26
that consume epiphytes on the seagrass leaves play an especially important role in
the sequestration and storage of blue carbon. The epiphytes growing on the leaves
are an important source of primary production that support the associated animal
community. However, if the epiphyte biomass becomes excessive, the epiphytes
will smother the leaves, hinder photosynthesis by the eelgrass itself, and may cause
the eelgrass to die. Small grazers therefore play an important role in removing
microalgae, preventing epiphytic biomass from becoming excessive, and thereby
improving the growth of the eelgrass shoots.
The importance of this function has been demonstrated in field experiments
throughout the entire area of eelgrass distribution in the northern hemisphere (Duffy
et al. 2015). In those studies, 15 experimental sites were established in all areas
where eelgrass is found in the northern hemisphere, and growth of eelgrass was
used as a short-term index of ecosystem functionality at each site. The diversity and
abundance of small invertebrates were artificially manipulated simultaneously at all
experimental sites for this large-scale comparison. The results showed that as the
diversity and abundance of invertebrate grazers increased, the amount of eelgrass
growth increased significantly (Hori 2015). This result suggests that the growth of
eelgrass and the associated rate of carbon sequestration are affected by invertebrate
grazers. If the grazers disappear, the growth of eelgrass will be reduced by the epiphytes. The reduction of growth would cause a partial collapse of the threedimensional structure and distribution of the eelgrass beds. Such an impact would
lower the tendency of the eelgrass beds to effect sedimentation (Chap. 2; Miyajima
and Hamaguchi 2018) and further reduce their storage of blue carbon.
The grazers, of course, affect more than the relationship between eelgrass and
the associated epiphytes and grazers. Predatory pressures of small fish on grazers
can change the diversity and abundance of grazers, and large fish can change the
predation pressure on grazers from small fish. In this way, the mechanism associated with sequestering and storing blue carbon in eelgrass beds includes not only the
biological characteristics of the above-mentioned eelgrass itself but also the interrelationships of the many creatures inhabiting the eelgrass beds. In other words, the
diversity of the whole biological community is involved. Also, the structure of the
eelgrass beds and the associated biological community are closely related to the
supply of nutrients, the cycling of materials, and the physicochemical environment
included in the ecosystem. Taking into consideration the entire ecosystem is important for its management of for maintaining and improving the role of eelgrass beds
in sequestering and storing blue carbon.
1.4.2 Ecosystem Management of Eelgrass
The UNEP report also emphasized the importance of implementing management
policies that target not only coastal vegetation but also the whole ecosystem, i.e.
ecosystem management. According to the literature (Iwasa et al. 2003), ecosystem
management is defined as managing not only for target species but also for multiple
M. Hori et al.
that consume epiphytes on the seagrass leaves play an especially important role in
the sequestration and storage of blue carbon. The epiphytes growing on the leaves
are an important source of primary production that support the associated animal
community. However, if the epiphyte biomass becomes excessive, the epiphytes
will smother the leaves, hinder photosynthesis by the eelgrass itself, and may cause
the eelgrass to die. Small grazers therefore play an important role in removing
microalgae, preventing epiphytic biomass from becoming excessive, and thereby
improving the growth of the eelgrass shoots.
The importance of this function has been demonstrated in field experiments
throughout the entire area of eelgrass distribution in the northern hemisphere (Duffy
et al. 2015). In those studies, 15 experimental sites were established in all areas
where eelgrass is found in the northern hemisphere, and growth of eelgrass was
used as a short-term index of ecosystem functionality at each site. The diversity and
abundance of small invertebrates were artificially manipulated simultaneously at all
experimental sites for this large-scale comparison. The results showed that as the
diversity and abundance of invertebrate grazers increased, the amount of eelgrass
growth increased significantly (Hori 2015). This result suggests that the growth of
eelgrass and the associated rate of carbon sequestration are affected by invertebrate
grazers. If the grazers disappear, the growth of eelgrass will be reduced by the epiphytes. The reduction of growth would cause a partial collapse of the threedimensional structure and distribution of the eelgrass beds. Such an impact would
lower the tendency of the eelgrass beds to effect sedimentation (Chap. 2; Miyajima
and Hamaguchi 2018) and further reduce their storage of blue carbon.
The grazers, of course, affect more than the relationship between eelgrass and
the associated epiphytes and grazers. Predatory pressures of small fish on grazers
can change the diversity and abundance of grazers, and large fish can change the
predation pressure on grazers from small fish. In this way, the mechanism associated with sequestering and storing blue carbon in eelgrass beds includes not only the
biological characteristics of the above-mentioned eelgrass itself but also the interrelationships of the many creatures inhabiting the eelgrass beds. In other words, the
diversity of the whole biological community is involved. Also, the structure of the
eelgrass beds and the associated biological community are closely related to the
supply of nutrients, the cycling of materials, and the physicochemical environment
included in the ecosystem. Taking into consideration the entire ecosystem is important for its management of for maintaining and improving the role of eelgrass beds
in sequestering and storing blue carbon.
1.4.2 Ecosystem Management of Eelgrass
The UNEP report also emphasized the importance of implementing management
policies that target not only coastal vegetation but also the whole ecosystem, i.e.
ecosystem management. According to the literature (Iwasa et al. 2003), ecosystem
management is defined as managing not only for target species but also for multiple
M. Hori et al.