Lack of local management and limited adaptive capacity are pushing the vulnerable seagrass (Halophila beccarii Aschers.) towards extinction across the Indo-Pacific

Abstract

Seagrass ecosystems worldwide are undergoing rapid decline due to intensifying anthropogenic pressures and climate change, leading to severe habitat degradation and species loss. Among these, Halophila beccarii Ashcers., a small intertidal seagrass species endemic to the Indo-Pacific, is particularly vulnerable. Despite its ecological importance in supporting biodiversity, sediment stabilization and carbon sequestration, the species remains understudied and its adaptive capacity (AC) to environmental change is poorly understood. Using published literature spanning 1977-2024, we systematically reviewed morphological, ecological, and genetic characteristics of H. beccarii across 14 countries in the Indo-Pacific bioregion. Following the current available AC framework, which considers species responses to environmental change through Persist in Place (PiP) or Shift in Space (SiS) pathways. Our synthesis revealed that H. beccarii exhibits generally low AC, with more than half of the assessed attributes indicating limited resilience. Although the species is reported from 13 Indo-Pacific countries, its area of occupancy is extremely restricted (312.7 ha) and populations occur as small, fragmented patches. Demographic observations from Malaysian population indicate an annual life cycle with rapid generational turnover and seasonal recruitment, suggesting short-term persistence potential. Additionally, limited dispersal ability, low genetic diversity, and narrow habitat specialization constrain largescale range shifts. Overall, the adaptive profile of H. beccarii indicates a strategy dominated by PiP responses, supported by physiological tolerance and clonal growth, but limited capacity for spatial distribution. Country-specific conservation policies remain scare, with only Malaysia and the Philippines incorporating the species with national conservation and management frameworks. Without targeted conservation interventions, H. beccarii populations across the Indo-Pacific may experience irreversible declines. Our assessments highlight the urgent need to strengthen research on key adaptive traits, particularly population genetics, reproductive ecology and demography dynamics to refine vulnerability predictions and guide regionally coordinated conservation actions. Enhancing the AC of H. beccarii through integrated management, restoration and monitoring programs is critical to prevent further local extirpations and secure the resilience of Indo-Pacific seagrass ecosystems under accelerating environmental change.