Seagrass Restoration in the Greater Southeast Asia Region: techniques, species, survival, comparisons among investigations

Anitra Thorhaug^1,2*Jennifer Joan Verduin³Wawan Kiswara^4,5Anhana Prathep⁶Xiaoping Huang⁷John Barry Gallagher⁸Tzuen-Kiat Yap⁹Rohani Ambo-Rappe¹⁰Susan E. Dorward¹¹Arthur Schwarz¹²Graeme P. Berlyn¹³

• ¹Greater Caribbean Energy and Environment Foundation, Miami, United States
• ²Yale Center for Natural Carbon Capture, Yale University, New Haven, Connecticut, United States
• ³Murdoch University, Perth, Western Australia, Australia
• ⁴Oceanography Research Center, Indonesian Institute of Sciences, Jakarta, Jakarta, Indonesia
• ⁵Indonesian Institute of Sciences, Jakarta, Jakarta, Indonesia
• ⁶Seaweed and Seagrass Research Unit, Prince of Songkla University, Kho Hong, Thailand
• ⁷Key Laboratory of Tropical Marine Bio-resources and Ecology, South China Sea Institute of Oceanology, Chinese Academy of Sciences (CAS), Guangzhou, Guangdong Province, China
• ⁸Institute for Marine and Antarctic Studies, College of Sciences and Engineering, University of Tasmania, Hobart, Tasmania, Australia
• ⁹Borneo Marine Research Institute, University Malaysia Sabah, Kota Kinabalu, Sabah, Malaysia
• ¹⁰Department of Marine Science, Faculty of Marine Science and Fisheries, Hasanuddin University, Makassar, South Sulawesi, Indonesia
• ¹¹Carbon Manager, Facilities & Grounds, Raritan Valley Community College, New Jersey, United States
• ¹²Department of Biological Sciences, Southwestern Adventist University, Keene, United States
• ¹³School of Forestry and Environmental Studies, Yale University, New Haven, Connecticut, United States

The Greater Southeast Asian region contains the largest global extent of tropical seagrass, however anthropogenic degradation is estimated greater than 7% yr -1 . Although the areal extent of seagrass is presently 36,765 km 2 , Fortes et al. ( 2022) estimate that 50% of the original seagrass has been degraded from a variety of impacts. One set of solutions to degradation is to restore tropical seagrass successfully, for which information from past results is needed to avoid failures. Van Katwijk et al (2016) provided a global seagrass restoration review of 1786 trials, but did not include the full Southeast Asian regional information. Thus, we review findings from 228 trials in the greater Southeast Asian region, involving 305,807 restored units with an extent of 372,649 m 2 . Seagrasses planted with varying success include 13 tropical species and five subtropical or near-subtemperate species. We compare methodologies as well as key factors of light level, energetics, and depth. This review demonstrates highest survival in seagrass restoration employing sprigs or plugs at medium depths (2-4m) with adequate light levels in medium to low energetics planting one to several dominant species. Substrate anchors improved successful establishment. Information gaps occur in quantified monitoring of seagrass services reassembled with tropical-seagrass restoration thus fisheries nursery potentials not provided. Future actions need national seagrass restoration policies and plans to restore degraded seagrasses. Presently such policies and plans are non-existent in most greater Southeast Asian regional nations, with the exceptions of Australia and the Philippines, although some nations have national plans for restoring corals or mangroves.