121
As described above, variation in the production of cold-temperate kelps is
extremely large among species and locations. Elsewhere, production as high as 6 kg
dry weight/m
2
/year was reported in Nova Scotia, Canada (Mann 1972). Therefore,
it seems that cold-temperate kelps can exhibit extremely high production under certain environmental conditions of their habitats. To explain why kelp can demonstrate such high production, Sakanishi (2010) considered water motion conditions
in habitats are responsible because thallus undulation under moderate water motions
can promote the supply of dissolved inorganic carbon and nutrients to the kelp. In
addition, it seems that the biomass and production of Saccharina species tend to be
higher on the coast in Japan with the cold current (Oyashio Current), which carries
abundant nutrients and may be a contributing factor for the high production of kelps.
Comparisons of the production of kelp among habitats with different environmental
conditions are needed, as well as on a global scale that includes climate variation.
4.3.4 Estimation of Carbon Sequestration by Seagrass
and Macroalgae on the Coast of Japan
Here, annual production, which is defined by subtracting DOM production from net
primary production (see Fig. 4.1), by seagrass and macroalgae in Japan is calculated
on a dry weight basis from the area of each of the seagrass and macroalgal beds and
the production per unit area of each bed shown in the previous sections. The annual
production is then converted into amounts of organic carbon and carbon dioxide,
and defined as the carbon sequestration potential of seagrass and macroalgal beds in
Japan. The basic procedure is as follows.
1. Amamo-ba: The daily production per unit area of eelgrass in each sea area shown
in Fig. 4.6 was integrated for 1 year to calculate annual production output. This
value was multiplied by each area of the eelgrass beds in each region and summed
as the nationwide total. For the Japan Sea region, which has no actual measured
production, we used the production value from the Seto Inland Sea region, which
has similar water temperature conditions. For the Nansei Islands region where Z.
marina is not distributed, the measured values of Thalassia hemprichii and
Cymodocea serrulata we obtained in our research (Hori unpublished) were used.
2. Garamo-ba: The mean value of maximum biomass in each of the four regions
shown in Fig. 4.9 was used and multiplied by the mean P/B MAX ratio of Sargassum
species (1.4; Murase 2010). For the maximum biomass in the Hokkaido and
Pacific Tohoku regions, we used the average of all values collected from past
studies of those respective areas and multiplied them by the Sargassum bed area
of each region.
3. Arame-ba: The mean annual production per unit area of Ecklonia and Eisenia in
each region, which was obtained from previous research or direct in situ measurements conducted in our survey, was multiplied by the warm-temperate kelp
bed area in each region. For the Japan Sea region for which no data were avail4 Carbon Sequestration by Seagrass and Macroalgae in Japan: Estimates and Future…
As described above, variation in the production of cold-temperate kelps is
extremely large among species and locations. Elsewhere, production as high as 6 kg
dry weight/m
2
/year was reported in Nova Scotia, Canada (Mann 1972). Therefore,
it seems that cold-temperate kelps can exhibit extremely high production under certain environmental conditions of their habitats. To explain why kelp can demonstrate such high production, Sakanishi (2010) considered water motion conditions
in habitats are responsible because thallus undulation under moderate water motions
can promote the supply of dissolved inorganic carbon and nutrients to the kelp. In
addition, it seems that the biomass and production of Saccharina species tend to be
higher on the coast in Japan with the cold current (Oyashio Current), which carries
abundant nutrients and may be a contributing factor for the high production of kelps.
Comparisons of the production of kelp among habitats with different environmental
conditions are needed, as well as on a global scale that includes climate variation.
4.3.4 Estimation of Carbon Sequestration by Seagrass
and Macroalgae on the Coast of Japan
Here, annual production, which is defined by subtracting DOM production from net
primary production (see Fig. 4.1), by seagrass and macroalgae in Japan is calculated
on a dry weight basis from the area of each of the seagrass and macroalgal beds and
the production per unit area of each bed shown in the previous sections. The annual
production is then converted into amounts of organic carbon and carbon dioxide,
and defined as the carbon sequestration potential of seagrass and macroalgal beds in
Japan. The basic procedure is as follows.
1. Amamo-ba: The daily production per unit area of eelgrass in each sea area shown
in Fig. 4.6 was integrated for 1 year to calculate annual production output. This
value was multiplied by each area of the eelgrass beds in each region and summed
as the nationwide total. For the Japan Sea region, which has no actual measured
production, we used the production value from the Seto Inland Sea region, which
has similar water temperature conditions. For the Nansei Islands region where Z.
marina is not distributed, the measured values of Thalassia hemprichii and
Cymodocea serrulata we obtained in our research (Hori unpublished) were used.
2. Garamo-ba: The mean value of maximum biomass in each of the four regions
shown in Fig. 4.9 was used and multiplied by the mean P/B MAX ratio of Sargassum
species (1.4; Murase 2010). For the maximum biomass in the Hokkaido and
Pacific Tohoku regions, we used the average of all values collected from past
studies of those respective areas and multiplied them by the Sargassum bed area
of each region.
3. Arame-ba: The mean annual production per unit area of Ecklonia and Eisenia in
each region, which was obtained from previous research or direct in situ measurements conducted in our survey, was multiplied by the warm-temperate kelp
bed area in each region. For the Japan Sea region for which no data were avail4 Carbon Sequestration by Seagrass and Macroalgae in Japan: Estimates and Future…