Islands with rich coral reefs are widely distributed in the tropics and subtropics. Water is very precious on coral reef islands, and inhabitants have used limited water resources, such as groundwater and spring water, carefully and creatively since ancient times. While water is essential for daily life, it also circulates while changing form and functions to connect the land and the sea. On islands, the scale of the water cycle connecting the land and sea is small, and the coral reef ecosystem that nurtures marine resources is closely connected to the land through this water cycle. Such coral reef island systems have nurtured a diversity of organisms and cultures unique to the region. In recent years, however, land use and socioeconomic changes have led to the depletion of water resources and deterioration of water quality on the islands, resulting in the deterioration of coral reef ecosystems via the water cycle. Changes in precipitation patterns, sea levels, ocean acidification, and sea temperatures due to climate change have further contributed to this deterioration of conditions. For inhabitants of coral reef islands to sustainably use the limited natural resources, including highly vulnerable water resources, fishery resources, and forest resources, it is necessary to strengthen adaptive governance and the response to both climate change and socio-economic changes.

The project aims are as follows: 1) to understand and predict changes in multiple resources in response to climate change and socio-economic change by clarifying the connection betweenthe land and sea via the water cycle using stable isotopes, environmental tracers, and metagenomic analyses, 2) to clarify the Biocultural Diversity and Community Capability, to elucidate the factors contributing to the maintenance of livelihoods in island communities with limited resources, 3) to clarify the transition and multilayered nature of individual attitudes and institutions that connect local and global governance through behavioral science and multi-level institutional analyses, and 4) to evaluate adaptive governance, which bridges scientific and local knowledge and attempts to create new values by integrating these sources of knowledge.These results are expected to contribute to the realization of a resilient natural symbiotic society able to cope with climate change and socioeconomic changes in coral reef island systems.

• The Natural System unit conducted a comprehensive survey of river water, groundwater, submarine groundwater discharge, and coral reefs in the southern area of Okinawa Island, Tarama Island, Yoron Island, and Sekisei lagoon (Fig. 1).
• On the southern area of Okinawa Island, we have been conducting groundwater monitoring for more than one year.The issue in this area is the high concentration of nitrate nitrogen in groundwater. We analyzed the boron concentration and isotope composition of groundwater samples and possible pollutant sources. As demonstrated in Fig. 2, it appears possible to quantitatively evaluate pollution sources using a unique tracer of boron.
• As a preliminary survey, we conducted interviews and material research, mainly on Yoron Island, in cooperation with local NPOs, fishermen cooperatives, the Board of Education, and the local archives. As a result of these efforts, an interactive “Yunnu Old Photography Exhibition” was held in February 2022 at Yoron Island.
• We published the first book of the LINKAGE Booklet Series “Narratives on Islands 01: Yoron Island in the Ryukyu Arc”, which compiles this year’s research (Fig. 3).
• To identify connections between people who live in and people who visit island communities, the Governance unit focused on conducting online surveys designed for both populations. We used Qualtrics, a tool for creating survey forms, and Lucid Marketplace, an international tool for collecting samples online, to set up the research system. The Governance unit conducted online surveys on the World Heritage sites and on the compatibility between human mobility and infection control.
• To strengthen joint research, MoUs were signed between RIHN and Halu Oleo University, Indonesia, and the Institute for Marine and Island Cultures, Mokpo National University, South Korea.
• We acted as the local committee of the Japanese Association of Groundwater Hydrology (December 2021, Naha City). We also organized a symposium titled “Water Cycle in the Southern Islands: Linkage between Land and Sea” to develop new collaborative research.
• Since the groundwater is invisible, resident’s awareness of its potential as a resource tends to fade. For the purpose of awareness raising, a 3D simulation study of groundwater flow was conducted based on our research results (Fig. 4), which will be upgraded into 3D projection mapping.

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