Persistent yet limited impact of protected areas on coastal wetland restoration in megacity cores

Coastal wetlands, vital hubs of economic activities, are under significant pressure, leading to the establishment of protected areas as a crucial conservation tool. Yet, uncertainties remain regarding the long-term effectiveness of these areas, especially in megacity cores subject to intense human disturbances. This study utilized long-term Landsat satellites monitoring to track the annual impact of protected areas on coastal wetland variations in the Guangzhou-Hong Kong-Macau Greater Bay Area from 1990 to 2020. Using annual classification datasets featuring 8 land cover/land use types with an average overall accuracy of 94.0±0.4 %, the research identified a significant increase in wetland areas before 2002, followed by a slight decline due to the exploitation of aquaculture and water bodies. Protected areas established for over seven years demonstrated a significantly positive impact on wetland restoration, underscoring the value of long-term conservation efforts. While mangrove protected areas showed strong recovery trends, other wetlands in developing regions continued to decline despite protection. This analysis indicated that the overall benefits of protected areas diminished when considering broader spatial contexts. These insights emphasized the need for adaptive management strategies to enhance the effectiveness of protected areas in urban environment. • Reserves positively influence wetland restoration after seven years. • Effectiveness of protected areas diminishes at broader spatial scales. • Mangroves show significant recovery despite urban pressures. • Adaptive strategies are needed for wetlands in developing regions.