Oral Presentation Australian Society for Limnology Congress 2013

Fair Dinkum Estuarine Zooplankton: hydrology, ecology and the vital planktonic-benthic link (#29)

Gina Newton 1
  1. ., Hughes, ACT, Australia

Investigations of the annual hydrological cycle of a salt-wedge estuary on the southern Australian coast (south-west Victoria) tested and supported the hypothesis that hydrological cycles (i.e. annual and tidal) are a major determinant of estuarine zooplankton ecology – including the adaptive responses and behaviours of various zooplankters. The annual hydrological cycle was found to comprise of three main phases of salt-wedge dynamics: reduction/absence, emplacement and presence. Importantly, the seasonal succession of the calanoid copepod assemblage, dominated by the estuarine endemic Gipplslandia estuarina, closely followed these phases. During the physically extreme and unstable phases of salt-wedge dynamics, physical environmental factors exerted the greatest influence on the ecology of the estuarine Calanoida. Conversely, biological interactions appeared to be of increased importance during the more stable phase of salt-wedge presence.

A variety of behaviourally mediated strategies were identified among the calanoids as mechanisms of population retention and position maintenance in the face of tidal and river flows – including during the extreme disturbance of annual scouring floods. These included the presence of dormant life history stages (e.g. dormant eggs in sediments, a first-time report for the estuarine Calanoida), and refuge in littoral vegetation (e.g. Gladioferens pectinatus). Thus traditional ‘plankton’ dwellers were linked to both the littoral-phytal and benthic habitats as a means of coping with environmental stress. It is recommended that future studies of estuarine zooplankton ecology consider:

·         all habitat components – planktonic (pelagic), benthic and littoral, and

·         the use of estuarine endemic species  as indicators of hydrological conditions.