Effects of salinity on the survival, growth and development of tadpoles of the brown tree frog, Litoria ewingii

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.