I took the opportunity of the British Diatom Meeting (see “In the footsteps of Sherlock Holmes …”) to wave some images of the diatoms I found in the sample from Pangong Tso (see “Diatoms from the roof of the world”) under the noses of some colleagues in the hope of confirming their names.
The most obvious species in the sample was a Gomphonema which grew on long, branching stalks. Cleaned valves of this had a broad rostrate head pole and a rostrate to sub-capitate foot pole, strongly radiate striae, and a single stigma (pore) in the central area. The specimens in this sample ranged from 14 to 29 micrometres in length and 6 to 7 micrometres in breadth. My colleague, Ingrid Jüttner from the National Museum of Wales, who has considerable experience of Himalayan diatoms, said that she had seen this species once before in a sample from Pakistan but it was, to the best of her knowledge, not yet formally described.
The other species that was very conspicuous when I made my initial scans of the sample belongs to the genus Diatoma. Were I to use a European Flora to identify this, I would call it Diatoma moniliformis. The length and breadth of the Pangong Tso specimens fell within the range reported for D. moniliformis, as did the density of costae (horizontal ribs) and the outline. However, as Ingrid is presently writing a paper on Himalayan Diatoma spp. I will wait a little longer before confirming that this is definitely D. moniliformis.
Gomphonema sp – possibly new to science – from the littoral zone of Pangong Tso, north India, September 2014. The right-hand specimen, which is narrower than the others, may represent a different species. Scale bar: 10 micrometres (= 100th of a millimetre).
Diatoma cf moniliformis from the littoral zone of Pangong Tso, north India, September 2014. Scale bar: 10 micrometres (= 100th of a millimetre).
Two other species in the sample look more familiar to me from my European samples. The first of these is a small species of Nitzschia, N. inconspicua. This species was, actually, the most abundant species in the sample, accounting for almost sixty per cent of all the diatoms though, as it is relatively small, it probably accounts for a much lower proportion of the total biomass or biovolume. I have, coincidentally, just published a paper on the ecology of this species and the habitat of Pangong Tso, as far as we know from the limited data available, matches these criteria very closely: slightly brackish with elevated phosphorus concentrations.
There were also a number of individuals of Achnanthidium minutissimum, a diatom that is very widely distributed in freshwaters around the world. Our understanding of A. minutissimum has changed a lot over the past twenty years and we now know that there is a complex of species with similar characteristics and, often, overlapping ecological characteristics. The Pangong Tso sample consisted mostly of individuals that belonged to “true” A. minutissimum, but there were also a few individuals that may belong to another species within the complex.
Nitzschia inconspicua from the littoral zone of Pangong Tso, north India, September 2014. Scale bar: 10 micrometres (= 100th of a millimetre).
Achnanthidium minutissimum from the littoral zone of Pangong Tso, north India, September 2014. The five specimens on the left are A. minutissimum sensu stricto; the two specimens on the right belong to a linear form closely related to A. minutissimum. Scale bar: 10 micrometres (= 100th of a millimetre).
Finally, I found a number of individuals of Berkeleya rutilans (synonym: Amphipleura rutilans), a small diatom which Krammer and Lange-Bertalot (1986) describe as living in coastal areas and inland saline waters and which Ralph Lewin describes as a “common littoral diatom of the Atlantic coast [of the USA]”, where it grows in branched mucilage tubes. This is another diatom m that has recently been shown to be a complex of closely-related but distinct species,
It is an intriguing mixture of species. First of all, the total number of species that I found was very low – less than ten, whereas I usually expect twenty, thirty or more species in a sample. Second, we have an interesting mix of truly freshwater taxa (Gomphonema, Achnanthidium minutissimum), alongside taxa that are found in both freshwater and brackish habitats (Diatoma moniliformis – if I am right – and Nitzschia inconspicua) and, finally, a species mostly associated with brackish and saline habitats (Berkeleya rutilans). All living together in a slightly saline lake over 4000 metres above sea level. Of course, we cannot conclude very much from a single sample and scant environmental data but then that just creates an incentive to get back to collect some more samples …
Berkeleya rutilans from the littoral zone of Pangong Tso, north India, September 2014. Photographed with phase contrast illumination. Scale bar: 10 micrometres (= 100th of a millimetre).
Hamsher, S.E. & Saunders, G.W. (2014). A floristic survey of marine tube-forming diatoms reveals unexpected diversity and extensive co-habitation among genetic lines of the Berkeleya rutilans complex (Bacillariophyceae). European Journal of Phycology 49: 47-59.
Krammer, K. & Lange-Bertalot, H. (1986) Süsswasserflora von Mitteleuropa. Bacillariophyceae. 1: Naviculaceae. Gustav Fischer-Verlag, Stuttgart, Germany.
Lewin, R.A. (1958). The mucilage tubes of Ampiphleura rutilans. Limnology and Oceanography 3: 111-113.