Seagrass Transplanting in Cockburn Sound, Western Australia: A Comparison of Manual Transplantation Methodology Using Posidonia sinuosa Cambridge et Kuo

Seagrass transplants (plant units [PUs]) were established to examine the feasibility of seagrass rehabilitation in Cockburn Sound, Western Australia. Five hundred and twenty plant units (plugs and sprigs) of Posidonia sinuosa Cambridge et Kuo were placed at seven locations at depths of 3, 5, and 9 m and monitored to determine the influence of transplant method, location, and depth upon survival and growth over 2 years. Depending on the site, more plugs had survived at the completion of the trial (mean survival 41%) than sprigs (mean survival 15%). Plug and sprig survival differed significantly with transplant depth, decreasing overall with increasing depth. Forty‐five percent of surviving plugs and 50% of sprigs exhibited horizontal rhizome extension. Mean rhizome extension after 2 years was 9.5 cm/plug (1–23 cm) and 18.3 cm/sprig (0.5–31 cm). Declines in PU survival and variable growth correlate with site‐specific variability in light climate. Plug transplantation was deemed the most suitable method for further manual seagrass rehabilitation, exhibiting higher survival across all sites and conditions; however, they are costly to deploy. Sprig PUs have greatest potential in shallow water with fine sands, moderate water movement, and maximum light availability. The low cost of deploying sprigs may outweigh their lower survival compared to plugs; further efforts should be directed to enhancing survival of sprig PUs under a wider range of conditions. Suitable locations for future rehabilitation efforts in Cockburn Sound were the Eastern and Western Banks and shallow areas off Woodman Point and Mangles Bay.