50
correlates with our observation that seedlings of
Zostera species were present in mid-June.
Germinated seeds require light, although some
studies have reported that light had no infl uence
on the germination of Z. marina seeds. Because
the tsunami removed fl owering and vegetative
shoots, the lack of shading from these absent
shoots enabled seedlings to receive light, as has
been reported previously (Olesen and SandJensen 1994 ; Abe et al. 2004 ).
4.5
Resilience of Seagrasses
to Disturbances
In general, seagrasses undergo asexual reproduction through production of shoots on the root systems in subtidal zones that provide a stable
environment (Philipps et al. 1983 ). However,
seedlings are also produced after disappearance
of seagrass beds caused by storm (Aioi and
Komatsu 1996 ) and tsunami events. It is believed
that seagrasses have two reproductive strategies:
asexual in a stable environment and sexual, when
a sudden loss of seagrass beds has occurred. The
huge tsunami hit Sanriku Coast in 1896 (off
Sanriku with moment magnitude, Mw 8.0–8.1),
1933 (off Sanriku with Mw 8.4), 1960 (off Chile
with Mw 9.5) (Iwate Prefecture 2014 ; Kanamori
1977 ; Omachi et al. 2003 ) and 2011 (off Sanriku
with Mw 9.0) (Takeuchi and Chavoshian 2011 ).
The last one in 2011 was caused by the great
earthquake which tends to occur at an interval of
700 years along this coastline facing Japan trench
(Satake 2011 ). Zostera species on the Sanriku
Coast invest energy to produce seeds as an insurance against the disappearance of the mother
plants; this provides the seagrass beds with resilience against catastrophic natural disasters, such
as huge tsunamis. Thus, it is recommended that
recovery operations after such events (e.g. restoration of ports and removal of debris (fragments
of dykes) in shallow waters) incorporate measures to avoid damage to recovering seagrass
beds and do not take place before regrowth of
broad seagrass beds near the sites of such operations because of the fundamental role of these
beds in fi sheries.
4.6
Socio-ecosystem Resilience
Coastal areas in Otsuchi Bay and Sanriku Coast
depend on fi sheries and aquacultures. Restoration
of the areas from the tsunami disaster needs
recovery of coastal fi sheries and aquacultures,
which are based on the coastal ecosystem. In
Sanriku Coast, damaged seagrass beds started to
regenerate on the beds where their mother plants
had been distributed. On the other hand, the
Ministry of Land and Transport with Miyagi and
Iwate Prefectures is constructing huge seawalls
with a wall height of 10–15 m and a base width of
43–63 m from the against the huge tsunami along
the coast in the places of broken seawalls to protect people and their properties without environmental assessments (Anon 2013 ) with a
far-fetched reason that construction of huge seawalls is a recovery work for sea-walls usually
with about 3–4 m high before the tsunami. If fortifi cation of the coast by the huge seawalls cuts
continuity of land and the sea and material fl ow
between them, it destroys an ecotone including
seagrass beds by direct and indirect ways due to
construction. It is needed to remember that society based on the fi sheries and aquacultures utilising coastal ecosystems exists with the nature that
has original resilience against natural disasters.
Thus, the recovery program from the tsunami
must be established on holistic approach including social and ecological aspects of land and the
sea based on the ecosystem-based concept that
secures material fl ows between land and the sea
from the sustainable point of view because the
coastal area is an ecotone of land and the sea and
also a “sociotone” between land and the sea.
Acknowledgements We thank Mr. Masataka Kurosawa
and Mr. Masaaki Hirano, staffs of the International Centre
for Coastal Oceanography, University of Tokyo, for their
assistance during this study. We are also grateful to Mr.
Kazuhiro Hantani of Toyo Corp. for his encouragement to
carry out our research. This study was supported by grants
from the Marine Alliance Organization of the University
of Tokyo, the Environment Research and Technology
Development Funds (S9) and (S13) of the Japanese
Ministry of the Environment and the Tohoku EcosystemAssociated Marine Sciences (TEAMS) research program
of the Ministry of Education, Culture, Sports, Science and
Technology (MEXT).
