Aquatic invertebrate assemblages of wetlands and rivers in the wheatbelt region of Western Australia

Abstract

-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.

Salinity as a driver of aquatic invertebrate colonisation behaviour and distribution in the wheatbelt of Western Australia

“…However, many Coleoptera in inland southwest WA appear to be relatively salt tolerant, and the same correlation was not found in this study (over 0-8 or 0-20 gl -1 TDS) or in other studies in the same region (Kay et al, 2001;Bailey et al, 2002;Pinder et al, 2004Pinder et al, , 2005. It is also possible that salinity differences in abundances of Coleoptera, between mesocosm and field samples, may partially be due to some field Coleoptera having developed from eggs within water bodies, whereas all Coleoptera colonised mesocosms as adults.…”

“…Ephemeral water bodies are characteristic of the Wheatbelt, where they show a range of salinities, especially in areas affected by secondary salinisation, making them ideal to investigate how salinity affects the colonisation and oviposition behaviour of insects. Numerous studies have investigated how salinity influences the distribution of aquatic organisms by examining patterns in species occurrence (Halse, 1981;Bunn & Davies, 1992;Kay et al, 2001;Williams, 2003;Halse et al, 2004;Marshall & Bailey, 2004;Pinder et al, 2004;Piscart et al, 2005a) and salt sensitivity (Roberts, 1996;Blasius & Merritt, 2002;Kefford et al 2003;Jeffery et al 2005;Hassell et al, 2006;Zalizniak et al, 2006). Studies have found a range of invertebrate fauna, such as the disease vector Ae.…”

Impacts of deep open drains on water quality and biodiversity of receiving waterways in the Wheatbelt of Western Australia

“…These water quality conditions were tolerated by only very hardy species, as increased salinity and acidity of sites impacted by deep drainage led to a sharp decline in species richness, and significant changes in macro-invertebrate community composition downstream of the drain. Kay et al (2001) showed a general tendency for family richness in Wheatbelt streams to decrease with increasing salinity, whilst Pinder et al (2004Pinder et al ( , 2005 further demonstrated that salinity has a major influence on the distribution of aquatic invertebrates in the Wheatbelt. They showed that the salinity range of 10-20 ppt (g l −1…”

“…The conversion between conductivity and salinity was performed using a conversion factor of 0.64. Following Pinder et al (2004), water was considered 'fresh' when salinity was <3 ppt, 'subsaline' when 3-10 ppt, and saline when >10 ppt. Values greater than 100 ppt signify hypersaline conditions.…”

Range decline and conservation status of Westralunio carteri Iredale, 1934 (Bivalvia:Hyriidae) from south-western Australia

“…In Australia, secondary salinisation is principally caused by rising watertables as a consequence of reduced evapotranspiration following changes in land use, typically land clearing for agriculture. The south-west corner of Australia, where~80-90% of the land has been cleared, is a hot spot in terms of secondary salinisation (NLWRA 2001;Halse et al 2003;Pinder et al 2004). As a result, most of the freshwater ecosystems in south-western Australia are affected by increasing salinity, with 56% having become brackish (1.0-2.0 g L -1 ) or saline (>2.0 g L -1 ) (see Mayer et al 2005).…”