DISTRIBUTION OF AQUATIC PULMONATE SNAIL SPECIES IN CONTRASTING HABITATS WITHIN THE ROSS-RIVER RESERVOIR (STAGE 2A), TROPICAL NORTHERN AUSTRALIA

Monthly distributions of three snail species in three distinct habitat types from February 1992 to May 1993 were found to be variable, with peak abundances occurring predominantly in the late wet season (March to May) for Amerianna carinata and Gyraulus gilberti and in the late d ry season (September to November) for Austropeplea lessoni. No consist ently positive or negative patterns of correlation were recorded betwe en numbers of snails and physico-chemical characteristics or the amoun t or composition of emergent and submerged macrophyte species. However , highest densities of A. lessoni a and A. carinata were recorded in t emporary ponds, where the biomass of periphyton was greatest. Signific antly lower amounts of periphyton were recorded from open bays and per manent creeks. Highest densities of G. gilberti occurred in permanent creeks. Physico-chemical variables, rainfall patterns and macrophyte s pecies were not good indicators of snail abundance in the Ross River r eservoir, The best indicator of snail density appeared to be whether v egetated habitat is located within open bays, permanent creeks or isol ated peripheral ponds.