Three months after my last visit to Deptford Creek and I am back, helping out with an event organised by the Creekside Discovery Centre that aimed to introduce the microscopic world of algae to the wider public. I’m interested to see what has changed since my last visit (see “Dispatches from the city of migrants …”) and the first thing I notice is a lush coating of vegetation on the upper part of the mudflats.
The muddle of prostrate stems and leaves is a species of Callitriche (water starwort) and will, when the tide comes in, lift up to create a submerged jungle amongst which the aquatic life of the creek can thrive. It sits amidst a filamentous algal undergrowth whose two-dimensional appearance is, similarly, only temporary. The tidal ecosystem is nature’s equivalent of flatpack furniture: neatly packing itself away during low tides but self-assembling into an instant three-dimensional habitat, perfect for a wide range of organisms of taste and discernment.
Callitriche sp. from the upper mudflats of Deptford Creek in June 2024 (see photo at top of post).
The other noticeable change from my previous visit was the addition of a darker green hue to the palette of colours on the mud surface, and also on the vertical surfaces of the training walls. Scraping some of this off revealed it to have abundant cyanobacterial filaments – a species of Oscillatoria whose filaments slowly glided across the field of view as I watched.
Oscillatoria sp. from the mudflats at Deptford Creek, June 2024. Scale bar: 20 micrometres (= 1/50th of a millimetre).
When I had got samples under the microscope, however, other changes became apparent. On earlier visits, I had noticed numerous cells of Nitzschia sigma in the samples we had collected on tissue paper from the mud surface (see: “Floundering around in Deptford Creek …” and “Deptford’s Heart of Darkness …”). This time, however, a different species of Nitzschia predominated. Nitzschia brevissima is also sigmoid, and I still wonder what advantages this shape confers on a single-celled organism (see “Nitzschia and a friend …”). There are at least three distinct sigmoid diatoms at Deptford Creek, so there must be something about the habitat that selects for this property. One other property of N. brevissima is that the two chloroplasts are not arranged in the typical “fore-and-aft” arrangement seen in other representatives of the genus Nitzschia, but are overlapping. I have not seen any reference to this (most images I found on the internet were of cleaned valves, but the sole image that showed a living valve also showed this property).
Nitzschia brevissima from Deptford Creek, June 2024, with characteristic overlapping chloroplasts. Scale bar: 10 micrometres (= 1/100th of a millimetre).
Several other diatoms were present alongside Nitzschia brevissima, one of which I could not identify readily. Navicula gregaria was also abundant, along with a small Luticola (probably L. mutica) and more. I had limited time to look at these samples so the list of species that I could record is shorter than the lists made during my earlier study. I can come back to this sample and make a fuller list once I have prepared a permanent slide.
Top row: unidentified (as yet) naviculoid (valve views with a girdle view on the right); bottom row: Navicula gregaria. Scale bar: 20 micrometres (= 1/50th of a millimetre).
Projecting the microscopic organisms we found on the mud at Deptford Creek onto a large video screen to show them to an audience unfamiliar with this world evoked plenty of “oohs” and “ahhs” and a string of questions. The volunteers at Creekside are busy collating the data they’ve collected over the past few months to give some insights into how the Creek changes with the seasons. Hopefully, this will help to put the observations I’ve made on my sporadic visit into a broader context.
Once the last visitor had drifted off and the staff and volunteers had tidied up, I had time on my hand and decided to walk the eight kilometres from Deptford Creek to Tower Bridge. The tide was now in, presenting a very different aspect, with no mudflats visible, but plenty of views of dockland and the city’s skyscrapers before, finally, Tower Bridge came into view. For the last kilometre or so, the walk alternated between the riverside path and narrow streets between Victorian warehouses that evoked a Dickensian London, gradually funnelling me towards the immediate environs of Tower Bridge, lined with pubs and restaurants and heaving with tourists. They respond to different stimuli and, like the diatoms, they ebb and flow. In a few hours, the riverside paths will be quiet and, a few hours after that, they will be packed again with a new horde. The fluxes in Deptford Creek becomes a metaphor for city life in general. Or is city life a metaphor for life in a tidal creek? Maybe the answer depends on your standpoint …
Some other highlights from this week:
Wrote this whilst listening to: Neon Flicker, new EP by Noaskk
Currently reading: The Next Great Migration by Sonia Shah. Compares migration in the natural world with current attitudes to human migration.
Cultural highlight: I’m in the Lake District, surrounded by the landscapes that inspired Wordsworth and my favourite as a child, Arthur Ransome.
Culinary highlight: I’m teaching in the Lake District, subsisting on carb-heavy pub food but driving past the Old Stamp House in Ambleside every day, so my culinary highlight this week is the memory of our meal there last December.
microscopesandmonsters 