Do Green and Golden Bell Frogs Litoria aurea occupy habitats with fungicidal properties?

The Green and Golden Bell frog Litoria aurea is in major decline in Australia, where its distribution is now confined mainly to the east coast of New South Wales (NSW). Infection by the newly emerged amphibian fungal pathogen Batrachochytrium dendrobatidis has been identified as one of the main threats affecting L aurea. Surprisingly, some of the sites in NSW sustaining the largest populations of this species are industrial and urban habitats that are often disturbed and polluted, which could protect L aurea from chytrid infection if pollution had fungicidal capacity. The aim of this study was to characterise the trace metal concentration of several L aurea breeding sites in the Sydney and Illawarra. regions of NSW and to evaluate the fungicidal efficacy of the main trace metals identified. Selected L aurea sites were sampled throughout the breeding season (September to February) to establish the concentration of trace metals in both surface sediment and waters. Physico-chemical parameters including pH and salinity were also measured. Of the trace metals identified, copper and zinc were consistently elevated across sites. Over 50% of sites exceeded the National Sediment Quality Guideline for both copper and zinc concentration, and over 90% of sites exceeded the National Water Quality Guideline for these metals. Consequently, we evaluated their effect on the growth and survival of a laboratory culture of B. dendrobatidis. These tests were performed in media containing dissolved metal concentrations of 0.02 - 0.65 mgL^-1 Cu and 0.24 - 5.0 mgL^-1 Zn. Growth rates were inferred by total fungal density in liquid culture (based on spectral absorbance measurements), final dry weight, and the density of zoospores in fungal cultures grown for 28 days. Both copper and zinc were found to reduce the growth and proliferation of B. dendrobatidis, but in a non-linear manner.This suggests that L aurea may be gaining some protection from B. dendrobatidis infection at several of the sites examined.