104
First, however, we introduce some points of discussion and terms used in the
chapter. Seagrass and macroalgae produce organic matter through photosynthesis.
The total amount of this organic matter is gross primary production. Part of the
gross primary production is mineralized by respiration and released as carbon dioxide. Gross primary production minus respiration is net primary production, which is
split between that used to form the tissues of seagrass and macroalgae and that
released into surrounding water as dissolved organic matter (DOM) (Fig. 4.1). In
the past researches on the production of seagrass and macroalgae in Japan, the
amount of DOM relative to total net primary production has been assumed to be
negligible, and only the amount of seagrass and macroalgal tissue production is usually considered as net primary production. However, recent studies have suggested
that the released DOM cannot necessarily be neglected quantitatively and that some
of the DOM is also refractory, which may greatly contribute to carbon storage in the
ocean (Wada et al. 2008; Kuwae et al. 2018). In this chapter, we only focus on the
production of seagrass and macroalgal tissues, which are the main pathways of
carbon sequestration by these macrophyte. To avoid confusion, we simply use the
term “production” for this tissue production instead of the term net primary
production.
4.2 The Area and Distributional Characteristics of Seagrass
and Macroalgal Beds in Japan
To estimate the total amount of production by seagrass and macroalgae along the
entire coast of Japan, data on their bed area are required. To ascertain the current
status of seagrass and macroalgal beds, nationwide and (more frequently) regional
surveys on the area and distribution of seagrass and macroalgal beds have been
conducted in Japan. However, the available data are spatiotemporally discrete, and
the last nationwide research by the Ministry of the Environment was conducted in
the early 1990s.
As was mentioned in the Introduction, there are many seagrass and macroalgal
species in Japan. Therefore, for convenience, seagrass and macroalgal beds have
often been classified into several types, depending on the main constituent species.
In this section, we first describe the classification types of seagrass and macroalgal
beds generally used in research in Japan. We then outline the area and distributional
characteristics of each type of bed along the Japanese coast obtained in the latest
survey in which the authors were involved recently (in 2009–2013).
4.2.1 Types of Seagrass and Macroalgal Beds
In research conducted by the Ministry of the Environment and the Fisheries
Agency of Japan, seagrass and macroalgal beds have generally been classified as
Amamo-ba (which contains all kinds of seagrass) and seven types of macroalgal
G. Yoshida et al.
First, however, we introduce some points of discussion and terms used in the
chapter. Seagrass and macroalgae produce organic matter through photosynthesis.
The total amount of this organic matter is gross primary production. Part of the
gross primary production is mineralized by respiration and released as carbon dioxide. Gross primary production minus respiration is net primary production, which is
split between that used to form the tissues of seagrass and macroalgae and that
released into surrounding water as dissolved organic matter (DOM) (Fig. 4.1). In
the past researches on the production of seagrass and macroalgae in Japan, the
amount of DOM relative to total net primary production has been assumed to be
negligible, and only the amount of seagrass and macroalgal tissue production is usually considered as net primary production. However, recent studies have suggested
that the released DOM cannot necessarily be neglected quantitatively and that some
of the DOM is also refractory, which may greatly contribute to carbon storage in the
ocean (Wada et al. 2008; Kuwae et al. 2018). In this chapter, we only focus on the
production of seagrass and macroalgal tissues, which are the main pathways of
carbon sequestration by these macrophyte. To avoid confusion, we simply use the
term “production” for this tissue production instead of the term net primary
production.
4.2 The Area and Distributional Characteristics of Seagrass
and Macroalgal Beds in Japan
To estimate the total amount of production by seagrass and macroalgae along the
entire coast of Japan, data on their bed area are required. To ascertain the current
status of seagrass and macroalgal beds, nationwide and (more frequently) regional
surveys on the area and distribution of seagrass and macroalgal beds have been
conducted in Japan. However, the available data are spatiotemporally discrete, and
the last nationwide research by the Ministry of the Environment was conducted in
the early 1990s.
As was mentioned in the Introduction, there are many seagrass and macroalgal
species in Japan. Therefore, for convenience, seagrass and macroalgal beds have
often been classified into several types, depending on the main constituent species.
In this section, we first describe the classification types of seagrass and macroalgal
beds generally used in research in Japan. We then outline the area and distributional
characteristics of each type of bed along the Japanese coast obtained in the latest
survey in which the authors were involved recently (in 2009–2013).
4.2.1 Types of Seagrass and Macroalgal Beds
In research conducted by the Ministry of the Environment and the Fisheries
Agency of Japan, seagrass and macroalgal beds have generally been classified as
Amamo-ba (which contains all kinds of seagrass) and seven types of macroalgal
G. Yoshida et al.