Coast & Estuaries
Page 211
Caulerpa taxifolia
Caulerpa taxifolia
is a pest weed that has colonised the waters of West Lakes
and Port Adelaide River. The main concern is the rapid spreading rate of the
weed as a result of ample nutrient supply. It was first discovered in West Lakes
in 2002, and was successfully removed by fresh water flushing of the lakes.
Caulerpa taxifolia
is bright green seaweed with main stems that can grow up to
three metres long with up to 200 fronds growing off these stems, resembling
feathers or ferns. It can grow up to 25mm a day and spreads independently.
New infestations start by dispersion of tiny plant fragments and are also thought
to spread via the release of spores. Caulerpa is a tropical species and its ideal
habitat is warmer waters, but the strain invading the Port Adelaide River is
capable of surviving and thriving in non-tropical waters. Anchoring of vessels
helps to spread the weed.
Caulerpa taxifolia
spreads quickly over the sea floor and takes over areas of
native species such as seagrass. It is a very real threat to the seagrass
meadows of Gulf St Vincent. When it takes over this flora, it destroys fish
nurseries and fish habitat. Fish do not eat
Caulerpa taxifolia
because it contains
a toxin that is distasteful to them.
Various methods have been used to eradicate the weed using salt, chlorination,
manual removal, and suction. Despite these efforts colonisation of the weed has
continued.
There appears to be no or little difference in the distribution of
C. taxifolia
between the 2004 and 2008 survey. The heavy and moderate algae blooms
south of the Jervois Bridge appear to have reduced in size in locations closest
to the bridge, compared to the much larger extent in 2004. Decreases in algae
south of the Jervois Bridge may have been influenced by the decommissioning
of the Port Adelaide Waste Water Treatment Plant used to discharge nutrient
freshwater into the upper Port River (PIRSA, 2009).
A 2007
Caulerpa Taxifolia
survey was undertaken to measure the distribution
and high risk areas. Overall results indicate that
Caulerpa taxifolia
is present in
high densities in many areas of the Port River system. It is particularly dense
around the eastern side of Garden Island, the Northern Arm area and the
western side of Torrens Island (PIRSA, 2007).
It was noted in the winter 2007 survey that isolated colonies of the algae have
been located further downstream than in previous surveys undertaken in the
summer periods, with fewer colonies found in the outer regions. It appears that
in winter the growth rate is low for the algae and therefore may have influenced
the low numbers of colonies recorded in 2007 and 2008 survey, due to
minimum light penetration (PIRSA, 2007&2008).
The South Australian Research & Development Institute (SARDI) has made a
decision to reduce the biomass in the high-density areas and not target the
