Saltmarsh – Diminuitive Cousins of Mangroves
Australia’s mangroves share their tidal habitat between mean sea level and the highest tides with another distinct group of plants – the tidal saltmarsh. Saltmarsh plants are largely distinguished from mangroves by their smaller size. They are described as a separate habitat with plants usually less than one half metre tall. This definition of tidal saltmarsh plants differs from the definition of mangroves only by the size and character of the vegetation – where tidal saltmarsh plants form shrubby ground cover. Saltmarsh plants dominate where mangrove plants are excluded by either low temperature or low moisture limitations, a feature which reflects their much hardier nature. Saltmarsh species typically proliferate in cooler areas subject to occasional frosts, but they also dominate in hotter arid conditions where annual rainfall is less than 1500 mm. There is recent evidence of a landscape-scale dynamic equilibrium between these two plant types such that one will replace the other in alternate climatic conditions. The chief driver of this change is rainfall. Some of the more common Australian tidal saltmarsh species include: Halosarcia halocnemoides (Grey Samphire), Halosarcia indica (Brown Head Samphire), Sarcocornia quinqueflora (Beaded Samphire), Sclerostegia arbuscula (Shrubby Glasswort), Sesuvium portulacastrum (Sea Purslane), Sporobolus virginicus (Marine Couch) and Suaeda arbusculoides (Jellybean Plant).
Left - Saltmarsh ‘floral pavement’ bordering mangroves near Bundaberg, Queensland.
- Tree of Avicennia marina amongst salt marsh bordering Leschenault Inlet, Western Australia.
- Typical saltmarsh species, Sarcocornia quinqueflora.
Associates – Occasional Residents with Mangroves
The separation of mangroves and upland plants across the high water mark is not always distinct. Australia’s mangroves sometimes include additional plant species that are not generally considered mangroves. However, some authors argue for the inclusion of some, or all, of these species as mangroves. Generally, the view taken here is that mangroves are those plants that grow almost exclusively in the tidal habitat. Associate species often include: Cerbera manghas, Clerodendron inerme, Dillenia alata, Hibisicus tiliaceous, Melaleuca sp., Pongamia pinnata, Randia fitzalani, plus creepers like Derris trifoliata, and the rare Finlaysonia obovata in the Northern Territory. Furthermore, there is often overlap also with the closely associated habitat of the beach zone where other species of Callophylum, Casuarina, Morinda and Thespesia are commonly found.
Invasive associate under control
A recently introduced pest species is Annona glabra, known as Pond Apple, has invaded mangroves in north eastern Queensland. It is listed in the top 20 Weeds of National Significance in Australia. Since its introduction as graft stock for custard apples, this species has spread aggressively into upstream estuarine areas like the Daintree River Wet Tropics Area. Its’ dispersal appears to have been widened by Cassowaries who like its fruit, and the ready dispersal of its buoyant fruits. An eradication program is currently being undertaken in affected Queensland estuaries by the Queensland Department of Natural Resources.
Right - Invasive Pond Apple trees, Annona glabra, in mangroves of the Daintree River, Queensland.
- Fruiting body of Dillenia alata.
- Casuarina clump on higher ground amongst saltmarsh and mangroves.