Aussie Billabongs as Diverse as Amazon Rivers?
Murray River a Biodiversity Jungle, Says Scientist
The legendary billabongs of Australia's Murray-Darling Basin might be as rich in biodiversity as the waters of the Amazon jungles, according to a scientist with the Murray-Darling Freshwater Research Centre at Albury.
Dr Russell Shiel said his study of billabongs on the Murray River floodplain had found the still water bodies to be teeming with life. The species in two neighbouring billabongs, sometimes only metres apart, were often utterly different, he said.
The billabongs, filled by floodwaters every few years, could carry up to 1,000 times more biodiversity than the river which flowed past them, Dr Shiel said. Where the river might have only a few species, a nearby billabong might contain thousands. Flowing water in the river channel provided few niches for species to live in, while still billabongs had a diverse range of areas for nesting, feeding and breeding. "It's early days yet, but what we're finding is that billabongs might be absolutely crucial to the health of all the wildlife of the river," he said. "We think the billabongs act like genetic banks which help replenish the biology of the whole river system.
"They are natural storehouses of thousands of different species - fish, crustaceans, insects, plants, algae, bacteria, plankton and many others. When the river floods these species spill out into the floodplain and breed up in the shallow flood water, providing instant food for native fish.
"It's well-known that many native fish won't breed unless there's a flood. Murray Cod, for example, will lay eggs every year, but the hatchlings won't survive unless there's a flood when they hatch. We think it's because in a flood the thousands of little species seeded by the billabongs provide easy tucker for the baby cod. You could say that billabongs are the tuckerbags of the Murray-Darling Basin.
"Many of the creatures and plants which live in billabongs can survive drying out. Any shovel-full of soil taken from a dry billabong, or from the floodplain itself, contains millions of eggs and other 'resting stages' of billabong species. They can be brought back to life by adding water, but the water has to come at the right time.
"How long these resting stages can survive without floods is not known, but it is certain that given enough time most of them will die. Over the past century we have dammed and regulated our rivers so much that now they don't flood nearly as often as they used to. The lack of floods is endangering this precious genetic 'seedbank'. Anything else humans do to damage billabongs is also a threat.
"Native fish, and the birds which eat them, depend on billabongs being regularly renewed by the river's natural cycle. So by changing the river's flow modern humans have directly contributed to massive declines in native fish and birds."
Dr Shiel said billabongs were not just short-lived puddles of water. Recent research into bottom sediments had found that individual billabongs could be 10,000 or more years old, and that they had been present on the Murray floodplain for hundreds of thousands, perhaps even millions, of years. In nature billabongs were filled in only very slowly, with about one millimetre of sediment being added each year.
"There has been plenty of time for individual billabongs to evolve their own, unique species," he said. "Every time people fill in, degrade or permanently drain a billabong Australia might be losing a priceless pool of unique creatures. We really have very little knowledge of what is there."
Dr Shiel said there were no accurate estimates of how many billabongs remained in the Murray-Darling Basin. More than 200 had been counted along just one stretch of river, 200 kilometres long, between the Hume Dam and Yarrawonga Weir. In some areas of the Basin's floodplain billabongs represented more than 60 per cent of the surface water.
"Clearly thousands of billabongs remain, but all of them are endangered," he said."Before European settlement there were no large freshwater lakes in the Murray-Darling Basin. Billabongs represented the most abundant standing fresh water. They were exploited ably by Aborigines for 40,000 years or more. All the reservoirs now in the Basin are recent and artificial. The only similarity they have to billabongs is that they contain water. They cannot sustain the diversity of life found in billabongs."
Biological diversity (or "biodiversity") means simply the variety of life on Earth. It includes three levels - genetic variation within a species, variation between different species and variation between different ecosystems. The International Convention on Biodiversity, which Australia and more than 50 other countries have now ratified, came into force around the world on December 29 last year.
Department of the Environment and Water Resources. April 2006.
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