15
Authority of Japan 2016). In addition, according to published data on seagrass beds
in Japan, 2000 ha of eelgrass beds disappeared in only 13 years from 1978 to 1991.
Moreover, in the Seto Inland Sea, where the area of eelgrass beds is large, about
16,000 ha of eelgrass beds disappeared between 1960 and 1991 because of coastal
development and deterioration of water quality (Port and Airport Department,
Chugoku Regional Bureau, 2016). Recently, however, seagrass beds have started to
increase in Japan because of water quality improvements that have resulted from
legal restrictions on nutrient inputs from the watersheds in some areas (Hori et al.
2018). This example illustrates the possibilities for restoring coastal macrophyte
communities through water quality control and natural ecosystem resilience.
1.2.4 Other Ecosystems as Carbon Sinks
The UNEP report emphasizes the importance of the blue carbon ecosystem, where
macrophytes sequester organic carbon and store it in the sediment. However, the
blue carbon ecosystem is not the only sink of blue carbon in the ocean. Of the blue
carbon storage capacity of the ocean, 30–50% is found outside the blue carbon ecosystem, and there are also shallow coastal water blue carbon sinks that have not yet
been evaluated. Macroalgae are the most abundant vegetation in addition to the
vascular plants found in blue carbon ecosystems.
In recent years, scientific evidence has shown that macroalgae that grow on rocks
in the absence of sediment also contribute to carbon storage after sequestering
atmospheric CO 2 (Krause-Jensen and Duarte 2016). The carbon may be stored
somewhere different from the place where the CO 2 is sequestered by the macroalgae, such as in tidal flats or the deep sea. If the connection between the discrete
sources and sinks of blue carbon can be explained, it will be possible to assess the
contribution of macroalgal vegetation to the blue carbon sink. Discussions about
macroalgal vegetation as a blue carbon sink are incomplete in the UNEP report
because there was inadequate understanding of the source–sink relationship at the
time the report was written. Although there are no sufficiently accurate published
summaries of the distribution of macroalgae at the global level, the UNEP report
mentions that the evaluation of macroalgae with the largest distribution area and the
largest amount of production on Earth is the next task. In this book, an example of
macroalgal sequestration of CO 2 from the atmosphere is described in Chap. 6
(Tokoro et al. 2018), and Chap. 4 describes an example of a calculation of the
amount of organic carbon sequestered by macroalgae along the coast of Japan
(Yoshida et al. 2018). Chapter 2, which concerns organic carbon storage within seagrass beds, includes a discussion of carbon sources derived from macroalgae and
phytoplankton that have drifted in and accumulated in the seagrass meadows
(Miyajima and Hamaguchi 2018). There are estimated values of eelgrass (but not
seaweed) exhibiting the same transportation process from shallow coastal areas to
the deep sea as Chap. 9 (Abo et al. 2018). There is also much carbon storage derived
from green carbon by a similar process in coastal marine ecosystems such as tidal
1 Blue Carbon: Characteristics of the Ocean’s Sequestration and Storage Ability…
Authority of Japan 2016). In addition, according to published data on seagrass beds
in Japan, 2000 ha of eelgrass beds disappeared in only 13 years from 1978 to 1991.
Moreover, in the Seto Inland Sea, where the area of eelgrass beds is large, about
16,000 ha of eelgrass beds disappeared between 1960 and 1991 because of coastal
development and deterioration of water quality (Port and Airport Department,
Chugoku Regional Bureau, 2016). Recently, however, seagrass beds have started to
increase in Japan because of water quality improvements that have resulted from
legal restrictions on nutrient inputs from the watersheds in some areas (Hori et al.
2018). This example illustrates the possibilities for restoring coastal macrophyte
communities through water quality control and natural ecosystem resilience.
1.2.4 Other Ecosystems as Carbon Sinks
The UNEP report emphasizes the importance of the blue carbon ecosystem, where
macrophytes sequester organic carbon and store it in the sediment. However, the
blue carbon ecosystem is not the only sink of blue carbon in the ocean. Of the blue
carbon storage capacity of the ocean, 30–50% is found outside the blue carbon ecosystem, and there are also shallow coastal water blue carbon sinks that have not yet
been evaluated. Macroalgae are the most abundant vegetation in addition to the
vascular plants found in blue carbon ecosystems.
In recent years, scientific evidence has shown that macroalgae that grow on rocks
in the absence of sediment also contribute to carbon storage after sequestering
atmospheric CO 2 (Krause-Jensen and Duarte 2016). The carbon may be stored
somewhere different from the place where the CO 2 is sequestered by the macroalgae, such as in tidal flats or the deep sea. If the connection between the discrete
sources and sinks of blue carbon can be explained, it will be possible to assess the
contribution of macroalgal vegetation to the blue carbon sink. Discussions about
macroalgal vegetation as a blue carbon sink are incomplete in the UNEP report
because there was inadequate understanding of the source–sink relationship at the
time the report was written. Although there are no sufficiently accurate published
summaries of the distribution of macroalgae at the global level, the UNEP report
mentions that the evaluation of macroalgae with the largest distribution area and the
largest amount of production on Earth is the next task. In this book, an example of
macroalgal sequestration of CO 2 from the atmosphere is described in Chap. 6
(Tokoro et al. 2018), and Chap. 4 describes an example of a calculation of the
amount of organic carbon sequestered by macroalgae along the coast of Japan
(Yoshida et al. 2018). Chapter 2, which concerns organic carbon storage within seagrass beds, includes a discussion of carbon sources derived from macroalgae and
phytoplankton that have drifted in and accumulated in the seagrass meadows
(Miyajima and Hamaguchi 2018). There are estimated values of eelgrass (but not
seaweed) exhibiting the same transportation process from shallow coastal areas to
the deep sea as Chap. 9 (Abo et al. 2018). There is also much carbon storage derived
from green carbon by a similar process in coastal marine ecosystems such as tidal
1 Blue Carbon: Characteristics of the Ocean’s Sequestration and Storage Ability…