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

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.

Environmental deterioration increases tadpole vulnerability to predation

“…This result is concordant with an earlier study in which L. ewingii tadpoles were observed to be 'sluggish' under saline conditions (Chinathamby et al 2006). In anurans, exposure to salt is known to affect both muscles and nerves, leading to physiological adjustments and biochemical changes that are often energetically demanding (Dole et al 1994).…”

“…The tadpoles in the saline treatment were maintained in 15% SW (equivalent to 5.25 g NaCl l K1 ). This is an environmentally meaningful concentration (Smith et al 2007) that falls below the lethal limit for the species (Chinathamby et al 2006). Water in both groups was prepared using Coralife Scientific Grade Marine Salt (ESU Inc., USA).…”

“…Chinathamby et al 2006). It is now generally accepted that elevated salinity can impact survival by interfering with key physiological and metabolic processes, such as osmoregulation.…”

“…Because breeding and tadpole development takes place in shallow water, evidence suggests that heightened salinity may already have excluded the species from certain wetland habitats (Smith et al 2007). Litoria ewingii tadpoles have also been observed to reduce their activity levels when exposed to salt concentrations comparable to those found in degraded aquatic habitats (Chinathamby et al 2006). The impact that reduced activity may have on the vulnerability of tadpoles to predation remains unknown.…”

Effects of Salinity on Survivorship of Wood Frog (Rana sylvatica) Tadpoles

“…Three concentrations of NaCl (Fisher Scientific, Certified for Biological Work) were created using deionized water: 1.4 g L-', 3.5 g L-', and 5.6 g L-I. These concentrations were similar to those used by Chinathamby et al (2006) and Sanzo and Hecnar (2006), and they were within the range observed in some freshwater habitats, Environment Canada 2001). Five replicates of each concentration were used, with each replicate container holding 400 mL of salt solution and five tadpoles pooled from multiple (> 5) egg masses.…”