Escape to Southwold


We took advantage of the quiet mornings at Latitude to drive off the site and explore the countryside around Southwold.  I had memories of a family holiday here in 1968 and little seems to have changed: it is traditional seaside town, seemingly frozen in time, with a pier, beach huts (as in the image above), a lighthouse and a row of cannons facing out into the North Sea.

As we followed footpaths along the dykes beside the creeks, I noticed a red mat of vegetation covering the surface in one of the stagnant areas close to the A1095.   Closer inspection revealed this to be the floating fern Azolla filiculoides, an introduced plant that is quite common in the south of England but which is an unusual sight to an adopted northerner such as myself (see also “No longer a dispassionate observer of nature…”).   Inevitably, I was soon down on hands and knees to pull out a small sample for closer inspection.


Azolla filiculoides in Buss Creek near Southwold, July 2016.  

When seen in close up, each individual plant is about a centimetre across, but is composed of tiny fronds, each no more than a couple of millimetres in size.   Long hair-like roots hang underneath the plant.   The red colour is due to pigments called anthocyanins, which belong to a class of compounds called flavonoids and which offer the plant some protection against very high light intensities (an alternative strategy to that seen in Cladophora in the previous post).   Interestingly, anthocyanin production also takes place in response to low temperatures, possibly because the generally low metabolism of the plant under such conditions leads to the same build-up of excess energy when there is abundant light, because the cell machinery is grinding along at too slow a pace to keep up with photosynthesis.


Left: collecting Azolla filiculoides from Buss Creek near Southwold, July 2016; right: fronds of Azolla filliculoides in the palm of my hand.

One of the intriguing features of Azolla is that it, along with the pea family and a few other groups of organism an ability to fix nitrogen.  This allows it to grow in habitats where nitrogen, a naturally scarce plant nutrient, is in short supply.  Like the pea family, Azolla does not, itself, capture and transform nitrogen into the compounds it needs to grow, but carries a complement of passengers who do this work for the plant.   The symbiotic organism in the case of Azolla is the cyanobacterium (blue-green alga) Anabaena and I was keen to have a closer look at my Azolla to see if I could tease these out.  However, as I mentioned in my previous post, festival conditions are far from ideal for preserving fragile plant specimens, and my material was not in a very healthy state by the time I got it under my microscope.

The blue-green filaments of Anabaena were, nonetheless, conspicuous, once I had squashed a few fronds gently under a coverslip.  Anabaena is a close relative of Nostoc (see “Nosing around for blue-green algae …”) and also forms long chains of bead-like cells that resemble rosaries.   Look at the photograph below and note how there is a larger cell spaced at intervals along each filament.   These are the “heterocysts”, the specialised cells that contain the enzymes responsible for nitrogen fixation.   The ease with which Azolla grows in damp habitats, particularly in warm climates, and the ability of “Team Anabaena-Azolla” to catch large quantities of nitrogen means that Azolla is grown as a “Green Manure” in some parts of the world, as it bypasses the need to buy expensive artificial fertiliser.



Anabaena filaments from a squashed frond of Azolla filiculoides from Buss Creek near Southwold, July 2016.   Scale bar: 10 micrometres (= 1/100th of a millimetre).

Sample safely collected, we followed the dyke across the marshes (all slightly below sea level here) until Buss Creek joined the River Blyth and we then turned towards the sea.   As we reached Southwold Harbour, we found a small café offering fresh crab sandwiches, which sounded too good to resist, even though it was barely 11:00.   And, from there, it was just a short walk back to Southwold.   A few kilometres away, the Latitude Festival was getting under way again, and our brief sojourn in Southwold had to be curtailed in favour of other attractions, culminating in a rather impressive headline set by The National.  For one weekend in the year, at least, Suffolk is not quite the boring county that most of us think.


Janes, R. (1998).  Growth and survival of Azolla filiculoides in Britain. 1. Vegetative reproduction.  New Phytologist 98: 367-375.


The National’s headline set from Latitude 2016


No longer a dispassionate observer of nature …

I wrote my previous post whilst on an EasyJet flight to Malta and, yes, I did feel pangs of guilt writing about climate change at the same time that I was adding significantly to my carbon footprint. That’s one of the great conundrums of my life: on the one hand, I need a global (or, at the very least, a European) perspective in order to do my job. Yet, in gaining that perspective I become part of the problem.20150417-082337.jpg

A pond at Argotti Botanic Gardens, Valletta, Malta, April 2015.

So here I am in Valletta, capital of Malta, a country whose properties as summarised by Luke in the Acts of the Apostles still remain true (ch. 28 v. 2: “… the natives showed us unusual kindness …”). And, Lo and behold, I find myself at the University of Malta’s Argotti Botanic gardens, (which may well be coming to a blog near you before too long) where there is a pond into which I stare. And in that pond I see a mass of vegetation that, from a distance, resembles duckweed in appearance. However, in close-up they resolve into a series of tiny overlapping leaves with, hanging beneath them, a bunch of roots, a couple of centimetres long. Most of the leaves are green but several are reddish in colour. This is Azolla, which is, despite appearances, an aquatic fern, very common in the warmer parts of the world. It contains a symbiotic nitrogen-fixing Cyanobacterium (blue-green alga) which means that, like terrestrial legumes, it can grow in situations where most other aquatic plants cannot thrive. There has been a lot of research over the years into the potential for encouraging Azolla to grow as a “green manure” in paddy fields.



Azolla sp. in a pond at Argotti botanic gardens.  There are a few leaves of Lemna in the foreground to give an indication of scale.

A little further on, I saw another pond whose surface was covered by another aquatic fern, Salvinia. This is larger than Azolla and lacks a nitrogen-fixing partner, but it is also very common in warmer parts of the world. Both grow by extending and branching their underwater stems and adding new leaves in such a way that they can rapidly cover large areas of a pond’s surface if conditions are favourable.



Salvinia sp in a pond at Argotti botanic gardens.

And there is evidence that conditions are getting increasingly favourable for both Azolla and Salvinia. Azolla filiculoides is not native to the UK but was introduced during the 19th century and, for a long time, the scattered records were confined to the south and midlands. The latest distribution maps, however, suggest that it is now widespread in these areas and has also been recorded from the north of England and Scotland.

Salvinia has not been recorded from the UK but there is an interesting study from Poland where this species, too, has been introduced and is on the increase. There is good evidence from northern Poland of warming associated with the North Atlantic Oscillation. This allows spores of Salvinia to germinate earlier in the year and, crucially, fewer frosts in the Spring means that the delicate young stages are more likely to survive. The fronds are also able to continue to grow – and spread – later in year too. All these factors combine to help this alien species extend it’s distribution not just in Poland but elsewhere in northern and Central Europe where it has not previously been seen.

There lies the irony. Plants such as Azolla and Salvinia are opportunists, adapted to spreading fast when conditions are favourable. You can find evidence for many other plants and animals whose distribution has changed in recent years. And, yes, I can’t avoid the comparison with the opportunism of humans, offered a cheap flight for a brief escape from the chilly British spring. At times such as these it is better that I accept that I am not a dispassionate observer of nature and, in fact, a small part of the systems that I study.

Gałka, A. & Smezja, J. (2012). Phenology of the aquatic fern Salvinia natans (L.) All. in the Vistula delta in the context of climate warming. Limnologica 43: 100-105.