Effectiveness of coral (Bilbunna) relocation as a mitigation strategy for pipeline construction at Hayman Island, Great Barrier Reef

Coral reef management techniques such as relocation and transplantation are increasingly implemented in the context of increasing coastal development and a global decline of coral reefs over the last 30 years. A 170 m submarine desalination pipeline was constructed in 2020 to discharge wastewater from the desalination plant for Hayman Island resort, Whitsundays, Queensland, Australia. Pre-construction site assessments were conducted indicating a healthy, diverse and recovering coral community between intertidal and 12 m depth in the proposed route of the pipeline. Mitigation options included the selection of a pipeline route that minimised impact on coral, and relocation and transplantation of hard corals. Two hundred and four corals comprising 35 species from 15 genera, with estimated sizes ranging from small (less than 2 kg) to extra large (over 50 kg), were relocated from the pipeline footprint to a similar nearby site. The estimated total weight of relocated corals was 873–2850 kg. The most common species transplanted were Hump Coral (Porites lutea) (27%), Lesser Star Coral (Goniastrea aspera) (8.3%) and Starflower Coral (Astreopora ocellata) (7.8%). Individual coral survivorship and growth was monitored at zero, one, six, 12 and 24 months. After 24 months total coral survival was 77.5%. The survivorship of relocated coral exceeded the mean for global coral restoration projects and was deemed successful by the regulator. To assist benchmarking of future coral relocation projects we propose a standard of below 50% as poor, 50–60% as below average, over 60% as acceptable and over 80% coral survival at two years as excellent.