Brackish-water plankton and their environment in the Werribee River, Victoria.

Abstract

A plankton and water sample were taken at each of 10 stations on 7 April, 22 September, and 30 October 1970. Surface chlorophyll a values as high as 1220 mg/m³ were recorded, although normally they were less than 100 mg/m³. The horizontal and temporal distribution of 16 species of calanoid and cyclopoid copepods is presented, together with their observed salinity tolerances. Four major species-Sulcanus conflictus, Gladioferens pectinatus, Gippslandia estuarina (all estuarine), and Acartia clausii (marine) -accounted for most of the copepod numbers. Evidence is outlined suggesting that the males of A. clausii can penetrate upstream more readily than the females. Zooplankton numbers varied markedly with time, the influence of river flow being quite evident. Variation in egg number and body size in G. pectinatus was studied, and the importance of rate of water renewal on egg number in an estuarine population is discussed. The results are compared with those obtained from two other Victorian ecological studies. Aspects of the Australasian genus Gladioferens are discussed.