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Journal of Tropical Oceanography

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Community structure of cryptofauna in the mesophotic coral ecosystem of Lingyang reef in Xisha islands

ZHANG Beiye1, 2, HU Simin1, 3, ZHANG Chen1, 2, LI Tao1, 3, 4, HUANG Hui1, 3, 4, LIU Sheng1, 3   

  1. 1. State Key Laboratory of Tropical Oceanography; 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 Joint Laboratory of Marine Science Research, Key Laboratory of Tropical Marine Biotechnology of Hainan Province, Sanya Institute of Marine Ecology and Environmental Engineering, South China Sea Institute of Oceanology, Sanya 572000, China;

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

  • Received:2025-07-29 Revised:2025-10-13 Accepted:2025-10-23
  • Supported by:
    National Science & Technology Fundamental Resources Investigation Program of China(2022FY100602); National Natural Science Foundation of China(42176118); Science and Technology Planning Project of Guangdong Province, China(2023B1212060047)

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Abstract: To examine the community structure of cryptofauna within the mesophotic coral ecosystem, Autonomous Reef Monitoring Structures were deployed at varying depths of 5 m, 15 m, and 40 m along the outer reef slope (ORS) of Lingyang Reef in the Xisha Islands from August 2023 to August 2024. Concurrently, in situ surveys were conducted using SCUBA diving at the same locations prior to the installation of the ARMS. The findings from the in situ surveys indicated that the substrate habitats in the shallow waters (5 m and 15 m) were predominantly composed of live coral, coral rubble, and rock. In contrast, the substrate at the depth of 40 m, classified as mesophotic, consisted of patch reefs, coral rubble, and sand. Notably, habitat roughness was greater in the shallow waters (5 m and 15 m) compared to that at 40 m. A total of 192 species were identified, representing 74 families, 17 classes, and 7 phyla of motile cryptofauna, alongside 6 phyla of sessile cryptofauna, encompassing a total of 10 phyla, including Mollusca, Arthropoda, Annelida, Echinodermata, Hemichordata, Chordata, Protista, Porifera, Tunicata, and Echiura. The average abundance of meiofauna was recorded at 55.60 ind.·L-1, with an average biomass of 3.36 g·L-1. Among these, Mollusca and Arthropoda emerged as the dominant groups within the meiofaunal communities, comprising 77.08% of the species number, 25.10% of the total abundance, and 92.59% of the total biomass. The cryptofauna communities exhibited significant differences in composition based on depth. The communities in the shallow sites (5 m and 15 m) displayed similar structures, with the highest species diversity, the greatest number of dominant species, and the highest biomass of mobile cryptofauna observed at 15 m. Conversely, the cryptofauna at 40 m depth within the MCE demonstrated a significantly higher abundance of mobile cryptofauna, primarily attributed to Larger Benthic Foraminifera (LBF) (p<0.05). The connectivity between the community at 40 m in the MCE and the shallow waters was found to be low, with only 7 species (8.14%) identified as common to both environments. These results underscore the distinct community characteristics of cryptofauna in the MCE compared to shallow coral reefs, highlighting the necessity for further research into their distribution patterns and ecological roles.

Key words: Lingyang reef, cryptofauna, community characteristics, depth, mesophotic coral ecosystem(MCE)