The wheatbelt region of Western Australia has been extensively cleared of indigenous vegetation for agriculture and is now severely affected by dryland salinity. Wetlands that were once freshwater are now saline and others are under threat, as are the animals and plants that inhabit them. Rising groundwater is also affecting the many naturally saline playas. To provide a framework for setting conservation priorities in this region a biological survey was undertaken, including sampling of aquatic invertebrates at 230 wetlands. In this paper, we have used data from the survey to summarise occurrence of species in relation to salinity. Total species richness at a wetland showed no response to salinity below 4.

Summary 1. AusRivAS (Australian River Assessment Scheme) models were developed, using macroinvertebrates as indicators, to assess the ecological condition of rivers in Western Australia as part of an Australia‐wide program. The models were based on data from 188 minimally disturbed reference sites and are similar to RIVPACS models used in Britain. The major habitats in the rivers (macrophyte, channel) were sampled separately and macroinvertebrates collected were identified to family level. 2. Laboratory sorting of preserved macroinvertebrate samples recovered about 90% of families present when 150 animals were collected, whereas live picking in the field recovered only 76%. 3. Reference sites clustered into five groups on the basis of macroinvertebrate families present. Using seven physical variables, a discriminant function allocated 73% of sites to the correct classification group. A discriminant function based on seven physical and two chemical variables allocated 81% of sites to the correct group. However, when the same reference sites were re‐sampled the following year, the nine variable discriminant function misallocated more sites than the seven variable function, owing to annual fluctuations in water chemistry that were not accompanied by changes in fauna. 4. In preliminary testing, the wet season channel model correctly assessed 80% of reference sites as undisturbed in the year subsequent to model building (10% of sites were expected to rate as disturbed because the 10th percentile was used as the threshold for disturbance). Nine sites from an independent data set, all thought to be disturbed, were assessed as such by the model. Results from twenty test sites, chosen because they represented a wide range of ecological condition, were less clear‐cut. In its current state the model reliably distinguishes undisturbed and severely disturbed sites. Subtle impacts are either detected inconsistently or do not affect ecological condition.

-We describe the origins, relevance, aims, specifications and sampling strategy of a six-year biodiversity survey of Western Australia's Pilbara biogeographic region (179,000 km 2 ). During the project, 422 terrestrial sites were sampled for perennial and annual vascular plants, of which 304 were also sampled for small ground-dwelling mammals, birds, reptiles, frogs, ground-dwelling spiders, ants, beetles and scorpions. Ninety-eight sites on waterbodies were sampled for aquatic invertebrates, macro-and microphytes and the fringing riparian vegetation; 508 boreholes were sampled for stygofauna; 69 sites were sampled for microbats; and mammal bone material from 15 late Holocene deposits was identifi ed. An introduction to literature on the region's physical environments and recent land-use history is provided, along with descriptions of the Pilbara's four sub-regions in terms of their different landforms and vegetations.

Saline water was common in south-west Western Australian aquatic systems prior to land-clearing because most streams and wetlands were ephemeral and evapo-concentrated as they dried, and there were high concentrations of stored salt in groundwater and soil profiles. Nevertheless, a 1998 review of salinity trends in rivers of south-west Western Australia showed that 20-fold increases in salinity concentrations had occurred since clearing in the medium-rainfall zone (300–700 mm). More recent data confirm these trends and show that elevated salinities have already caused substantial changes to the biological communities of aquatic ecosystems. Further substantial changes will occur, despite the flora and fauna of the south-west being comparatively well adapted to the presence of salinity in the landscape. Up to one-third of wetland and river invertebrate species, large numbers of plants and a substantial proportion of the waterbird fauna will disappear from the wheatbelt, a region that has high biodiversity value and endemism. Increased salinities are not the only threat associated with salinisation: increased water volumes, longer periods of inundation and more widespread acidity are also likely to be detrimental to the biota.

