Global high-resolution mapping of seagrass to support conservation.

Abstract

Seagrass ecosystems underpin coastal biodiversity¹ and provide vital ecosystem services, including shoreline protection², food security³ and climate mitigation⁴. Despite growing recognition as a nature-based climate solution, seagrasses are among the least mapped and most poorly understood vegetated coastal ecosystems⁵. Here we present, to our knowledge, the first global 10-m spatial resolution maps and change analysis of seagrass extent in clear, shallow coastal waters, derived from 4.75 million Sentinel-2 MSI satellite images for two periods (2019-2020 and 2023-2024). Using a deep-learning classifier trained on curated reference data, we identified 148,506 km² of seagrass globally, including 5,961 km² of intertidal and 142,545 km² of subtidal areas. Sixty-nine per cent of global seagrass extent is concentrated in The Bahamas, Cuba, the USA, Australia and Indonesia, yet only 21% of seagrass areas are located within marine-protected areas. Over the 4 years of the study, 5,969 km² (4%) of seagrass was lost, and an additional 6,221 km² (4.2%) was degraded from dense to sparse cover in tropical regions. Our findings identify seagrass meadow hotspots and vulnerable regions to inform conservation and climate policy.