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Although Southeast Asia is a hotspot of global seagrass diversity, there are considerable information gaps in the distribution of seagrass beds. Broad-scale seagrass distribution has not been updated in the global seagrass database by UNEP-WCMC since 2000, although studies on seagrasses have been undertaken intensively in each region. Here we analyze the recent distribution of tropical seagrass beds, their temporal changes, causes of decline and conservation status in Southeast Asia (plus southern mainland China, Taiwan and Ryukyu Island of Japan) using data collected after 2000. Based on the 195 literature published since 2000, we identified 1,259 point data and 1,461 polygon data showing the distribution of seagrass beds. A large discrepancy was found in the seagrass bed distribution between our updated data and the UNEP-WCMC database, mostly due to inaccurate and low resolution location information in the latter. Temporal changes in seagrass bed area analyzed for 68 sites in nine countries/regions demonstrated that more than 60% of seagrass beds declined at an average rate of 10.9% year–1, whereas 20% of beds increased at an average rate of 8.1% year–1, leading to an overall average decline of 4.7% year–1. Various types of human-induced threats were reported as causes for the decline, including coastal development, fisheries/aquaculture, and natural factors such as typhoons and tsunamis. The percentage of seagrass beds covered with existing marine protected areas (MPAs) varied greatly among countries/regions, from less than 1% in Brunei Darussalam and Singapore to 100% in southern Japan. However, the degree of conservation regulation was not sufficient even in regions with higher MPA coverage. The percentage of seagrass beds within EBSAs (Ecologically and Biologically Significant Area determined by the Convention of Biological Diversity) was higher than that within MPAs because EBSAs cover a greater area than MPAs. Therefore, designating EBSAs as legally effective MPAs can greatly improve the conservation status of seagrass beds in Southeast Asia.

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TÓM TẮT: Nghiên cứu góp phần cung cấp thêm những thông tin cơ bản về chức năng-ý nghĩa sinh thái môi trường của cỏ biển trong hệ đầm phá, thông qua sinh khối để đánh giá khả năng lưu trữ cacbon của chúng. Trên cơ sở đó phát triển và mở rộng các khu vực bảo tồn cỏ biển, ngoài việc duy trì, tái tạo hệ sinh thái ven biển và hệ đầm phá, còn cung cấp cơ sở khoa học cho Việt Nam chuẩn bị tham gia vào thị trường cacbon, hướng đến giảm thiểu khí CO 2 bảo vệ môi trường sống. Kết quả nghiên cứu cho thấy, đầm Thị Nại có 7 loài cỏ biển, phân bố trên tổng diện tích 180 ha, mật độ và sinh khối trung bình toàn vùng lần lượt là 1.649 ± 428 chồi/m 2 và 125,68 ± 23,40 g.khô/m 2. Hàm lượng cacbon trong cỏ biển trung bình đạt 34,30 ± 1,82%, tổng trữ lượng cacbon và cacbon dioxit lần lượt là 136,7 tấn và 501 tấn, tương đương với 24.583 USD.

The Tam Giang - Cau Hai lagoon in Thua Thien-Hue province is the largest lagoon in South East Asia and also one of the places having the largest area of seagrass in Vietnam. The study results from 2009 to 2017 showed that 6 seagrasses species were identified (Halodule uninervis is a newly recorded species, however, Halophila minor is not recorded) and there were 8 freshwater grass species (with the exception of Potamogeton maackianus), with a total area of 2,840 ha. In particular, the area of seagrass has been recovering significantly from 1,000 hectares in 2009 to 2,037 hectares in 2017.