Back to the Himalayas …

It is always nice to tie up loose ends left in earlier posts, so I was pleased to find a recent paper that put a name on a diatom that I had illustrated, but not been able to name, during my examination of material from a high altitude lake in Ladakh (see “Diatoms from Pangong Tso”).   I had assumed that this was a species of Gomphonema; however, Pat Kociolek and colleagues have placed it in a completely new genus, Gomphosinica.

Following their paper, the diatom that was abundant in the littoral of Pangong Tso is most likely Gomphosinica lacustris and this would be the first record of the genus in India.  The type location for this species is Kalakule Lake in the Kunlum Mountains of Xianjiang Province, northwest China, some 800 km north of Ladakh, and on the other side of the Tibetan Plateau.   They describe their sample as “planktonic in the lake”, whereas the populations I described formed distinct growths in the littoral zone (see “Return to Pangong Tso”).  They also have recorded it from Sichuan province, in southwest China.   Pangong Tso actually marks the Indian-Chinese border, so it should not be a great surprise to have found it here.

Altogether, Pat Kociolek and colleagues found three new species of Gomphosinica in China, and transferred a previously-described species of Gomphonema found in Nepal to the genus.  However, they also found four species in Montana, in the USA, and made one further transfer of a Gomphoneis first described from the Great Lakes.  Bear in mind, too, that Gomphosinica species are distinctive, so it is unlikely that the absence of Gomphosinica in regions other than China and the USA is an oversight on the part of diatomists.  There is clearly more to learn about the biogeography of this genus.

Having said that Gomphosinica is distinctive, it is hard to say exactly how it differs from Gomphonema based on what we can see with the light microscope alone.  The distinctive features can only be seen with scanning electron microscope, and it would be interesting to get some molecular barcodes from members of this genus to see how these compare with those from Gomphonema and relatives.  This might also shed some light on the differences between the North American and Asian species.

The same journal part also contained a paper on diatoms from the Doon Valley, near Dehra Dun in Uttarakhand, which may shed some light on the diatoms that I found nearby in the Ganges at Rishikesh (see “Diatoms from a holy river”).   I named these using the identification literature that I had to hand (mostly from Europe) and included “Gomphonema pumilum” in my list.  This new paper suggests that there may be local species which look very similar, including G. juettnerii and G. doonensis.   My population does not fit the dimensions of either of these exactly, and my inclination would still be that at least the larger of the two specimens I illustrated is G. pumilum, but there is enough in this paper to remind me that trusting a European flora when studying the diatoms of Asia is dangerous.   Whether these diatoms actually fill different niches in their respective ecosystems, or whether they are just genetically-distinct forms of what is, basically, food for relatively unfussy invertebrate larvae on both continents is a question for another day.

Note: the photograph at the top of the post is an early-evening view of a river in the Outer Himalaya Zone in the vicinity of Dehra Dun.

Reference

Karthick, B., Nautiyal, R., Kociolek, J.P. & Ramachandra, T.V. (2015).  Two new species of Gomphonema (Bacillariophyceae) from Doon Valley, Uttarakhand, India.  Nova Hedwigia, Beiheft 144: 166-174.

Kociolek, J.P., You, Q-M., Wang, Q-X. and Liu, Q. (2015).  A consideration of some interesting freshwater gomphonemoid diatoms from North America and China, and the description of Gomphosinica gen. nov..  Nova Hedwigia, Beiheft 144: 175-198.

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Return to Pangong Tso

Pangong_Tso_150710

Pangong Tso, from the Indian shore, looking towards China, July 2015 (photograph: Heathe Kelly).

You may remember that a year ago I wrote some posts about a high altitude lake on the India-China border (see “Subaquatic landscapes in Pangong Tso” and references therein).   This year, Heather made a second trip to Pangong Tso (described here) under the auspices of Indus Experiences and brought me back another sample from the littoral zone.   There was a beautiful thick biofilm here, an unusual bright yellow-brown colour and a jelly-like consistency, but bubbling away as the algae photosynthesised busily.   Once again, local vodka was pressed into service as a preservative and, once again, peering through my microscope a few days later, I could see that the sample was dominated by the same long-stalked Gomphonema species that I recorded a year ago (see “Diatoms from Pangong Tso”). The jelly-like consistency did worry me, as this is not what I would expect of a pure growth of diatoms and I did wonder if there were cyanobacteria growing amongst the diatoms that had not survived the journey home in their marinade of cheap vodka.

Pangong_littoral_diatoms_Ju

Growths of diatoms (predominately a long-stalked Gomphonema sp) on a boulder in the littoral zone of Pangong Tso, India, July 2015. The right hand image is a close up showing oxygen bubbles being produced by the the jelly-like masses. Photographs: Heather Kelly.

