Answer:
Complete immersion in water is not essential for life for the yabby. If its gills are kept moist (humid air is sufficient), it can absorb oxygen from the air and survive for many days out of water. To breed, however, it must be in water.
The yabby has evolved an ingenious mechanism for surviving drought. As the ground dries up it burrows down following the falling water table, and seals the burrow entrance with an earthen plug. In a small, moist chamber at the bottom, the yabby enters a state resembling suspended animation, its bodily functions (respiration, pulse and digestion) practically ceasing. This mechanism is called aestivation (not hibernation, which is a winter adaptation of warm-blooded animals). The yabby can remain like this for years on end. Burrows well over 5 metres deep have been found.
The yabby is rarely found in clear water. Its natural habitat is usually muddy water, which (although probably not essential to life) may give some protection from predators. Some predators, such as fish, do not depend upon sight alone but can sense pressure changes, tracking their prey even in muddy water; cormorants too can find their prey in muddy waters.
Substrate type is not critically important, although the yabby is commonly found on muddy or silted bottoms with the occasional rock or fallen branch (in contrast to the leaf-littered, rocky or pebbly streams of the spiny crayfishes). Experiments have shown that growth is faster on a natural substrate such as mud or stones, than on an artificial one such as plastic tanks.
Explanation:
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