Zooplankton Distribution in Relation to the Hydrology of the Derwent River Estuary

Abstract

The zooplankton of the Derwent River estuary was sampled during periods of high freshwater flow (October) and low freshwater flow (April). Zooplankton distribution was found to be similar at both times with only minor shifts in location. Observed plankton distribution is shown to correlate well with a hydrologically established zonation scheme. Despite continual exchange between oceanic, coastal and inshore coastal waters, there is only occasional estuarine penetration into the inshore region and little penetration of inshore plankton into the estuary. The tidal zone is shown to be stable, well defined and characterized by estuarine and marine species. It is suggested that in a similar estuarine system, where the zooplankton distribution is well known, the hydrological zones can be inferred. The estuary of the Werribee River, Victoria, contains most of the same copepod species and is similar in other ways to the Derwent River estuary. But the occurrence of indicator species in the marine region of the Derwent estuary suggests that it is subject to a stronger influence of open coastal and oceanic waters.