Frogs and Environmental Water: The Story So Far
Updated: Aug 1, 2020
The flow of water in dry areas of Australia has always been very variable. Because water levels need to be relatively consistent for people to use for agriculture and industry, many of Australia’s rivers have become modified with infrastructure such as weirs to regulate flows. As a result, some wetlands that used to dry out regularly now do not and some wetlands that used to be regularly filled by flood waters do not or get less water than before.
Water for the environment, or ‘environmental water', is water that is released into rivers and wetlands to sustain and improve the condition of waterways and wildlife. Environmental water is used to fill wetlands that are running dry and to top up wetlands that would naturally contain more water. Environmental water is being used to make flow regimes more natural and better suited to the wildlife that rely on wetlands.
Margooya Lagoon (near Robinvale in north west Victoria), a wetland that receives environmental water
Frogs have been in Australia for millions of years and their breeding cycles have adapted to the natural water cycle. Despite having been around so long, frogs are quite fussy when it comes to breeding! They are limited by temperature (because they are cold-blooded) and because they have sensitive amphibian skin (through which they absorb oxygen) they are dependent on moisture. Most species of frogs need water-bodies in which to breed. Changing the way water behaves in the ecosystem can significantly impact frogs and their reproduction.
Because frogs are so sensitive to changes in water and are so important as components of the ecosystem, how they react to environmental watering is vital information for water managers. But it’s not as simple as more water means more frogs! Although they do need water, sometimes less is more. Wetlands that dry out periodically often have fewer predators (like fish) than permanently wet ponds. The vegetation that grows around ephemeral pools is also different and potentially better for frogs. The water also needs to stay in the wetland for the whole of the breeding period and for as long as it takes for the tadpoles to metamorphose and be able to live on land. Each species also differs in its requirements for timing and duration of breeding as well as specific habitat and weather requirements. On top of that, because of the complex combination of all the different factors, there are often differences between each individual wetland.
A study by Emily Hoffman, from South Australia’s Department of Environment, Water and Natural Resources, showed that the delivery of environmental water to dry temporary wetlands triggers frogs to breed. What’s more, it seems as though there were more frog species and greater abundance (higher numbers of individuals) of tadpoles at dry wetlands that received environmental water than at permanent wetlands. A Wassens and Maher study examining frog ecology in relation to inland creeks with weir systems found that temporary pools were more likely to contain rarer species than permanent pools, but that the temporary pools had to contain water for long enough for tadpoles to metamorphose and move out. A team of scientists led by CSIRO’s Heather McGinness investigated how flooding and habitat influenced frog diversity (number of species) and abundance (number of individuals) in Barmah Forest. They found that the males of each species called at slightly different times of the year (although there was some overlap) and only some of the species seemed to do better in wetter years. They concluded that although frogs definitely benefited from water, each species seemed to do so differently.
This all suggests that environmental water is extremely important for frogs, but we need to know a lot more about how and why. Because water is getting scarce and more valuable as our climate warms and dries, it is vital that we understand as best we can what frogs need and when. There is still lots to learn about the requirements for each frog species at different wetlands across Victoria. That’s where WetMAP and citizen scientists come in, to investigate how frogs respond to watering regimes to help inform water management.