Water fleas in Middle Earth

Daphnia 'pulex'

Daphnia are one of the several small aquatic crustaceans commonly called water fleas because of their erratic swimming style. They live in various aquatic environments ranging from acidic swamps to freshwater lakes.

The identification of Daphnia species is difficult particularly in the so-called Daphnia pulex species complex . Determination of species based on morphological methods is only possible in a small number of species. Most others lack reliable morphological traits as a result of morphological stasis combined with a poor taxonomy. Initially the Daphnia pulex complex was considered to comprise of a few species but in recent years a number of new species have been identified genetically. Furthermore, each of these taxa comprises separate species in North America and Europe, despite carrying the same names.

There seems to be no alternative to a DNA Barcoding approach although there is an additional complicating factor, because similar to several other Daphnia species, North American Daphnia pulex members are able to form viable hybrid populations with Daphnia pulicaria. Any analytics should therefore include an allozyme analysis to confidently determine species status

Researchers from New Zealand have now used DNA Barcoding to identify invasive Daphnia specimens occurring in New Zealand lakes. They were able to document the establishment of non-indigenous North American Daphnia pulex members on the South Island. Cellulose allozyme electrophoresis was used to confirm that individuals were not hybrids with Daphnia pulicaria. 

New Zealand has only one recognized native Daphnia species, the relatively uncommon Daphnia carinata. These first confirmed recordings of members of the Daphnia pulex complex in New Zealand come from South Island lakes that are popular for overseas recreational fishers, indicating a possible means of  introduction in association with fishing and boating equipment.

The question is if this recent invasion will have any perhaps detrimental effect on the local fauna and flora. The authors think that the establishment of non-indigenous Daphnia might have large effects on lake and pond biota by probably reducing the abundances of both phytoplankton and other zooplankton (particularly rotifers). 

Who knows - lets hope that there might be ways to not find this out.