Abstract:Climate change and global warming are one of the main reasons of coral bleaching. The 2016 heat event caused 40% of coral bleaching and death on the Great Barrier Reef. It is generally believed that marine heat waves can lead to serious losses in coral populations, including increased coral mortality, reduced coral distribution density, and reduced biomass. The rapid decline of coral reefs around the world has prompted increasing attention to the protection and restoration of coral reef ecosystems. Coral reefs are one of the typical ecosystems on Earth, providing ideal living conditions for many species of fish and marine invertebrates and enriching marine biodiversity. It provides important services and products to mankind, such as coastal protection, fishery resources and pharmaceutical raw materials, and has important cultural value, playing a vital role in the health and sustainable development of human society and the marine ecological environment.Octocoral corals is an important component of coral reefs ecosystem, playing a crucial role in maintaining the structural integrity and biodiversity of marine ecosystems. In order to understand the species diversity of Octocoral corals in the waters of Dabai island and Xiaobai island in Xiamen Bay, 137 and 42 Octocoral coral samples were collected respectively in July 2017 and April 2021.Traditional morphological identification methods were used to identify the samples. The results showed that there were 16 species of Octocoralcorals in 6 families, 8 genera in Dabai island, and 13 species of corals in 5 families, 7 genera in Xiaobai island. Seven newly recorded species were found in Xiamen Bay, including Euplexaura amerea, Euplexaura robusta, Menella flora, Menella simplex, Menella woodin, Parisis laxa and Dendronephthya purpurea. Comparing records from China, five new recorded species were found, including E. amerea, M. flora, M. simplex, M. woodin and P. laxa, which were described in detail. In addition, phylogenetic analysis of coral samples was performed using gene fragment sequencing techniques (COI, mtMutS and ND2 gene fragments).The results showed that the genus Euplexaura, Menella, Dendronephthya, Astrogorgia and Echinogorgia were clearly separated by the mtMutS gene phylogenetic tree. In addition, the phylogenetic tree of COI and ND2 genes was obtained, which can separate species of the genus Euplexaura, Carijoa, Parisis, Astrogorgia and Dendronephthya.These findings have not only enriched the recorded species of corals in China and Xiamen Bay, but also enriched the geographical distribution information of the world'sOctocorals coral species, and can provide data support for biodiversity conservation and management in Xiamen Bay.