『Sowing the seeds: South Australia’s quest to green the blue with seagrass.』のカバーアート

Sowing the seeds: South Australia’s quest to green the blue with seagrass.

Sowing the seeds: South Australia’s quest to green the blue with seagrass.

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 In this episode of OzCast, Jason Tanner dives beneath the surface of South Australian waters to unveil how he is working to “green the blue” by dropping sandbags in strategic areas to bring back the lost seagrass meadows of yesteryear. After spending over 25 years developing this technique from the ground up, he explains how his work went from an idea to a now industrial-level program that sees tens of thousands of bags being deployed every year.   Jason has 30 years’ experience overall in marine ecology, working in tropical and temperate systems. He has published over 80 papers, most in high-profile international journals, and numerous reports. He undertakes field and laboratory studies of marine ecosystems and also has a strong grounding in statistics and mathematical modelling.  His first exposure to seagrass was as a teenager snorkelling in the coastal lakes of southern NSW, although it would be many years before he would return to them, taking a detour via the coral reefs of the Great Barrier Reef in between.    This detour involved a PhD and postdoctoral studies on corals at Heron Island, before moving to the South Australian Research and Development Institute to study the impacts of prawn trawling on the seafloor.  From here he became interested in the way fragmentation of seagrass habitats influenced the fauna that lived in them, which then progressed to an interest in the seagrasses themselves and how to reverse the extensive habitat loss seen along the Adelaide coast (and elsewhere).   Throughout the episode, Jason explains that this interest led him to develop novel low-cost techniques for seagrass restoration tailored to the main species found in South Australia.  His hessian sandbag technique can be deployed for 5-10% of the cost of traditional transplantation involving divers and doesn’t require the removal of seagrass from a donor meadow.    Instead, it relies on providing a firm substrate for naturally present seedlings to attach to (for wireweed - Amphibolis) or collecting beachcast fruits that would otherwise dehydrate and be lost (for strapweed – Posidonia australis).  He is now in the process of establishing a 20-hectare restoration plot just north of Adelaide, funded by the Commonwealth Government, which will be the largest single seagrass restoration in Australia.   Jason offers a wealth of information on how programs like this develop and transform, to the point where he is now dropping over 25,000 bags in a single deployment.   Having spent countless hours researching seagrass, Jason highlights the impacts that seagrass has faced on the South Australia metropolitan coastline. Over the last half-century or so, more than 6,000 hectares of seagrass has been lost off the Adelaide coast due to anthropogenic nutrient and sediment inputs.  This loss has led to coastal erosion, decreased habitat, loss of carbon storage and decreased fish abundance.  Recent improvements to wastewater treatment and stormwater runoff have led to some natural recovery, but changes in sand movement resulting from the loss now prevent the recolonization of many areas.  While the hessian bag method has resulted in the successful establishment of small patches of seagrasses that have persisted for around a decade, and which are now functioning like natural patches due to colonisation by other marine plants and animals, the development of the technique has not been straightforward.  Throughout the episode, Jason unveils how he has had to refine the technique over the years when it comes to developing of a good understanding of the timing of recruitment, and methods to ensure the maximum number of bags are dropped in a given season.   Jason explains that the sandbags provide a stable environment that overcomes sand movement and allows the seedlings to establish, before the bags rot away. Without the bags, seedlings don’t have much to attach to, and any that do settle get washed away in storms. This approach avoids the need to use divers, costs less than 10 per cent of what traditional restoration techniques that involve the direct planting of seagrass cost, and avoids disturbing remaining seagrass beds to obtain planting material.    Seedlings of tape weed can also be pre-planted into the bags following their summer fruiting period before they are dropped to the seafloor. This area has experienced extensive seagrass loss over the last 60 to 80 years due to decreased water quality. While water quality has improved, there are only limited signs of natural seagrass recovery. 

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