Study

Experimental use of salt to control invasive marine alga Caulerpa taxifolia in New South Wales, Australia

  • Published source details Glasby T.M., Creese R.G. & Gibson P.T. (2005) Experimental use of salt to control invasive marine alga Caulerpa taxifolia in New South Wales, Australia. Biological Conservation, 122, 573-580.

Summary

Study 1

The invasive marine green microalga Caulerpa taxifolia was first confirmed in New South Wales, Australia, in April 2000. It subsequently spread to nine waterways, covering approximately 8.1 km² by 2005. An experiment was undertaken at Lake Macquarie (New South Wales) to determine the effectiveness of different salt concentrations in killing C.taxifolia. (See Case 281 for efficacy of control at Narrawallee Inlet).

Study sites: In Lake Macquarie, New South Wales (Australia), salt application experiments to attempt to control an invasive marine alga, Caulerpa taxifolia, were set up at two sites, separated by about 1 km, in March 2002. Each site had twelve 1 m² plots marked out, each 1-3 m deep. Pairs of treatment plots had salt concentrations of 50, 100, 150 and 200 kg/m² applied. A pair of control plots were positioned near to the treatment plots, and a pair were positioned 50 m from the treatment plots.

Plot sampling: Each plot was sampled prior to salt application, and then after one week, one month and six months. In three 30 x 30 cm quadrats, that were randomly placed within the plot, the number of fronds of Caulerpa, as well as of stems of the seagrass Zostera capricorni was recorded. Also, to investigate possible effects of salting on benthic fauna, three cores (65 mm diameter, 100 mm deep) were taken in each plot. Benthic fauna was identified to family level.

After one week Caulerpa taxifolia frond density in salted plots had decreased by 70-95%, and salted plots had a significantly lower density than unsalted control plots. No fronds were present after one and six months. There was also a decrease in C.taxifolia in the control plots across the experiment, possibly due to winter dieback. Salting also reduced Zostera capricorni shoot density after one and six months compared to control plots. However, Z.capricorni was less adversely affected than C.taxifolia and at salt concentrations below 200 kg/m² it began to recover after six months.

The abundance and diversity of benthic fauna decreased in treatment relative to control plots after one week. It then began to recover after one month. After six months there was no difference between treatment and control in diversity, and in the 150 and 200 kg/m² treatments abundance was higher than the control.

 

Study 2

The invasive marine green microalga Caulerpa taxifolia was first confirmed in New South Wales, Australia, in April 2000. It subsequently spread to nine waterways, covering approximately 8.1km² in 2005. An experiment was undertaken in Narrawallee Inlet, New South Wales, to determine the effectiveness of different salt concentrations in killing C.taxifolia. (See Case 280 for efficacy of control at Lake Macquarie).

Study site: In Narrawallee Inlet, New South Wales (Australia), four sites colonised by the invasive alga Caulerpa taxifolia were selected in February 2003 for salt application experiments. The idea behind the experiments was to test the efficacy of salt application as a method of Caulerpa contol. Each site was in water 1-2 m deep, separated by about 100 m and within 500 m of the mouth of the inlet.

Treatments: At each site, six 2 x 2 m plots were marked and equally divided between three treatments: (1) 50 kg/m² salt covering the whole plot; (2) patches of salt applied to visible Caulerpa taxifolia; and (3) no salt control. The number of C.taxifolia fronds was counted in each plot prior to application of the treatment and then after four days, 27 days and 86 days.

The number of Caulerpa taxifolia fronds in both salting treatments were equally reduced after four and 27 days relative to the unsalted control. After 86 days, the 50 kg/m² treatment had reduced frond density by about 90% and the patch treatment by about 75% relative to the control.


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