John Dodge

If you take a sample in a bottle or specimen tube from any lake, pond, bird-bath, semi-permanent puddle, river, stream or ditch and then examine it with a microscope you are almost sure to find some algae. Whether you can identify them is another matter. Algae are by far the least well recorded of the 'green' plants because they are usually small and therefore need microscopy to discern their features. They are also difficult to identify, but more of that later. In general the only time when freshwater algae are noticed is when the occurrence of large numbers gives rise to a brown or blue-green water bloom or green blanket-weed. Then the cry is 'what can I do to get rid of this nuisance?'

Algae come in various colours: grass-green, blue-green, brown, golden and even, occasionally, red. These colours are all due to the range of chloroplast pigment found in members of the different classes and phyla into which the algae are classified. There were originally only three or so classes but the number has steadily increased over the years as more details have emerged of their structure and biochemistry. Morphologically, algae may be single celled or colonial flagellates or coccoid cells; they may form simple or branched filaments, or may have a primitive thallus. Some are actively motile, some are free-floating whilst many are found attached to a substrate. Most reproduce by asexual division but a variety of types of sexual reproduction are also known.

So, what freshwater algae are present in Worcestershire? We really do not know. There would appear to have been very little work done in this county, although I will be happy to be proved wrong and to be shown that this impression is due to my poor homework. At the start of the 20th century a celebrated algologist, G.S. West, was Professor of Botany at Birmingham University. He and various of his students sampled for algae throughout the Midlands. One, B.M.Griffiths, took regular samples in 1908-9 from Stanklin Pool at Stone, SE of Kidderminster, and identified almost 100 taxa from four algal phyla. He noted how the populations changed with the seasons and with the changes of water temperature. His paper describing this work was published in 1912 (The algae of Stanklin Pool, Worcestershire; an account of their distribution and periodicity. Proc. Birmingham Nat. Hist. and Phil. Soc. 12, no. 5, 1-23.). All the algal records collected by Prof. West and his students over the period 1916-19 were brought together and published after his death (The flagellates and algae of the district around Birmingham, W.B. Grove, B.M. Bristol and N. Carter, 1920. J. of Botany, 53, supp. 3, 1-55.). This contains many records for Worcestershire but generally with only the crudest of locations, eg. the name of the nearest town or village. I have yet to discover any published records from the subsequent 80 years!

Having moved to Ashton under Hill in S Worcestershire in 1997 I decided to look around for freshwater members of the Dinophyceae, a group on which I had researched for almost 40 years, but mainly on marine members. First stop was the garden pond which I had cleared out and repaired in the autumn. In February 1998 I noticed that the water (temperature around 7C) was brown, and microscopical examination revealed a bloom of a small naked dinoflagellate which I identified as Gymnodinium inversum (Fig. 1). This had never been recorded from the British Isles and had originally been described from Denmark. Regular sampling revealed that as the temperature increased large cells, which were probably motile zygotes, increased in number and then knobbly thick-walled cysts appeared (Fig. 2). Many euglenas, cryptophytes and green flagellates were subsequently found in the pond and the progress of the various main taxa was followed by making counts at intervals. Subsequently this Gymnodinium has appeared at about the end of November each winter.

Some dinoflagellates from Ashton under Hill.
Fig. 1. Gymnodinium inversum, motile vegetative cell.
Fig. 2. G. inversum cyst.
Fig. 3. Gymnodinium pseudopalustre, motile stage.
Fig. 4. Peridium palatinum, motile stage of an armoured dinoflagellate.
(From J.M.Lewis & J.D.Dodge, Phylum Pyrrophyta. In: The Freshwater Algal Flora of the British Isles.)

Another exciting discovery came in August 1999 when I was brought a sample from a large spring-fed pond used as an irrigation reservoir by a farmer. Previous sampling had suggested that this was a pretty barren pond so imagine my surprise when the sample was brown with what I eventually identified as Gymnodinium pseudopalustre, (Fig. 3), previously recorded from continental Europe but not from the UK. The water temperature was 19 C so this species is clearly one of warm water. The bloom did not last very long but it has appeared around the middle of August each year since. A few other dinoflagellates have also been found in the autumn of which the most easily recognisable is the armoured species Peridinium palatinum (Fig. 4). A number of interesting euglenoids and chrysophytes have also been seen in this pond.

It would be interesting to begin to collect algal records from various parts of Worcestershire. Until recently the big problem has been that of identification for, although it is not so hard to get to the genus, the literature for keying out to species has been very difficult both to obtain and to use, since the majority of it was in German. Now, with the publication of 'The Freshwater Algal Flora of the British Isles' (D.M. John, B.A. Whitton & A.J. Brook, editors; 2002, CUP,702 pp plus CD photo catalogue. ISBN 0 521 77051 3. ) we have a work which covers all the algae, with the exception of diatoms, which are known to have been found in the UK. There are user-friendly keys and clear line drawings of all the species described plus the photographs on the CD, most of which are in colour.

If any one has a problem alga they would like help with please contact me (

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