Ecological outcomes and management of purpose-built Estuarine Artificial Reefs

Past fisheries enhancements with artificial structures made from materials of opportunity in NSW estuaries provided little comprehensive scientific evaluation of post-deployment goals. This study presented the first opportunity for the research into purpose-built, estuarine artificial reefs (Reef Balls®), in eastern Australia. Replicate artificial reefs in three temperate estuaries allowed detailed pre- and post-deployment assessment of fish assemblages determined from approximately 1,500 individual Baited Remote Underwater Video (BRUV) deployments and over 850 h of video. The three estuaries in New South Wales were Lake Macquarie (a large extensively urbanised wave-dominated coastal barrier lagoon); Botany Bay (a large extensively urbanise tide-dominated coastal bay); and St Georges Basin (a semi-urbanised wave-dominated coastal barrier lagoon).In Lake Macquarie, colonisation of the artificial reefs was rapid, with the majority of species identified within the first year post-deployment. Key colonising species were primarily yellow-fin bream, Acanthopagrus australis; pink snapper, Pagrus auratus; tarwhine, Rhabdosargus sarba (Sparidae) and the striped trumpeter Pelates sexlineatus (Terapontidae), all important contributors to assemblage development. Species richness displayed seasonal fluctuations, higher in warm water Summer/Autumn months (Dec – May), and lower in Winter/Spring months (June - Nov), while species diversity increased significantly with reef age, up to 2 years post-deployment. Fish assemblage composition remained relatively stable after the first year of sampling. Distinct separation in reef age groupings was identified during the second year of sampling; a pattern primarily driven by a decrease in abundance of P. sexlineatus, a result of the artificial reefs being spatially isolated from natural reef, and the interrelated effects of density dependence and predation. Comparisons within the three estuaries identified significant differences in the species composition between artificial and natural reefs, potentially as a result of structural differences and location. Eighteen months post-deployment, abundance, species richness and diversity of fish assemblages was found to be greater on the artificial reefs than on either naturally occurring reef or sand-flat habitats in all estuaries, while the artificial reefs were found not to be absolute surrogates for natural reef, as the assemblage remained distinct from naturally occurring habitats. When fish assemblages were assessed before and after reef deployment, total abundances, diversity and richness remained higher on the artificial reef post construction than on natural reef. Species with the highest correlations to the observed community transition were demersal, reef associated sparids (A. australis, R. sarba and P. auratus). Many species exhibited an overall increase in abundance post reef deployment on natural reef sites, suggesting the existence of some synergy between the addition of artificial reef and increased abundances on adjacent rocky reef (located along the fringing bed-rock perimeter typically located