Abstract
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.
Highlights
Seagrass beds consist of marine flowering plants and are one of the most important habitats in the coastal ecosystem of the world (Hemminga and Duarte, 2000; Short et al, 2007)
This study clarified the recent distribution of tropical seagrass beds, their temporal changes and conservation status based on the updated information taken on and after 2000 in Southeast Asia, where information has been scattered among local literature
We found large differences in the estimation of seagrass bed areas between our updated information and the previous version of the seagrass database by Global Distribution of Seagrasses” (GDS), which is mostly ascribed to inaccurate information and many remaining gaps
Summary
Seagrass beds consist of marine flowering plants and are one of the most important habitats in the coastal ecosystem of the world (Hemminga and Duarte, 2000; Short et al, 2007). Seagrass beds have been threatened by various types of human-induced stressors, including eutrophication, coastal development, and global climate change (Orth et al, 2006; Waycott et al, 2009; Japar Sidik et al, 2018; Muta Harah et al, 2019). Such multiple human-induced impacts cause rapid loss and deterioration of this important coastal habitat. It is urgently needed to collect more data and compile already existing data on the distribution of seagrass beds, and to conduct analyses of their recent status and temporal trends for promoting their effective conservation and management
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