Introduction Secondary (or anthropogenic) salinisation results from the mobilisation of salt stored in the soil profile and/or ground- water by human activities, principally irrigation and clearing of deep-rooted native vegetation (Williams 2001). These activities change the natural hydrological balance, raising water tables, increasing pressure of confined aquifers, and creating an upward leakage of water (and salt) to surface aquifers. When the water table approaches the soil surface, evaporation occurs, leaving salts behind and causing sec- ondary salinisation and degrading of terrestrial environ- ments. The mobilised salt or salty groundwater leaches into streams, rivers and wetlands, increasing salinity levels from nominally ‘fresh’ (<0.3–0.5 g NaCl L –1 ) to ‘salty’ (0.5–10 g NaCl L –1 ). Freshwater organisms exhibit a range of toler- ances to increasing salt levels (Hart et al. 1991; Halse et al. 1998; Bailey et al. 2002; James et al. 2003; Nielsen et al. 2003; Kefford et al. 2003; Marshall and Bailey 2004; Brock et al. 2005), but much of that data is based on mature life stages. Early stages of development of plants and animals have been shown to be more sensitive to salt than mature forms. For example, seed germination (Delesalle and Blum 1994), and seedling development (Warwick and Bailey 1997, 1998) are adversely affected at lower salt concen- trations compared with mature, established plants. Similarly, egg survivorship of Macquarie perch (Macquaria austral- asica) is reduced at a salinity of 4.0 g L –1 , whereas adults have been shown to have a salinity tolerance of 30 g L –1 (O’Brien and Ryan 1997). A significant proportion of the area affected by increas- ing salinity consists of wetlands, lowland streams and rivers, and riparian corridors (NLWRA 2001). These aquatic systems are used by adult frogs and their larvae for breeding and development respectively. A combination of habitat loss or degradation and mortality due to salt toxicity following salinisation has been proposed as one of the potential causes for the decline in Australian frog populations (Ferraro and Burgin 1993; Roberts et al. 1999). Moreover, wetlands and streams are commonly used for the temporary storage or discharge in the management of groundwater that has been pumped to lower the water tables. This saline groundwater is intermittently released into irrigation drains or directly into rivers. The environmental impacts of such releases on biodiversity, instream water quality and ecological pro- cesses are poorly known (Hart et al. 1990; James et al. 2003) but are likely to be of major significance to flora and fauna in intermittent wetlands due to the concentrating of salt during drawdown (James et al. 2003) and the lack of flushing, once common, due to altered water regimes (Nielsen et al. 2003). Increasing salt concentration in aquatic habitats will affect adult frogs, eggs and tadpoles differently. Adult frogs may escape rising salinity by dispersing to a favourable environment, recolonising or possibly selecting better ovipo- Australian Journal of Zoology, 2006, 54, 97–105 10.1071/ZO06006 0004-959X/06/020097 © CSIRO 2006 Kavitha Chinathamby A , Richard D. Reina A,C , Paul C. E. Bailey A,B and Belinda K. Lees A A School of Biological Sciences, Monash University, Clayton, Vic. 3800, Australia. B Australian Centre for Biodiversity: Analysis Policy Management, Monash University, Clayton, Vic. 3800, Australia. C Corresponding author. Email: richard.reina@sci.monash.edu.au Abstract. We investigated the effects of 4% seawater (sw), 8% sw, 12% sw and 16% sw (1.4 g NaCl L –1 , 2.8 g NaCl L –1 , 4.2 g NaCl L –1 and 5.6 g NaCl L –1 , respectively) on survival, mass and development of larvae of the brown tree frog, Litoria ewingii. Salinity of 16% sw significantly decreased survival of tadpoles such that 39% of tadpoles in 16% sw treatment survived to metamorphosis compared with 92% in the control group (freshwater). Growth (mass) of 16% sw tadpoles (0.048 g ± 0.005 g) slowed significantly during early development compared with control tadpoles (0.105 g ± 0.004 g); however, there was no significant difference in final metamorphosis mass between 16% sw (0.192 g ± 0.008 g) and control tadpoles (0.226 ± 0.006 g). Time taken to reach metamorphosis was greater for 16% sw tadpoles (84 ± 1.8 days) than for control tadpoles (55 ± 0.84 days). Tadpoles at salinity concentrations of 4% sw, 8% sw and 12% sw were significantly heavier than control tadpoles at metamorphosis. Our results show that moderate levels of salinity (16% sw) are sufficient to significantly reduce survival and retard development of tadpoles of L. ewingii. Effects of salinity on the survival, growth and development of tadpoles of the brown tree frog, Litoria ewingii www.publish.csiro.au/journals/ajz CSIRO PUBLISHING