On an overcast winter day with just a sprinkling of snow on the fells the Lake District can appear very monochrome. Look closely at the bed of some rivers, however, and you are confronted by a much more vibrant palette with browns, greens and reds vying for your attention. Somehow, paradoxically, the stream algae are at their most prolific and vigorous when the rest of Cumbria’s biological diversity has hunkered down to wait for the onset of Spring.
One of the most conspicuous groups at this time of the year are the red algae. The green algae, diatoms and cyanobacteria are there all year round, even if winter is the time when they are most abundant. The red algae, however, are barely evident – and certainly not to the naked eye – during the summer months. It is only when autumn is well underway that the first blushes of pinkish red appear on the stones lining the beds of rivers. This is in contrast to the red seaweeds which can be found on our coasts all year round, and indeed, to the many red algae that inhabit warm tropical seas. What is so different about red algae in streams that leads them to favour the colder periods of the year? What is it about streams, too, as I rarely see red algae in lakes (Batrachospermum is the exception: see “More algae from Shetland lochs”)?
This post will not answer those questions, but will give a quick overview of the red algae we find in freshwaters, in the manner of an earlier post about green algae (see “The big pictures …”). The table below shows the systematics of the red algae, following a molecular phylogeny study by Hwan Su Yoon and colleagues from 2006. There are two sub-phyla, of which one, Cyanidophytina, has no representatives recorded from the UK or Ireland. There are just eight species in this group of primitive red algae, associated mostly with extreme environments.
The other subphylum, by contrast, has over 7000 species, divided between six classes, but 94 per cent of these are marine. There are just thirteen genera of red algae recorded from freshwaters in the UK and Ireland, but spread amongst five of these six classes. This seems to suggest that an ability to thrive in freshwaters has evolved several times during the evolution of this group.
The organisation of the red algae (Rhodophyta) showing division into two subphyla and seven classes. Pink fill indicates the classes that are represented in UK and Irish freshwaters. Organisation follows Algaebase and Yoon et al. (2006). The photo at the top of this post shows Audouinella hermainii in the River Ehen, Cumbria, in December 2019.
Of the five classes that do have freshwater representatives, well over half of the genera and species recorded from the UK and Ireland are found in the Floridiophyceae. This class has over 6900 species (95% of all red algae) split between 34 orders, of which five contain genera found in UK and Irish freshwaters. Of these, the Batrachospermales, one of the few red algal orders that is exclusively freshwater, contains five genera and eleven species, whilst the other four contain just one genus each.
The Batrachospermales contain two morphologically-distinct groups of genera: Batrachospermum, Sheathia and Sirodotia form one of these, whilst Lemanea and Paralemanea form the other (see links below for more details and images). Whilst we have molecular evidence that suggests that the Batrachospermales are a natural group, it is hard to point to a single characteristic that helps someone more interested in identification than taxonomy. In fact, it is the life-cycle that is most distinctive (“… diplohaplontic … heteromorphic and contains a reduced tetrasporophyte”) but few of us are as well-schooled in algal life-cycles now as our predecessors were (see “Reflections from the Trailing Edge of Science”). A hundred years ago, we would have had to rely upon the same limited set of morphological characters for both identification and taxonomy; now the taxonomist’s toolkit has expanded considerably whilst identification is still mostly reliant on features we can see with the naked eye or a light microscope. For the red algae, this is still mostly enough to answer questions about what species we have found but unravelling the logic behind a classification may need a broader perspective.
Organisation of the Florideophycae showing the orders that include genera found in UK and Irish freshwaters.
Entwisle, T.J., Vis, M.L., Chiasson, W.B., Necchi, O. & Sherwood, A.R. (2009). Systematics of the Batrachospermales (Rhodophyta) – a synthesis. Journal of Phycology 45: 704-715.
Yoon, H.S., Müller, K.M., Sheath, R.G., Ott, F.D. & Bhattacharya, D. (2006). Defining the major lineages of red algae (Rhodophyta). Journal of Phycology 42: 482-492.
van den Hoek, C., Mann, D.G. & Jahns, H.M. (1995). Algae: an Introduction to Phycology. Cambridge University Press, Cambridge.
And some other cultural highlights from the week:
Wrote this whilst listening to: Dave’s Psychodrama,
Cultural highlights: Dave’s performance of Black (from Psychodrama) at the Brits Award Show. I would not normally have watched this but was stuck in a hotel room with no wifi reception and was totally blown away by the power of his performance.
Currently reading: Bill Bryson’s The Body
Culinary highlight: I’m trying to cook one meal each month using only UK-sourced ingredients, in order to help me focus on seasonal cycles. My February effort was a beer and cheese fondue: very easy to cook, using beer from about 500 metres from my house (Durham Brewery’s Evensong) and a mixture of Cheddar and Lancashire cheeses from Durham Indoor Market.
Links to posts describing representatives of the major groups of red algae found in freshwaters. Only the most recent posts are included, but these should contain links to older posts (you can also use the WordPress search engine to find older posts).
|Bangiophyceae||Watch this space …|
|Bangiophyceae||Watch this space …|
|Compsopogonophyceae||Watch this space …|
|Achrochaetiales||Something else we forgot to remember|
|Balbianiales||The Hilda Canter-Lund prize|
|Batrachospermales||Lemanea: The complicated life of simple plants
Batrachospermum: More algae from Shetland lochs
|Hildenbrandiales||More about red algae|
|Thoreales||Watch this space|
|Porphyridiophyceae||Watch this space …|
|Stylonematophyceae||More pleasures in my own backyard|