-A biological survey of wetlands in the Wheatbelt and adjacent coastal areas of south-west Western Australia was undertaken to document the extent and distribution of the region's aquatic invertebrate diversity. Two hundred and thirty samples were collected from 223 wetlands, including freshwater swamps and lakes, salinised wetlands, springs, rivers, artificial wetlands (farm dams and small reservoirs), saline playas and coastal salt lakes between 1997 and 2000. The number of aquatic invertebrates identified from the region has been increased five-fold to almost 1000 species, of which 10% are new and known to date only from the Wheatbelt, and another 7% (mostly rotifers and cladocerans) are recorded in Western Australia for the first time. The survey has provided further evidence of a significant radiation of microcrustaceans in south-west Western Australia. Comparison of the fauna with other regions suggests that saline playas and ephemeral pools on granite outcrop support most of the species likely to be restricted to the Wheatbelt. Most species were collected infrequently, but for many of the least common species the Wheatbelt is likely to be on the periphery of their range.Cluster analysis was used to identify 10 assemblages of species with similar patterns of occurrence. Richness of these assemblages was best predicted by salinity and climate variables, or by physical habitat characteristics (granite outcrop pools, flowing water), although the amount of variation explained by models was variable (RZ 0.36 to 0.79). Fourteen groups of wetlands were recognised from cluster analysis of sites based on community composition. Wetlands of these groups differed primarily in their physical habitat, salinity, degree of secondary salinisation, pH and their occurrence across geographic and climatic gradients. Some assemblages were closely associated with particular wetland groups but others occurred across a range of wetland types. Salinity was identified as the primary influence on the occurrence of aquatic invertebrates in the Wheatbelt, although other variables are important in particular situations.Secondary salinisation dramatically alters composition and richness of freshwater aquatic invertebrate communities, involving gradual replacement of salt sensitive species by a smaller set of salt tolerant and halophilic species as salinity increases. These altered communities are relatively homogeneous compared with those of freshwater or naturally saline wetlands. Communities of naturally saline wetlands are comprised of a heterogeneous array of halophilic species, but these communities and species are also threatened by altered hydrology and chemistry associated with dryland salinity.

In this review of Australian phreodrilid oligochaetes, several descriptions are amended, some species are reclassified and additional distribution data are provided for most species. One new genus (Nesodrilus) and 11 new species (Phreodrilus diemenensis, Phreodrilus melaleucensis, Phreodrilus mitodes, Antarctodrilus acanthaseta, Antarctodrilus micros, Antarctodrilus horwitzi, Nesodrilus southwellensis, Insulodrilus parviseta, Insulodrilus unisetoides, Insulodrilus bifidus and Astacopsidrilus myothyros) are described from Australia. Insulodrilus lacustris (Benham, 1903) is recorded in Australia for the first time, while Phreodrilus mauienensis Brinkhurst, 1971, and Astacopsidrilus campbellianus (Benham, 1909), comb. nov., are removed from the Australian species list. The latter is the first phreodrilid to be recorded on Macquarie Island. One new species, Insulodrilus novaezelandiae, is described from New Zealand and three new species, Antarctodrilus spinosus, Nesodrilus isochaeta and Astacopsidrilus beckettae, are described from Campbell Island. Aspects of phreodrilid zoogeography and anatomy are discussed.

No abstract

Summary 1. The northern half of Western Australia is a large, sparsely populated area with a climate that ranges from monsoonal in the Kimberley to arid in the Gascoyne and Pilbara regions. The aquatic invertebrate fauna is poorly known. 2. Fifty‐one sites located on 14 river systems were sampled three times between August 1994 and October 1995. A total of 90 taxa, most identified to family level, were collected. The fauna was dominated by insects, which constituted 74% of the total number of taxa collected. 3. Major habitats at each site were sampled separately and sites with more habitats tended to have a richer fauna. All habitats showed significant differences in taxonomic richness between regions. Family richness decreased with increasing latitude, being highest in the Kimberley region and lowest in the Gascoyne. 4. Despite the differences in taxon richness between regions, community composition of the aquatic invertebrate fauna at the family level did not differ greatly. Four major groups of sites were identified by cluster analysis, based on the invertebrate families present at each site, but differences between groups were small. 5. Significant temporal variation in taxon richness was found in channel habitat but not the three other habitats sampled (riffle, macrophyte, pool‐rocks). Community composition in channel habitat varied temporally among groups of sites identified by cluster analysis but the pattern was not consistent.