Pathway · about 15 minutes · 2 steps
A day on the samphire coast
Read the salt threshold of the gulf-to-range gradient in the field: recognise the samphire flats and their mangroves, understand the backwards sea that drives them, and meet the threatened birds that depend on the mud.
This one is for the field, and for the bottom of the gradient. Begin on the samphire flats north of the city — learn to read the crimson salt-storing plants, the world’s most southerly mangroves and the mudflat larder that fuels a hemisphere’s worth of shorebirds. Then climb, in your mind, to the other end of the gradient: the wet Fleurieu and Mount Lofty swamps, and the tiny southern emu-wren that holds on there, to see how the same scarcity of water sorts life all the way from the salt flat to the range.
Take it with you. The end-check is the kind of reading you can do standing on the flat at low tide: name the country from its cues, and explain why this sea runs backwards. Close the page and go outside.
- The samphire coast — The salt-soaked frontier where Gulf St Vincent meets the plains — samphire flats, the world's most southerly mangroves, and a mudflat larder that fuels shorebirds all the way to the Arctic.
- The southern emu-wren — A tiny, secretive bird with a filamentous tail like six wisps of a moulting emu, bound to the dense sedgy swamps of the high Fleurieu and Mount Lofty country — a living token of the ranges' wet refuge, and of how little of it is left.
The end-check — put it together
You've walked the steps. Now answer these from what the pathway taught, not from the pages — getting them here is what tells you it stuck.
You are standing on a flat, treeless plain just north of the city at low tide. Underfoot is soft grey mud that smells faintly of sulphur. Low, fleshy, jointed plants like strings of little green sausages carpet the ground, and in the late-summer heat whole sweeps of them have flushed deep crimson. Seaward, a band of low dark trees stands in the tidal mud on a bed of upright, pencil-thin roots. Which of the region's worlds are you standing in?
Cues: Soft grey mud that smells of sulphur underfoot · Low, fleshy, jointed 'sausage' plants carpeting the flat · Whole sweeps of them flushed crimson in late-summer heat · A seaward band of low dark trees standing on upright pencil-roots
Every cue says salt and tide. The jointed 'sausage' plants that flush crimson as they concentrate salt are samphire (Tecticornia); the sulphurous grey ooze is airless tidal mud; and the band of low trees on a bed of upright pencil-roots is grey mangrove breathing through pneumatophores. Mallee, stringybark forest and an inland saltbush plain are all somewhere else on the gradient — none of them grows salt-storing samphire in tidal mud. (Ch 10.)
Gulf St Vincent is described as an 'inverse' or 'backwards' estuary. As you travel from its mouth off Cape Jervis up to its northern head past the city, what happens to the salinity of the water — and why?
An ordinary estuary is freshened by a river at its head and grows saltier toward the sea. Gulf St Vincent runs backwards: it has no major river, and its broad, shallow northern third loses water to evaporation faster than rain and runoff replace it through the long dry summer. So salinity climbs from an oceanic ~36.5 at the mouth to ~39 in winter and past 42 by late summer at the head — saltier than the open sea. (The desalination brine is a real concern precisely because the head flushes slowly, but it is not the cause of the natural gradient.) (Ch 9; Lennon 1987.)