Studies on the ecology of some temporary freshwater pools in Victoria with special reference to microcrustaceans

Abstract

Fifty-three temporary freshwater pools (mean depth 23 cm) located mainly in eastern Victoria were studied from February to September 1973.

Chemical parameters determined were pH (range 5.7-8.2, mean 6.9), conductivity (K₁₈, range 55-5500, mean 340 µS/cm), dissolved oxygen (range 23-170, mean 72% saturation) and turbidity (range 2-310, mean 50 Formazin turbidity units).

A total of 60 microcrustacean species was recorded.

The Australasian endemic cladoceran, Saycia cooki (King), was of common occurrence from June through to August. The fact that it tends to reach peak numbers early in the life of a pool is probably related to the production of large numbers of ephippial eggs. In contrast, cladocera which produce only one or two ephippial eggs, such as Chydorus, Moina and Simocephalus, tend to appear later in succession. Simocephalus expinosus (benthic) and Daphnia carinata, s.l. (planktonic) had mutually exclusive distributions and are apparently unable to coexist in shallow waters.

Endemic cyclopoid copepods encountered included three new species of Microcyclops, M. arnaudi (Sars), Acanthocyclops australis Sars, and Acanthocyclops, sp. nov. Like Saycia, Microcyclops varicans and Acanthocyclops bisetosus exhibited maximal numbers early in succession.

Several new combinations of coexisting calanoid copepod species belonging to the genera Boeckella and Hemiboeckella are reported.

Computer analysis showed that the following four groups of species had a high probability of co-occurrence: (1) Cypretta sp., Attheyella australica, Ilyodromus sp., Saycia cooki; (2) Cyprinotus leanus, Acanthocyclops bisetosus, Moina tenuicornis; (3) Boeckella major, B. pseudochelae, Cypris sp., Daphnia carinata, s.l. ; (4) Simocephalus exspinosus, Microcyclops varicans.