Amphibians Under Threat

Why Care about Amphibians?

Why Care about Amphibians?

These are some reasons why some people DON'T like frogs but this is an unfortunate point of view. Frogs are an important animal to our environment besides being endearing creatures to admire. Ever notice how a frog calmly sits and appears not to notice what's happening around it? The food might scurry past it several times but it doesn't make a move until the food reaches a certain distance and then the frog suddenly pounces on it. Are you as calm, cool and composed? Doesn't that kind of genuine patience and self control make you envious?

Frogs have a body surrounded by a skin with some unusual properties. It holds the tissues and fluids in just like our skin but it is also porous, allowing both air and water to pass directly through it. In fact, frogs do not drink water through their mouths at all - it is absorbed through the skin on their lower abdomen. Because of this porous skin which allows water to pass directly into the body cavity without being filtered through the stomach, frogs are susceptible to any and all pollutants in the environment. This is why frogs are so often referred to as 'environmental indicators' - which is a more formal way of saying that they are our 'canaries in the coal mine'.

Being a 'canary in the coal mine' is pointless if we don't actually pay attention to what the canary is telling us. When diseases appear in frogs, this can provide us with an open door to discovering other problems that might not be so easy to find and fix. For example, before category 5 cyclone Larry in March 2006, the furthest north the Australian govt had found Ustilago (the fungus that causes cane smut in Australia and corn smut in North America) was Mackay. However, after cyclone Larry, frogs in the Cairns area started to die in droves and many of the sick ones we received had green slime for droppings instead of digested bugs. We had this slime sent to a lab who identified it as the indicator of a heavy infestation of Ustilago! Although primarily a plant disease, Ustilago is capable of killing animals and it does so quickly. Thankfully, Ustilago has a treatment and we were able to start recovering frogs that came in with this problem. Four years after cyclone Larry, Ustilago has now spread to the majority of cane fields in Far North Queensland (DPI, pers. comm.). But we knew it was going to be a future problem because the frogs told us so!

Frogs also have a major role to play in helping us understand and prepare for the sorts of problems that might be caused by climate change that aren't usually thought about. Discussion on possible climate change impacts usually includes an expected increase in vector bourne diseases because of expanded areas becoming more available for mosquito breeding. However, when was the last time you heard a climate change modeller talk about increased fungal and bacterial diseases?

Environmental fungi and bacteria have jobs to do in the soil and water but when extreme conditions cause individual species to grossly overpopulate, epidemics result and the targets could be plant life and crops, or wildlife, or people! We know from the severe drought of 2000-03 in this region that the soil ecology took a beating and a new disease problem appeared in the frogs and reached outbreak proportions in July 2002. We have not found a lab with the right equipment to identify the culprit but we are still convinced that it is a drought tolerant soil fungus creating a mycotoxin in the body. The most likely suspects are in the Fusarium or Mucor genus'. A damaged soil ecology can interfere with our ability to grow crops, erode the health and functionality of intact forest cover, promote the growth of soil diseases, and contaminate water supplies. The frogs are telling us now that we need to be aware of the health of our soil and be mindful of our damaging activities.

The severity of cyclone Larry also caused new problems with pathogens. In technical terms, Larry's core zone was the equivalent of an F3 tornado about 40km wide! That is a force of nature that is going to really move things around, and Larry certainly did. It demolished old buildings in Innisfail made of old timber and fibrous asbestos, containing 100 years of dust from attics and wall cavities. It also passed through what was some of the best rainforest in the Wet Tropics. It vacummed up hundreds of species of microfungi and bacteria that were previously confined to the rainforest environment. All this pulverised concoction of debris was sucked up and blown over a 400 km wide path of the cyclone. After Larry, a half dozen new skin problems appeared on local frogs and the lab results we received listed a dozen bacteria and fungi we've never seen before -- some of them of concern to human health. This is useful information that needs to be considered if storms of that magnitude are going to become commonplace in a modified world.

Aside from telling us when there is something wrong in our environment, frogs' skin also has some unusual chemical properties of it's own. For example, many species have anti-fungal agents in their skin which help to protect them from fungus attack in the wet and humid habitats they live in. Some of these skin properties have been studied by Prof. Mike Tyler at the University of Adelaide in South Australia and he has reportedly made some discoveries which are of medical benefit to people.

Frogs aren't on this planet just to serve us, however. They have their own roles in the food chain. The most numerous life forms on earth are insects and most urban dwellers are familiar with how rapidly pest insects like cockroaches can take over your residence. Frogs keep insect populations in check and the larger species can consume some hefty quantities of bugs each night.

Being a member of the food chain also goes in the other direction. Frogs and tadpoles are an important food resource for other animals such as predatory birds, fish snakes, other reptiles and even some mammals.

Well then, if frogs are so important, why are their populations doing so badly? There are so many, many reasons why and you can find out what they are in the threats section.

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