There is a point when you know it's time to leave the mangroves. If on a field trip, it's when fish start leaping en masse. You leave then because you know that whatever's scaring the bejeezus out of them is likely to do the same to you.
But if you're on a casual stroll along the boardwalks at Cairns Airport, the time to leave is when the insect repellent wears off. I didn't. I'm paying for it now. Scratch.
Two boardwalks lead from a car park on the airport approach road. Although they differ in the details both pass through a range of mangrove types from Avicennia and Ceriops at the landward edge to Rhizophora close to the water.
They grow on mud — a substrate that is unstable, low in oxygen and high in salt. A number of adaptations allow mangroves to thrive under conditions that would be hostile to most other plants. Perhaps the most obvious of these adaptations is the form of the roots. In addition to the standard below-ground roots, mangroves also have pneumatophores — above-ground roots covered in bark. Pneumatophores have pores in their bark to allow oxygen to pass from the air into the spongy tissue within. In this way, all the roots are supplied with oxygen, even those buried in the anerobic mud.
The grey mangrove (Avicennia marina) occurs on the landward edge. Its pneumatophores push up through mud like fingers. (This mangrove has the widest distribution in Australia — it occurs all the way down the east coast to Melbourne.)
Yellow mangrove (Ceriops) has a combination of buttress roots with nobbly 'knees'.
The roots of the orange mangrove (Bruguiera) are similar to those of Ceriops. It often occurs with the red or tall-stilted mangrove (Rhizophora), which has characteristic arching above-ground roots.
The state government takes mangroves very seriously. You're not even allowed to mow them.
