Back in early July I wrote about a visit to a pond in a local nature reserve (see “Pleasures in my own backyard”) and ended with the hint that there was one other abundant alga there that I was unable to name at the time. I was reticent about naming it, as it seemed to be a rare alga and the habitat where I had found it did not match the locations where it had been found to live.
I’ve now shown it to Brian Whitton and he has joined me on another excursion to the same pond, and I can confirm that it is, in fact, Chroothece richteriana, a freshwater red alga. We’ve met (and even eaten) red algae several times over the lifetime of this blog (see “More from the Lemanea cookbook …”), but Chroothece is different in that it does not form filaments or thalli, but lives in mucilaginous masses. The individual cells, each of which are ovoid, with a single star-shaped chloroplast, live embedded within this mass.
A colony of Chroothece richteriana growing on marl-encrusted rocks from Crowtrees Pond, County Durham, July 2016. Scale bar: 10 micrometres (= 1/100th of a millimetre).
This is a species that was, until recently, known only from two very old records. However, searches over the past few years have found it growing at a number of different locations. There are now half a dozen locations in the UK, plus one in the Isle of Man. Interestingly, the population at Crowtrees matches these other records in respect to the underlying geology – limestone – which yields very hard water, but differs in being permanently submerged. The other records are from seepages and other semi-aerial habitats. The population at Crowtrees formed a thin film that was firm to the touch due to the deposition of calcite crystals within the matrix. There were also some cyanobacterial filaments mixed in amongst the Chroothece, as well as the diatoms that I mentioned in the previous post. I suspect that the snails that I observed on my earlier visit were scraping up a mixture of all these species from the thin surface layer that had not yet had time to become hardened by calcite crystals.
One theory for the success of Chroothece here is that habitats such as this are naturally low in phosphorus, an essential nutrient that is naturally scarce but which is relatively insoluble and consequently is precipitated out of the water along with the calcite. Studies in Spain (in a river, rather than a seepage or pond) showed that Chroothece shares the characteristic of several other algae from this type of habitat, of producing enzymes that can scavenge phosphorus from tiny particles that are suspended in the water. The enzymes are thought to be concentrated in the mass of mucilage (which is actually formed from the organism’s stalks)
Ironically, our excursions to Crowtrees Nature Reserve have become more frequent over the past year or so as our usual running and walking beats in the countryside around Bowburn have been changed as a local quarry expands its activity (seen in the gouge in the skyline in the picture below). The pond, itself, looks natural, but local drainage is strongly influenced by mining and quarrying. The area around here, especially associated with the Permian limestone, abounds in nature. But whether or not this nature is natural is a topic for another day …
The view from Crowtrees Nature Reserve towards the Tarmac quarry, July 2016.
Aboal, M., García-Fernández, M.E., Roldán, M. & Whitton, B.A. (2014). Ecology, morphology and physiology of Chroothece richteriana (Rhodophyta, Stylonematophyceae) in the highly calcareous Río Chícamo, south-east Spain. European Journal of Phycology 49: 83-96.
Pentecost, A., Whitton, B.A. & Carter, C.F. (2013). Ecology and morphology of the freshwater red alga Chroothece in the British Isles. Algological Studies 143: 51-63.