The Cladocera Interest Group - guest blog by Adrian Chalkley

Sample of Cladocera.  Photo: A Chalkley

Scapholeberis mucronata.  An unusual species which swims upside down under the surface film grazing on food particles blown onto the surface. Photo: A ChalkleyThe Cladocera Interest Group have an entry in the ID Signpost section of the TomBio website, because we supply aids to Water Flea identification. This guest blog will explain more about identification aids available from the CIG website and a little bit about how the group started. But it's probably best to explain why Water Fleas are unfortunately one of the 'Cinderella taxa' of biological recording, and why they deserve more attention.

Many people reading this will probably be thinking 'Water Fleas are just too tiny and difficult to identify'.  Well, it is true that Cladocera are tiny, require more work in order to identify than most otherMale Daphnia ambigua spine. Males are rare, mainly recognisable by larger spines and different head shape.  Photo: A Chalkley creatures, are very under-recorded and are almost never mentioned in the various metrics involved in biological surveys.  Because of these reasons, techniques assessing water quality such as BMWP, Rivpacs, PSYM and Community Conservation Index take no heed of any species of water flea recorded in a survey.  Thus it's no surprise many people ignore them.  All levels of the aquatic ecosystem are important however, and those towards the base of the food web are fundamental to the success of all those riverflies, water beetles, fish etc in providing a healthy and biodiverse aquatic community.  To paraphrase Buglife, we need to conserve even the smallest things that run the aquatic world.  But how can we conserve anything if we have little idea of its rarity or distribution?

Ephippia.  Photo: A ChalkleyA look at the life history of Cladocera only increases their fascination and importance, for they are nature's incredible survivors.  Almost all you will usually find in a pond will be females which parthenogenetically continue to produce more females when conditions are right.  So a small early spring population quickly becomes a large population by feeding on the late spring algal bloom, caused by sunlit, lengthening days.  This growing population provides food for overwintering invertebrate larvae and fish as they mature.  Then later in the year environmental stressors such as falling water levels, seasonal changes or increasing predation causes those females to spontaneously produce males and gamogenetic females which mate.  After mating, these new females produce resting eggs called ephippia instead of live offspring.  They  will wait until conditions are right before hatching and in the meantime they may either float or sink.

Scapholeberis mucronata.  An unusual species which swims upside down under the surface film grazing on food particles blown onto the surface. Photo: A ChalkleyThose that float can be transported by animals or blown by the wind into new waterbodies, which is why they can be found in shallow puddles on a farm track, for example.  Ephippia that sink can be buried in the bottom mud of a water body, awaiting their chance to hatch.  And they can wait a long, long time!  Ephippia have been successfully hatched from a sediment core taken from an American lake bed which was carbon dated to 700 years old!  'Resurrection ecology' is the wonderful term coined for studying the evolution and adaptation shown by these tiny resurrected crustaceans!  Fascinatingly, studies of the water fleas hatched after 700 years clearly showed that evolutionary changes had occurred corresponding to the increased phosphate levels in the lake after the introduction of artificial fertilisers on farmland in the late 1800s.   This is the maximum survival time we know of for Ephippia, but simply clearing bottom silt when restoring a pond will expose previous generations of resting eggs and reinvigorating the Cladocera population.  A process which has gone on for a long, long time.

Alona quadrangularis.  Photo: A ChalkleySo, when you take your dog for a walk and he jumps into a pond it's quite possible that he may collect ephippia on his fur, possibly depositing them in the puddle he drinks from on the homeward route.  As well as furry mammals, ducks and other water fowl collect and disperse ephippia both on their feathers and in their gut.  It has been shown that avian gut acids have little effect on the viability of these resting eggs.  This alone may not justify my description of Cladocera as incredible survivors, but consider the case of woolly mammoths frozen in the permafrost of Siberia.  Professor Alexey Kotov attended such a fossil mammoth exhumation and combed hundreds of ephippia out of its wooly hair.   Dissecting the mid gut revealed many more ephippia, which were identifiable to families still present in Siberia today.  So, as well as using your pet dog or the local park ducks, water fleas used woolly mammoths as a vector for dispersal, for Cladocera are truly of ancient lineage!

Polyphemus pediculus Giant Eyed Predatory Water Flea.  Photo: A ChalkleyFossil Cladoceran parts, such as Head Shields and Carapace parts, show that modern Cladoceran lineages were well established by the upper Jurassic and, although fossil evidence has yet to be found, their ancestors probably arose in the lower Jurassic, the Triassic, or even before.  In other words, they co-existed with the dinosaurs, many of which have recently been shown to be feathered.  Is it too far-fetched to surmise therefore that the tiny, unimportant water flea was dispersed by dinosaurs?  Then, surviving the mass extinction which wiped out the dinosaurs 66 million years ago, they just carried on hitchhiking on the mammals and birds which evolved to fill the ecological void left behind.

As this process continued the humble water flea carried on driving the aquatic ecosystem as it too evolved and adapted to the changes caused by human interaction. Cladocera are key primary consumers whose evolution is crucial to the understanding of the Mesozoic Lacustrine Revolution that helped to shape aquatic ecosystems of today. They are also no less important in the understanding of the changes which will be wrought by global warming in the rest of this century.

Cladocera Interest Group logoHopefully you may now have a little more respect for the humble Water Flea.  This is why the Cladocera Interest Group was formed to stimulate interest in them and encourage recording.  The Freshwater Biological Association last published its key to Water Fleas, by Scourfield & Harding, in 1966.  Whilst this is still available, name changes to several species have occurred, there are errors in the text and the minimal distribution data is very much out of date.  When the CIG was formed one of the first tasks was to publish a revision to the species list for Great Britain and, like everything else we have done, this review is freely available to download from our website at along with documents supporting all name changes.

On the website you will also find other keys, notably a French key by Amoros which helps a great deal in conjunction both with the FBA key and our revised list.  We have also just published, along with our latest newsletter, a key to the known Bosminidae of Britain and the Netherlands.  So far we have published eight newsletters which are written by the members and deal with many of the specific identification problems there are, give new habitat information and of course publish modern records.  Newsletters are emailed to all members but they too may also be freely downloaded.

Daphnia obtusa distribution map.  A ChalkleyWith regard to stimulating modern recording, this is very much a work in progress. We are a registered dataset provider for the National Biodiversity Network and have submitted 2199 modern records. This is of course a small number compared to many other taxa; but then each record involves carefully capturing specimens, preserving them and using both low power stereo and high power compound microscopes to identify - much longer than jotting down a bird seen through binoculars. 

Possibly the most useful product of these and past records has been the publication on our website of distribution maps for 89 of the 92 species on the British list.  As these are built up we hope to gain a much better appreciation of the rarity of each of our species.  All of these maps have been assembled into a pdf Atlas of Water Fleas in Britain and Ireland, the current version of which can be found on our website.

Daphnia obtusa page with arrows and ID tips.  A ChalkleyAs a further aid to identification the group is putting together a gallery of photographs of known species with identification features highlighted - this should be going live later in 2017.  We hope this will prove useful to compare with the image in your microscope eyepiece if you make a start on identification.  The CIG of course welcomes records of water fleas both on line using iRecord and by email. Membership of the Cladocera Interest Group is free to all those interested in these fascinating creatures.

Adrian Chalkley

Founder, Cladocera Interest Group.