they provide a larger carbon sink than mangroves which se- quester 1.39 x10-3 GtC/ha/year (Duarte et al., 2005). However, they are also considerable sources of methane, but over a long time period (~500 years) remain a greenhouse gas sink (Whit- ing and Chanton, 2001).

Seagrass meadows are particularly good carbon sinks, as the leaves last much longer than other marine biomass such as phytoplankton (Duarte et al., 2005) and because they deposit carbon into the ocean soil, resulting in long-term sequestration (Romero et al., 1994).

The greatest oceanic absorption of CO2 occurs in cold waters or in areas with high organic matter (Barry and Chorley, 1998).

The carbon cycle in the oceans is influenced by physical and biological processes (Reid, 2009). Global ocean services2 may be worth about USD 23 trillion a year, only slightly less than the world’s GNP (GESAMP, 2001) and therefore maintaining healthy ecosystems is economically important. There is also evidence that healthy functioning marine ecosystems are nec- essary to enable the continued marine sequestration of carbon from the atmosphere (e.g. EC 2009; Herr and Galland 2009; Laffoley and Grimsditch 2009).

Climate change is in itself a driver of ecosystem degradation and affects carbon sequestration and storage. Climate change impacts on ecosystems and on mitigation efforts should be taken into account during restoration activities to ensure long-

2 Services include provisioning (e.g. fish and minerals), regulating (e.g. role in climate), supporting (e.g. role in water cycle) and cultural (e.g. tour- ism, recreation)

Mangrove planting in Indonesia 2008–2009 © Sahabat Alam

Table 1: Costs and benefits of direct and indirect use values of mangrove restoration (adapted from Tri et al. 1998)

Discount rate

Benefits

(direct – marketable products; indirect – avoided maintenance cost of sea dyke system)

3 6

10

64

19.66 13.12 8.47

Costs

(of establishment and extraction) Present value, million Vietnam Dong/ha

3.45 2.51 1.82

5.69 5.22 4.65

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