Coupling coordination between integrated transport–shipping system and nearshore marine ecology in China’s coastal cities: spatiotemporal evolution and XGBoost–SHAP-based mechanism identification

IntroductionAchieving a dynamic balance between the integrated transport–shipping system (ITS) and nearshore marine ecology (NME) is essential for the sustainable development of China’s coastal cities.MethodsUsing panel data for 53 Chinese coastal cities from 2013 to 2024, this study constructs an assessment framework for the coupling coordination degree (CCD) between the ITS and NME. The XGBoost–SHAP approach is further employed to examine the spatiotemporal evolution, regional differences, and influencing mechanisms of the ITS–NME CCD.ResultsThe ITS–NME CCD increased steadily during the study period, although persistent regional heterogeneity remained. Economic development and social development were the primary dimensions associated with CCD disparities, whereas environmental pressure and governance support showed stronger context dependence. Key factors, including urbanization rate and trade dependence, exhibited non-linear, threshold-dependent, and interaction-based relationships with the ITS–NME CCD. Urbanization rate acted as the dominant interaction hub, trade dependence served as a conditional bridge between economic openness and governance support, and environmental pressure affected the transformation of economic and social development into coordination outcomes. Urban typology analysis further showed that high-coordination cities relied on balanced multi-factor support or accumulated socioeconomic vitality, whereas low-coordination cities faced multidimensional constraints involving economic restructuring, knowledge support, and urban vitality.DiscussionThese findings provide interpretable empirical evidence for understanding the differentiated coordination pathways of China’s coastal cities and support the formulation of city-specific and land–sea integrated governance strategies.