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of which has complex intricate coastlines made up both of rocky reefs protruding
into the sea and calm coves with intrinsic beaches or tidal flats. The diversity in
environments allows the formation and coexistence of both eelgrass and Sargassum
beds (Yoshida et al. 2010).
Only eelgrass beds have been detected in the Nansei Islands region (Fig. 4.3).
Though Z. marina is not distributed in this region, many tropical seagrass species
exist, including Thalassia hemprichii and Cymodocea rotundata. Although some
Sargassum species are also distributed in the Nansei Islands, the distribution of
Sargassum beds was not also reported in the 4th National Survey. There are many
coral reefs in the rocky shores of the Nansei Islands, and large stands of Sargassum
may not develop and have not been perceptible as a bed.
4.3 Estimation of Carbon Sequestration by Seagrass/
Macroalgae
To calculate the production of seagrass and macroalgae for the entire coastal area of
Japan, the area and estimated production per unit area of each type of seagrass and
macroalgal bed is needed. Here, we introduce the production rate directly measured
from those beds throughout Japan and compare the rates with those obtained worldwide to clarify the characteristics of seagrass and macroalgal production in Japan.
We then calculate the total nationwide production rate in seagrass and macroalgal
bed areas and convert that to an organic carbon sequestration rate on a yearly basis.
The amount of seagrass and macroalgae existing in their beds at some point in
time is called its biomass. Seagrass and macroalgae exhibit seasonal growth and
withering as land plants do, and the fluctuations appear as seasonal changes in biomass. Generally, plant biomass increases with the accumulation of newly-formed
tissues and organs during the growth season and reaches a peak with the peak of
growth. However, the tissues and organs of seagrass and macroalgae are relatively
short-lived and generally do not persist for long periods, unlike tree trunks, for
example, which grow gradually from year to year and accumulate biomass with age.
That means that, in seagrass and macroalgae, new formation and loss of tissues or
organs proceed simultaneously throughout the year. Biomass increases as the total
amount of newly formed tissues and organs exceeds the total amount of their loss,
and it decreases when the opposite phenomenon occurs. Consequently, it is generally not possible to grasp the annual amount of seagrass and macroalgal production
simply by investigating biomass. It is also necessary to investigate the temporal
amounts of new tissue formation and to acquire the annual net totals.
Fortunately, direct measurement methods of production corresponding to in situ
growth characteristics have been developed for eelgrass, Sargassum, and kelps,
respectively. We used these methods in our estimations as detailed in the following
sections.
4 Carbon Sequestration by Seagrass and Macroalgae in Japan: Estimates and Future…
of which has complex intricate coastlines made up both of rocky reefs protruding
into the sea and calm coves with intrinsic beaches or tidal flats. The diversity in
environments allows the formation and coexistence of both eelgrass and Sargassum
beds (Yoshida et al. 2010).
Only eelgrass beds have been detected in the Nansei Islands region (Fig. 4.3).
Though Z. marina is not distributed in this region, many tropical seagrass species
exist, including Thalassia hemprichii and Cymodocea rotundata. Although some
Sargassum species are also distributed in the Nansei Islands, the distribution of
Sargassum beds was not also reported in the 4th National Survey. There are many
coral reefs in the rocky shores of the Nansei Islands, and large stands of Sargassum
may not develop and have not been perceptible as a bed.
4.3 Estimation of Carbon Sequestration by Seagrass/
Macroalgae
To calculate the production of seagrass and macroalgae for the entire coastal area of
Japan, the area and estimated production per unit area of each type of seagrass and
macroalgal bed is needed. Here, we introduce the production rate directly measured
from those beds throughout Japan and compare the rates with those obtained worldwide to clarify the characteristics of seagrass and macroalgal production in Japan.
We then calculate the total nationwide production rate in seagrass and macroalgal
bed areas and convert that to an organic carbon sequestration rate on a yearly basis.
The amount of seagrass and macroalgae existing in their beds at some point in
time is called its biomass. Seagrass and macroalgae exhibit seasonal growth and
withering as land plants do, and the fluctuations appear as seasonal changes in biomass. Generally, plant biomass increases with the accumulation of newly-formed
tissues and organs during the growth season and reaches a peak with the peak of
growth. However, the tissues and organs of seagrass and macroalgae are relatively
short-lived and generally do not persist for long periods, unlike tree trunks, for
example, which grow gradually from year to year and accumulate biomass with age.
That means that, in seagrass and macroalgae, new formation and loss of tissues or
organs proceed simultaneously throughout the year. Biomass increases as the total
amount of newly formed tissues and organs exceeds the total amount of their loss,
and it decreases when the opposite phenomenon occurs. Consequently, it is generally not possible to grasp the annual amount of seagrass and macroalgal production
simply by investigating biomass. It is also necessary to investigate the temporal
amounts of new tissue formation and to acquire the annual net totals.
Fortunately, direct measurement methods of production corresponding to in situ
growth characteristics have been developed for eelgrass, Sargassum, and kelps,
respectively. We used these methods in our estimations as detailed in the following
sections.
4 Carbon Sequestration by Seagrass and Macroalgae in Japan: Estimates and Future…