Thursday, November 22, 2012

Blue Carbon - Opportunities for the Regional Seas Conventions and Action Plans

A good status review for blue carbon is included in a UNEP report titled 'Blue Carbon - Opportunities for the  Regional Seas Conventions and Action Plans'. The report was released for the 14th Global Meeting of the Regional Seas Conventions and Action Plans Nairobi, Kenya 1st – 3rd October 2012, and can be found through the following link:

Wednesday, November 21, 2012

Seagrass Role in Carbon Sequestration (Part I)

Nov 21, 2012 Seagrass Recovery

Recent studies have emphasized that conserving and restoring seagrass meadows may reduce greenhouse gas emissions and increase carbon stores.5,17 Seagrasses occur over a wide distribution range along the shores of every continent, except Antarctica, to maximum depths down to 50 meters, depending on water clarity.8 The total area of the Earth covered by seagrasses has not been cataloged to-date; however, different estimates are available. The current documented area of seagrass coverage is approximately 177,000 km2, but this is acknowledged as an underestimate since many regions with large seagrass cover have not been fully monitored.2,7 Recent estimates most commonly used in literature are between 300,000 km2 and 600,000 km2, with the global area potentially suitable to support seagrass growth estimated at 4,320,000 km2.1,3,4,6,12,13 That’s equivalent to between 74,131 and 148,263 acres of seagrass or roughly 56,160 to 112,320 football fields of estimated global cover. Considering the global area potentially could support over one billion acres of seagrass, the aforementioned numbers are just a drop in the bucket.

Not only are seagrass meadows highly productive ecosystems that play a key role in supporting high biodiversity they also provide an enormous source of carbon to the detrital pool. Some of this carbon gets exported to the deep sea, where it provides a supply of organic matter in sometimes extremely food-limited environments.14,15 Most of the organic carbon produced by seagrasses is stored within the sediments making these areas hot-spots for carbon sequestration.4,14 Seagrass sediments are organic-rich, with an average organic concentration of 4.1% and can be characterized by their capacity to sequester and store considerable amounts of carbon in their sediments (known as blue carbon).5 Seagrasses remove carbon dioxide from the atmosphere and incorporate it into organic matter; in other words, they convert sunlight and carbon dioxide efficiently into organic form. Seagrasses are also responsible for approximately 10% of the yearly global carbon sequestration in marine sediments even though they only occupy less than 0.2% of the ocean surface.4,5,8,9

Recent studies have shown that coastal seagrass beds store up to 83,000 metric tons of carbon per square kilometer, predominantly in the sediments beneath them.5,17 As a comparison, a typical terrestrial forest stores about 30,000 metric tons per square kilometer, mostly in the form of wood.5,17 The total global carbon pool in seagrass beds is estimated to be as much as 19.9 billion metric tons.5,9 Seagrass meadows have occupied coastal environments over thousands of years and can combine a high metabolic capacity to act as carbon sinks with the capacity to accumulate large carbon pools in the sediments. These pools are able to form thick carbon deposits or mattes, raising the seafloor by about 1 mm per year.5,9 The thickest documented sedimentary deposit has been reported to be 11 m thick from the Posidonia oceanica meadow at Port Lligat, Spain, in the NW-Mediterranean Sea which is equivalent to an accumulation of approximately 0.18 tons C m-2, that’s over 6000 years of seagrass growth at that site.5,11 Other seagrass deposits up to several meters in thickness, have also been reported at other sites in the Spanish Mediterranean, Shark Bay (Western Australia) and Florida Bay in the United States.9

Unfortunately, seagrass meadows are declining globally at a rapid rate, with about 5% of seagrass meadows lost annually.2 This decline is mostly due to dredging and degradation of water quality which has accounted for at least 1/3 of the area present lost since World War II, which means the existence of an important blue carbon sink is at stake.2,12,14,16 The long retention times of carbon in these sedimentary deposits is quite unique and qualifies seagrass meadows as one of the most carbon-rich ecosystems on the planet. That is why it is fundamentally necessary to understand the processes for the capacity of seagrass meadows to capture and store carbon so we can manage these ecosystems in support of strategies to mitigate climate change. Necessary management strategies should include both conservation and reforestation of seagrass meadows.5,14 There is also a critical need for targeted global conservation efforts that include protection, monitoring, management and policy regimes for seagrass habitats, as well as targeted educational programs informing regulators and the public of the value of seagrass meadows.5,14 Without proper management and conservation practices and increased global awareness, seagrass meadows will continue to decline. But if restored, these ecosystems have the capacity to effectively and efficiently sequester carbon, reestablishing lost carbon sinks in the ocean. 5,17 Let’s take that as a challenge.



