Lack of epifaunal response to the application of salt for managing the noxious green alga Caulerpa taxifolia in a coastal lake
Since the discovery of the green seaweed Caulerpa taxifolia in Lake Macquarie in 2001, NSW DPI has attempted various control methods. The most successful method involves covering the alga with granulated sea salt to induce osmotic shock and death of the seaweed. In Lake Macquarie, Caulerpa often occurs in patches within beds of the native seagrass Zostera capricorni. Although previous studies have demonstrated no significant effects of the salt treatment on Zostera or small invertebrates living in the sediment, there have been no formal tests of any potential effects on other native species. In this study, we tested whether the abundance and diversity of invertebrates living on seagrass would be reduced by salting. These invertebrates include animals such as amphipods, marine worms and snails (many of which are important food sources for fishes) and are collectively termed epifauna. Our experiment involved sampling epifauna 3 months, 6 weeks and 6 days before salting and then at the same time periods after salting. Epifaunal abundances at the salted location were compared to those at 4 control locations (where no salt was applied).
Numbers of most organisms varied a great deal among times and among many locations, but importantly, this variation was natural and not associated with the application of salt. Overall, there was no evidence of any consistent effect of salting on the diversity or abundance of epifauna. This study is an example of the use of a large-scale managerial action as a scientific experiment and the results further support the notion that salting has minimal impacts on the marine environment whilst helping to control the spread of Caulerpa.