Saturday, 26 January 2008

Cape Bridgewater: cliff top saltmarsh

It's easy to think of salt marshes as being … well … just a tad dull. Expanses of green with only a few species of plants, none of which sent up bright and lively flowering heads. This lack of floral exuberance probably contributes to the enthusiasm with which salt marshes are cleared for housing developments. (Who cares? It's just a bunch of boring weeds. Well, the proud new home owners start to care when their bowling green lawns develop bald patches from acid sulphate scald. But that's another story.)

Coastal salt marshes develop on sediments just above the high water level of neap tides. They are still affected by spring tides, which inundate them periodically, but they dry out in between. As the plants grow, they impede water flow during spring tides. This allows water-borne sediment to settle. Over time, the deposits build up. Eventually they are high enough to be free of direct tidal influence.

But high for a coastal salt marsh is usually measured in centimeters not metres. Certainly not tens of metres. So the top of a cliff isn't where you'd usually expect to find salt marsh plants. At Cape Bridgewater, water seeping from the dune limestone combines with spray from the Southern Ocean to create just the right conditions.

How could anyone say this is a tad dull? Creeping brookweed (Samolus repens) covers the cliff top in a swathe of green. The tiny white flowers are almost luminous. I bet at night the salt marsh looks like the Milky Way.

Succulent beaded glasswort (Sarcocornia quinqueflora) grows with the brookweed. This species is common on salt-affected land. It forms extensive stands at Lake Corangamite and other inland lakes in western Victoria.

A second species, thick-head glasswort (Sarcocornia blackiana), also grows on the cliff top. That common name may be unflattering but there is a certain pudginess to the stems.

Although a few other species appear among the brookweed carpet, the plant diversity is low. Unlike the salt marshes as sea level, this one doesn't appear to be home to many invertebrates either. Were this by an estuary, I'd expect to find a few snails. No, not Theba but the miniature pulmonates Salinator and Ophicardelus. But because these snails lay their eggs in the ocean — and they don't tend to do a Christmas Island crab-style migration up and down the cliff face — there is no chance of them setting up a self-perpetuating population. Mind you, there wasn't any Theba either so that was good news.

And that concluded the trip to Portland. Not a bad haul for two days!

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