Piggy-back algae in Kilmartin Glen

The skies are finally clear and we actually felt the sun on our faces for the first time this year on Monday, even if the biting wind made a fleece essential and views south down Loch Fynne were dominated by the snow-covered fells of Arran.

I had travelled about ten kilometres north from Knapdale to Kilmartin Glen, an area rich in Neolithic, bronze and iron age remains.  It is a wide, flat-bottomed former valley with scattered basalt outcrops, leading down towards the Sound of Jura at Crinan.  The valley bottom is grazing land, with the steeper slopes either moorland or plantation forestry or left as open moorland. Kilmartin Burn, which flows down the middle of the valley, looks far too small for the catchment it drains, as is often the case in these recently glaciated environments.

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Kilmartin Glen, near Carnassarie Castle, Argyll and Bute, Scotland, April 2013.

The stream bed was surprisingly rich in vegetation, perhaps reflecting the relatively shallow slope here.  Alongside the usual bryophytes that we expect in streams such as this there were some extensive growths of the water milfoil, Myriophyllum alterniflorum.  I pulled up three shoots, popped them into a small glass vial with a few millilitres of stream water and shook them.  The photograph below shows the water in the tube after I had removed the stems, brown with the epiphytes – the algae that live attached to and associated with the plant (the aquatic equivalent of ivy).

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The left hand picture shows Myriophyllum alterniflorum in Kilmartin Burn, Argyll and Bute, Scotland in April 2013; the right hand picture shows three stems after they had been shaken in a few millilitres of water to remove epiphytes.

Myriophyllum has whorls of very finely-divided leaves – as if each had been reduced to just the veins.  This means that it has a much higher surface area : volume ratio than a conventional leaf, making it easier to absorb nutrients and dissolved gases that it needs to grow.  However, this also creates sheltered areas where diatoms and other algae (mostly diatoms in this example) can live a piggy-back existence protected from the stream current.

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Diatoms growing on Myriophyllum alterniflorum in Kilmartin Burn.  a. Ulnaria (Synedra) ulna; b. Meridion circulare; c. Cocconeis placentula.  Scale bar: 10 micrometres (1/100th of a millimetre).

Under the microscope, I can see long, needle-like cells of Ulnaria ulna, fan-like colonies of wedge-shaped cells of Meridion circulare and elliptical cells of Cocconeis placentula.  We encountered C. placentula in a very different habitat in Cassop Pond and it is a very common species in freshwaters throughout the UK and beyond.   Ulnaria is a relative of the Fragilaria rumpens which we met at Cassop, albeit much larger.   This population was composed mostly of cells that were about a tenth of a millimetre long, but they can grow to a quarter of a millimetre or more: veritable giants in the microscopic worlds where I spend so much of my time.

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In pursuit of beavers

I’m taking a temporary break from writing about the unfashionable end of British biodiversity to gaze out across a Scottish loch at a large hemispherical construction built from tree trunks and branches.  The loch is Loch Linne, about 10 kilometres from Lochgilphead in Argyll and the structure in front of me is a beaver lodge.  I’ve just walked to where I am standing from Loch Coille-Bharr, where an even more impressive structure, a dam stretching for some 50 metres, has blocked the narrow outflow stream from the smaller Dubh Loch, almost doubling this loch’s size as a result.

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Left: the beaver lodge at Loch Linne, Knapdale and, right, the dam between Dubh Loch and Loch Coille-Bharr.  Both are part of the Scottish Beaver Trial in Knapdale Forest, Argyll and Bute, Scotland.

Beavers were once indigenous to Britain but were hunted to extinction, largely because of the value of their fur (see Vermeer’s Hat by Timothy Brook for a fascinating account of the beaver trade).  The Knapdale Forest region is the location for a large scale trial to investigate the possibility of reintroducing beavers more widely in Scotland.   As I have a long-standing interest in what we mean by a “natural” ecosystem, I’ve been following this trial with interest.

Beavers live on a diet of aquatic vegetation and the dams are a means of flooding lake and stream margins in order to create extra habitat with water deep enough for them to swim.  It takes a lot of timber to build the dam and the lodge and we can see the evidence in the gnawed stumps of trees around the loch margin.  As an ecological curiosity these very visible signs of an elusive mammal in a remote area are fascinating, and the flooded landscapes that they create is host to many other types of wildlife.   However, you wouldn’t want a family of beavers living too close to your own land. Part of the irony of the Knapdale trial is that new raised paths have had to be built to let visitors access areas that the beaver have flooded.  As ever in ecology, ‘nuisance’ is a matter of perception and proximity, never an absolute.  A couple of years ago I told a German colleague about this project and he turned to me with an incredulous look on his face and said “you must be mad: we’ve been trying to get rid of them for years”.

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Left: the beaver lodge at Loch Linne, Knapdale and, right, the dam between Dubh Loch and Loch Coille-Bharr. Both are part of the Scottish Beaver Trial in Knapdale Forest, Argyll and Bute, Scotland.

The other thought that passes through my mind as I look at the beaver’s engineering exploits is how little we can ever understand about the ‘natural’ condition of our landscape purely by looking at contemporary evidence.   We all come to Scotland with pre-conceptions about babbling highland burns.  Yet, if we turn back the clock 400 years to a time when beavers were common in Scotland, then a proportion of those burns will have been dammed, with the water spilling out of the channel and flooding the valley floor.  The animals and plant communities that would have lived in those streams would  have been similar to those we find today in remote regions of Scotland, but not identical. Some species that we think of as rare would have been more common and vice versa.  This is of more than just semantic interest as ecologist’s views of the past defines our expectations for  modern aquatic ecosystems. Sometimes it is good to be reminded that we can, at best, look at the past as through a glass, darkly.