Intriguingly, the Gomphonema seems to occur in two forms: a fatter form, with a width around eight micrometres, and a narrower form, about six micrometres wide. I’ve written before about how diatoms tend to get shorter over time (see “Diminishing with age”). What I did not make clear in this post is that cell breadth tends to stay relatively constant during this process.   This does not happen with every species but it is interesting to see that the fat and narrow forms have overlapping sizes, so it is not a simple matter of the narrow ones being the far end of the size reduction sequence. More work is definitely needed here although, alas, I don’t think Pangong Tso is on the itinerary for next year’s visit to India.

Gomphonema_Pangong_July15

Gomphonema sp from the littoral zone of Pangong Tso, north India, July 2015.   a. – d. represent the “fat” form; e. – h. are the narrower form(s). Scale bar: 10 micrometres (= 1/100th of a millimetre).

Subaquatic landscapes in Pangong Tso

My own private counterweight to inclination of fellow diatomists to base their science on the study of empty shells of dead organisms is to reconstruct images of what those diatoms might have looked like when they were still in their natural habitat.   The latest of these thought experiments is based on the samples I’ve described from Pangong Tso (see “Diatoms from the roof of the world” and “Diatoms from Pangong Tso”).   It comes with a number of caveats, not least of which is that the only preservative available (local vodka) would not have been kind to the non-diatom algae in the sample, so I may have over-estimated the contribution of diatoms to the total community.

Pangong_Tso_140928

A visualisation of the subaquatic flora of Pangong Tso, September 2014, including the diatoms Gomphonema (on long stalks), Diatoma (zig-zag chains), Berkeleya rutilans (in mucilage tube, bottom left corner), Achnanthidium minutissimum (epiphytic on Gomphonema stalks) and motile Nitzschia inconspicua.  The Gomphonema cells are approximately 25 micrometres (1/40th of a millimetre) long.

The diatoms that I saw as I looked done the microscope is one that suggests a fairly mature community with only limited grazing. This may reflect the harsh environment endured in this high altitude desert or the brackish nature of the lake, or it may just be a temporary situation. It is impossible to say with so little data.   The organisms that I did see suggest several different ecological strategies.   The giants in my underwater landscape were the Gomphonema cells, which lived on the end of long branched polysaccharide stalks.   As the film of microscopic algae on any surface grows thicker, so the amount of light that penetrates through is reduced and there is a benefit to any organism that can reach up above the hoi polloi to gain access to the limited light.   Entangled amongst these are zig-zag chains of Diatoma cf moniliformis which, like the lianas of tropical forests, are entangled around these stalks.   I also saw cells belonging to the Achnanthidium minutissimum complex and I know, from other samples I’ve looked at, that these are capable of growing as epiphytes on the stalks of Gomphonema species.   Berkeleya rutilans is a species that I have not previously encountered in my studies of the microscopic world but I have followed descriptions in the literature and included a couple of cells in a mucilage tube towards the bottom left corner of the picture.   Finally, the most numerically abundant species in the sample was one that I do know very well: Nitzschia inconspicua. This is a motile diatom which is able to move through the tangle of Gomphonema stalks and Diatoma filaments in search for light.   I was co-author of a paper on the ecology of N. inconspicua published earlier this year and was pleased to see that the habitat of Pangong Tso matches our prescription almost exactly (based on the limited published data). The assumption that most diatoms are cosmopolitan has rightly been challenged in recent years but there are species that do appear to be very broadly distributed.   Even when the species is not familiar (as for the Gomphonema), the genus is identifiable from my experience in Europe. This is in stark contrast to many other groups of organisms encountered in the tropics and sub-tropics.   It does make life easier for the travelling phycologist though, fortunately, there are still plenty of surprises waiting for us out there.

If you want to see Pangong Tso for yourself, Indus Experiences are organising a two-week geology and ecology excursion to Ladakh next year.   See you there.

Reference

Kelly, M.G., Trobajo, R., Rovira, L, & Mann, D.G. (2014). Characterizing the niches of two very similar Nitzschia species and implications for ecological assessment. Diatom Research DOI:10.1080/0269249X.2014.951398

 

Diatoms from Pangong Tso

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.

Pangong_Gomphonema_clean

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).

Pangong_Diatoma.clean

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.

Pangong_Nit_inconspicua

Nitzschia inconspicua from the littoral zone of Pangong Tso, north India, September 2014. Scale bar: 10 micrometres (= 100th of a millimetre).

Pangong_Achnanthidium_minut

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 …

Pangong_Amphipleura_rutilan

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).

References

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.