Meetings with remarkable Gomphonema …

Having written about Gomphonema rhombicum in my previous post, I thought it would be worth staying with Gomphonema and showing some images of G. vibrio.   This is a diatom that I had rarely encountered previously but which cropped up in separate email conversations with Chris Carter and Geoff Phillips in the space of a couple of months.  Chris’ samples come from a small man-made pond at Yardley Chase, an SSSI in Northamptonshire (photographed above), whilst Geoff’s was from Phragmites stems in a Norfolk marsh dyke.  Both have hard water (Geoff’s location: pH: 7.6; alkalinity: 275 mg L-1 CaCO3; conductivity: 700 mS cm-1) and good water quality (TP: 60 mg L-1; TN: 1.5 mg L-1).   This set of conditions prompted me to dig out some samples from Croft Kettle, a location I wrote about a couple of years ago (see “The desert shall rejoice and blossom …”) where I had a vague memory of having seen something similar.

Valves of Gomphonema vibrio are relatively large (30 – 95 x 7 – 10 mm, according to Hofmann et al., 2017) and club-shaped with a slight swelling at the centre.  Overall, the valves are more slender than was the case for G. rhombicum (see illustrations in the previous post).   The striae are coarse (7 – 10 in 10 mm) and mostly radiate, but there is a distinct central area where there is a single stria on each side more distantly spaced from the adjacent striae than in the rest of the valve.  On one side, this stria is very short (sometimes it can be hard to see); on the other side, it is longer and ends with a distinct stigmoid (an isolated pore).    The central endings of the raphe are often turned to the same side.

Cleaned valves of Gomphonema vibrio from a pond at Yardley Chase, Northamptonshire.  Yardley Chase is shown in the image at the top of the post.   Images are in pairs, each at a slightly different focus plane.   All photos by Chris Carter.

Chris also sent me some photographs of the living cells, showing a clear stalk protruding from the narrower “foot” pole, as well as a beautifully-clear H-shaped chloroplast.  The presence of a stalk in this species just doubles my annoyance at not having checked for the same in G. rhombicum before cleaning the valves.

There are, it seems, remarkably few records of Gomphonema vibrio from the UK.  I can find no other records from rivers and Helen Bennion found just two other records of recent samples in the UCL database, both from Scotland: Loch Levan and Loch Davan.  Three of the five records are from ponds, which may be significant, and two of these were epiphytes, though there are not enough records here to make any firm pronouncements about habitat preferences.  However, the picture that is emerging is of a species that definitely has a preference for moderately hard to hard water with relatively low nutrients. If that is the case, then it could well be a species that used to be more common that it is now, as many habitats such as these will have deteriorated in recent decades due to agricultural enrichment.   It is certainly a very different habitat from the soft water, fast-flowing stream from which I recorded G. rhombicum in Bulgaria.

Live cells of Gomphonema vibrio from a pond at Yardley Chase, Northamptonshire.  Photos by Chris Carter. 

That makes a total of five records from the UK which, even allowing for the muddled taxonomy (which I’ll talk about in the next post) and the fact that the diatoms of small ponds are rarely studied, suggests that this may be a genuinely rare. It is listed as an “endangered species with persistent risk factors” on the German red list, with a forecast of further decline over the next ten years.   I’ve voiced my concerns about “rarity” and red lists before (see “A red list of endangered British diatoms?”) but will stick my neck out on this one and suggest that Gomphonema vibrio might be a candidate.

Reference

Lange-Bertalot, H., Hofmann, G., Werum, M. & Cantonati, M. (2017).   Freshwater Benthic Diatoms of Central Europe: Over 800 Common Species Used In Ecological Assessment (edited by M. Cantonati, M.G. Kelly & H. Lange-Bertalot).   Koeltz Botanical Books, Schmitten-Oberreifenberg.

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Who needs a “red list” anyway?

The previous two posts suggested that it might be possible to construct a provisional red list of freshwater diatoms, albeit with several caveats.   The question that still needs to be answered is whether there is any real benefit to such an exercise.

I think we can say with some confidence that a red list of freshwater diatoms will not precipitate a crisis of conscience amongst the national conservation bodies or wildlife trusts, there will be no rush to draw up plans to add rare diatoms to Biodiversity Action Plans and no Sites of Special Scientific Interest will be designated because of the unique diatoms found there.   So why bother?

One problem that I identified in the first post in this series (see “A red list of endangered British diatoms?”) is that those of us who have been studying algae have never been part of the widespread tradition of wildlife recording that takes place around Britain and which is the basis for the red lists of many other groups of plants.   We make our own lists, for sure, but there is no centralised system for either recording or validating records.   This activity has, for many groups, been the preserve of enthusiastic amateurs and, whilst there are amateur phycologists, numbers are well below that required to develop meaningful distribution maps. At present, for many freshwater algae, the distribution maps are more likely to show you where the small number of collectors are most active, rather than offer any profound insights into biogeography.   The freshwater diatoms are an exception here, as I hope I have shown, albeit with several caveats.

The benefits of better recording are twofold.   The first is simply to raise the profile of algae amongst the conservation movements.   I have already shown that algae represent a large part of UK’s total biodiversity (see “The sum of things …”).   In so doing, I added myself to the long list of phycological whingers and windbags who vent their spleens at the way that algae are invariably overlooked by conservationists.   If we want to be taken seriously, we need to start producing evidence of a quality equivalent to that for other groups of organisms.   Distribution maps are a step in that direction.   They are possible not just for some freshwater diatoms but also for some other types of freshwater algae (see ““Looking” is not the same as “seeing”” for an example).   My hope is that production of a preliminary list might, itself, flush out further records and generate a dialogue amongst phycologists and beyond.

The second point is that systematic recording of distributions will, itself, throw up some testable hypotheses. I suggested, in the previous post, that Gomphonema tergestinum might have a restricted distribution that cannot be explained solely by chemical conditions. I’ll return to that in a future post but I suspect that there may be others that also show unexpected patterns. In other words, better recording might well lead to better insights into the ecology of these organisms. We may, indeed, have missed the boat on this topic: the distribution patterns of many species have already been shown to change in response to climate warming (see below for a reference to one example).   Last year I wrote about Hydrurus foetidus, a chrysophyte that I found growing in high altitude streams in Norway (see “A brief excursion to Norway”).   I know that it has been recorded in this country but I have never seen it here. It would be interesting to look at locations where it has been found in the past and see if there is any evidence for it growing now and, indeed, whether there have been any shifts in its distribution patterns.

And my final point is even more basic.   There is already a provisional atlas of the slime moulds of Britain and Ireland. If they can do it for slime moulds, surely we can do it for freshwater algae too. Our professional pride is at stake …

Reference

Fox, R., Oliver, T.H., Harrower, C., Parsons, M.S., Thomas, C.D. & Roy, D.B. (2014.) Long-term changes in the distribution of British moths consistent with opposing and synergistic effects of climate and land use change. Journal of Applied Ecology, 51, 949-957.