Loss and fragmentation of China's tidal wetlands.

Tidal wetlands are critical natural assets, yet they face dual pressures from anthropogenic development and climate change. While tidal wetland loss is well-documented, habitat fragmentation - and its consequences for ecological connectivity - remains poorly quantified at large scales. This study investigates changes in tidal wetland area and structural connectivity, the latter assessed through the foreground area density metric, along the mainland coast of China from 2000 to 2022. Using high-resolution global annual 30-m wetland maps, we quantified pixel-level tidal wetland gain, loss, and fragmentation and integrated these metrics to identify landscape-scale patterns. Our results show a net tidal wetland loss of 5.0% (approximately 646 km2), with a simultaneous decline in mean national connectivity from 77.4% to 72.2% over the same period. Landscape clustering analysis revealed six distinct patterns of change. This analysis showed that approximately 14% of coastal units experienced severe ecological degradation characterized by both substantial net area loss and a significant increase in fragmentation. We found that transitions between tidal wetlands and open water (i.e., erosion and accretion) had a stronger effect on the connectivity of persistent tidal wetland patches than direct anthropogenic land-cover conversions. These findings suggest that China's transition from exploitation-driven to protection-oriented policy could (i) integrate ecological connectivity into wetland monitoring frameworks, (ii) explicitly manage seaward erosion and sediment processes in addition to regulating reclamation, and (iii) prioritize restoration that reconnects existing wetlands as well as expanding total area, to enhance long-term coastal resilience.