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Dredge spoil dumping
Dredging of the boat channel at entrance to Holdfast Shores marina
Regular accumulation of sand and decaying detrital seagrass occurs within the boat channel
leading to the Holdfast Shores marina, causing problems for launching of boats.
It was also claimed to be a significant factor in the demise of the Enigma III ferry service
to Kangaroo Island in late 1998.
The channel requires frequent dredging and the spoil is dumped off-shore in the Gulf.
Dredging of the Outer Harbour shipping channel
Currently there is a proposal to dredge the main shipping channel to Outer Harbor
to enable access for larger ships. This would involve excavating some three million
cubic metres of sediment. Since land-based disposal is considered to be too expensive,
the proponents (Flinders Ports, supported by the State Government)
favour dumping the spoil off-shore in the Gulf.
FoGStV members oppose this aspect of the proposal, since the Outer Harbor channel
is already infested with the introduced marine alga Caulerpa racemosa.
C. racemosa is considered to be a greater threat to marine ecosystems than C. taxifolia,
which caused the recent scare in West Lakes, the Port River and Barker Inlet.
Although not as toxic as C. taxifolia, C. racemosa is also fast growing,
especially in the waters warmed by thermal emissions near the power stations
of the Port River and Barker Inlet, where it has become established.
C. racemosa can also propagate from small fragments
(even those taken out of the water for several weeks but kept moist).
It has already spread beyond the confines of the Port River Estuary,
with a reported outbreak near the O'Sullivans Beach boat ramp.
It is likely that dumping the dredge spoil in the gulf may rapidly increase
the spread of this invasive alga, which is capable of smothering seagrass beds,
to the Orontes Bank and other areas of the Gulf.
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