An international team of researchers has found that the disappearance of seagrass meadows could be contributing to the release of carbon dioxide which has been stored for centuries.
The researchers studied the impact of disappearing seagrass meadows (Posidonia australis), at Oyster Harbour in Albany, where long-term restoration of seagrass has been highly successful. They used sediment-dating techniques to quantify the accumulation of carbon in repopulated areas and calculate the erosion of carbon in areas that were not revegetated.
Published in the Journal of Ecology, and co-authored by researchers from The University of Western Australia's Oceans Institute, the results suggest that restoring these meadows would prevent the erosion of important deposits of organic carbon.
Lead author Professor Núria Marbà, from the Mediterranean Institute for Advanced Studies (Spain), said the loss of underwater seagrass meadows posed two problems.
"These areas can no longer capture and store atmospheric carbon dioxide, and they can become a source of this gas by eroding and freeing decades, and even centuries, old carbon stored in the meadow," she said.
"Seagrass meadows act as carbon sinks on a global scale and the conservation and restoration of heavily impacted areas can help mitigate man-made emissions."
The researchers assessed whether revegetation of underwater meadows was effective in restoring their capacity to act as carbon sinks in relation to the time needed to achieve this (decades).
Professor Marbà said revegetation of meadows prevented the erosion of these organic carbon deposits that had accumulated over hundreds of years.
"Our results indicate that the loss of this ecosystem must have also represented an important loss in the capacity to sequester and store carbon in the sediments of underwater meadows," she said.
Oyster Harbour is colonised by a meadow of Posidonia australis that largely was lost from the 1960s to the end of the 1980s. After 1994, the meadow recovered in part, thanks to revegetation efforts under the direction of co-author Geoff Bastyan, an Honorary Research Fellow in UWA's School of Plant Biology.
Mr Bastyan was named the Southseas Oceans Hero in 2014, an award given annually to a champion from the community whose work addresses solutions to degradation and loss of ocean resources. This seagrass restoration project, which was carried out until 2006, has grown to be the most successful seagrass restoration project in the world.
Visiting UWA Oceans Institute researcher and co-author of the study, Professor Pere Masqué from the Universitat Autonoma de Barcelona, said the potential areas available worldwide to carry out seagrass revegetation projects were enormous.
"These can help reconstruct carbon sinks, as well as preserve older deposits", Professor Masqué said.
Professor Masqué is a UWA Gledden Visiting Fellow with the Institute of Advanced Studies, working collaboratively with Oceans Institute researchers, Professor Gary Kendrick and Professor Carlos Duarte on the role of the oceans as a source, and sink, of carbon dioxide.
The results of this study help dispel doubts that were hindering the development of ‘blue carbon' strategies in underwater meadows. ‘Blue carbon' is the term given to carbon captured by marine and coastal ecosystems in the form of biomass and sediments.
Professor Pere Masqué (UWA Oceans Institute) (+61 4) 75 238 922
Professor Gary Kendrick (UWA Oceans Institute) (+61 4) 48 793 090
David Stacey (UWA Media and Public Relations Manager) (+61 8) 6488 3229 / (+61 4) 32 637 716