T. Komatsu et al.
correlates with our observation that seedlings of
Zostera species were present in mid-June.
Germinated seeds require light, although some
studies have reported that light had no infl uence
on the germination of Z. marina seeds. Because
the tsunami removed fl owering and vegetative
shoots, the lack of shading from these absent
shoots enabled seedlings to receive light, as has
been reported previously (Olesen and SandJensen 1994 ; Abe et al. 2004 ).
4.5
Resilience of Seagrasses
to Disturbances
In general, seagrasses undergo asexual reproduction through production of shoots on the root systems in subtidal zones that provide a stable
environment (Philipps et al. 1983 ). However,
seedlings are also produced after disappearance
of seagrass beds caused by storm (Aioi and
Komatsu 1996 ) and tsunami events. It is believed
that seagrasses have two reproductive strategies:
asexual in a stable environment and sexual, when
a sudden loss of seagrass beds has occurred. The
huge tsunami hit Sanriku Coast in 1896 (off
Sanriku with moment magnitude, Mw 8.0–8.1),
1933 (off Sanriku with Mw 8.4), 1960 (off Chile
with Mw 9.5) (Iwate Prefecture 2014 ; Kanamori
1977 ; Omachi et al. 2003 ) and 2011 (off Sanriku
with Mw 9.0) (Takeuchi and Chavoshian 2011 ).
The last one in 2011 was caused by the great
earthquake which tends to occur at an interval of
700 years along this coastline facing Japan trench
(Satake 2011 ). Zostera species on the Sanriku
Coast invest energy to produce seeds as an insurance against the disappearance of the mother
plants; this provides the seagrass beds with resilience against catastrophic natural disasters, such
as huge tsunamis. Thus, it is recommended that
recovery operations after such events (e.g. restoration of ports and removal of debris (fragments
of dykes) in shallow waters) incorporate measures to avoid damage to recovering seagrass
beds and do not take place before regrowth of
broad seagrass beds near the sites of such operations because of the fundamental role of these
beds in fi sheries.
4.6
Socio-ecosystem Resilience
Coastal areas in Otsuchi Bay and Sanriku Coast
depend on fi sheries and aquacultures. Restoration
of the areas from the tsunami disaster needs
recovery of coastal fi sheries and aquacultures,
which are based on the coastal ecosystem. In
Sanriku Coast, damaged seagrass beds started to
regenerate on the beds where their mother plants
had been distributed. On the other hand, the
Ministry of Land and Transport with Miyagi and
Iwate Prefectures is constructing huge seawalls
with a wall height of 10–15 m and a base width of
43–63 m from the against the huge tsunami along
the coast in the places of broken seawalls to protect people and their properties without environmental assessments (Anon 2013 ) with a
far-fetched reason that construction of huge seawalls is a recovery work for sea-walls usually
with about 3–4 m high before the tsunami. If fortifi cation of the coast by the huge seawalls cuts
continuity of land and the sea and material fl ow
between them, it destroys an ecotone including
seagrass beds by direct and indirect ways due to
construction. It is needed to remember that society based on the fi sheries and aquacultures utilising coastal ecosystems exists with the nature that
has original resilience against natural disasters.
Thus, the recovery program from the tsunami
must be established on holistic approach including social and ecological aspects of land and the
sea based on the ecosystem-based concept that
secures material fl ows between land and the sea
from the sustainable point of view because the
coastal area is an ecotone of land and the sea and
also a “sociotone” between land and the sea.
Acknowledgements We thank Mr. Masataka Kurosawa
and Mr. Masaaki Hirano, staffs of the International Centre
for Coastal Oceanography, University of Tokyo, for their
assistance during this study. We are also grateful to Mr.
Kazuhiro Hantani of Toyo Corp. for his encouragement to
carry out our research. This study was supported by grants
from the Marine Alliance Organization of the University
of Tokyo, the Environment Research and Technology
Development Funds (S9) and (S13) of the Japanese
Ministry of the Environment and the Tohoku EcosystemAssociated Marine Sciences (TEAMS) research program
of the Ministry of Education, Culture, Sports, Science and
Technology (MEXT).
T. Komatsu et al.