RELATIVE ABUNDANCE AND SEASONAL CHANGES IN THE MACROZOOPLANKTON OF THE LOWER SWAN ESTUARY IN SOUTH-WESTERN AUSTRALIA

WA Museum Records and Supplements | Updated 1 decade ago

Abstract - Macrozooplankton, i.e, plankton collected with a 500 Ilm mesh net (Kennish 1990), was sampled in twelve consecutive months at three sites, located 0.3 (site A), 2.5 (site B) and 7.2 km (site C) from the mouth of the 7,5 km long entrance channel of the Swan Estuary, The macrozooplankton community underwent marked seasonal changes in abundance, with concentrations at particularly sites A and B increasing markedly between November and January, as water temperatures rose towards their annual maxima, Concentrations then fell precipitously at each site in February, before rising sharply again at the two downstream sites (A and B) in April. These trends reflected to a large extent those exhibited by the cladoceran Penilia avirostris, which contributed 80.7% to the total number of individuals collected during the study, The other main contributors were Acartia (Acartiura) sp. (3.4%), leucosiid (brachyuran) zoea (2,0%), the larvacean Oikopleura dioica (1.3%), anomuran crab zoea (1.2%), the penaeid Lucifer hanseni (l.l %) and the zoea of the brachyuran Halicarcinus ovatus (1.1%). Crustaceans contributed about three quarters of the approximately 100 species collected, with the copepods, most of which were calanoids, contributing 21 of those species, The majority of the species were marine, which accounts for the progressive decline in the concentrations of the macrozooplankton in an upstream direction, with the numbers at sites A, Band C contributing 58.0, 34.0 and 8.0%, respectively, to the total number obtained from all sites.