Joseph Conrad set the opening passage of Heart of Darkness on a boat on the Thames, waiting for the tide to turn so that it could set off, carrying Marlowe, Conrad’s protagonist to Africa. Conrad starts his story with a river that would have been familiar to many of his readers before taking them to the Congo, which would have been alien and exotic. Only the hardiest and most intrepid of souls would have been able to face the challenges that the tropical climate – and the plants, animals and diseases that thrived there – presented. Marlowe and his companions were, most likely, just a few kilometres from Deptford Creek, the urban intertidal habitat whose diatoms I described in two posts towards the end of last year (see “Floundering around in Deptford Creek …” and “Commuting to work …”). They were, ironically, surrounded by organisms that were, then as now, just as exotic and unbelievable as the inhabitants of the African rain forests, if only they had cared to look.
In my earlier posts, I covered the macroscopic and live microscopic views of the diatoms. In this one, I am taking the “classical” approach of examining cleaned valves at high magnification, in which the information about chloroplasts and motility that we lose is offset, to some extent, by the close detail of surface ornamentation that is revealed. There is also an element of circular reasoning here: the traditional taxonomists who write the essential identification guides all assume that their readers are viewing a cleaned valve at high magnification, which puts anyone observing a living cell at an instant disadvantage.
Overall, I found 53 species in the two samples that I collected back in November, of which 32 are illustrated here. Both samples were dominated by motile diatoms (63 and 66 percent respectively), reflecting the silty nature of the habitats here. The first plate shows the diatoms from the stones in the centre of the creek, many of which I also find in lowland fresh water habitats. The second is a scraping of the diatom film growing on the mud surface, and most of these diatoms are genuinely brackish or marine. I did, however, find a surprising number of valves that I associate with good ecological status – Tabellaria flocculosa, Achannthidium spp. and Brachysira microcephala. It is not unusual to find a few cells of these that have drifted into samples from habitats further upstream, but 8.5 percent of the cells in this sample had this preference, which is more than I would have expected. I see no plausible habitats for these species in the densely-urban catchment of Deptford Creek so this is something of a mystery. Missing from the list is Hydrosera triquetra, a tropical diatom that has become common in the lower Thames over the past 50 years. I did see one girdle band but have not yet found an intact cell or frustule.
I’m a Londoner, born less than 10 kilometres from Deptford Creek and, in some ways, the diatoms in these samples remind me of the city itself. They are diverse, some are immigrants that have chosen to settle here, others are indigenes, adapted to intertidal muds. The mudflats, themselves, are forever changing. What I see in November 2023 might not be what I will see a few months later just as the London I remember from the 1960s and early 1970s is very different to London in 2024. Indeed, the docklands skyline, which we can see from the Creek, was not there in my childhood, nor were many of the skyscrapers in the city, a short distance upstream. Watching nature ebb and flow in the shadow of these apparently substantial structures helps to remind us that change is the only constant. Even in a city with a history as rich as London’s. Looking at diatoms in mudflats reminds us that we do not have to get on a boat and travel vast distances to get to unknown and unexplored places, as Marlowe was doing in Conrad’s tale. It only takes a short journey on the Dockland Light Railway to find worlds still waiting to be explored.
Deptford Creek diatoms, plate 1. Scale bar: 10 micrometres (= 1/100th of a millimetre).
| a., b. | Nitzschia filiformis var. conforta | c. | Nitzschia dissipata |
| d., e., f. | Nitzschia sociabilis | g. | Nitzschia amphibia |
| h. | Nitzschia inconspicua | i. | Nitzschia sigma |
| j. | Tryblionella angustatula | h. | Gyrosigma acuminatum |
| l., m.,n.,o. | Rhoicosphenia abbreviata | p. | Amphora pediculus |
| q. | Delphineis surirelloides | r., s., t.u., v. | Navicula gregaria |
Deptford Creek diatoms, plate 2: centric diatoms. Scale bar: 10 micrometres (= 1/100th of a millimetre).
| a., b. | Actinoptychus sp(p) | c. | Actinocyclussp. |
Deptford Creek diatoms, plate 3: Nitzschia and Tryblionella. Scale bar: 10 micrometres (= 1/100th of a millimetre).
| a. – d. | Nitzschia sigma | e. | Nitzschia cf. capitellata |
| f. | Nitzschia pusilla | g. | Nitzschia … |
| h. | Nitzschia inconspicua | i., j. | Tryblionella apiculata |
| k. | Tryblionella littoralis |
Deptford Creek diatoms, plate 4. Scale bar: 10 micrometres (= 1/100th of a millimetre).
| a. | Raphoneis amphiceros | b.,c. | Frustulia vulgaris |
| d., e. | Achnanthes brevipes | f. | Tabellaria flocculosa |
| g.,h.,i. | Achnanthidium spp. | j. | Brachysira microcephala |
| k. | Cocconeis pediculus | l. | Cocconeis euglypta |
| m.,n. | Navicula gregaria | o. | Navicula sp. |
| p. | Fallacia subpygmaea | q. | Luticola mutica |
| r. | Surirella sp. |
Reference
Hartley, B., Barber, H.G. & Carter, J.R. (1996). An Atlas of British Diatoms. Biopress, Bristol.
Tittley, I. (2014). Non-native marine algae in southeastern England. Bulletin of the Porcupine Marine Natural History Society 1: 28-32.
Witkowski, A., Lange-Bertalot, H. & Metzeltin, D. (2000). Iconographica Diatomologica 7: Diatom Flora of Marine Coasts 1. Koeltz Scientific Books.
Some other highlights from this week:
Wrote this whilst listening to: Dire Straits first album. Mainly because, whilst Googling “Deptford Creek”, I learned that Dire Straits first got together in this part of London in the mid-1970s
Currently reading: A Gentleman in Moscow by Amor Towles.
Cultural highlight: Small exhibition of charcoal portraits by Frank Auerbach at the Courtauld Gallery. Intense records of encounters with a few close friends worked and reworked in classic Auerbach style. Emerging from the exhibition into the room holding the Courtauld’s collection of classic Impressionist paintings seemed almost anticlimactic.
Culinary highlight: Dhosa in Chutneys in Drummond Street near Euston Station in London following the first British Diatom Meeting since lockdown. Mostly for the sheer pleasure of spending a day and sharing a meal with friends I had not seen for a long time.
microscopesandmonsters 