Seagrass rehabilitation in South Australia: a story of loss, action, failure, and success

More than 5,200 ha of seagrass habitat were lost from the metropolitan coast of Adelaide, South Australia, between ~ 1940 and 2002, primarily due to excessive nutrient pollution that promoted the overgrowth and smothering of... [ view full abstract ]

More than 5,200 ha of seagrass habitat were lost from the metropolitan coast of Adelaide, South Australia, between ~ 1940 and 2002, primarily due to excessive nutrient pollution that promoted the overgrowth and smothering of seagrasses by epiphytic algae. In the years since, improved wastewater management has seen nitrogen inputs reduced by 75 %, coinciding with a small amount of natural seagrass recovery (4 %) at the most severely impacted sites. In an attempt to facilitate faster recovery, traditional seagrass rehabilitation methods of transplants and seedling propagation were tested and largely failed due to relatively strong hydrodynamic forces in the region. Under threat of discontinuation of funding, a fortuitous and novel combination of simple engineering and a biological peculiarity produced encouraging results, whereby fibrous hessian bags were used to entangle the ‘grappling hook’ possessed by seedlings of the seagrass Amphibolis antarctica. By retaining seedlings in the local area instead of being washed ashore, this method allowed seedlings to establish roots and grow. While initially promising, the hessian proved 100 % biodegradable, which meant that seedlings were sometimes unable to establish in time and were ultimately lost. Over several years, numerous experiments tested potential improvements to the hessian bag technique to overcome such limitations, with the method now refined to the point that a fully-funded large scale (1 ha) rehabilitation project is underway (June 2014). The most recent data show that experimentally rehabilitated patches are coalescing, and that some biological parameters of rehabilitated seagrass are matching or exceeding nearby natural meadows (e.g. stem density). This hard-won success in the face of continued threats to funding, changing personnel, and some unique environmental challenges, was ultimately built on the integration of natural history, creative engineering, enthusiasm, and a decade of trial and error to produce a reliable yet cost-effective tool for seagrass rehabilitation.