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Journal of Tropical Oceanography

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Investigation and assessment of seagrass resources on the eastern Yongle Atoll, Xisha Islands

LIU Songlin 1, 2, 3, 4, HUANG Yuying1, 2, GAO Sai1, 2, YIN Tingting1, 2, HUO Da1, 5, ZHANG Xia1, 5, JIANG Zhijian1, 2, 3, 4, WU Yunchao1, 2, 3, 4, CHEN Chang1, 5, HUANG Xiaoping1, 2, 3, 4   

  1. 1. State Key Laboratory of Tropical Oceanography, and Guangdong Provincial Key Laboratory of Applied Marine Biology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China;

    2. University of Chinese Academy of Sciences, Beijing 100049, China;

    3. Sanya National Marine Ecosystem Research Station, Tropical Marine Biological Research Station in Hainan, Chinese Academy of Sciences, Sanya 572000, China;

    4. Key Laboratory of Tropical Marine Biotechnology of Hainan Province, Sanya Institute of Ocean Eco-Environmental Engineering, Sanya 572000, China;

    5. Xisha Marine Environment National Observation and Research Station, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Sansha 573199, China



  • Received:2025-12-18 Revised:2026-02-28 Accepted:2026-03-12
  • Supported by:
    National Survey of Science and Technology Resources(2025FY101402); National Key Research and Development Program of China(2022YFF0802201); Youth Innovation Promotion Association CAS(2023359); Guangdong Basic and Applied Basic Research Foundation(2025B1515020078); Science and Technology Planning Project of Guangdong Province, China(2024B1212050003)

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Abstract: The Yongle Atoll in the Xisha Islands is a typical tropical coral island and reef system in China. Seagrass beds serve as a crucial ecosystem there, working together with coral reef ecosystems to jointly sustain the ecological health of the atoll. However, current understanding of the seagrass resources and their habitat conditions in the Yongle Atoll remains limited. In September 2025, we conducted surveys along the eastern rim of Yongle Atoll (Jinqing Island, Longdong Station, Longdong, Yagong Island, and Quanfu Island) to characterize seawater environmental conditions and assess the current status of seagrass resources, including species composition, growth performance and spatial extent. During the survey, seawater temperature ranged from 28.7 to 31.0°C, salinity from 32.5 to 34.6, pH from 8.09 to 8.51, and dissolved oxygen from 7.85 to 12.50 mg/L, indicating a stable and favorable environment. Two seagrass species, Thalassia hemprichii and Halophila ovalis, were recorded within the study area. The density and coverage of T. hemprichii ranged from 876 to 1792 shoots/m² and 45–85%, while those of H. ovalis ranged from 3934 to 7723 shoots/m² and 35–55%, suggesting generally healthy growth conditions. Significant differences in leaf length, root biomass, aboveground biomass, and above-/below-ground biomass ratios of T. hemprichii indicate distinct responses and adaptive strategies to micro-environmental variation. Ship-based survey results indicate that seagrass beds covering over 50 ha are distributed along the eastern coast of Yongle Atoll. Due to survey constraints, this study did not cover all the islands and reefs within Yongle Atoll. This study fills a critical knowledge gap regarding seagrass distribution in Yongle Atoll and provides essential baseline information for the conservation and long-term monitoring of seagrass ecosystems in the South China Sea.

Key words: Seagrass meadows, Yongle Atoll, Thalassia hemprichii, Halophila ovalis, Biomass allocation