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© Springer Nature Singapore Pte Ltd. 2019
T. Kuwae, M. Hori (eds.), Blue Carbon in Shallow Coastal Ecosystems,
https://doi.org/10.1007/978-981-13-1295-3_10
Chapter 10
Carbon Dynamics in Coral Reefs
Atsushi Watanabe and Takashi Nakamura
Abstract Coral reefs show high organic and inorganic carbon production and create unique landforms on tropical coastlines. The balance between organic and inorganic carbon production is determined by benthic organisms such as corals,
macroalgae, and seagrasses, and also by reef hydrodynamics, which in turn determine CO 2 sinks and sources within the ecosystem. Many studies have shown that
net organic carbon production in coral reef ecosystems is almost zero (balanced),
with net positive calcification resulting in reefs acting as CO 2 sources. However, the
relationships among productivity, benthic organisms, and hydrodynamics have not
been well documented; more detailed information is required from both field observations and coupled physical–biological models. Reef sediments have low organic
carbon content (median, 0.35% dry weight), approximately 50% those of tropical
and subtropical seagrass beds (median, 0.67%) and 5% those of mangrove forests
(median, 6.3%). Sedimentation rates do not vary significantly between these three
ecosystems, so organic carbon input and decomposition in the surface sediments are
key factors controlling organic carbon burial rates. Coral reefs provide calm conditions that enhance sedimentation of fine sediments, which facilitates the development of seagrass beds and mangrove forests. Seagrass meadows and mangrove
forests in turn trap fine sediments from terrestrial sources and prevent high-turbidity
water from reaching coral reefs. Coral reefs, seagrass meadows, and mangrove forests are thus interdependent ecosystems; to effectively store and export blue carbon
in tropical coastal areas, it is necessary to maintain the health of these ecosystems.
A. Watanabe (*)
Department of Transdisciplinary Science and Engineering, School of Environment and
Society, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8550, Japan
Policy Ocean Policy Research Institute, The Sasakawa Peace Foundation,
Minato-ku, Tokyo 105-8524, Japan
T. Nakamura
Department of Transdisciplinary Science and Engineering, School of Environment and
Society, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8550, Japan
© Springer Nature Singapore Pte Ltd. 2019
T. Kuwae, M. Hori (eds.), Blue Carbon in Shallow Coastal Ecosystems,
https://doi.org/10.1007/978-981-13-1295-3_10
Chapter 10
Carbon Dynamics in Coral Reefs
Atsushi Watanabe and Takashi Nakamura
Abstract Coral reefs show high organic and inorganic carbon production and create unique landforms on tropical coastlines. The balance between organic and inorganic carbon production is determined by benthic organisms such as corals,
macroalgae, and seagrasses, and also by reef hydrodynamics, which in turn determine CO 2 sinks and sources within the ecosystem. Many studies have shown that
net organic carbon production in coral reef ecosystems is almost zero (balanced),
with net positive calcification resulting in reefs acting as CO 2 sources. However, the
relationships among productivity, benthic organisms, and hydrodynamics have not
been well documented; more detailed information is required from both field observations and coupled physical–biological models. Reef sediments have low organic
carbon content (median, 0.35% dry weight), approximately 50% those of tropical
and subtropical seagrass beds (median, 0.67%) and 5% those of mangrove forests
(median, 6.3%). Sedimentation rates do not vary significantly between these three
ecosystems, so organic carbon input and decomposition in the surface sediments are
key factors controlling organic carbon burial rates. Coral reefs provide calm conditions that enhance sedimentation of fine sediments, which facilitates the development of seagrass beds and mangrove forests. Seagrass meadows and mangrove
forests in turn trap fine sediments from terrestrial sources and prevent high-turbidity
water from reaching coral reefs. Coral reefs, seagrass meadows, and mangrove forests are thus interdependent ecosystems; to effectively store and export blue carbon
in tropical coastal areas, it is necessary to maintain the health of these ecosystems.
A. Watanabe (*)
Department of Transdisciplinary Science and Engineering, School of Environment and
Society, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8550, Japan
Policy Ocean Policy Research Institute, The Sasakawa Peace Foundation,
Minato-ku, Tokyo 105-8524, Japan
T. Nakamura
Department of Transdisciplinary Science and Engineering, School of Environment and
Society, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8550, Japan