Australian Plants Society Mornington Peninsula Inc.
Meeting – Tuesday 16 February 2016
Western Port Mangrove Revegetation
Presenter: Ian Stevenson, Chairman, Western Port Seagrass Partnership
Western Port Mangrove Revegetation
What’s going on beyond the old Koo Wee Rup Swamp?
Do any of us driving along near Tooradin have any idea of what’s going on at the northen part of the Western Port coastline? Particularly when there’s few or no roads giving access to that part of the coast. We see the drainage channels from the Koo Wee Rup swamp heading out to Western Port, notice a few boats bobbing on their moorings, but what’s really happening further out?
The brief answer is that one metre of coastline is being lost each year through erosion.
And the so-called erosion prevention methods of the dumping of rubble, car tyres, concrete blocks or rocks doesn’t stop it.
Ian Stevenson, the chairman of the Western Port Seagrass Partnership, proceeded to give us a fascinating insight into the ecology of Western Port, and the role of the Partnership. He’s one of a group of retired scientists who were interested in using their scientific background and community networks to help improve the understanding, protection and restoration of the ecosystems of Western port and its iconic seagrass communities.
Seagrasses are the foundation stone of Western Port’s ecology, and the substantial losses of seagrass communities from the mid 1960s onwards have been seen internationally as an ecological disaster, particularly given its status as a recognised Ramsar Wetland.
(Ramsar is the small town in Iran where the Convention on Wetlands was established in 1971, with the broad aim of halting the worldwide loss of wetlands)
Ian went on to describe the three main factors impacting on the loss of seagrassses:
- The draining of the Koo Wee Rup swamp from the 1870s – 1970’s resulting in sediment being washed down the channels into the northern end of Western Port
- Continuous erosion along the northern coastline cliffs, which are approximately one metre high
- The churning of the tides, which are up to 3 metres (compared with Port Phillip Bay which has a tide of just one metre)
In the early years of the Partnership (which was established in 2001), experiments were carried out planting seagrass plugs. These trials initially went well but then became covered in mud following runoff from the Koo Wee Rup swamp after heavy rains. Seagrass doesn’t survive being suffocated in mud.
Attention then turned to mangroves to build a protective layer between the shoreline and the seagrass communities.
Western Port has just the one species of white mangrove Avicennia marina, the farthest south it is found.
Mangroves have been impacted by a range of man-made activities over the past 100+ years, including being harvested to produce barilla ash for soap-making; cleared to allow boating access; and dying from reduced salinity caused by flood waters off the drained Koo Wee Rup swamp.
Trial and error has been the order of the day – there’s very little research worldwide into mangrove revegetation.
Salvaging mangrove seedlings and transplanting them was tried without success. From about 2008 onwards the focus has moved to collecting seed and propagating mangrove plants. Volunteers have been propagating seeds and experimenting with various methods of planting them in the mud flats. The Seagrass Partnership has been working with the Mornington Peninsula Youth Enterprises nursery in propagating mangrove seedlings, and they currently have the capacity to propagate up to 28,000 mangrove seedlings.
Mangrove seeds grow quickly. The viable seed sheds its husk and sinks into the mud within 24 hours; shoots will appear in 2 weeks; within 3 months there will be 8-10 leaves, ready for planting.
In the early years the seedlings were lost through storm surge and barnacles, which smother the plant and kill it. Experimentation is now going on using 90mm diameter plastic pipe, which is sunk into the mudflats and protects the new plant from both surge and barnacles. Different growing techniques are also being trialled, for example keeping some seedlings back for 12 months; and direct planting of seeds.
Of course not everyone likes mangroves on their patch of coastline, and there’s been an education program ongoing to inform landowners of the reasons for trying to revegetate the mangrove populations. Schools have been recruited to help grow seedlings and volunteers sought for seed harvesting and planting.
There’s a wealth of information about the Seagrass Partnership and their work at their website
And now we know just a little bit more about what’s happening in Western Port, unseen to many of us.
Report by Jenny Bolger
Plant Table List – 16 February 2016
Correa “Dusty Bells”
Eremophila “Yarra Road”
Grevillea “Lady O”
Grevillea nivea “Silver Princess”
Lomandra confertifolia ssp rubiginosa
Myoporum parvifolium (fine leaf form)
Scaevola aemula “Aussie salute”
Scaevola albida “Mauve carpet”