24
cycle, a rhizome is not created, and the aboveground part of the plant withers after
1 year. The eelgrass enters a non-vegetative state once each year.
The other life cycle is a perennial life cycle that uses both reproductive modes to
propagate. First it germinates from a seed and resembles an annual shoot, but later
it grows rhizomes and leaves as vegetative shoots. In the summer, when the seawater temperature rises, some leaves die, but many aboveground and belowground
parts survive. From autumn to winter, the rhizome expands again, new vegetative
shoots sprout from the expanded rhizomes, and vegetative growth continues.
Depending on the nutritional status of the plants, seed propagation similar to the
annual cycle may also occur.
It is unclear how the eelgrass switches between the life cycles for different purposes and how environmental conditions determine which life cycle will be used. In
general, it is thought that perennial life cycles predominate when the habitat is suitable for eelgrass, and an annual life cycle is more common in harsh environments
(Hemminga and Duarte 2000). For example, at the southern limit in Kagoshima
Bay, the life cycle of eelgrass is annual. This life cycle enables the eelgrass to survive over the summer as seeds when the high temperatures would otherwise be
lethal (Japan Fisheries Agency 2007, Shimabukuro et al. 2012). Of these two life
cycles, the perennial cycle is associated with the highest rate of storage of blue carbon. In the case of the annual cycle, even if blue carbon is stored in the sediment via
sedimentation facilitated by the aboveground parts, it is often resuspended during
the summer season when the vegetative structure completely disappears. Therefore,
even though the annual cycle can sequester carbon, the annual cycle of eelgrass, like
that of macroalgae, is considered to store relatively little blue carbon compared to
the perennial cycle.
1.4 Toward Maintenance, Improvement, and Management
of Blue Carbon Sinks with Co–benefits
To explain the choice of topics discussed in detail in this book, we have summarized
the UNEP report on blue carbon, the current status of blue carbon sinks, and the
importance of seagrasses as blue carbon sinks. In this section, we explain the knowledge needed from a management standpoint to maintain and improve the blue carbon sink as an ecosystem service of the seagrass ecosystem along with other
ecosystem services. Knowledge of the biological community and the interactions
therein, the trophic level structure, and the physical environment suitable for growth
are required to conserve and restore perennial eelgrass communities. Such conservation and restoration are important for the sequestration and storage of blue carbon. We therefore first introduce the characteristics of eelgrass plants as an
ecosystem and then discuss ecosystem management based on that knowledge.
M. Hori et al.
cycle, a rhizome is not created, and the aboveground part of the plant withers after
1 year. The eelgrass enters a non-vegetative state once each year.
The other life cycle is a perennial life cycle that uses both reproductive modes to
propagate. First it germinates from a seed and resembles an annual shoot, but later
it grows rhizomes and leaves as vegetative shoots. In the summer, when the seawater temperature rises, some leaves die, but many aboveground and belowground
parts survive. From autumn to winter, the rhizome expands again, new vegetative
shoots sprout from the expanded rhizomes, and vegetative growth continues.
Depending on the nutritional status of the plants, seed propagation similar to the
annual cycle may also occur.
It is unclear how the eelgrass switches between the life cycles for different purposes and how environmental conditions determine which life cycle will be used. In
general, it is thought that perennial life cycles predominate when the habitat is suitable for eelgrass, and an annual life cycle is more common in harsh environments
(Hemminga and Duarte 2000). For example, at the southern limit in Kagoshima
Bay, the life cycle of eelgrass is annual. This life cycle enables the eelgrass to survive over the summer as seeds when the high temperatures would otherwise be
lethal (Japan Fisheries Agency 2007, Shimabukuro et al. 2012). Of these two life
cycles, the perennial cycle is associated with the highest rate of storage of blue carbon. In the case of the annual cycle, even if blue carbon is stored in the sediment via
sedimentation facilitated by the aboveground parts, it is often resuspended during
the summer season when the vegetative structure completely disappears. Therefore,
even though the annual cycle can sequester carbon, the annual cycle of eelgrass, like
that of macroalgae, is considered to store relatively little blue carbon compared to
the perennial cycle.
1.4 Toward Maintenance, Improvement, and Management
of Blue Carbon Sinks with Co–benefits
To explain the choice of topics discussed in detail in this book, we have summarized
the UNEP report on blue carbon, the current status of blue carbon sinks, and the
importance of seagrasses as blue carbon sinks. In this section, we explain the knowledge needed from a management standpoint to maintain and improve the blue carbon sink as an ecosystem service of the seagrass ecosystem along with other
ecosystem services. Knowledge of the biological community and the interactions
therein, the trophic level structure, and the physical environment suitable for growth
are required to conserve and restore perennial eelgrass communities. Such conservation and restoration are important for the sequestration and storage of blue carbon. We therefore first introduce the characteristics of eelgrass plants as an
ecosystem and then discuss ecosystem management based on that knowledge.
M. Hori et al.