Kandelia obovata trees

The early life of little mangroves

Dreaming of the days when I could still do fieldwork, I find myself making up stories about mangroves seedlings bravely trying to establish in a brutal world.

The early life of Kandelia obovata trees starts out quite fun. At least, I think so. The Kandelia seeds germinate when they’re still on their parent tree, so that a stem is already formed before the seedling has even left the tree. Basically, they are born alive, just like us humans, but they have found a much less painful way to do so.  

Kandelia obovata at Ting Kok mangrove.JPG
Kandelia seedlings getting ready for life – the long green seedling is growing out of the brown fruit. Germination happening while still on the parent tree is called vivipary and can be considered the plant equivalent of live birth in mammals. Source: wikipedia

But that, though quite remarkable, is not the most fun part. When these seedlings are ready to move out into the real world – or their parent tree tells them it’s time to go… I’m not sure who decides – they do so freefalling! They fall straight down from their parent tree. That sounds like so much fun! And then they don’t even have to worry about the landing. Because with a little bit of luck they plunge straight into the water.* Even better: after that superfun freefall they just get to float around in the warm waters of some tropical sea. SO relaxing.

*Don’t worry, if it’s lowtide they don’t hit the ground hard. Most mangroves grow in soft mud, so their seedlings make a nice and soft landing.

These (not Kandelia, but Aegiceras corniculatum) seedlings were less adventurous and decided to stay close to mom. Seems like a bad choice, there’s no space. Picture taken at Nansha District, Gangzhou, January 2019 (CC-BY).

Unfortunately, after that, life gets a bit rougher…The seedlings can’t float around forever, cause they’ll start rotting. So they’re gonna have to settle at some point, establish some roots. Now, this is a tricky part. They are trying to root in an environment that isn’t exactly calm. The tides come and go twice a day. There’s wind. There’s waves. If they’re not rooted enough the sea will just wash them away again.

Rough life as a young mangrove seedling. Better outgrow those annoying waves. Picture taken at Nansha District, Gangzhou, January 2019 (CC-BY). Not sure of the species.

Gotta get those roots growing! Not all of the seedlings make it. Some have bad luck and are growing in a storm season, or in a shipping lane that’s causing too much wave action, or the mud they are trying to root in keeps getting washed away. So much can go wrong! But, if they manage to overcome all of these hurdles – fingers crossed! – we get to admire more beautiful mangrove trees.

Some Kandelia trees that made it. Yay!
Picture taken at Qi’ao Island, Guandong, January 2019 (CC-BY).

This post is based on Balke et al 2011Windows of opportunity: thresholds to mangrove seedling establishment MEPS 440:1-9 (2011) and my own work (of which manuscripts are still very much in prep).

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