Effects of salinity on tadpoles of the green and golden bell frog (Litoria aurea)

We investigated the effects of various salinities on larval growth, metamorphosis and survival in the green and golden bell frog (Litoria aurea). This large hylid was formerly common on the east coast of Australia, but now occurs in only a few scattered localities where rising salt is one of a number of potential threats. Tadpoles tolerated salinity up to 4% seawater (sw; 1.58parts per thousand) without apparent effect, but salinity of 5.5% sw (1.87parts per thousand) and above significantly decreased growth rates and increased mortality. Salinity of 10% sw (4.41parts per thousand) caused mortality of all individuals within 72 days, 20% sw within four days, and 25% sw within five hours. Salinities from 10-15% sw (4.41-6.73parts per thousand) were tolerated for short periods (up to 3 weeks) before significant weight loss and mortality resulted, indicating a detrimental cumulative effect with high salinity. Metamorphosis occurred frequently below 5.5% sw but did not occur above 5.5% sw. Although L. aurea tadpoles can tolerate moderate salinities, increased salinisation caused by substantial land clearing, urban run-off and accumulation of salt in some waterbodies may contribute to the reduction of populations.