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.
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.
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