Focusing on coral reef island systems located in the Ryukyu Arc as well as in the tropical and subtropical western Pacific, we are elucidating the connections between land and sea through the water cycle, the biocultural diversity and community capability, and the evolution and structure of organizations and institutions that govern the use and management of multiple resources. By integrating and visualizing the above interconnected components, we aim to shed light on adaptive governance of multiple resources based on the water cycle.

People living in tropical and subtropical islands where coral reefs develop utilize the blessings of limited water resources such as groundwater and spring water, as well as marine and forest resources.

Water circulates between the land and the sea while changing its shape, connecting the coral reef ecosystem and the land, and nurturing the biodiversity and culture unique to the region.

However, recent land use and socioeconomic changes have led to the depletion of water resources and deterioration of water quality, as well as changes in precipitation patterns due to climate change, rising seawater temperature and sea levels due to global warming, and ocean acidification. Due to changes in the marine environment, the deterioration of coral reef ecosystems is progressing, making it difficult for people to use natural resources such as water resources, fisheries resources, and forest resources, that is, multiple resources.

Therefore, we are conducting research to strengthen “adaptive governance,” in which social mechanisms and institutions for environmental conservation and natural resource management are adjusted to the situation together with local people, so that people living on coral reef islands can continue to use multiple resources.

To this end, this project first aims to elucidate the realities of water circulation and multiple resources through various means of analyzing groundwater and coral reef ecosystems. We seek to understand and predict the responses of multiple resources to changes in socio-economic factors and climate change. Additionally, utilizing a historical ecological approach, the project aims to uncover the cultural values, connections, and diversity of nature nurtured within island communities. By doing so, we will elucidate the mechanisms for sustaining livelihoods in island communities with limited resources.

On the other hand, through behavioral science and institutional analysis, we will clarify the transition and multilayered nature of the system, organization, and awareness of adaptive governance. In addition, we will create new value by visualizing and integrating the relationships between scientific knowledge, indigenous knowledge, policy knowledge, and other knowledge necessary for adaptive governance.

Through these results, we hope to shed light on the connections between land and sea through water cycle as well as on the adaptive governance of multiple resources, in order to contribute to the realization of a resilient nature-symbiotic society in coral reef island systems.

What we know so far

In 2024, a severe phenomenon occurred in Japan’s largest coral reef, Sekisei Lagoon, where 84 % of coral colonies experienced bleaching. While rising sea temperatures are considered the main cause of bleaching, we also focused on phosphorus in the seabed sediment.

Previous studies have shown that phosphorus in the sediment hinders coral skeleton formation and negatively affects coral growth. In Sekisei Lagoon, a significant correlation was also found between phosphorus levels and coral bleaching or reduced density.
As a result of three years of monitoring, we created a map of sedimentary phosphorus distribution (Figure 1) and, for the first time, clarified the relationship between phosphorus levels and coral coverage or bleaching. By using concentration thresholds (0.3–0.7 µg/g) as indicators, we can estimate the permissible load from land-based sources, enabling more effective management.

We also conducted an awareness survey in Japan and Indonesia on how the “invisibility” of groundwater resources affects public interest. As a result, we found that in Japan, there is generally low interest in groundwater, whereas this trend was not observed in Indonesia.

Noteworthy items

In the Wakatobi Islands, Indonesia, full-scale field research is underway, including investigations of groundwater and coral reef sediments, as well as interviews with local residents (Photos 1 and 2)

On Yoron Island, we are continuing the “Yunnu Historical Photo Survey: Reflecting on Nature and Daily Life,” which aims to document the relationship between the island’s natural environment and local lifestyles. This collaborative effort involves local residents, the board of education, and researchers, who work together to collect and record materials on environmental and lifestyle changes, develop educational resources, and build a digital archive accessible to all. The theme of the fourth photo exhibition was “Preparedness and Transition” (Figure 2; https://yunnu-photo.org/).

Additionally, on Yoron Island, we created a “Projection Mapping Model (P+MM)” to visually convey land use changes based on a 3D water circulation simulation model and aerial photographs (Photo 3). Information sharing with the local community is also progressing, and we are broadly disseminating our findings through the LINKAGE booklet series (Figures 3 and 4).