Surface pollen assemblages as indicators of mangrove ecosystem dynamics and anthropogenic disturbances along southeastern China

Modern pollen assemblages from mangrove wetlands provide sensitive ecological indicators for separating climate-driven biogeographic patterns from human disturbance in threatened coastal ecosystems. This study examines pollen and spore assemblages from 32 surface-sediment samples collected at eight mangrove wetlands along a 10° latitudinal transect (18–28°N) on the southeastern coast of China. The assemblages clearly captured temperature-related mangrove zonation: Tropical southern sites, particularly Dongzhaigang and Qingmeigang, contained high proportions of mangrove pollen dominated by Rhizophora and Sonneratia , whereas the northern range-margin site at Yueqingwan was dominated by regional arboreal pollen, especially Pinus and Quercus . Redundancy analysis further identified the latitudinal thermal gradient as the main control on pollen composition. Superimposed on this climatic signal, anthropogenic disturbance was evidenced by reductions in mangrove pollen content alongside significant increases in disturbance indicator pollen taxa, including Poaceae, Chenopodiaceae and fern spores ( Dicranopteris ). Disturbed mid-latitude sites, including Quanzhouwan, showed high palynological richness but relatively low Shannon diversity, indicating assemblage dominance by opportunistic or disturbance-tolerant taxa. In contrast, relatively intact tropical mangroves showed lower richness but higher evenness, consistent with mature canopy structure and niche differentiation. Furthermore, this research establishes diagnostic pollen thresholds indicative of ecosystem degradation (mangrove pollen <12%; fern spores >64%) and fragmentation (presence of Corylus and Myrica ) within mangrove communities. Collectively, these results demonstrate that pollen assemblages constitute highly sensitive proxies for assessing climatic and anthropogenic pressures, thereby providing robust scientific evidence to guide mangrove restoration efforts and paleo-vegetation reconstructions in vulnerable coastal ecosystems