Seagrasses are the main diet of dugongs and green turtles as well as providing habitat for smaller marine animals like prawns and fish, which are commercially important, especially to communities such as those of the Clarence Valley. The high primary production rates of seagrasses are closely linked to the high production rates of their associated fisheries. Seagrasses also absorb nutrients from coastal run-off and stabilise sediment, helping to keep the water clear. 1
Particular conditions are required for Seagrasses to thrive. These include access to available light, water salinity and nutrient and sediment loading. Waves, water depth and temperature all impact on seagrass to either encourage or destroy growth.2 Anchor chains for boats are also capable of destroying areas of seagrass.
Tidal and freshwater marshes, which include mangroves, and seagrass beds are being lost around the world at a rate of 1-2% per year. Major threats to tidal marsh ecosystems include draining for coastal development, conversion to agriculture, and rising sea levels.
What is truly exciting about seagrass is its importance to a emerging field of research into what has been termed ‘Blue Carbon’. This is the carbon captured in coastal ecosystems, specifically mangrove forests, seagrass beds, and salt marshes. Although smaller than the area of terrestrial forests, their contribution to long-term carbon storage is much greater, partly because of their efficiency in trapping suspended organic carbon during tidal movement.
Seagrasses are important for:
- Carbon sequestration - the process of capturing carbon dioxide from the atmosphere, measured as a rate of carbon uptake per year.
- Carbon storage - the long-term confinement of carbon in plant materials or sediment, measured as a total weight of carbon stored.
Seagrasses are capable of storing large quantities of carbon dioxide (CO2) in both the plants and the sediment below. Over 95% of the carbon in seagrass meadows is stored in the soils. This means Seagrass captures carbon dioxide from the atmosphere and oceans at significantly higher rates, per unit area, than land based forests. The amazing quality of seagrass is its capacity to grow far more quickly than a forest.
At the Paris Climate summit in December of 2015 Environment Minister Hunt outlined plans to protect seagrasses and its carbon storing potential. A spokesperson for Minister Hunt stated that ‘Blue Carbon’ could be significant to reducing emissions, supporting biodiversity conservation and fisheries habitat. There are plans to account for greenhouse gas emissions from coastal wetlands in Australia’s National Inventory from 2017.
Work in the area of riparian repair is being carried out by Wetland Care Australia, who have already successfully completed a riparian restoration project on the South Arm of the Clarence Estuary. Wetland Care identified the Clarence Estuary as a highly significant area for aquatic biodiversity and is the most important wild catch fishery in NSW, accounting for 30% of the States total annual catch.
The Wooloweyah Lagoon is one of the significant features of the Clarence Estuary and one that has documented significant destruction of seagrass beds since 1983. It forms part of the Wooloweyah – Ashby biolink identified by ecologist Mark Graham in his 2009 study of the Clarence Biolinks (funded by Valley Watch). He described The Broadwater and Wooloweyah Lagoon as two of the most significant wetland areas in NSW.
Wooloweyah Lagoon is extensively trawled despite being less than one metre depth in the majority of its basin. Nets are flattening contours and ripping away seaweed. Turbidity is dramatically increased and then black sludge deposited to the areas of the lake where seagrass struggles to grow. This has been going on for many years but it is time for government to rethink and plan for the protection of the estuary.
While rainforests lock in carbon for a century at most, seagrass does so for thousands of years. The Clarence Estuary must be protected as a carbon sink and promoted for restoration and regeneration of the seagrass beds that at this time are fast disappearing.
“When someone is cutting down a forest, it’s quite noticeable, and you can chain yourself to a tree, but most people don’t care or notice when seagrasses are being destroyed; they are out of sight and out of mind – a tragedy of the commons.” Dr Peter Macreadie UTS
The Blue Carbon Initiative: http://thebluecarboninitiative.org
O.U.C.H. (Order of Underwater Heroes): http://www.ouchvolunteers.com/seagrass.php
A blueprint for blue carbon: toward an improved understanding of the role of vegetated coastal habitats in sequestering CO2 Elizabeth Mcleod et al: http://www.mangroverestoration.com
Failure to protect seagrass may cost Australia $45b Sunanda Creagh & Will Mumford The Conversation February 11, 2013 9.32am AEDT