关键词: Sentinel-2, 无瓣海桑, 生长演变, 遥感监测, 长时序

Abstract: Aims The exotic species Sonneratia apetala has been extensively introduced for mangrove restoration and coastal protection along the southern coast of China because of its high environmental adaptability. Nev-ertheless, its rapid expansion may pose potential impacts on native mangrove species and ecosystem structure, necessitating urgent quantitative evaluation. Methods Using high-resolution remote sensing imagery acquired between 2016 and 2023, this study de-lineates the spatial distribution of Sonneratia apetala in Maowei Sea (Guangxi) and Leizhou Bay (Guang-dong) and characterizes its spatiotemporal evolutionary trajectories. Landscape pattern metrics were then employed to evaluate the effects of its expansion on mangrove landscape fragmentation. Furthermore, a Contact Pressure Index (CPI) was developed to quantify the spatial pressure associated with interactions between S. apetala and native mangrove species, thereby elucidating the spatial differentiation patterns between the two regions. Important findings The results indicate that: (1) From 2016 to 2023, the total mangrove area in both re-gions exhibited an overall expansion trend, increasing by 263.87 hm² (+16.15%) in Leizhou Bay and by 113.28 hm² (+5.84%) in Maowei Sea. This expansion was primarily attributable to Sonneratia apetala, whose area increased by 251.41 hm² (+94.05%) in Leizhou Bay and by 339.99 hm² (+376.34%) in Maowei Sea. In contrast, native mangrove species showed relatively limited changes, with a slight increase of 12.46 hm² in Leizhou Bay but a decrease of 226.71 hm² in Maowei Sea. (2) With respect to landscape fragmentation, the rate of increase in fragmentation for S. apetala was generally higher than that for native species. The growth rates of the fragmentation index for S. apetala and native species were 11.54% and 68% in Leizhou Bay, and 1090.90% and 322.22% in Maowei Sea, respectively. (3) CPI outcomes further reveal that the overall level of contact pressure in Maowei Sea was higher than that in Leizhou Bay, with a rate of change approximately three times greater. In hotspot transition zones along shared boundaries, high-grade hotspot patches in both regions displayed a clustered distribution, and the CPI generally increased initially and then stabilized. Collectively, these findings elucidate the regional heterogeneity in the expansion of S. apetala and its as-sociated pressure effects, providing a scientific basis for the conservation and management of mangrove ecosystems.

Key words: Sentinel - 2, Sonneratia apetala, Growth and evolution, Remote sensing monitoring, Long - time series