Blue Carbon is Significant in Coastal Marine Ecosystems

14 June 2017 Geoffrey Craggs, Research Analyst, Northern Australia and Land Care Research Programme

Background

Substantial research continues into carbon dioxide as a greenhouse gas and its contribution to climate change. In this field, the term “green carbon” is in general use when referring to reducing atmospheric carbon by sequestering it into the soil. Research in Australia and elsewhere is also focusing on “Blue Carbon” – the capture and storage of carbon in coastal marine ecosystems.

Comment

Scientists in recent decades have concentrated important carbon sequestration research on forests, grasslands and terrestrial soils. Far less research, however, has been conducted to improve our understanding of the enormous capacity of the marine environment for capturing and storing carbon. Vast quantities of carbon are contained in ocean organisms and in the sedimentary biomass in the sea floor that supports and maintains seagrasses, mangroves and salt marsh ecosystems. This carbon also plays a significant role in the global carbon cycle. The sequestration of blue carbon is a developing strategy that may contribute to mitigating the causes of climate change by reducing atmospheric greenhouse gas.

Seagrasses, mangroves and salt marshes in coastal regions provide carbon sinks, by capturing and holding atmospheric carbon through the natural process of photosynthesis. These coastal systems, though smaller in size than forests, grasslands and other land ecosystems, sequester carbon at a much faster rate and have done so for millions of years. According to the Blue Carbon Initiative, coastal habitats covering less than 20 per cent of the total ocean floor account for approximately half of the total carbon sequestered in ocean sediments. Seagrass meadows are prominent in the Australian coastal regions of Western Australia, South Australia and Queensland. For example, the over 4,000 km² region of Shark Bay in WA contains 12 species of seagrass. As one of the largest and most biologically diverse marine systems of its type in the world, these meadows of seagrass, in turn, support a large diversity of marine fauna, including many species of small fish, crustaceans and molluscs.

Though seagrass ecosystems constitute the major contributing fraction of blue carbon sequestration capacity, important also are mangroves and saltmarshes. In Australia, mangrove marine ecosystems extend from the eastern seaboard around the northern coast to central WA. They are the dominant coastal vegetation communities in this vast coastline and are a significant carbon sink. They perform the functions of coastal protection, providing nursery grounds for coastal fish and crustaceans, promoting marine forest products and by acting as nutrient filters. Though not as extensive in Australia, saltmarshes cover an area of over 13,000 km², with greater species diversity in southern coastal regions. Saltmarshes have the highest rates of organic sedimentation. In some areas, the biomass can be as deep as eight metres, providing the capacity to sequester carbon on a scale that is globally significant.

The growing awareness of blue carbon and its potential to reduce atmospheric greenhouse gas was acknowledged with the establishment of the International Partnership for Blue Carbon at the 2015 Paris Global Landscapes Forum. Australia is a founding member of that partnership which commits governments, non-profit organisations, intergovernmental agencies and scientists to improving the understanding of Blue Carbon ecosystems. This Partnership also aims to develop innovative approaches to biodiversity conservation, protecting and enhancing coastal ecosystems and the commitment of funding to support coastal ecosystem management.

The protection, preservation and restoration of marine coastal ecosystems should be an environmental priority. When ecosystems are damaged, the potential exists for the stored carbon to be released back into the atmosphere, resulting in an increase in greenhouse gases. Protection can involve physical activities such as planting to restore habitat and promote an increase in coastal biomass.  This has the added benefit of coastal protection against storm and cyclone damage and the possible increase in commercial and recreational fishing resources. Coastal wetlands marine ecosystems may also be incorporated into the carbon market through the trading of carbon offsets.

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