1.3 Frogs as indicators of river health
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Curriculum Alignment

1, 2, 10, 14, 18, 19, 25, 26

Years K-6: Science And Technology, HSIE, Creative Arts
Years 7-10: Science, Geography 
Years 11-12: Biology, Community And Family Studies, Science, Agriculture, Earth And Environmental Science, Society And Culture

SOSE, Science, Geography 

Futures, Interdependence, Thinking


Science, Thinking Processes, Geography

>Students describe the threats to the frog species in their region 
>Students explain how identified threats to frogs indicate larger aquatic habitat concerns

2 hours

Materials required
>Torches covered in red cellophane
>Tape recorder or mobile phone with a recording function Frog Field Guide 
>Frogwatch Frog Calls CD 
>Information about creating frog habitat (hyperlink available on Sustaining River Life cd and web versions)
>“Frogs: The Thin Green Line” video (hyperlink available on Sustaining River Life cd and web versions)
>Frogwatch Field Datasheet (see below)

Green Tree Frog (Litoria caerulea). Photograph: Richard Tate
Green Tree Frog (Litoria caerulea). Photograph: Richard Tate

Beginning in the early 1980s, biologists began to realise that amphibians such as frogs are extremely sensitive to pollution and other environmental stresses. Declines in amphibian numbers and increases in the number of deformed bodies led scientists to investigate the role of habitat loss, increased ultraviolet radiation (due to ozone depletion), and chemical pollution in these important changes. 

Frog populations have declined dramatically since the 1950s. Habitat loss is a significant cause of this decline, as are pollutants, climate change, ozone depletion, the introduction of non-indigenous predators/competitors, and emerging infectious diseases including Chytridiomycosis.

Many environmental scientists consider amphibians, including frogs, to be excellent biological indicators of broader ecosystem health because of their intermediate position in food webs, their permeable skins, and their typically biphasic life (aquatic larvae and terrestrial adults). It appears that the species with both aquatic eggs and aquatic larvae are most affected by the decline.
Chytridiomycosis is an infectious disease affecting amphibians worldwide. Originally from Africa, Chytridiomycosis appears to have been brought to Australia with the live animal trade. This highly virulent fungal pathogen of amphibians is capable at the minimum of causing sporadic deaths in some populations, and 100 per cent mortality in other populations. Because Chytridiomycosis requires cool temperatures, frog species in the shrinking alpine regions are most at risk. 

A number of studies indicate that the introduction of Gambusia (Mosquito fish) has contributed to the decline of many frog populations. Studies have shown that Gambusia will attack and eat tadpoles. 

There is evidence of chemical pollutants causing frog developmental deformities (extra limbs or malformed eyes). Pollutants have varying effects on frogs. Some alter the central nervous system while others cause a disruption in the production and secretion of hormones.

Experimental studies have also shown that exposure to commonly used herbicides such as glyphosate (Roundup) and insecticides greatly increase the mortality of tadpoles. Additional studies have indicated that terrestrial adult stages of amphibians are also susceptible to non-active ingredients in Roundup. The herbicide Atrazine has been shown to cause male tadpoles of African clawed frogs to become hermaphroditic with development of both male and female organs. This has been repeated in many parts of the world.
Habitat loss, degradation and fragmentation have further pressured frogs in the face of climate change, as fewer areas now meet the breeding requirements of frogs. 

The construction of dams and weirs across the Murray-Darling Basin has significantly altered the flow regime of the system. Flooding, which once fed off-stream fish-free wetlands, occurs less and less often. Other sites have been impacted by grazing, ploughing or irrigation infrastructure and practices. 

Like many other organisms, increasing ultraviolet-B (UVB) radiation, due to stratospheric ozone depletion and other factors, may harm the DNA of amphibians, particularly their eggs. The amount of damage depends upon the life stage, the species type and other environmental parameters. 

Climate change has also caused amphibian declines. The general drying trend in eastern Australia associated with climate change bodes poorly for water-dependent species such as frogs. Climate change, coupled with habitat loss and fragmentation, could well be the final stressor that pushes some species to extinction. 

Some of the frogs of special concern in the Murray-Darling Basin include:

>Green and Golden Bell Frog
>Yellow-spotted Bell Frog
>Booroolong Frog
>Northern Corroboree Frog

The Green and Golden Bell Frog has been found in association with almost every type of waterbody except fast flowing streams. In NSW, it inhabits many disturbed sites including abandoned mines and quarries. Sites which support breeding populations are waterbodies which are still, shallow, ephemeral, unpolluted, unshaded, with aquatic plants, and free of Gambusia and other predatory fish. They also have terrestrial habitats that consist of grassy areas and vegetation no higher than woodlands, and a range of diurnal shelter sites.
The Yellow-spotted Bell Frog on the southern tablelands of NSW has suffered an extensive decline, with no confirmed records since 1980 where it was formerly known from Namadgi and Kosciusko National Parks and extensive areas of grassland. 

