If the photograph below looks vaguely familiar it may be because you are old enough to remember the 1970s as this scene of the Ouseburn valley in Newcastle is part of the opening sequence of Whatever Happened To The Likely Lads? Were they to revisit now, Terry would be appalled, but proto-bourgeois Bob delighted, to see the first stages of gentrification creeping through the area.
Lime Street, Ouseburn valley, Newcastle, March 2015, looking upstream towards Jesmond Dene. The entrance to Seven Stories, the National Centre for Children’s Books, is just visible on the right of the picture.
Follow the road off to the right and you pass the Cluny, a pub with a good range of real ale and a strong reputation as a live music venue, then past a warehouse (now converted to artist’s studios) to an old ford across the Ouseburn. I wrote about the Ouseburn back in October, when I made my annual visit with a group of undergraduates but the section I have brought you to today is close to the point where the stream joins the Tyne, and is tidal. I had seen some interesting growths of diatoms here in the past so had come back at low tide to add a brackish dimension to the story I was telling in The Ecology of Cold Days.
I was looking for the chocolaty-brown film on the tops of rocks, similar to those that I described in my earlier post but these were not obvious today. Instead, I found some intriguing diatom growths on the vertical wall of the old warehouse just above the water level. I scraped up some of this film and took it home for a closer look.
These samples were, as I expected, teeming with diatoms, though the assortment of diatoms that I could see was quite different to those I had seen before. I have written about estuarine diatoms in a couple of posts (see “In the shadow of the Venerable Bede”) but do not pretend to any great expertise. However, most of the genera are familiar to me from freshwaters, even if I cannot name the species. I could see Navicula and Nitzschia, both common in the river samples that I wrote about in The Ecology of Cold Days; however, the most abundant genera were a species of Surirella (also common in freshwaters) and, in particular, Entomoneis; a genus that is relatively rare in freshwater (see “The Really Rare Diatom Show“).
The view down the Ouseburn; the former warehouse (now artist studios) is on the right foreground; beyond is the back of Seven Stories. The right hand image shows the diatom film just above the waterline on the side of the warehouse.
Entomoneis is a diatom whose structure is difficult to capture in a photograph as the cells are twisted around the apical axis (see Chris Carter’s photographs in The Really Rare Diatom Show). The right hand image below is an empty frustule lying in girdle view; the other four images are live cells. The constant motility of the living cells was an additional complication as I was trying to photograph them.
Common features about all these biofilms that I’ve written about over the past year is that they are dominated by diatoms that are capable of movement and they seem to be especially luxuriant in the cooler times of the year. Being able to adjust their position is, obviously, an advantage in an unstable environment where there is a chance that particles will shift or new ones be deposited, robbing the cell of the light it needs for photosynthesis. Luxuriance in the winter and early spring may reflect the absence of grazers at these times of the year, but there are also hints in the literature that some algae are particularly well adapted to growing at low temperatures. It is natural selection in action: having a physiology that functions in cold water lessens the chances of the fruits of their photosynthesis being turned into another organism’s roughage.
Entomoneis’ fondness for the cold extends far beyond north-east England: a recent paper recorded it as the most abundant alga growing on the underside of sea ice in the Antarctic. It is, in other words, a typical Geordie alga, swaggering through the Ouseburn’s biofilms dressed in a tee-shirt, regardless of the weather. Terry would have approved.
Entomoneis sp. from the tidal section of the Ouseburn, March 2015. The right hand image is an empty frustule. Scale bar: 10 micrometres (= 100th of a millimetre).
Archer, S.D., Leakey, R.J.G., Burkill, P.H., Sleigh, M.A. & Appleby, C.J. (1996). Microbial ecology of sea ice at a coastal Antarctic site: community composition, biomass and temporal change. Marine Ecology Progress Series 135: 179-195.