Distribution and environmental tolerances of aquatic macroinvertebrate families in the agricultural zone of southwestern Australia

Abstract

The agricultural zone of southwestern Australia is an extensively modified landscape. Ninety percent of the perennial native vegetation has been cleared and replaced by annual cereal crops and pasture. Consequently, groundwater has risen and much of the region is affected by dryland salinity. River geomorphology and water quality have been severely impacted by land clearing, anthropogenic patterns of land use, and secondary salinization. The objectives of this study were to determine patterns of distribution of aquatic macroinvertebrates in the region, and to identify environmental variables influencing these patterns. Aquatic macroinvertebrates were sampled at 176 river sites during spring 1997 and a range of environmental data were collected at each site. Eighty-one families were collected, with the fauna being dominated by insects. At the family level, macroinvertebrate communities were homogeneous and depauperate, and consisted of families that tolerated a broad range of environmental conditions. The fauna was particularly resilient to high salinities, with some families tolerating salinities orders of magnitude greater than previously reported for lotic waters. The most significant environmental factors influencing the distribution of aquatic invertebrates were rainfall, salinity, land use, and instream habitat.

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

“…In this study, it is not surprising that the effect of site is influential over individual and assemblages of insects or that some groups vary between sites and others do not. Kay et al (2001) and Pinder et al (2005) also found aquatic invertebrates in the study region were locally heterogeneous due to variation in habitat.…”

“…1). At this time of year there were few water bodies, because negligible rainfall occurs during summer and autumn, and the occurrence of insect families in mesocosms would be the result of opportunistic colonisation by highly mobile species (Kay et al, 2001). Each mesocosm consisted of a circular hole dug into the soil (25 cm diameter 9 10 cm depth), lined with black polythene and filled with approximately 5 l of aged tap water.…”

“…Dipteran families in the WA Wheatbelt occur within relatively wide salinity boundaries (Kay et al, 2001;Pinder et al, 2005). For example, Chironomidae, Ephydridae and Dolichopodidae are observed up to and exceeding salinities of 100 gl -1 TDS (Kay et al, 2001;Pinder et al, 2005).…”

“…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.…”

“…As such, it was expected that most aquatic fauna of mesocosms would be freshwater taxa. Dispersal of aquatic insects in the wheatbelt is widespread, but locally heterogeneous, due to variation in habitat (Kay et al, 2001;Pinder et al, 2005). It is anticipated that insects colonising mesocosms vary in space and time.…”