The 20th Party Congress initiated efforts to strengthen maritime power and advance marine ecological civilization, which is essential for promoting sustainable development. To achieve this goal, this study combines field measurements, drone imagery, and high-resolution remote sensing data, using GIS technology to analyze changes in marine resources in Hangzhou Bay and assess marine area usage, intertidal zone area changes, and coastline erosion. The key findings show that the industrial sector accounts for the largest usage of marine area, with the industrial sea area growing by 110.3% from 2018 to 2020. The diversity index for marine area usage in Hangzhou Bay has remained stable, consistently at 0.6 and above over the past five years. The continental coastline of Hangzhou Bay has shown a decreasing trend in recent years from 2018 and 2021, with a total intertidal area of Hangzhou Bay decreased by 73.44 km², where the overall shoal pattern in Hangzhou Bay remained relatively stable from 2008 to 2016. Erosion has been the predominant force, with maximum erosion surpassing 3 m and causing significant spatial changes. Between 2012 and 2016, the total erosion volume reached 192,473.74 × 10⁶ m³, with an average annual erosion rate of 48,118.44 × 10⁶ m³. This process has led to a gradual reduction in the size of affected areas over the period from 2001 to 2021. This research provides valuable insights for authorities to make informed decisions regarding the management of marine spatial resources in Hangzhou Bay.

The scarcity of land resources has become a bottleneck restricting the development of photovoltaic (PV) energy, and it is imperative to expand PV layout into the ocean. However, existing studies lack a refined site selection framework for large-scale sea areas. This study takes the Northwest Pacific coastal waters as the research area and constructs a three-stage evaluation framework for the suitability of offshore PV site selection, which includes “resource potential–spatial exclusion–multi-criteria assessment”. The results show that the theoretical power generation potential is generally “higher in the south and lower in the north”, with some deviations in local areas due to differences in temperature and wind speed. Only 4.3% of the sea area is feasible for development. The high-suitability areas are concentrated in the southeast coast of Vietnam and the northwest side of Taiwan Island. The South China Sea has superior development potential, while the Bohai Sea and the Yellow Sea are relatively less suitable. This study generates the first offshore PV site selection map covering the research area, providing a scientific basis for the formulation of differentiated development strategies for regional offshore PV. It has important practical value for promoting the sustainable development of blue energy.

The manuscript adopts the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) protocol to conduct a comprehensive analysis of the methodologies and critical factors influencing the site selection for offshore photovoltaic (PV) projects. The study innovatively proposes a three-stage site selection method model of “exclusion–optimization–correction” and a four-dimensional factor framework, which encompasses “technology, economy, environment, and policy.” The study underscores the pivotal roles of solar radiation, water depth, and grid connection conditions in site selection, while also highlighting the “veto” impact of military exclusion zones and ecological redlines. Additionally, it identifies the challenges associated with data acquisition and standardization in site selection, advocates for the establishment of standardized assessment procedures, and offers theoretical underpinnings and decision-making guidance for the rational site selection of offshore PV projects.