21
rhizomes and roots in the sediment are collectively referred to as the belowground
part. Differences in the biomasses of the aboveground and belowground parts as
well as differences in reproductive and vegetative growth strategies of course influence the amount of blue carbon that is sequestered and stored. The aforementioned
Posidonia is a typical example. Posidonia species such as Posidonia oceanica produce more belowground biomass than other seagrass species, and because accumulation of the belowground biomass forms a stratified structure, the storage of carbon
is considerably greater for Posidonia oceanica than for other seagrass species. Also,
even within the same species, the amount of production in the aboveground and
belowground parts varies with local environmental factors. It is therefore difficult to
say how much sequestration and storage of blue carbon takes place in a certain location if the data were collected in other locations or for other species. At the time the
UNEP report was published, there were no data about eelgrass and no information
about its role in sequestering and storing blue carbon. The absence of such information was one of the incentives for the publication of this book. In the next section,
we explain the ecological characteristics of eelgrass to provide a better understanding of how eelgrass beds sequester and store blue carbon, as explained in Chap. 2
and later chapters.
1.3.4 Eelgrass: Characteristics of Zostera marina
Among the Japanese blue carbon ecosystems, we focus in this section on eelgrass.
Eelgrass, Zostera marina, is said to be the most widely distributed marine plant on
Earth and spreads uniformly from the temperate zone of the northern hemisphere to
the subarctic zone (Orth et al. 2006). Fig. 1.3c shows the approximate global distribution of seagrass species. About 100 million years ago, Zostera species evolved in
the temperate waters of Asia. After that time the habitat of Zostera sp. expanded as
continental drift changed ocean basins and currents (Orth et al. 2006). At that time,
the Indian continent and the African continent were not connected to the Eurasian
continent. The Tethys Sea separated Asia from the Mediterranean Sea/European
continent and extended through the present location of the Atlantic Ocean to the
North American continent. Eelgrass is thought to have passed through this ocean
corridor, circled the earth, and reached the Pacific coast of North America. This
Tethys Sea corridor is believed to be the reason why eelgrass was able to spread
throughout the northern hemisphere.
In addition, although eelgrass plants have an average lifespan of about 60 years
(Hemminga and Duarte 2000), in a suitable habitat a single genet can live for more
than 1000 years (Reusch et al. 1999). This long lifetime makes it possible for an
eelgrass bed to store carbon in the sediments for a long period of time, similarly to
the way terrestrial forests store carbon in soil. Studying eelgrass therefore helps to
elucidate carbon sequestration and storage mechanisms in coastal macrophyte communities found throughout both hemispheres. The broad geographical distribution
of eelgrass is extremely important from the standpoint of identifying countermea1 Blue Carbon: Characteristics of the Ocean’s Sequestration and Storage Ability…
rhizomes and roots in the sediment are collectively referred to as the belowground
part. Differences in the biomasses of the aboveground and belowground parts as
well as differences in reproductive and vegetative growth strategies of course influence the amount of blue carbon that is sequestered and stored. The aforementioned
Posidonia is a typical example. Posidonia species such as Posidonia oceanica produce more belowground biomass than other seagrass species, and because accumulation of the belowground biomass forms a stratified structure, the storage of carbon
is considerably greater for Posidonia oceanica than for other seagrass species. Also,
even within the same species, the amount of production in the aboveground and
belowground parts varies with local environmental factors. It is therefore difficult to
say how much sequestration and storage of blue carbon takes place in a certain location if the data were collected in other locations or for other species. At the time the
UNEP report was published, there were no data about eelgrass and no information
about its role in sequestering and storing blue carbon. The absence of such information was one of the incentives for the publication of this book. In the next section,
we explain the ecological characteristics of eelgrass to provide a better understanding of how eelgrass beds sequester and store blue carbon, as explained in Chap. 2
and later chapters.
1.3.4 Eelgrass: Characteristics of Zostera marina
Among the Japanese blue carbon ecosystems, we focus in this section on eelgrass.
Eelgrass, Zostera marina, is said to be the most widely distributed marine plant on
Earth and spreads uniformly from the temperate zone of the northern hemisphere to
the subarctic zone (Orth et al. 2006). Fig. 1.3c shows the approximate global distribution of seagrass species. About 100 million years ago, Zostera species evolved in
the temperate waters of Asia. After that time the habitat of Zostera sp. expanded as
continental drift changed ocean basins and currents (Orth et al. 2006). At that time,
the Indian continent and the African continent were not connected to the Eurasian
continent. The Tethys Sea separated Asia from the Mediterranean Sea/European
continent and extended through the present location of the Atlantic Ocean to the
North American continent. Eelgrass is thought to have passed through this ocean
corridor, circled the earth, and reached the Pacific coast of North America. This
Tethys Sea corridor is believed to be the reason why eelgrass was able to spread
throughout the northern hemisphere.
In addition, although eelgrass plants have an average lifespan of about 60 years
(Hemminga and Duarte 2000), in a suitable habitat a single genet can live for more
than 1000 years (Reusch et al. 1999). This long lifetime makes it possible for an
eelgrass bed to store carbon in the sediments for a long period of time, similarly to
the way terrestrial forests store carbon in soil. Studying eelgrass therefore helps to
elucidate carbon sequestration and storage mechanisms in coastal macrophyte communities found throughout both hemispheres. The broad geographical distribution
of eelgrass is extremely important from the standpoint of identifying countermea1 Blue Carbon: Characteristics of the Ocean’s Sequestration and Storage Ability…