Mark Anthony B. Trapa Mark Anthony J. Torres Cesar G. Demayo Lawrence M. Liao Department of Biological Sciences, College of Science and Mathematics, Mindanao State University-Iligan Institute of Technology, Tibanga, Iligan City, Philippines Center of Integrative Health, Premier Research Institute of Science and Mathematics, Mindanao State University-Iligan Institute of Technology, Tibanga, Iligan City, Philippines School of Interdisciplinary Studies, Mindanao State University-Iligan Institute of Technology, Tibanga, Iligan City, Philippines Graduate School of Integrated Sciences for Life, Hiroshima University, 1-4-4 Kagamiyama, Higashi-Hiroshima 739-8528, Japan Proceedings of the International Academy of Ecology and Environmental Sciences ISSN 2220-8860 http://www.iaees.org/publications/journals/piaees/online-version.asp 2024 14 1 12 30 International Academy of Ecology and Environmental Sciences Hong Kong 22 December 2023 10 January 2024 1 March 2024 diversity distribution Mapun Island seaweeds species composition Seaweeds are found in mild temperate and tropical waters across the globe, where they thrive in a diverse array of habitats and are affixed to a variety of substrates, including rocks, sediment, and seagrass beds. The Philippines' periphery islands, situated in the expansive Sulu Sea basin, may contain a wealth of seaweed resources that have yet to be thoroughly explored and investigated with regard to their complete composition. For the first time, a macroalgae survey was carried out in five sampling areas located on Mapun Island, Tawi-Tawi. The research investigated the constitution of seaweeds and ascertained the diversity of species. A total of fifty-seven (57) macroalgae species were identified and organized into three main algal divisions: Chlorophyta, Rhodophyta, and Phaeophyta. Among these species, 27 were green algae, 18 were red algae, and 12 were brown algae. The green algae accounted for the most significant proportion of species diversity (47%), followed by the red algae (32%), and finally the brown algae (21%). The diversity index for Sikub is the highest among the five sampling areas, measuring 3.17. Based on species distribution, the Sorensen similarity index revealed that Sikub, Umus Mataha, and Duhul Bato have comparable Sorensen index values (37%). The results of this research would offer valuable insights for informing the development of more effective policies pertaining to the conservation of biodiversity and the management of resources. http://www.iaees.org/publications/journals/piaees/articles/2024-14(1)/species-composition-diversity-of-marine-macroalgae.pdf