The samphire coast

Between the sea and the solid ground of the plains lies a strip of country that cannot make up its mind which it is. Twice a day the tide floods across it and twice a day it drains away, leaving a low, glistening world of mud and salt-crusted flat that is neither properly sea nor properly land. To a passing eye it looks like wasteland — flat, grey-green, treeless, humming with mosquitoes. It is one of the most productive and improbable environments in the whole Adelaide region, and it runs on a single difficult trick: living in salt.

The plant that gives the coast its name is samphire — not one plant but a family of low, fleshy, jointed glassworts that the botanists file under Tecticornia. Samphire do the thing most plants find fatal: they drink salt water, swelling with the brine and packing the salt away in their succulent flesh (Tecticornia 2024). In the heat of late summer, as they concentrate the salt, whole flats flush from blue-green to deep crimson, and the coast north of the city turns, for a few weeks, a startling red. Where the flats meet open water, the samphire gives way to the one tree tough enough to stand with its roots in the tide: the grey mangrove, Avicennia marina. South Australia has just this single mangrove species, and the forests it makes around St Kilda and Barker Inlet are among the most southerly on the planet, a tropical way of life growing at its cold limit. It handles the salt the other way — turning most away at the roots, sweating the rest out through its leaves, and pushing up beds of little breathing snorkels through mud too airless for ordinary roots.

None of this looks valuable, and all of it is. The waterlogged mud buries carbon and keeps it, hectare for hectare outpacing most forests; the channels are a nursery where the gulf’s prawns, whiting and blue swimmer crabs begin life; the flats soak up storm surge that would otherwise gnaw at the shore. Ugly and useful in equal measure, Australia’s temperate coastal saltmarsh is now formally listed as a Vulnerable, threatened community, having been drained, filled and written off as wasteland for two centuries (Saltmarsh 2013). And the mudflat larder feeds a spectacle you would never guess at: each spring, tens of thousands of shorebirds arrive here from the Arctic, fatten on the tiny invertebrates of the mud, and throw themselves back north to breed — so that every scrap of this grey ooze is helping to power a journey to the top of the world and back.

It is not durable. In 2020 a stretch of the St Kilda mangroves and saltmarsh abruptly died, poisoned by hypersaline brine that leaked from an adjacent salt field into the tidal flats — a blunt reminder of how finely balanced life at the salt limit is. The samphire itself is losing its seaward edge as the sea creeps up faster than the plants can colonise new ground behind (Delta 2017). And bound to this shrinking habitat is a small dun bird found almost nowhere else, the slender-billed thornbill of Gulf St Vincent, so tied to the samphire that it, too, is listed as vulnerable. Lose the samphire and you lose the thornbill, a rung of the great migration, a carbon store and a nursery. Which is rather the point of learning to see it as something other than wasteland.