The struggle to restore a seagrass meadow in an urbanized estuary: a long‐term perspective

Introduction Seagrasses are ecological foundation species that are under threat globally from a range of anthropogenic disturbances. In many jurisdictions, seagrasses are protected under legislation, although this can be overridden. We provide an example pertaining to the installation of sub‐surface electricity cables across Botany Bay in eastern Australia, which caused the loss of 2225 m 2 of Posidonia australis . Objectives Our goals were to prevent additional damage to the seagrass meadow following cable installation and to facilitate seagrass reestablishment via natural colonization and transplantation of colonizing seagrass ( Zostera muelleri ) and P . australis . Methods After restoring the original sediment profile, which slumped during cable burial, various seagrass planting methods were trialed, including seedlings, plugs, and sprigs. Over 2.5 years, approximately 3600 P. australis shoots were planted, 94% of which were under jute mesh panels, the remainder in plugs. Results Although Z. muelleri transplanting was successful, efforts were overwhelmed by natural recolonization within 2 years. Monitoring over 11 years showed greater than 70% of the damaged area was recolonized by seagrass, albeit at reduced densities. Revegetation was due to natural recolonization and growth of transplanted P. australis sprigs, both of which were significantly reduced in deeper (3–4 m) parts of the meadow. Final densities of P. australis ranged from 43% of pre‐disturbed densities in shallow areas to just 14% in deep areas. Conclusions Despite partial restoration of P. australis , these gains were negated by other anthropogenic impacts to the meadow, highlighting the critical need to prevent ongoing impacts to this now locally endangered seagrass.