102
integrated annual plant tissue production converted to organic carbon, which was
defined by subtracting dissolved organic matter production from net primary production. Plant tissue production of the main constituent macrophyte of the seagrass
and macroalgal beds was directly measured in each coastal region, and production
values from past reports were also collected and utilized. Annual carbon sequestration by seagrass and macroalgal beds in Japan, expressed in a CO 2 -converted base,
was about 4.7 million tons per year, which is comparable to the CO 2 emissions of
the industrial sectors of agriculture and fisheries.
4.1 Introduction
The Japanese archipelago is long from south to north and lies within a wide climatic
range, from subarctic to subtropical. Warm and cold currents flow near the Japanese
coast, affecting and characterizing the local climate of coastal habitats. In addition,
topographic characteristics along the coast are also diverse, from rocky shores
struck by waves to gentle coves with sandy beaches or tidal flats. Many species of
seagrass and macroalgae with diverse physiological and ecological features inhabit
these diverse climatic and physical environments along the coast. As a result, various forms of seagrass and macroalgal beds are distributed throughout Japan.
As discussed in other chapters in this volume, blue carbon ecosystems store substantial amounts of carbon, and it has become clear that they make a great contribution to carbon sequestration and storage on a global scale (Endo and Otani 2018;
Inoue 2018; Miyajima and Hamagichi 2018). UNEP’s “Blue Carbon “report
(Nellemann et al. 2009) suggested that seagrass beds such as eelgrass meadows
deposit considerable amounts of organic carbon of biological origin in the soft sediment within the beds and store it for long periods. Since publication of the report,
increasing attention has been paid to the potential of seagrass beds as carbon sinks,
which could be an effective measure against global warming.
Macroalgal beds formed mainly of large brown algae on rocky shores do not
share the same depositional function as the seagrass beds, so there has been little
discussion of their contribution in terms of blue carbon and carbon sequestration in
the UNEP’s “Blue Carbon” report. However, a considerable amount of macroalgae
may flow out from their beds and be transported and deposited to the deep seafloor
(Krause-Jensen and Duarte 2016). If this is the case, macroalgal beds also serve as
a source of long-term stored organic carbon, even though it is stored in different
locations from its origin.
Seagrass and macroalgal beds have high primary production (and carbon sequestration potential), which is comparable to that of forests (Kurashima 2010). In shallow coastal waters, seagrass and macroalgae are often more abundant than other
primary producers such as phytoplankton and benthic microalgae. Therefore, seagrass and macroalgae are the major ecosystem members responsible for sequestration and storage of carbon in shallow coastal waters.
To estimate how much carbon dioxide is absorbed and sequestered from the
atmosphere by seagrass and macroalgal beds in Japan, we first need to determine
how much seagrass and macroalgae actually grow in Japan. Organic carbon, constiG. Yoshida et al.
integrated annual plant tissue production converted to organic carbon, which was
defined by subtracting dissolved organic matter production from net primary production. Plant tissue production of the main constituent macrophyte of the seagrass
and macroalgal beds was directly measured in each coastal region, and production
values from past reports were also collected and utilized. Annual carbon sequestration by seagrass and macroalgal beds in Japan, expressed in a CO 2 -converted base,
was about 4.7 million tons per year, which is comparable to the CO 2 emissions of
the industrial sectors of agriculture and fisheries.
4.1 Introduction
The Japanese archipelago is long from south to north and lies within a wide climatic
range, from subarctic to subtropical. Warm and cold currents flow near the Japanese
coast, affecting and characterizing the local climate of coastal habitats. In addition,
topographic characteristics along the coast are also diverse, from rocky shores
struck by waves to gentle coves with sandy beaches or tidal flats. Many species of
seagrass and macroalgae with diverse physiological and ecological features inhabit
these diverse climatic and physical environments along the coast. As a result, various forms of seagrass and macroalgal beds are distributed throughout Japan.
As discussed in other chapters in this volume, blue carbon ecosystems store substantial amounts of carbon, and it has become clear that they make a great contribution to carbon sequestration and storage on a global scale (Endo and Otani 2018;
Inoue 2018; Miyajima and Hamagichi 2018). UNEP’s “Blue Carbon “report
(Nellemann et al. 2009) suggested that seagrass beds such as eelgrass meadows
deposit considerable amounts of organic carbon of biological origin in the soft sediment within the beds and store it for long periods. Since publication of the report,
increasing attention has been paid to the potential of seagrass beds as carbon sinks,
which could be an effective measure against global warming.
Macroalgal beds formed mainly of large brown algae on rocky shores do not
share the same depositional function as the seagrass beds, so there has been little
discussion of their contribution in terms of blue carbon and carbon sequestration in
the UNEP’s “Blue Carbon” report. However, a considerable amount of macroalgae
may flow out from their beds and be transported and deposited to the deep seafloor
(Krause-Jensen and Duarte 2016). If this is the case, macroalgal beds also serve as
a source of long-term stored organic carbon, even though it is stored in different
locations from its origin.
Seagrass and macroalgal beds have high primary production (and carbon sequestration potential), which is comparable to that of forests (Kurashima 2010). In shallow coastal waters, seagrass and macroalgae are often more abundant than other
primary producers such as phytoplankton and benthic microalgae. Therefore, seagrass and macroalgae are the major ecosystem members responsible for sequestration and storage of carbon in shallow coastal waters.
To estimate how much carbon dioxide is absorbed and sequestered from the
atmosphere by seagrass and macroalgal beds in Japan, we first need to determine
how much seagrass and macroalgae actually grow in Japan. Organic carbon, constiG. Yoshida et al.