[A-HW22] Material transportation and cycling in watershed ecosystems; from headwaters to coastal areas

[AHW22-05] Phosphate bound to calcareous sediments in coastal area inhibit skeletal formation of juvenile coral.

*Mariko Iijima¹, Jun Yasumoto², Akira Iguchi¹, Takashi Nakamura³, Kazuhiko Sakai⁴, Mina Hirose⁵, Kanami Yasumoto⁶, Mizusawa Nanami⁷, Atsushi Suzuki¹, Mitsuru Jimbo⁷, Shugo Watabe⁷, Yasumoto Ko⁷ (1.National Institute of Advanced Industrial Science and Technology, 2.Faculty of Agriculture, University of the Ryukyus, 3.Faculty of Science, University of the Ryukyus, 4.Tropical Biosphere Research Center, University of the Ryukyus, 5.Tropical Technology Plus, 6.Faculty of Pharmaceutical Sciences, Tokyo University of Science, 7.School of Marine Biosciences, Kitasato University)

Keywords:phosphate, calcification, sediment, coral

To test the hypothesis that terrestrial runoff affects the functions of calcareous sediments in coral reefs and hampers the development of corals, we analysed calcareous sediments with different levels of bound phosphate, collected from reef areas of Okinawajima, Japan. We confirmed that phosphate bound to calcareous sediments was readily released into ambient seawater, resulting in much higher concentrations of phosphorous in seawater from heavily polluted areas (4.3 to 19.0 µM as compared with < 0.096 μM in natural ambient seawater). Additionally, we examined the effect of phosphate released from calcareous sediments on the development of Acropora digitifera coral juveniles. We found that high phosphate concentrations in seawater clearly inhibit skeletal formation of coral juveniles. The present study demonstrated that terrestrial phosphate is bound to calcareous sediments in coastal areas and the bound phosphate is readily released into ambient seawater, resulting in high concentrations of phosphorous in surrounding seawater. These high phosphate concentrations were found to inhibit the skeletal formation of coral juveniles. Based on these data, we propose calcareous sediments in reef areas play a crucial role in mediating the impact of terrestrial runoff on corals by storing and releasing phosphate in seawater. We need more detailed surveys about phosphate bound to calcareous sediments near coasts for better managements of sustainable coral reef ecosystem services.