Combining ex situ and in situ methods to improve water quality testing for the conservation of aquatic species

Abstract

1. Determining whether water quality is suitable is an important part of managing aquatic species for conservation, although it is often challenging to achieve. Past approaches have largely consisted of tests exposing individuals to artificial solutions, or field studies that examine the effect of a subset of water quality parameters on the distribution or abundance of a species. 2. Owing to the complex nature of water chemistry in natural systems, which is difficult to replicate using laboratory studies or to capture entirely with correlational field studies, these types of study may not be suitable for determining accurately whether or not water quality at a particular site is suitable for a target species. In situations where conservation outcomes rely heavily on achieving this, an alternative approach is therefore needed. 3. Embryos of the threatened green and golden bell frog Litoria aurea were placed in water collected from ponds that were used by this species for breeding and ponds where breeding was not detected at Sydney Olympic Park, Australia. After 19 days, the tadpoles were placed in enclosures in the same breeding and non-breeding ponds, and monitored until they metamorphosed. 4. There was no difference in tadpole survival, time to metamorphosis or body condition between the two treatments, indicating that poor water quality was not a cause of low pond occupancy by tadpoles at the site and resources should be directed towards investigating other potential causes. 5. We suggest that this method of an ex situ followed by an in situ exposure study is an effective approach to eliminating or confirming poor water quality as a cause of population declines and reduced occupancy, for species that are aquatic for at least part of their life cycle. Other applications include establishing that artificially created habitat provides suitable water chemistry, or identifying a potential location for a reintroduction project.