Frog ecology in coastal wetlands of eastern Australia: assessing the risk of climate change to the vulnerable wallum sedge frog (Litoria olongburensis)
Katrin Lowe, The Griffith School of Environment, Griffith University
Katrin Lowe at one of her sedgeland study sites: important breeding habitat for the wallum sedge frog.
Photo © Katrin Lowe
Coastal freshwater wetlands of eastern Australia are critical for the survival of a threatened group of Australian frogs known as 'acid' or 'wallum' frogs. The 'acid' refers to the fact that these frogs and their tadpoles can tolerate the acidic waters of eastern Australia’s coastal wallum swamps and wet heathlands, making them a unique ecological class of frogs. The four acid frog species are the wallum froglet Crinia tinnula, wallum rocket frog Litoria freycineti, Cooloola sedge frog Litoria cooloolensis, and wallum sedge frog Litoria olongburensis, which are all listed as rare or vulnerable in Queensland and New South Wales. Acid frogs play an important role in terrestrial and aquatic food webs in these coastal ecosystems. For example, tadpoles are important herbivores and help clean waterways by feeding on algae as well as being important prey. Adult frogs are important regulators of prey assemblages, feeding on insects, such as mosquitoes, and providing food for predators such as birds and reptiles.
All of the acid frog communities are threatened by habitat loss and fragmentation, as well as alterations to wetland hydrology through ground water extraction and canal modification. This can significantly alter wetlands, affecting the reproductive success of many species. Additionally, introduced fish, such as the mosquitofish (Gambusia holbrooki), feed on many native Australian frog eggs and larvae and pose a significant threat to tadpole survival. The effects of climate change on breeding habitats may also be a significant threat to these species in the future by drying up wetlands or increasing flooding to areas, bringing fish into the wetlands.
wallum sedge frog Litoria olongburensis
Photo © Katrin Lowe
My PhD research focuses on the wallum sedge frog (L. olongburensis), which is currently restricted to coastal fore-dune swamps, sedgelands and lagoon systems in wallum habitats from Fraser Island (Qld) to Woolgoolga (NSW), and is listed as vulnerable under the Commonwealth Environment Protection and Biodiversity Conservation Act 1999. Wallum sedge frogs are highly sensitive to disturbance with only very low frog densities in disturbed areas. Furthermore, the ecology and habitat requirements of the wallum sedge frog are poorly understood, creating much uncertainty for the management of this species.
My project will assess the complex relationships between climate, hydrology, water chemistry, and the wallum sedge frog abundance and breeding success. I am currently monitoring the changes in monthly abundance of wallum sedge frogs and tadpoles across their entire range. I am also measuring wetland characteristics, such as pond permanence and water chemistry, and the abundance of other vertebrates and invertebrates, including predators. My wetland field sites are located in four national parks within the entire range of the species and I am currently more than half way through my two years of field work. The large spread of my field sites is critical for understanding broad scale patterns applicable to the whole species, including northern and southern populations.
juvenile wallum sedge frog Litoria olongburensis
Photo © Katrin Lowe
I will use the data from these surveys and climate data to understand how the frogs are responding to environmental conditions, and how their reproductive success is influenced by the timing of rainfall and temperature. What may interest decision makers the most, however, is how the frogs will respond to climate change and wetland alterations in the long term. Thus, I will be utilising my two years of survey data to model and predict the impacts of climate change, specifically how the longevity of wetlands will be affected and how this will in turn affect frog abundance and reproductive success.
To make decisions about conservation actions, we need to be able to understand the interactions between climate, wetland hydrology and frog ecology so that impacts can be anticipated, and appropriate management strategies implemented. My research will reveal key environmental parameters required for the successful maintenance of suitable breeding habitats, particularly coastal wetlands essential for successful reproduction of wallum frog species. Furthermore, information from my field research will be used for predictive modelling of the influence of climate change on coastal wetlands of eastern Australia and provide critical baseline information for managing coastal wetlands in response to global climate change.