More from the River Ehen

When I was visiting the Ehen back in February, I found tufts of a blue-green alga called Tolypothrix tenuis (see post).  I also found that these were smothered, in turn, by a smaller blue-green alga, Heteroleibleinia rigidula (which, until recently, was included in the genus Lyngbya, which we met in the previous post).  I had another look at the Tolypothrix during my last visit and was surprised to see that the Heteroleibleinia had disappeared and had been replaced by another epiphytic blue-green alga, Chamaesiphon (probably) incrustans.   The entire surface of the filament was smothered by the short, club-shaped cells of this species.   I said it is “probably” C. incrustans because there is another species with very similar appearance, C. minutus, but this is not illustrated in the Freshwater Algal Flora of the British Isles so I cannot be 100% sure.

Tolypothrix tenuis from the River Ehen, smothered by epiphytic Chamaesiphon cf incrustans.   Scale bar: 10 micrometres (1/100^th of a millimetre).  The inset shows a single cell of Chamaesiphon with its characteristic exospore.

It is hard to make out the individual Chamaesiphon cells in the photograph so I have sketched a single cell to illustrate the main features.  It is attached by the narrow end to the host organism and many of the cells have a characteristic “exospore” at the other end which buds off to produce a new cell.

About a dozen different species of Chamaesiphon have been recorded from the UK.  A few of these are epiphytes, but most form colonies on submerged rocks.  Most are just brown patches that sometimes resemble lichens but more often look like … brown patches.   Consequently, they are easily overlooked and, probably, under-recorded.  Back in March, I commented on the “trailing edge” of science where we were forgetting more than we were learning (see post) and the ecology of Chamaesiphon is a good example of this.