The Yellow-spotted Bell Frog occupies habitat which includes permanent ponds, swamps, lagoons, farm dams

Crucifix Frog (Notaden bennetti). Photograph: Jodi Rowley
Crucifix Frog (Notaden bennetti). Photograph: Jodi Rowley

Salmon Striped Frog (Limnodynastes salmini). Photograph: Jodi Rowley
Salmon Striped Frog (Limnodynastes salmini). Photograph: Jodi Rowley

and the still backwaters of rivers usually with tall reeds present. The species was also found in ponds or slow moving streams with overhanging grassy banks in the absence of reed beds. The Yellow-spotted Bell Frog was found to overwinter in the hollow centres of rotting logs and in the earth surrounding the roots of uprooted trees.

The Booroolong Frog inhabits rocky permanent streams in a broad range of habitats, ranging from small slow-flowing creeks to large rivers in both forested areas and open farmland. The species is predominantly found along the western-flowing streams and their headwaters of the Great Dividing Range catchments that drain from the Northern Tablelands to the Tumut River in the Southern Highlands, and other tributaries of the Murrumbidgee River.
Over the past two decades, the Booroolong Frog has apparently undergone a severe contraction across its former known range, though there are no historic population estimates. 

The Northern Corroboree Frog is restricted to montane and subalpine woodlands, heathland and grassland above 850 m above sea level. The species prefers to breed in Sphagnum bogs and wet heath in subalpine areas and dense patches of herbs in openings or seepages amongst fallen tussocks at lower elevation. Non-breeding habitat is forest, sub-alpine woodland and heath adjacent to breeding sites. 

The Northern Corroboree Frog is one of a number of Australian alpine species which have experienced pronounced population declines for unknown reasons. There is no single aspect of the field biology of these species which stands out as a feature in common that may help explain the declines.

Indicator species
Food web 

Lesson plan
1. Have the class review and practice identifying frog calls from the Frogwatch Frog Call CD.

2. Take the students to a site on a nearby river, stream or wetland at dusk or dawn. Have them sit, and explain that the more quiet they are, the better their survey will be.

3. Complete the Frogwatch Field Data Sheet (see below).

4. Discuss the importance of habitat features for frogs and factors involved with their decline.

5. Have the students speculate about the habitat quality of the area. What aspects of the habitat do they feel are conducive to frog breeding? What aspects do they see which causes them concern?

6. Inventory the species present. If you are able to immediately identify frog species on-site do so. Record the calls with a mobile phone or cassette player to reference against the identification CD back in the classroom.

7. For each species you can hear, estimate the number of individuals calling. Use the following groupings: 1-5, 5-20, 20-50 or 50-100.

8. Start recording 2-5 minutes after you have finished talking and point the microphone towards the frog calling area.

9. Back in the classroom, encourage students to explain what elements of the habitat were linked to the frogs discovered.

10. Have students identify aspects in (or missing from) the habitat that limited expected frog species from being present.

To finish why not have 
students use what they
now know to draw a mural
of excellent frog habitat
that would suit one of the
species of concern referred to above. 

Spotted Marsh Frog (Limnodynastes tasmaniensis).  Photograph: Joanne Ocock
Spotted Marsh Frog (Limnodynastes tasmaniensis). Photograph: Joanne Ocock

Peron’s Tree Frog (Litoria peroni).  Photograph: Marie Attard
Peron’s Tree Frog (Litoria peroni).  Photograph: Marie Attard

Draw the Frogwatch site the class visited (or maybe get it from Google Earth) as precisely as possible, or draw a map so that the spot can be found again. Include:

>An X at the point where the group sat during the recording
>Any access route to the site and the name of those access roads
>Any permanent landmarks that would assist someone reading the Field Data sheet in the future to find the exact sampling spot
>A north arrow to indicate direction.

Have students design and create their own ‘frog bog’ on the school grounds using the information on frog habitats – see link under Materials required.

In-class room adaptation
View in class “Frogs: The Thin Green Line” and then proceed to Step 9 of the Lesson plan. 

Secondary pathway
Take on a Frogwatch site as a class or as individual projects. 
Contact your local Frogwatch group (if there is one) to arrange for a training program in your area, and for information on frog censuses taking place.