (IPA) for freshwater algae. IPAs are an initiative of the charity Plantlife as a way of identifying those areas of the country of greatest botanical importance. The problem we have with freshwater algae is the strong tradition of recording that is central to understanding distributions of organisms is less well established for freshwater algae than it is for many other groups (see “A “red list” of endangered British diatoms?”). This, in turn, probably links back to the small number of amateurs interested in the microscopic world. Competent amateurs form the backbone of recording networks for much of the UK’s flora and fauna.
The desmids are one of the few exceptions to this generalisation, and the freshwater algae IPAs are largely based on the careful observations of one expert amateur, David Williamson. Loughrigg Fell was one of a number of sites that fell out of an analysis of his data, as a large number of species of desmid have been recorded from here, including a few that have rarely been recorded elsewhere.
Euglena mutabilis, from a Sphagnum pool on Loughrigg Fell, close to Lily Tarn, May 2015. Scale bar: 10 micrometres (= 1/100th of a millimetre).
However, the most distinctive taxon that I found in the first sample I looked at (from a squeezing of Sphagnum living in a boggy pool near Lily Tarn) was not a symmetrical and sedate desmid (see “Hunting for desmids in Upper Teesdale”) but a wriggly and squirming alga that I recognised as Euglena mutabilis. When I was teaching at university in Nigeria, I used to set my students an essay “Euglena: plant or animal? Discuss”. The Euglena that I found in this boggy pool on Loughrigg had distinct green chloroplasts for photosynthesis, but not all species in this group have these. Some, instead, obtain their nutrition from carbon compounds dissolved in the water. What is more, I expect “plants” to have rigid cell walls whereas Euglena has a flexible “pellicle” (made of protein, not cellulose) which enables the organism to constantly change its shape, and to move around. Most Euglena species have a flagellum; E. mutabilis is an exception and the photographs and video show characteristic euglenoid movement (“metaboly”) as the cell changes shape and the cytoplasm streams in to fill this up. Of course, modern biologists do not really hold with a rigid distinction between “plants” and “animals” but it was still a useful way to get undergraduates thinking.
Euglena mutabliis is a very characteristic species of acidic environments, found not just in Sphagnum bogs, but also in acid mine drainage, where the pH can be as low as 2.0. Living in such acid environments creates considerable problems for organisms so E. mutabilis has attracted much attention from people wondering how it copes. The inside of all cells tends to be more-or-less neutral and most enzymes are optimised to work best under such conditions. However, cell interiors also naturally have a negative charge, which means that hydrogen ions – the ‘active ingredient’, if you like, of acidity, naturally flow into cells. The evidence that we have shows that the pH inside E. mutabilis cells adjusts as the pH outside changes, though it is never as acid as conditions outside the cell. This must mean that the cells are using a lot of energy pumping the unwanted hydrogen ions out.
There are some great views from Lily Tarn, though the clouds were quite low during my visit. Windermere spreads out to the south, and I could just make out Wray Castle on the west shore, the original home of the Freshwater Biological Association. To the north, I could see the flanks of Helvellyn when the clouds parted, and the track that led up to the Fairfield Horseshoe. The ground falls away steeply to the east of Lily Tarn, and you can look down into Ambleside itself, only a couple of kilometres away. And that’s where I’m heading for my next post …
Brodie, J., John, D. M., Tittley, I., Holmes, M.J.,Williamson, D.B. (2007) Important Plant Areas for algae: a provisional review of sites and areas of importance for algae in the United Kingdom. Plantlife International, Salisbury, UK.
Hargreaves, J.W. & Whitton, B.A. (1976). Effect of pH on the growth of acid stream algae. British Phycological Journal 11: 215-223.
Hargreaves, J.W., Lloyd, E.J.H. & Whitton, B.A. (1976). Chemistry and vegetation of highly acidic streams. Freshwater Biology 5: 563-576.
Pentecost, A. (1982). The distribution of Euglena mutabilis in Sphagna, with reference to Malham Tarn North Fen. Field. Studies 5: 591-606.