The Structure of the Littoral Invertebrate Communities of the Kosciuszko Region Lakes

The littoral macroinvertebrate assemblages of Lakes Albina, Blue, Club andCootapatamba in the Mt. Kosciuszko region were sampled by two methods: sweeps and cobble picks. Thirty-six species were collected with total abundance and species richness greatest in Lake Albina. Common species included themolluscs Pisidium kosciusko and Glacidorbis hedleyi, the crustaceans Metaphreatoicus australis and Neoniphragus n. sp., and an unidentified limnephidtrichoperan. Community structure was influenced by the nature of the substrate, with cobble sites having greater richness and abundance than boulder sites. The importance of the major taxonomic groups (crustaceans, insects and molluscs) varied with sampling method and among lakes. Crustaceans (isopods and amphipods) usually dominated in sweeps, with molluscs and insects varying in importance among lakes, while insects mostly dominated in cobble pick samples. Oligotrophic lakes are typically thought to be dominated by insects, however this study shows such lakes may appear to be dominated by insects or crustaceans depending on the sampling method used and the presence of fish

Population Dynamics and Life History of Paratya australiensis Kemp, 1917 (Decapoda:Atyidae) in Upland Rainforest Streams, South-Eastern Queensland, Australia

Aspects of the life history and population dynamics of Paratya australiensis were examined in headwater streams of the Conondale Range, south-eastern Queensland, particularly in relation to spatial and temporal variation in temperature and flow dynamics. Breeding period and population structure at nine sites in three subcatchments were examined during three years of monthly sampling using a non-destructive, photographic method. Breeding was restricted to the warmer months of late spring and summer. Peak abundances of ovigerous females and release of larvae occurred earlier at warmer, lower-altitude sites than at cooler, upper-altitude sites. This is consistent with the general trend for seasonal breeding in temperate and subtropical species of atyids, and perennial breeding in tropical species, and suggests that the summer breeding period of P. australiensis was strongly influenced by temperature. In subtropical, south-eastern Queensland, larvae were released just before and during the wet season. Although populations were quite resilient, disturbance from high-flow events also shaped the life history. Hydrology modified the breeding period by influencing overall abundance and recruitment success and by favouring the early release of larvae before peak flows. The reasonably well defined seasonal cycle and synchronized development appear to result from the combined effects of temperature and hydrology

Ecology of Four Turbid Clay Pans During a Filling-Drying Cycle in the Paroo, Semi-arid Australia

The clay pans studied were small (\u3c2 \u3eha), shallow (\u3c30 \u3ecm) and contained very turbid, alkaline water of low conductivity for 40-90 days. Nutrients peaked early but chlorophyll-a values varied through time. Water temperatures ranged from 3.5 to 25.5°C. Cumulative species richness ranged from 30 to 55, with mean momentary species richness varying from 15.5 to 29.1 among the four pans. Macroinvertebrate assemblages were dominated by adult phyllopods, hemipterans and coleopterans, and zooplankton was dominated by juvenile phyllopods, copepods and cladocerans. No macrophytes were present. Ordination showed two pairs of pans (A+B and C+D) which matched ordination of physicochemical data, with turbidity the factor best explaining the pattern. Macroinvertebrate assemblages varied between the centre and littoral zone of all pans, particularly in C and D in which CPOM was more abundant in the littoral. Grouping of assemblages was directed as much by differences in abundance as variation in species composition. Succession was directional and continuous. Among macroinvertebrates, insects dominated initially and terminally, but phyllopod crustaceans were important much of the time. In the zooplankton, phyllopods dominated initially then entomostracans, with final assemblages mostly consisting of copepods. Succession was quicker and later assemblages more stable in zooplankton. The feeding group of filter feeders/collectors dominated during the life of the pans, except at the beginning and end when predators were important. The major carbon source was algal, despite the high turbidity and abundant detrital matter

Swimming Response to Water Current in Paratya australiensis Kemp, 1917 (Decapoda, Atyidae) under Laboratory Conditions

The swimming response to flow of the freshwater shrimp Paratya australiensis Kemp, 1917, was examined in a small recirculating laboratory stream. On three occasions during 1993 larvae, juveniles, small and large adults, and ovigerous females were collected from headwater populations and tested in the laboratory at current speeds of 10 and 30 cm·s-1. Juvenile and adult shrimps showed the same strong positive rheotactic response at velocities of 10 and 30 cm·s-1. However, large adults moved upstream more rapidly than juveniles and small adults. This response was not influenced by the time of year of collection or time of day tested (day/night). Ovigerous females showed a weak response to flow and tended to maintain position rather than move into the current. Early stage larvae (stages III and IV) were not able to maintain position at the lowest velocities. The positive rheotactic response of shrimps, particularly large adults, is seen as an adaptation to compensate for downstream movement of larvae by drift and juvenile and adult displacement during high discharge events

Direct Measures of Instream Movement in a Freshwater Shrimp Using a Genetic Marker

This study was designed to examine movement by the shrimp Paratya australiensis between adjacent pools within headwater streams in southeast Queensland. Previous work had found fixed allele differences between populations from two nearby subcatchments. By translocating samples of shrimps between these two populations it was possible to monitor movements of the translocated adults and subsequent larvae and juveniles over a 12 month period. Overall movement was very limited, with juveniles and larvae only moving downstream. Adults, but not breeding females, tended to move upstream rather than downstream. These results indicating some movement downstream by juveniles and very restricted movement upstream by adults, help to explain the genetic structure of the species, with fixed differences among populations at headwater sites, sometimes even within the same subcatchment