Estimation of Seagrass Biomass by In Situ Measurement and Remote Sensing Technology on Small Islands, Indonesia

As one of the major blue carbon ecosystems, studying, conserving, and monitoring seagrass meadows, especially on small populated islands, has become very important due to their vulnerability to anthropogenic and global environmental factors. In this study, we used satellite image analysis and biological data to map seagrass percent cover (SPC), above-ground biomass (AGB), and below-ground biomass (BGB) on the three most populated islands of the Spermonde Archipelago, Indonesia, i.e., Kodingareng Lompo, Barrang Lompo, and Barrang Caddi. Refectance and Normalized Diference Vegetation Index (NDVI) values of Sentinel-2 (S2) imagery were used to classify and calculate SPC and AGB. In situ biological data measurements were carried out from 3 to 14 of June, 2020, on the three islands to measure AGB and BGB. The result from image classification shows a total area of 126.37 Ha of seagrass, which was divided into three SPC categories: medium (30–59.9%) with a total area of 78.38 Ha; low (0–29.9%) with a total area of 13.1 Ha; and high (60–100%) with a total area of 34.89 Ha. The highest SPC area was observed on Kodingareng Lompo Island with 61.07Ha, followed by Barrang Lompo Island with 53.18Ha, and Barrangcaddi Island with 12.12Ha. The total AGB on Barrang Lompo, Kodingareng Lompo, and Barrangcaddi in tons of dry weight/ha were 1.83, 1.05, and 2.38, respectively. The highest BGB was reported on Barrangcaddi Island with 8.61 tons of dry weight/ha, followed by Barrang Lompo Island with 6.78 tons of dry weight/ha, and Kodingareng Lompo Island with 2.78 tons of dry weight/ha. Regression analysis showed a linear correlation between NDVI value and in situ SPC with R2=0.8255. The framework of this study can be applied to monitor temporal changes of seagrass meadows distribution on small islands to promote a more sustainable ecosystem.