How do mangroves survive in salty sea water?

How it works

Most plants wilt in sea water, because salt draws water out of them. Mangroves have special tricks. Some kinds have roots that work like filters and keep most of the salt out. Others get rid of extra salt through their leaves, and you can sometimes see tiny white salt crystals on them.

Muddy shores are soft and short of oxygen, so roots struggle to breathe. Some tropical mangroves grow stilt roots that arch out from the trunk into the mud, holding the tree steady. Other kinds send up rows of straight little breathing roots that poke out of the mud like pencils, taking in air.

This tangle of roots works like a natural sea wall. Waves lose their strength as they push through, and mud settles out of the water instead of washing away, so the shore is protected. The roots are also a nursery for young fish, crabs and shrimp, and birds come to feed there.

Where to see it in New Zealand

New Zealand's mangrove, called mānawa in Māori, grows only in warm harbours and estuaries in the upper North Island, such as the Firth of Thames and many Northland harbours. Instead of stilt roots, it has pencil-like breathing roots.

Try it together

In a tray, build a sandy shore at one end. Push a row of small twigs into the sand on one half to act as roots, and leave the other half bare. Add water and make waves with your hand many times. Which side loses less sand?