Naturally-detached fragments of the endangered seagrass Posidonia australis collected by citizen scientists can be used to successfully restore fragmented meadows

Posidonia australis is a slow-growing seagrass that forms extensive meadows in sheltered coastal locations which are often popular areas for recreational boating. Traditional block-and-chain boat moorings can directly impact P. australis meadows, with the action of heavy chains eroding the seafloor and creating bare sand scars that fragment meadows. The installation of new environmentally friendly moorings (EFMs) can reduce damage to seagrasses, but natural re-establishment by P. australis to scars can be very slow. Given the endangered status of this species in New South Wales, Australia, we developed an innovative restoration procedure to re-establish P. australis transplants within old scars without damaging existing meadows. Naturally-detached rhizome fragments were collected from the shore by citizen-scientists, stored within aquaculture tanks and then planted underwater. We planted a total of 863 fragments into six mooring scars at three different times. Survival of fragments after one year was significantly greater for those planted in June (54%) than in January (31%). The planting techniques (with or without natural fibre mats to stabilize sediments) and environmental conditions (surrounding habitat, depth and presence of the EFM) did not influence survival. Many surviving fragments (36.3%) had produced new shoots during the year. Our results show that naturally-detached seagrass fragments can be used to effectively restore P. australis meadows. This is an important new approach for supplying propagules for restoration without damaging remaining populations of an endangered seagrass, and presents a compelling management approach that engages local communities and enhances conservation efforts.