Seagrass restoration off the Adelaide coast

A/Prof. Jason Tanner1

1SARDI Aquatic Sciences, West Beach, Australia

Since 1949, ~6200 ha of seagrass has been lost off the Adelaide coast.  Much of this loss has occurred in shallow waters, with the seagrass line receding seaward, and has been attributed to increased nutrient levels from waste water treatment plants, industrial development and urban runoff.  With a concerted effort to reduce nutrient inputs, a seagrass rehabilitation program was commenced in 2002, initially trialling techniques used elsewhere, such as transplanting and planting seedlings.  However, the relatively high wave energy along the Adelaide coastline resulted in poor success.  This high wave energy, as well as high levels of bioturbation, also limit natural recolonization.  The use of hessian sandbags has proven to be more promising, as well as relatively low cost, as it works with the life history of the local Amphibolis antarctica, which viviparously produces seedlings that have evolved to entangle in things such as exposed Posidonia root matte.  The hessian sand bags provide a substitute for this root matte, which seedlings naturally attach to, and persists long enough for them to become established.  After 5-7 years, stem densities reached natural levels.  As well as recovery of the seagrasses,  the fauna have also returned to what is present in nearby natural meadows.  While more labour intensive as seedlings need to be manually planted, the bags can also be used for Posidonia.  Initially, seedlings were planted in situ by divers, but recent trials indicate that 1 year survival is similar for seedlings planted into the bags and glued in place before deployment.


Biography:

Jason has been leading a team at SARDI that has been working on developing novel seagrass restoration techniques since 2002.  Among his other roles, he studies interactions between aquaculture and the environment, and the deepwater benthos of the Great Australian Bight.

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