Assessing the return of carbon sequestration following the restoration/recovery of Amphibolis antarctica and Posidonia sinuosa seagrass in South Australia

Author Identifier

Jack Robinson

Date of Award


Document Type



Edith Cowan University

Degree Name

Master of Science by Research


School of Science

First Supervisor

Paul Lavery

Second Supervisor

Oscar Serrano


Occupying < 0.1% of the world’s seafloor, seagrasses provide key ecosystem services including habitat provision underpinning biodiversity, sediment stabilisation, and carbon sequestration. Despite this, seagrasses face significant losses, with an estimated 19% of global seagrass cover lost since the 20th century. Globally, there is an increasing effort to incorporate seagrasses into blue carbon projects through conservation and rehabilitation actions. In Adelaide, South Australia, restoration projects have been conducted using Amphibolis antarctica, with initial results showing the return of structural characteristics comparable to nearby natural meadows. In addition, an unprecedented natural recovery of Posidonia sinuosa has occurred in recent years along the Adelaide coastline. This research assessed the return of carbon sequestration functions and the avoided emissions linked to the restoration of A. antarctica and the recovery of P. sinuosa meadows in Adelaide. Comparisons of organic carbon (Corg) stocks among undisturbed and restored A. antarctica (0.6 ± 0.04 and 1.2 ± 0.4 kg Corg m-2, respectively) and undisturbed and recovering P. sinuosa (1.5 ± 0.4 and 0.5 ± 0.3 kg Corg m-2, respectively) meadows did not clearly show a return of Corg storage within 10-yrs post-recovery. Direct sediment elevation measurements between 2003 and 2019 via sediment elevation rods in P. 47 sinuosa meadows allowed the estimation of sediment and carbon accumulation rates. The rods identified 2 cm of accumulation in the undisturbed site, 20 cm of accumulation post-recovery in the Recovery site, and approximately 32 cm of erosion in the Bare site over 9-years post meadow loss. Based on sediment Corg stocks, the change in elevation across treatments and recent hyperspectral mapping of seagrass along Adelaide’s coastline, we estimated the enhanced sequestration of 231 Mg Corg ha-1 in the recovered meadow between 2011 and 2019, equating to 85,400 ± 6,800 Mg Corg across 876 ha of recovered meadows, while the loss of 188,000 ± 20,500 Mg Corg has occurred from 1406 ha of lost meadows over 9 years. Assuming 50% of this loss was remineralised at a decay rate of 0.0005 yr-1, we estimate 298,500 ± 92,200 Mg CO2-eq emissions from Adelaide’s seagrass loss over a 9-year period. In conclusion, this study is pioneering in demonstrating that the restoration and recovery of seagrasses at scale can lead to large carbon abatement, and thereby supports the development of seagrass rehabilitation in verified carbon crediting schemes. The use of in-situ direct sediment elevation iii measurements, which can be established at the onset of any carbon crediting project, can provide reliable estimates of additionality.



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