Springtime surprises …

My last few trips to the Lake District have been plagued by indifferent, if not inclement, weather.  High flows are the ultimate curse of anyone working on rivers, and recent trips have all been uncertain until almost the last moment as I watched the fluctuations of weather forecasts and hydrographs.  Even once we had arrived, clouds were low and we never seemed to be out on one of those crisp winter days that offers views of distant, snow-capped peaks.   Finally, last week, the sun was able to break through the clouds, at least occasionally, daffodils, primroses and cowslips were in flower and the woodlands were heady with the scent of wild garlic.   

Life under water, however, follows a different trajectory to life on land.   At this time of year, stream beds in West Cumbria tend to look less, not more, verdant.   The algae that are so prolific during the winter were still there, but nowhere near as prolific now.   That was the case at several of the sites we examined but one – the River Cocker just below Crummock Water – bucked this trend in quite a dramatic way.  Peering through my bathyscope, I saw bright pink-red growths, particularly on fronds of the moss Fontinalis antipyretica.   These turned out to be filaments of the red alga Audouinella hermainii, which also smothered many of the stones.

Audouinella hermainii epiphytic on the moss Fontinalis antipyretica in the River Cocker, just downstream from Crummock Water, April 2014.  The photo at the top of the post shows the site where this photograph was taken.

The growths on the stones looked different to those on the mosses, with longer filaments and a brownish, rather than red, colour.  The colour difference may simply be due to the balance between reflected and transmitted light in the two locations; however, the difference in growth form between the two habitats is harder to explain.  In the River Ehen the same alga (so far as I can tell) has the habit shown in the top photo, but here growing on rocks rather than on mosses (see “Not so bleak midwinter?”)

The other complication is that, in the River Ehen, Audouinella hermainii is extremely abundant in the winter and early spring but is not visible between about May and August, after which it starts to become obvious again.   The growths I saw last week were not the first records from this site, but they are both the most abundant records and the only time it has been so prolific this late in spring.   I also found one record from the River Crake, just below Coniston Water, where A. hermainii was prolific in June.  What’s more, neither the Freshwater Algal Flora of the British Isles nor West and Fritsch’s Treatise on the British Freshwater Algaemakes reference to this species having a particular predilection for winter and spring.   The former says it is “… most common as an epiphyte on … bryophytes” whilst the latter says “… usually attached to rocks and stones in rapid rivers”.   Both agree, however, that it is more likely to be encountered in streams and rivers than in lakes.  It is the Ehen that seems to be the outlier, but it is also the river where I find it most often, hence my inference about its seasonality.   

Audouinella hermainii on stones in the same stretch of the River Cocker as the epiphytic growths in the previous photograph.   

Another reason for treading cautiously is that the red algae present us with some particular challenges when it comes to identification (see “Something else we forgot to remember” and “Reflections from the trailing edge of science”).   Although the view through a microscope shows similarities amongst these populations, these differences in habit and seasonality make me question whether I am looking at the same organism across all these locations. 

I’m conscious that my understanding of this species is drawn from records from a limited geographical area.  On the other hand, the “big picture” for other people may encompass different sites to mine but, I suspect, will include fewer records from the depths of winter.   Then again, mid-winter and early spring in rivers flowing out of lakes will have quite different thermal and hydrological characteristics to the same seasons in unregulated streams flowing off the Alps, for example.   Is anyone’s “big picture” ever big enough to make generalisations?

Vegetative filaments of the red alga Audouinella hermainii from the River Cocker, just downstream from Crummock Water.   Scale bar: 20 micrometres (= 1/50th of a millimetre).  

There are certain other algae that I also associate with late winter and early spring (Ulothrix zonata, Draparnaldia glomerata, for example).  However, most of these turned out to show similar patterns to Audouinella hermainii when I collated my data, with just enough outliers to confound my expectations.  The likelihood is that these plants do not have circannual rhythms hard-wired into their physiology, but are opportunistic, reacting to circumstances.  Their optimal conditions may be more likely to occur at particular times of the year, but there are also exceptions, giving rise to my observations last week.   

That unpredictability is what keeps me wanting to head out into the field, even when the weather is not ideal.  It is also a reason to want to keep going back to the same sites, so that I can watch patterns unfold, and also a reason to want to visit different sites, so that I can fit my observations drawn from a limited area into a broader perspective.  Beware the ecologist who speaks with too much confidence.  The chances are that they are not spending enough time getting cold and wet in the field.   

Records of Audouinella hermainii from West Cumbrian rivers and streams, 2020 – 2022.  The y axis shows the cover of the alga using the 9-point scale adopted for macrophyte assessments in the UK.   Vertical lines indicate the twelve months of the year.  

Some other highlights from this week:

Wrote this whilst listening to:  Easter music: Stanier’s Crucifiction and Bach’s St Matthew’s Passion.

Currently reading:   Still Colm Tóibín’s The Magician.

Cultural highlight: The Raphael exhibition at the National Gallery.   

Culinary highlight: Grilled mackerel on Asian salad, prepped and made at the Cordon Bleu cookery school in London during a short course on knife skills.

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One thought on “Springtime surprises …

  1. Pingback: More than just hitchhikers … – microscopesandmonsters

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