Restoration Objective:
The initial objectives of the project were as follows: Rehabilitate 8 ha of urchin barrens through targeted culling, drawing on the support, skills and experience of commercial abalone and SUTS divers. This was to include: Culling 200,000 urchins, Significant regeneration of macroalgae (75% coverage), and a substantial increase in native biodiversity, including commercially important species such as abalone , Improved roe quality of remaining urchins at the cull sites, supporting development of the sea urchin fishery.
Site Selection Criteria:
Given the project was foremost a ‘rehabilitation’ project, sites were primarily chosen because divers had indicated that they had previously harvested abalone at those site when there was less barrens habitat, and hence offered a high chance of restoration success. Site were also considered in terms of whether they were: > Readily accessible for culling (in this project), and for future maintenance and harvesting by urchin divers > Previously culled as part of FRDC project no. 2014-224 (in the case of Saltwater).
Cause Of Decline:
The purple urchin (also known as black urchin or long-spined urchin), Centrostephanus rodgersii, can clear and maintain areas of reef free from macroalgae, termed barrens or white rock, and in doing so, can reduce the productivity of abalone populations and other reef species dependent on macroalgal habitat. Its impact on reef habitats in Victoria and Tasmania has been particularly severe in the last few decades, and its spread south from a historical limit to NSW may be related to climate change (e.g. see FRDC 2009/070). In NSW, large scale barrens have been present at least since 1928 (i.e. as seen in the oldest available aerial photographs) and possibly occur naturally. In 2003, approximately 50% of nearshore reef was measured as barrens (see FRDC 99/128). Although wave action in the shallows likely imposes physical limitations on the ability of urchins to establish densities sufficient to create a barren, the abalone divers and Glasby and Gibson (2020) have provided evidence that the shallow edges of barrens in NSW can still increase by large amounts in some places. Indeed, Glasby and Gibson (2020) estimated that there has been an overall increase in barrens in NSW in the last 30 years of ~20 m2 per hectare per year, although at some sites they measured no change, or a reduction (Glasby and Gibson, 2020). When these increases occur at sites that were historically productive sites for collection of abalone, this is problematic, given there are limited numbers of productive abalone sites on the south coast of NSW that are accessible to divers.
