Australia: The Land Where Time Began

A biography of the Australian continent 

Claypans & Salt lakes

Unexpectedly, there is an amazing amount of life in the claypans and salt-lakes of arid Australia. In the Lake Eyre Basin, amid the plain and sand hills, is a large number of claypans and salt lakes, varying in size from the small, a few metres across, to the very large to more than a kilometre across.

They are usually bone-dry, having a thin covering of curled flakes, or on the ones with thick mud, roughly hexagonal blocks separated by fissures.

Signs of life on these desiccated claypans are evident, such as mollusc shells, crustacean carapaces, and in the ones that held fresh water, the foot prints of frogs.

This cryptic life consists mostly of invertebrates that flourish in  newly filled lakes. The salt lakes are notable for their endemic faunas unique to Australia.

Crustaceans are the most noticeable of the invertebrates. They are mostly endemic, demonstrating tolerance to the high salt concentrations, high temperatures and extreme desiccation. The ostracods, seed-shrimps or shell-shrimps, are the most diverse groups in Australia. There are 37 species of them, higher than on any other continent. They are enclosed in a bivalved shell, from 1.25-6 mm long, their legs protruding through the gape between the shell valves. They can be swimmers, climbers, burrowers, clingers. Their eggs can withstand complete desiccation.

There are 2 species of amphipod common in Australian salt lakes, freshwater shrimps or 'side-swimmers'. They are laterally compressed.

There are also 9 species of Anostracan  brine-shrimp or fairly shrimp that are endemic to Australia. These are thumbnail-sized animals. Like the shield shrimps, they are some of the most primitive crustaceans.

Another significant component of salt lake faunas are gastropods (snails).

The presence of insects depends largely on the length of time water is present. Insects have evolved a number of strategies for dealing with the harsh conditions. Some dragon fly nymphs can survive for months in damp soil. Others complete their life cycle in 36 days, breeding in large numbers.

Mosquitoes have no problems, they can breed in very small amounts of water, and can complete their breeding cycle in a few days. They can also contend with high water temperatures and high salinity. Their food source, bacteria, begin multiplying as soon as these ephemeral water arrives. Mosquito numbers can rise very quickly, as their larvae have few predators and competitors in these harsh environments. They have even evolved a way to survive when the water oxygen levels go too low, some can get air from the tissues of vascular plants they pierce with their proboscis.

Other aquatic insects overcome the oxygen problem by collecting a bubble of oxygen from algae. Some have long snorkels. Some of the most salt tolerant insects are mosquitoes, midges, and gnats, caddis flies and a number of water beetles.

  1. Mary E White, Running Down, Water in a Changing Land, Kangaroo Press, 2000
  2. Penny Van Oosterzee, The Centre - The Natural history of Australia's Desert Regions, Reed Australia, 1993

 

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Last Updated 05/11/2008

 

  
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                                                                                           Author: M.H.Monroe  Email: admin@austhrutime.com     Sources & Further reading