1Charpy-Roubaud, C. & Sournia, A. 1990. The comparative estimation of phytoplanktonic and microphytobenthic production in the oceans. Mar. Microb. Food Webs 4, 31-57.
2Duarte, C.M., et al., Assessing the capacity of seagrass meadows for carbon burial: Current limitations and future strategies, Ocean & Coastal Management (2011), doi:10.1016/j.ocecoaman.2011.09.001
3Duarte, C.M., Borum, J., Short, F.T., Walker, D.I., 2005. Seagrass ecosystems: their global status and prospects. In: Polunin, N.V.C. (Ed.), Aquatic Ecosystems: Trends and Global Prospects. Cambridge University Press.
4Duarte, C. M., Middelburg, J. J. & Caraco, N. 2005.Major role of marine vegetation on the oceanic carbon cycle. Biogeosciences 2, 1-8.
5Fourqurean, J.W., Duarte, C.M., Kennedy, H., Marbà, N., Holmer, M., Mateo, M.A., Apostolaki, E.T., Kendrick, G.A., Krause-Jensen, D., McGlathery K.J. and Serrano,O. 2012. Seagrass ecosystems as a globally significant carbon stock. Nature Geoscience, 5: 505-509.
6Gattuso, J.-P., Gentili, B., Duarte, C.M., Kleypas, J.A., Middelburg, J.J., Antoine, D., 2006. Light availability in the coastal ocean: impact on the distribution of benthic photosynthetic organisms and their contribution to primary production. Biogeosciences 3, 489-513.
7Green, E.P. and Short, F.T. (2003) World Atlas of Seagrasses. Prepared by the UNEP World Conservation Monitoring Centre, University of California Press, Berkeley, USA.
8Hemminga, M.A., Duarte, C.M., 2000. Seagrass Ecology. Cambridge Univ. Press, Cambridge.
9Kennedy, H., Beggins, J., Duarte, C.M., Fourqurean, J.W., Holmer, M., Marbà, N., Middelburg, J.J., 2010. Seagrass sediments as a global carbon sink: isotopic constraints. Global. Biogeochem. Cycles. 24 doi:10.1029/ 2010GB003848.
10Laffoley, D.d’A., Grimsditch, G., 2009. The management of natural coastal carbon sinks. IUCN, Gland, Switzerland, 53 pp.
11Lo Iacono, C., Mateo, M.A., Gracia, E., Gasch, L., Carbonell, R., Serrano, L., Danobeitia, J., 2008. Very high-resolution seismo-acoustic imaging of seagrass meadows (Mediterranean Sea): implications for carbon sink estimates. Geophys. Res. Lett. 35, L18601. doi:10.1029/2008GL034773.
12Mcleod, E., Chmura, G.L., Bouillon, S., Salm, R., Björk, M., Duarte, C.M., Lovelock, C.E., Schlesinger, W.H., Silliman, B., 2011. A blueprint for blue carbon: towards an improved understanding of the role of vegetated coastal habitats in sequestering CO2. Front. Ecol. Environ. doi:10.1890/110004.
13Nellemann, C., Corcoran, E., Duarte, C.M., Valdés, L., De Young, C., Fonseca, L., Grimsditch, G., 2009. Blue Carbon. A Rapid Response Assessment. United Nations Environment Programme, GRID, Arendal.
14Orth, R.J., Carruthers, T.J.B., Dennison, W.C., Duarte, C.M., Fourqurean, J.W., Heck Jr., K.L., Hughes, A.R., Kendrick, G.A., Kenworthy, W.J., Olyarnik, S., Short, F.T., Waycott, M., Williams, S.L., 2006. A global crisis for seagrass ecosystems. Bioscience 56, 12; 987-996.
15Suchanek TH,Williams SW,Ogden JC,Hubbard DK, Gill IP. 1985.Utilization of shallow-water seagrass detritus by Caribbean deep-sea macrofauna: 13C evidence. Deep Sea Research 32: 2201–2214.
16Waycott, M., Duarte, C.M., Carruthers, TJ.B., Orth, R.J., Dennison, W.C., Olyarnik, S., Calladine, A., Fourqurean, J.W., Heck Jr., K.L., Hughes, A.R., Kendrick, G.A., Kenworthy, W.J., Short, F.T., Williams, S.L., 2009. Accelerating loss of seagrasses across the globe threatens coastal ecosystems. Proc. Nat. Acad. Sci. USA (PNAS) 106, 12377e12381.
17Wilson, H.W. 2012. Seagrasses Store More Carbon Than Forests Do. Science Teacher, 79.6; 26-27. Available from: OmniFile Full Text Mega, Ipawich, MA. Accessed November 2012.

