Koura

Crusty Crustacea

Koura. Photo courtesy of DOC

Koura belong to the crab family – the Crustacea – so called because they have a hard shell like a crust, called an exoskeleton. This protects the koura from its enemies but it has a big drawback. It doesn’t expand as the koura grows. So when the koura grows and its shell gets too tight, it splits open. The koura squeezes out and makes a new shell. This is called moulting. Koura hide while they are moulting because they are soft and unprotected so it is a very dangerous time.

Koura at home

Koura live under rocks, roots or in holes in the bank. They come out at night to avoid being eaten by eels, shags and trout. They are scavengers, eating rotting plants, insects and worms. By eating and recycling leaves and dead things that fall into the water, they help keep streams clean. Their big pincers are useful for tearing up food, fighting other koura and scaring their enemies away. They will nip you too!

Escape artists

Koura walk about on their four pairs of walking legs. If they get a fright, they can flick their tails forward really fast and zoom backwards into hiding.

Koura can grow up to 30 cm long and live for 20 years – that’s pretty old! They can also change their appearance to match their surroundings – becoming green, brown, grey, black or patterned.

The Koura’s life cycle

Koura start life as eggs. The female koura lays up to 200 eggs and carries them under her tail for safety. After 3 or 4 months, the baby koura hatch. They look exactly like their parents but they are very, very tiny. They hang on their mother’s pincers until they are 4mm long.

Then they are on their own. They will moult again and again and get bigger and bigger. When they are four years old they will become adults.

Koura are in trouble

Their numbers are falling. They are now classed as ‘threatened species’
Why?
• They have lost their homes. They die where stream sides are cleared and the water is muddy with soil and cow poo.
• They are killed by pollution. Chemicals and rubbish in streams are the culprits.

You can help!

• Don’t take Koura out of streams. Look at them and then put them back.
• Help fence and plant stream sides with shady trees. Koura love clean, cool water.
• Take part in Koura Kraze!

Koura Kraze month

Every March and April the Royal Society of New Zealand helps schools count the koura populations in their local streams. It’s great fun doing hands-on science and learning about the environment.

For more information go to www.emap.rsnz.org or email emap@rsnz.org