Island infrastructure material stock (MS) analysis reveals resource flow and accumulation, providing policymakers with insights for managing resources and planning. This study comprehensively analyzed the MS of infrastructure on Miao Island using a bottom-up approach and multi-source data. Key findings include the following: In 2020, the total in-use MS was 249.8 kt, with stone, gravel, and sand accounting for 80%. Transportation infrastructure held the largest share (40.8%). Over the past 40 years, Miao Island’s infrastructure MS increased by 256%, with a net addition of 179.6 kt. The three distinct development periods were closely linked to China’s reform and local stimulus plans. Miao Island has a lower construction intensity than urban areas, with a per capita MS growth rate of 10.12 t/yr. Despite this, future waste remains a challenge to the island’s capacity. Given the constraints of limited investment due to population decline and the aging of in-use stock, island infrastructure should conform to local resource availability and long-term plans. Priority should be given to environmental compatibility, resilience to resource disruptions, and establishing a circular system to support sustainable island development.

As an indispensable part of the marine ecosystem, the health status of the sea affects the stability and enhancement of the overall ecological function of the ocean. Clarifying the future land and sea utilization pattern and the impacts on the carbon stocks of island ecosystems is of great scientific value for maintaining marine ecological balance and promoting the sustainable development of the island ecosystem. Using Pingtan Island as an example, we simulate and predict changes in island utilization and carbon stocks for historical periods and multiple scenarios in 2030 via the PLUS-InVEST model and the marine biological carbon sink accounting method. The results show that (1) from 2006 to 2022, the carbon stock of Pingtan Island decreased by 7.218 × 10⁴ t, resulting in a cumulative economic loss of approximately USD 13.35 million; furthermore, from 2014 to 2018, the implementation of many reclamation and land reclamation projects led to a severe carbon stock loss of 6.634 × 10⁴ t. (2) By 2030, the projected carbon stock under the three different policy scenarios will be greater than that in 2022. The highest carbon stock of 595.373 × 10⁴ t will be found in the ecological protection scenario (EPS), which will be 4.270 × 10⁴ t more than that in 2022. With the strong carbon sequestration effect of the ocean, the total social carbon cost due to changes in island utilization is projected to decrease in 2030. (3) The factors driving changes in island utilization will vary in the design of different future scenarios. The results of this study not only provide a solid scientific basis for the sustainable development of island areas, but they also highlight the unique contribution of islands in the field of marine ecological conservation and carbon management, contributing to the realization of the dual-carbon goal.