THE FRESHWATER ALGAE OF WORCESTERSHIRE
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 7°C) 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 (jdodge3458@aol.com).
WBRC Home | Worcs Record Listing by Issue | Worcs Record Listing by Subject |