Is algal gloop on the increase?

This post summarises a series of emails that piqued my interest last week.   The first was from Paul Brazier of Natural Resources Wales, asking for information about terrestrial algae. Behind the query lay a concern amongst some bryologists that the quantities of gelatinous algae in some habitats in the west of Britain was increasing and threatening rare mosses and liverworts found in these places.   He quoted bryophyte expert Nick Hodgetts who has recorded less of the rare moss Sematophyllum (Hageniella) micens who had also noted that the sites where he once found it now have a great deal of algal slime.   Other experts had confirmed this trend, and expressed concerns that it was out-competing small oceanic mosses and liverworts. Des Callaghan, another bryophyte specialist noted that a “gelatinous gloop” (which turned out to be the green alga Gloeocystis polydermatica) had overwhelmed the rare liverwort Lejeunea patens at Glen Trool in Galloway, south-west Scotland.

Des also gave me the photograph below, showing the gelatinous algae Coccomyxa confluens on Betula pubescens, competing for space with the neighbouring oceanic liverwort Scapania gracilis. He commented that at this site (Gallwyd, near Dolgellau, in North Wales), the algae is most abundant in the most humid locations, notably in the mist zone of the main waterfall. It appears that, at least here, it is a normal part of the flora and isn’t so abundant that it is something to worry about. At other sites, though, these terrestrial gelatinous species can be much more abundant.


Coccomyxa confluens growing on Betula pubescens at Gallwyd, near Dolgellau, Wales (photo: Des Callaghan)

The other photograph Des sent shows another green alga, Klebsormidium growing on heather (Calluna vulgaris) at Wybunbury Moss in Cheshire. I described Klebsormidium in one of my posts about the River Ehen (see “The River Ehen in November”) noting how it was often found in habitats that were not fully submerged although I had not previously seen it competing for epiphytes on terrestrial plants, as Des’ image shows.   Des directed me to some circumstantial evidence that Klebsormidium may benefit from high N-deposition.

Interestingly, Glen Trool, mentioned above, is close to Round Loch of Glenhead, the subject of intensive studies on the causes and consequences of acid deposition by Rick Battarbee and colleagues at University College London.   These studies have shown a gradual recovery from the worst effects of acid deposition since the 1980s but the decline in sulphur-containing compounds has been more significant than the decline in nitrogen-containing compounds. They suggested that one result is that Galloway lochs such as Round Loch of Glenhead may, as a result, be slightly more nitrate-rich now than in the far past. Until very recently, the effects of this extra nitrogen was masked by the generally negative consequences of the acidity but now the sulphur deposition has reduced, it is possible that the algae are able to benefit from this nitrogen and thrive at the expense of other plants.   Whether the same may hold true for the terrestrial and semi-terrestrial vegetation in the surrounding woods must remain speculation for a little longer but it may help to explain why bryologists are seeing more algae at locations where they hoped to find rare bryophytes.


The green alga Klebsormidium growing on Calluna vulgaris (heather) at Wybunbury Moss, Cheshire, March 2015 (photo: Des Callaghan).


Battarbee, R.W., Simpson, G., Shilland, E., Flower, R.W., Kreiser, A., Hong, Y. & Clarke, Gina (2012). Recovery of UK lakes from acidification: an assessment using combined palaeoecological and contemporary diatom assemblage data. Ecological Indicators 37: 1-16.

I also discuss the ecology of Round Loch of Glenhead in:

Kelly, M. (2012). The semiotics of slime: visual representation of phytobenthos as an aid to understanding ecological status.   Freshwater Reviews 5: 105-119.

Fieldwork tales from the tail of a hurricane …

I had more or less decided to cancel my fieldwork when I heard the weather forecast a couple of weeks ago. The last remnants of Hurricane Gonzalo were blowing themselves out over western and northern Britain and the prediction was for heavy rain over the Pennines. I heard the rain during the night and checked the river levels in the morning. They were not outrageously high, but the trend was upwards and common sense dictated that I wait a day and try again.   You can see from the hydrograph below just how quickly the river rose and then fell again over the course of 24 hours.   Even by 09:00 the following day the river was not at its lowest, but at least it was safe to wade in and collect some samples.


River Levels in the River Wear at the Environment Agency’s monitoring station at Stanhope, 20th – 22nd October 2014 ( The arrows indicate the approximate time of the rainfall associated with Hurricane Gonzalo.

A sign that the river was still higher than usual was that some cushions of moss that are usually well clear of the water were at or, in a few cases, still below water level.   There are a few species of moss, including members of the genus Cinclidotus and Racomitrium aciculare, that seem to thrive on the upper parts of boulders.   They spend most of their life out of the water, then just a few days each year submerged. Those few days will bring down suspended material which will become entrapped around the dense network of stems in the cushions and, in the process, provide a nice little “compost heap” that will keep the moss supplied with nutrients. The stems also trap water, through capillary action, so that the cushions stay moist for some time after the water levels have dropped again.   Yet such generalisations do not explain why a few genera thrive in this habitat whereas others are never found here.

Much of the magic of rivers is associated with organisms which are rarely, if ever, seen: the fish, of course, but also otters, kingfishers and other vertebrate organisms. I’m also fascinated by the microscopic world of rivers. Mosses have the opposite problem: we always see them on visits to rivers yet almost never notice them, let alone spend time unravelling the stories that they can tell us.   I am reminded of Mungo Park’s words back in 1795 (see “More about mosses…”). Perhaps I should write a little more about the extraordinary diversity of mosses over the next few months?


Cushions of Cinclidotus mucronatus just above water level in the River Wear at Wolsingham, October 2014.