Story link:

Wednesday, November 7, 2012

Blue Carbon Blog back on-line

March 2013

Dear colleagues,

The blog has been out of service for a wee bit. Blue carbon posts will be updated and post-dated from Nov 2012 till March 2013.

Best wishes,


Tuesday, November 6, 2012

Seagrass and Blue Carbon Emissions

Seagrasses are an important store of ‘blue carbon’ (Image credit Blue Climate Solutions).

Seagrass decline releasing large quantities of carbon

Oct. 25, 2012 / European Commission, Environment DG

Grasses growing at the bottom of our oceans lock away large quantities of ‘blue carbon’, according to a new study. The results suggest that the soil that seagrass grows on is capable of storing more carbon than soils on land and as a result of the current global decline in seagrass, vast stores of carbon may be being released into the ocean and atmosphere.

Seagrass is widely distributed in the world’s oceans, including in Europe, but is declining rapidly; the global loss rate of its extent has averaged 1.5% a year since the beginning of the twentieth century and accelerated in recent decades. In the EU, the Natura 2000 network and the Nitrates, Urban Wastewater, Water Framework, Marine Strategy, Birds and Habitats Directives offer direct or indirect protection to seagrasses. Around a quarter of the Mediterranean’s seabed, at depths between 1-40 metres, is covered in seagrass. However, disease, pollution, eutrophication and disturbances, such as dredging and construction of dams, harbours and pipelines, all pose threats to seagrass.

Seagrasses are an important store of ‘blue carbon’, the carbon stored by marine life, and may release an amount of carbon that is equivalent to 10% of that released by land use changes, according to the study. To reach this figure, the researchers analysed a database containing 3640 observations of 946 seagrass meadows around the world to try to understand how much carbon is locked away in seagrass plants and soils.

They estimated that around 3 tonnes of carbon are stored in living seagrass per hectare covered. For soils, organic carbon stocks had been measured down to the depth of a full metre, but in some, estimates were only available for shallower depths. The researchers combined data from the metre-deep measurements with their own estimates, based on extrapolation, for the remaining sites. Their conservative calculations suggest that an average of 140 tonnes of organic carbon are stored in the top metre of each hectare of seagrass soil, which is around twice that found in soils on land.

The researchers went on to estimate the total amount of carbon sequestered by seagrass globally. Assuming that seagrass meadows cover between 30-60 million hectares (around 0.2% of the area of the world’s oceans) they estimate that a total of between 4.2 to 8.4 petagrams of organic carbon (where one petagram is equal to a thousand million tonnes) is stored in the top metre of seagrass soils. A less conservative estimate suggests the figure could be as high as 19.8 petagrams. Terrestrial soils, by comparison, cover 15 billion hectares and are estimated to contain between 1500-2000 petagrams of organic carbon. A further 75.5 to 151 teragrams of carbon was estimated to be stored in seagrass itself (where one teragram is equal to one million tonnes).

