Sediment Stabilisation in Western Port Ramsar Area (Project 4.09)

This was a partnership project between the WPSP, the Natural Heritage Trust and the Port Phillip and Westernport Catchment Management Authority, with a $35,000 contribution from the NHT. The project was focused on the eroding NE coastline near Lang Lang and had two elements:

Seagrass Planting

Using techniques developed earlier, cores of seagrass were planted in the fine silts along the Lang Lang coastline. Although seagrass transplants had been successfully grown in these silts in an aquarium, they failed to survive in the natural environment. The twin effects of fine silts covering the transplants and ongoing poor water quality in this sector were seen as the key factors.

Seedlings from donor site. Photo: T. Ealey WPSP

Seagrass plug smothered by sticky Lang Lang sediment. Photo T. Ealey WPSP

The result was consistent with predicted outcomes using a transplant site evaluation tool. No further seagrass planting will be undertaken in this part of Western Port until mobile sediment loads are reduced.

Planting Mangroves

Special techniques for planting mangrove seedlings were tested along this open section of coastline. Here waves up to 2 metres high, hit and undermine mini cliffs at the edge of the old Koo Wee Rup Swamp, causing backwash and soil slumping to occur. Approximately 4000 Mangrove seedlings from Blind Blight were transplanted to the planting area, where they were staked and tied using a variety of methods. Approximately 5000 Mangrove seeds were also collected and planted as part of the trial.

Various staking techniques resulted in survival rates between 36% and 80%, but overall there were still considerable losses due to frost and storms.

Dehusking mangrove seeds prior to planting. Photo: T. Ealey WPSP.

Volunteers planting seedlings. Photo: T.Ealey WPSP.

Never-the-less, some 2000 plants were still surviving at the end of the trial period. The trial also raised concerns about the effect of transplant and handling trauma, especially root damage. Smaller quantities of seedlings grown in containers appeared much healthier and were more vigorous growers, suggesting this may be the preferred source of stock for future planting trials.

Techniques used to prepare and plant seeds also showed great variability in success, with fresh stock planted immediately and to an optimal depth showing good results. Stored seeds showed signs of deterioration and loss of vigour and care was required with germinating seeds to minimize handling and planting trauma. A closer examination or techniques deployed in Shoalhaven NSW will be undertaken to improve the rate of success for future direct seeding activities.

Final Report Project 4.09 – PDF