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

Abstract

The presence of dormant life history stages was investigated for the zooplankton of an annually flooding salt-wedge estuary. Such stages are seen as a potential mechanism for population persistence following environmental adversity. Laboratory incubation experiments were conducted on estuarine sediments. As a result, dormant eggs in Australian estuarine-endemic copepods are reported for the first time. Nauplii of the dominant estuarine-endemic calanoids Gippslandia estuarina and Sulcanus conflictus commonly hatched from the sediments. Manipulation of the salinity and temperature of experimental media indicated that temperature was the more important hatching trigger for S. conflictus, and that both high salinity and high temperature were important for G. estuarina. Results of the incubation experiments, including those of ‘conversion’ experiments (i.e. from freshwater to saline conditions or low temperature to high temperature), help to elucidate the type of dormancy characteristic of each species; it appears that S. conflictus may have diapause eggs and G. estuarina may have quiescent eggs, although this is yet to be confirmed. Other estuarine fauna developed from the mud during the incubation experiments, most notably the harpacticoids Onychocamptus chathamensis, an ectinosomatid and Schizopera sp., and the medusa Australomedusa baylii. Ecological and evolutionary consequences of dormancy in these estuarine-endemic zooplankton are briefly discussed.