Dear Julian,

I have never published on this topic but have several observations on algal paper formation in a lake in the southeastern Alps: Lake Tovel (Brenta Dolomites; Adamello-Brenta Nature Park).

The lake undergoes relevant, natural water-level fluctuations (on average 4 m over the seasons). This causes the southwestern part (known as Red Bay) to almost fall dry in winter. Green filamentous algae (mainly different genera and species of Zygnemales) tend to concentrate in this southwestern part that benefits from a large groundwater input (cold & nutrient-richer as compared to the lake) (see attached paper). The development of these green filamentous algae is often massive, and, when the level drops during winter, the algae are exposed and bleached by the sun. The bottom of the buy is thus covered by whitish sheets resembling paper. In snow-poor winters, I often receive requests from people who are curious to know what these paper-like structures are (sometimes even worried about possible pollution).

Best wishes for 2018!

Marco Cantonati

Dear Marco,

Many thanks for your interesting observations on algal paper in Lake Tovel, and its formation from dense green algae (Zygnematales). I read your informative paper on the lake with much interest.Lake Tovel is very different from Irish lakes, leading me to believe that many more examples of algal paper formation will present themselves.

In the humid space beneath the paper felts I have seen various invertebrates, including leeches (Hirudinea), snails (Lymnaea sp.) and dragonfly nymphs (Odonata), I speculate that its ultimate breakdown is facilitated by terrestrial macrofauna, but I have not so far made observations at the right time.

My best wishes for the new year

Julian

Maybe this work will allow you to understand the phenomenon you are asking about.

With best wishes

Konrad W.

Dear Konrad,

thank you for this interesting paper.

Similar but not completely the same.

The main constituent of the 'algal paper' we are talking about are typically green algae, to allow for a cellulose-based matrix.

The cyanobacteria-dominated epilithon described in your paper is also typical of the littoral of artificial and natural lakes that undergo marked water-level fluctuations (including the Main Basin of Lake Tovel; please see the paper I attached to my previous answer + the one in attachment). The greyish color is determined by the UVA photoprotective compound scytonemin (appearing yellow-golden in the sheaths of cyanobacteria at the microscope).

Best wishes for 2018! Marco

Many thanks Konrad and Marco, for your helpful suggestions and insights.

The whole issue of biofilms is interesting (another, cyanophyte-dominated, occurs on limestone rocks in some western Irish turloughs, and is the food basis for a rare beetle, Ochthebius nilssoni; see attached).

The chlorophyte-dominated 'algal paper' can occur widely if the conditions are right; warm shallow lime-rich water, gradually drying. I am attaching a short description from the Aran Islands off western Ireland.

Julian

Dear Julian,

I have more impressive images of algal-paper formation at Lake Tovel but can't find them at the moment... However, I like the one I attached because it shows a series of different stages of algal paper formation: - looking carefully one can see the filamentous green algae (Zygnemales) amassing on stones in the shallow near-shore water, then there are light-green dried green algae that still retain some chlorophyll, and finally the bleached whitish algal paper.

Best regards.

Marco

Dear Marco, thanks for your impressive photo of Lake Tovel and algal paper!

Perhaps this summer I can find some Irish examples.

Best wishes

Julian