Decline of Amphibians

I want to talk to you about the Green and Golden Bell frog (Litoria aurea) today.  This is an amphibian which is native to New South Wales (NSW) Australia and an invasive species in both New Zealand and New Caledonia. It’s also the species which I spent almost a year focusing on during my time in Australia for my professional training year, so a species I know quite a bit about. Now although many of you will have no idea what a Bell frog is and are unlikely ever to see one in the wild, the contents of this post is extremely relevant. This is because all amphibians across the world have all been struggling. In fact 34% of amphibians are endangered while 22.5% are data deficient (there is not enough information on them to deduce their conservation status), Bell frogs are in the same boat as they too are endangered in NSW.

The decline of amphibians has been down to a number of different selection pressures some of which a specific to particular species and while others cover a broad range of species, such as habitat destruction, the spread of disease and also the introduction of invasive or ‘alien’ species.

The Bell frog is under pressure for all these categories, habitat destruction is a key factor along NSW, as agriculture and development has been expanding along the central coast as the population expands. This expansion means that the remaining Bell frog populations are fragmented into several isolated populations, in some cases they are refined to just a single pond such as in the case of Avoca Lagoon. This fragmentation is a problem as it stops migration and immigration of individuals between populations; this means areas are unable to be repopulated after a disaster. However the development in the area is not always a bad thing as in the case of the redevelopment of Sydney Olympic Park has meant that two new self-sustaining populations have been created whilst maintaining a third successful population. Although the recent planning permission of a 4^th coal terminal on Kooragang Island in Newcastle means the populations found there will be under even more pressure in future years.

Invasive species are also an issue for the Bell frog as the introduction of a mosquito fish in 1920s (Gambusia holbrooki) has dramatically increased tadpole mortality. This is not direct predation however as the fish aren’t big enough to directly predate on the tadpoles but they do conduct a process called fin nipping. This reduces the area of a tadpole tail and so reduces their ability to escape from larger predators and search for food. These fish are an extreme problem in Australia and have successfully spread across the whole of Australia except from the Northern territories.

The third main reason the Bell frog populations are in decline like many amphibians around the world is due to the spread of the Chytrid Fungus, Batrachochytrium Dendrobatidis. This fungus is thought to have originated from Africa, due to the movement of people and produce across the world it has been found on nearly every continent. Although some frogs are capable of surviving being infected by this fungus such as the African Long Clawed frog, while to many other frog species contracting this is fatal. The Fungus can be contracted at any life stage from spores which are suspended in the water. The fungus basically affects the epidermis of the frog, which is vital for the survival of an amphibian as they absorb water and oxygen through their skin. There are currently many people looking into a method to control and treat the spread of this fungus, and research is looking into the effects of salinity and heat on the survival of Chytrid.

So like I said at the beginning this post mainly focuses on the Green and Golden Bell frog but the selection pressures being put on this species are either the same or similar to many amphibians which are under pressure throughout the world.

Thanks for reading

Check out these videos

 Not a Bell Frog but pretty cool piece of footage