The most southerly mangroves in the world

Mangroves are tropical. Most of us know that, but just how far beyond the tropics will they grow?

Back in 2015 I wrote about mangroves in Victoria, which I took for granted as a child but are actually amongst the furthest-South mangroves in the world at around 38 S. I published a friend’s photo in the comments to that post, showing the accepted record-holder, the Grey Mangroves (Avicennia marina) of Corner Inlet at 38.9 S.

Now I have been there to see them for myself. My photo looks over them from the end of the Miller’s Landing track on Wilson’s Promontory, and there are just as many more to the left of the picture.

It’s a thriving population, then. Why doesn’t it spread further South?

Firstly because Corner Inlet is peculiarly suitable for them, with its shallow (and therefore warm) protected waters.

Secondly because the Prom is Australia’s Southern tip. To go further South they would have to jump to King or Flinders Islands in Bass Strait, or all the way to Tasmania, and the currents are unfavourable. Climate change is assisting a polewards spread of mangroves, as we might have expected, but that step is a big one.

Wikipedia has distribution maps,  of course, but the best and most up-to-date are on iNaturalist. This page has a world map (scroll down to it) of observations of the genus Avicennia, to which all our extreme mangroves belong. The other main genus, Rhizophora (map), extends just as far North but not so far South.

New Zealand has a similar population of far-South mangroves along the Northern coast of its North Island, and they don’t face such a big journey as ours. In fact, seedlings have already been found on the South coast of the North Island and the North coast of the South Island at 41.25 S. The finders’ comments are, “It’s too cold here for them to establish,” or words to that effect. That will probably change.

• Introduction and index to South Gippsland blog posts December 2022.