Effects of Herbicide Treatments on Spartina anglica and Invertebrates in an Australian Saltmarsh

The spread of the European cordgrass Spartina anglica is of worldwide concern. The effectiveness and indirect effects of 2 herbicide treatments were tested in a Victorian estuary over 6 months. Fifteen plots were established... [ view full abstract ]

The spread of the European cordgrass Spartina anglica is of worldwide concern. The effectiveness and indirect effects of 2 herbicide treatments were tested in a Victorian estuary over 6 months. Fifteen plots were established on the North coast of Anderson Inlet. Five replicate plots were sprayed with Fusilade Forte, 5 with a mixture of Fusilade Forte® and the adjuvant HASTEN®, and 5 were left as controls. Fusilade Forte® has been shown to have moderate toxicity to some aquatic invertebrates but almost nothing is known of its toxicity to saltmarsh invertebrates in field studies. Both Fusilade Forte® and the HASTEN® mixture were equally effective in reducing Spartina cover. There was a significant reduction in cover from ≥ 95% to 64% in both the Fusilade Forte® and mixture plots at 2 months post spraying, while Spartina cover in the controls remained high. Sediment cores were taken before and 2 months after herbicide spraying to determine effects in macrofaunal abundance and diversity. Results from replicates examined to date suggest that total macrofauna, Annelid and Oligochaete abundances declined over time in all plots, including controls. This result may be due to seasonal variation. There were no significant differences in abundance between treatments and controls at 2 months post-spraying. Crustacean diversity in the treatment plots was seen to differ significantly from the controls before spraying but at 2 months after spraying this difference no longer existed. The disappearance of significance seems to be caused by a slight (though not significant) increase in control diversity while the mixture plots diversity decreased slightly. Laboratory ecotoxicology tests were performed on 3 of 4 common species from the field site. Results showed increasing sensitivity from Molluscs to Oligochaetes to Polychaetes and finally Crustaceans. Three of the four species were more sensitive to the Fusilade Forte® and HASTEN® mixture rather than Fusilade Forte® alone. Using herbicide controls are effective, and early results suggest little to no impact of the herbicide or mixture on the invertebrate inhabitants of the saltmarsh. Final conclusions from the completed samples will be presented.