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 alga Caulerpa taxifolia in Lake Macquarie (New South Wales, Australia) in 2001, the New South Wales Department of Primary Industries (Fisheries) has attempted various control methods, including covering the alga with granulated sea salt to induce osmotic shock and cell lysis. In Lake Macquarie, C. taxifolia often occurs in patches within beds of the native seagrass Zostera capricorni. Although the effects of the salt treatment on blades of Z. capricorni and infauna have been shown to be minimal, there have been no tests of any effects on other native biota, including seagrass epifauna. In this study, we tested the general hypothesis that the abundance and diversity of epifauna would be reduced by salting. We used a ‘Beyond BACI’ experimental design whereby epifaunal invertebrates were sampled 3 months, 6 weeks and 6 days before and then again after salting. Epifaunal abundances at the putatively impacted (salted) location were compared to those at 4 control locations (where no salt was applied). Abundances of most organisms varied significantly among times and locations with no evidence of the consistent effect of salting on diversity or abundance of epifauna. The study represents an example of the use of large-scale managerial action as a scientific experiment.