EFFECTS OF THE LEEUWIN CURRENT ON THE DISTRIBUTION OF CARNIVOROUS MACROZOOPLANKTON IN THE SHELF WATERS OFF SOUTHERN WESTERN-AUSTRALIA

Plankton samples were collected using 500-mu m nets in the surface wat ers (up to a depth of 70 m) of the continental shelf in three regions (Albany, Bremer Bay and Esperance) off southern Western Australia in J uly 1992 (winter) and January 1993 (summer). The carnivorous zooplankt on of these samples were characterized by low species richness and hig h variability in abundance. Abundances of most of the major taxa colle cted differed significantly between seasons and many also differed bet ween regions. Siphonophores and chaetognaths dominated the carnivorous plankton, with lower abundances of hydromedusae and raptorial copepod s. The most abundant siphonophores were Chelophyes appendiculata and E udoxoides spiralis in summer and winter, respectively. The most abunda nt chaetognaths were Sagitta minima in summer, with Pterosagitta draco and Sagitta enflata dominant during winter. Overall, the numbers of s pecies of both siphonophores and chaetognaths were highest during wint er. At this time, there was also a trend for decreasing numbers of spe cies in an easterly direction between Albany and Esperance, which was probably due to the presence of subtropical species entrained within t he warm Leeuwin Current, which was flowing east along the continental shelf during winter. During summer, when the current was not present i n this region, there was an even spread of fewer species along the coa st. (C) 1997 Academic Press Limited.