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

WA Museum Records and Supplements | Updated 7 years ago

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.

Author(s) A.M. Pinder, S.A. Halse, J.M. McRae and R.J. Shiel
Volume
Supplement 67 : A Biodiversity survey of the Western Australian agricultural zone
Article Published
2004
Page Number
7

DOI
10.18195/issn.0313-122x.67.2004.007-037