Mediterranean meadows held the largest stores of organic carbon yet identified, although data for the Pacific and South Atlantic are currently limited. In the Mediterranean, seagrass soils containing 11-metre thick organic carbon deposits that have built up over thousands of years have been found. Elsewhere, carbon stores also go deeper, but the researchers focused on the top metre as it is the most easily returned to the atmosphere when seagrass meadows are lost.

Press release: Seagrass decline releasing large quantities of carbon (European Commission)

Journal article: Fourqurean, J. W., Duarte, C.M. Kennedy, H. et al. (2012). Seagrass ecosystems as a globally significant carbon stock. Nature Geoscience. 5(7): 505-509. DOI: 10.1038/ngeo1477.

Monday, November 5, 2012

Legal implications of blue carbon

Legal implications of blue carbon

By Ben Milligan, on 25 October 2012

Matthew Potenski (Marine Photobank
The Centre for Law and Environment has recently commenced a research project entitled Binding blue carbon: developing global legal and policy responses to an emerging risk of climate change. Ben Milligan is the project’s principal investigator. Contributions are also provided by Professor Richard Macrory QC. Funding is provided by the AXA Research Fund through the Fund’s Postdoctoral Fellowship scheme.

The term ‘blue carbon’ refers to carbon stored, sequestered and released from the ocean’s vegetated habitats, including mangroves, tidal marshes, and sea-grass beds. Recent scientific studies have drawn attention to the critical role played by these ecosystems in regulating climate change. The Centre for Law and Environment’s blue carbon project will map the extent to which blue carbon management activities are consistent with, or already enabled by, international legal and institutional governance frameworks of relevance to nature-based climate change mitigation. In collaboration with several inter-governmental organisations, it will also develop detailed recommendations for enabling blue carbon management activities in selected developing countries.

Detailed project overview

The critical role of blue carbon and associated risks
 The term ‘blue carbon’ refers to carbon stored, sequestered and released from the ocean’s vegetated habitats, including mangroves, tidal marshes, and sea-grass beds. Recent scientific studies have drawn attention to the critical role played by these ecosystems in regulating climate change. A report published in 2009 by the United Nations Environment Program (UNEP) estimates that marine vegetated habitats store 55% of the world’s naturally absorbed carbon dioxide. These habitats contain less than 1% of the plant biomass on land, but absorb a comparable amount of carbon dioxide per year. The marine ecosystems that bind blue carbon are being damaged or destroyed at an increasing rate by anthropogenic factors including aquaculture, marine and land-based pollution, and coastal development. If this trend is not arrested, there is a risk that:
  • the global capability of natural ecosystems to mitigate climate change will be significantly eroded; and
  • on-going damage and destruction of marine vegetated habitats will cause previously stored blue carbon to be released back into the atmosphere (thereby accelerating climate change).
How can law and policy respond to these risks?
Over the last 20 years, several international legal and institutional governance frameworks have been developed in an attempt to preserve the climate change mitigation function of natural ecosystems. These ‘nature-based’ mitigation frameworks are designed to encourage three key responses to climate change related risks:
  1. protection of vegetation and natural ecosystems;
  2. provision of financial incentives for developing countries to establish such protection measures;
  3. relevant capacity building and technical assistance for developing countries.
At present the clear focus of nature-based climate change mitigation efforts is to encourage the protection of terrestrial vegetation (in particular tropical rainforests). Current nature-based climate change mitigation frameworks were developed before the importance of blue carbon was well understood. How they need to be modified to enable management of blue carbon and accommodate the acute need to protect marine plant life (for climate-related objectives) is at present unclear. Building on existing preliminary studies, the projects key research objectives are to:
  • map the extent to which blue carbon management activities are consistent with, or already enabled by, international legal and institutional governance frameworks of relevance to nature-based climate change mitigation; and
  • develop detailed recommendations for enabling blue carbon management activities at a national level through progressive development and implementation of these international frameworks.
The recommendations will focus primarily (but not exclusively) on challenges faced by developing countries in tropical regions, where blue carbon sinks are primarily located.