Egg dormancy in the Australian estuarine-endemic copepods Gippslandia estuarina and Sulcanus conflictus, with reference to dormancy of other estuarine fauna

The presence of dormant life history stages was investigated for the zoopla nkton of an annually flooding salt-wedge estuary. Such stages are seen as a potential mechanism for population persistence following environmental adv ersity. Laboratory incubation experiments were conducted on estuarine sedim ents. As a result, dormant eggs in Australian estuarine-endemic copepods ar e reported for the first time. Nauplii of the dominant estuarine-endemic ca lanoids Gippslandia estuarina and Sulcanus conflictus commonly hatched from the sediments. Manipulation of the salinity and temperature of experimenta l media indicated that temperature was the more important hatching trigger for S. conflictus, and that both high salinity and high temperature were im portant for G. estuarina. Results of the incubation experiments, including those of `conversion' experiments (i.e. from freshwater to saline condition s or low temperature to high temperature), help to elucidate the type of do rmancy characteristic of each species; it appears that S. conflictus may ha ve diapause eggs and G. estuarina may have quiescent eggs, although this is yet to be confirmed. Other estuarine fauna developed from the mud during t he incubation experiments, most notably the harpacticoids Onychocamptus cha thamensis, an ectinosomatid and Schizopera sp., and the medusa Australomedu sa baylii. Ecological and evolutionary consequences of dormancy in these es tuarine-endemic zooplankton are briefly discussed.